Nee Boiler-inspection Guideline

BOILER INSPECTION GUIDELINE

Regardless of the original equipment manufacturer, NEE Process Solutions can offer engineering know how not only to improve unit performance and reliability but also to eliminate operating and maintenance problems Boilers of the PC or CFB type.

BOILER INSPECTION GUIDELINE

PURPOSE OF BOILER INSPECTION

The purpose of a Boiler Inspection is to:

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Use planned outage time effectively to ensure that unit availability, safe operation and equipment life is maintained.

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Reduce forced outages due to maintenance failures.

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Effectively plan outage-required preventative maintenance activities and periodic replacement of normal wear parts.

A typical boiler inspection will deal with the following component areas:

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Waterside

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Fireside

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Boiler Externals

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Fuel Firing Equipment

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Air/Flue Gas Systems

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Auxiliary Equipment

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Controls (if necessary)

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OUTAGE OBJECTIVES Major scheduled outage should be structured around customer objectives: 

Perform known maintenance tasks.

These items are scheduled based on historical data, past outage inspections or items noted during the pre-outage operational unit walk down. 

Inspect equipment to identify areas needing repairs.

Certain equipment can only be inspected during non-operational periods. 

Perform preventive maintenance tasks.

Scheduled or routine maintenance includes such items as turbine bearing inspections, hydrostatic testing of pressure parts, checking and documenting tube minimum wall thickness, packing valves, etc. 

Upgrade equipment and make design changes as part of a plant betterment program.

Implement state-of-the-art improvements to enhance unit operation and eliminate generic design problems identified by the manufacturer. 

Establish a maintenance history for future use.

This objective is perhaps the most important. It helps reach the goal of all the proceeding objectives and is required if an ongoing comprehensive maintenance program is to be effective. A maintenance history is developed by thoroughly documenting the outage and inspection findings for every scheduled outage.

PERFORMING THE INSPECTION 01/2016

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The boiler inspection identifies and evaluates problem areas (current and potential). This allows the service engineer to recommend repairs and solutions. The problem areas will have varying levels of priority. During an outage, every portion of the unit is thoroughly inspected. The inspection is divided into three general categories: 

The pre-outage walkdown, in which the entire unit and its subsystems are inspected under operating condition.

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The internal inspection of the unit after shutdown and its subsystems

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The post-outage start-up inspection in which all the equipment is checked as it is returned to service.

Inspection activities include visual observations, comparisons, measurements and non-destructive examination techniques. Accurate record keeping of findings as well as careful labeling of items in the field will make it easier to communicate punch list items and write the final report. Photographs are another method to capture and express details. PRE-OUTAGE WALKDOWN The pre-outage operational unit walkdown is a significant first-step of the unit inspection. While the unit is on line, the inspector can assess the operating conditions of the unit and note any discrepancies that require attention during the outage. Several problem areas are more apparent or best observed while the unit is still in operation, i.e. safety valve leakage, expansion trams, loadspring hangers, insulation leakage, etc. The walkdown should cover the complete unit from top to bottom and all the auxiliary systems. Auxiliary systems are noted here to demonstrate the scope of a complete unit walkdown. Structure Components Boiler Support Inspect all boiler hanger rods for integrity. Inspect variable load and constant load spring hangers for loading indications. Note any bottomed-out spring hangers. Also, note any loose hanger rods. Check all vertical and horizontal buckstays for warpage or misalignment. Inspect all buckstay stirrups, bolts, nuts, and washers for integrity. Check expansion trams for alignment and note readings at all reference points with the boiler hot. Structural Steel Inspect the structural steel for any interference with the boiler or auxiliary equipment. Inspect the grating and walkways for missing or loose sections. Check handrails for any missing or broken sections. Make note of all discrepancies. Insulation and Lagging During walkdown, inspect for any areas of missing insulation. Check for discoloration of the insulation, which would indicate leakage of hot gases or air. 01/2016

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Check duct insulation in areas of expansion joints for signs of buckling. Ensure the presence of insulation in areas around inspection ports, sootblowers, and access doors. If possible, check areas of poured refractory for damage. Note all problem areas observed. Upper Level Components Safety Valves Inspect for leakage around the stem or packing. Note if the valve is leaking across the seat so that some amount of vapor is discharging from the vent piping. Check for pluggage in the drip pan. Check for binding or interference between the safety valve and vent piping. Make note of abnormal conditions. Sootblowers and Furnace Probe Check for local and remote operation by cycling each sootblower through its operating sequence. Check for steam leakage in the sootblower supply lines, valves, and swivel tubes. Check the sootblower wall box for damage. Check the drive mechanism on all sootblowers. Make sure that cranks and tools are available to retract a sootblower that has stopped in the "advanced" position. Observe movement of air heater sootblower swivel mechanism. The furnace temperature probe is usually made by the same manufacturer as the sootblowers and should also be inspected at this time. Fuel Components Ignitors Operator to remove operating ignitors from service in order to check the indicator lamps on the local ignitor control station. Have operator place each ignitor in service to verify operation and to check the indicator lamps. Inspect electrical cables, oil, gas, and air supply lines. Tilting Tangential Firing System During walkdown, check the nozzle tilt indicators for degree of tilt indication of the fuel and air nozzles. Check all overfire air nozzles for degree of tilt. All corners of tilt indicators should be within 5° of each other. While in this area, inspect all coal piping entering the windbox for wear, damage, or leakage at elbows or couplings. Also check all fuel pipe hangers. Note the position of all windbox air dampers as indicated by the scribe mark on the damper shaft. All dampers on the same elevation should be at the same position. Inspect the windbox and related duct work for leakage. Oil Guns The oil guns are located with the fuel and air nozzles in the corners of the furnace. Check all oil and steam or air lines for leakage; check all related piping and valves; inspect the oil gun advance and retract mechanism; and check that spare oil guns are properly cleaned and stored. Coal Piping Inspect the coal pipes for indications of wear. Check the coal pipe couplings for signs of leakage. If so equipped, check the coal pipe constant load spring hangers. Examine for any coal pipe related expansion problems. 01/2016

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Coal Feeders During the inspection of an operating gravimetric feeder, check the position of the tension pulley, the feeder belt tracking, and the integrity of the feeder housing. Broken observation windows or improperly closed doors negate this safety feature of the feeder. On a C-E volumetric feeder, inspect the drive clutch assembly, the movement of the hinged leveling gate lever, and the feeder housing. Check the drive motor and gear reducer for unusual noises and verify proper lubrication levels. Pulverizers Inspect the mill foundation for cracks. Check the gear case for proper oil level, temperature, and signs of leakage. Examine the material being rejected from the mill; excessive coal discharge could indicate worn or improperly adjusted mill internals. Verify the movement of the three journal assemblies for uniformity. Inspect the separator body for signs of coal leakage. Make a notation of the classifier settings; they should all be the same. Inspect the mill motor, filters and foundation. On exhauster type mills, check the exhauster casing, foundation, and bearing assembly. Check for excessive noise or vibration from the pulverizer gear housing and exhauster bearing housing. On pressurized pulverizers, check the gear case and journal seal air systems for leakage or crimped lines. Fuel Handling Systems Inspect all coal handling systems. Note any excessive spillage or accumulation, and check all oil and gas piping for leakage. CFB Boiler Limestone Feed System Inspect the limestone feed system for erosion, loose mounting hardware, proper clearances and binding of rotating equipment. Note any excessive spillage or accumulation, and check all oil and gas piping for leakage. Auxiliary System Components Air Preheaters Inspect the upper and lower bearing assemblies. Check oil level and for oil leakage. Listen for any loud noise, which might indicate problems with the air preheater seals. Check the drive motor and gear reducer for signs of oil leakage, and verify the operation of the air preheater sootblowers. Fans/Air and Gas Ducts Check for the following: foundation cracks or loose anchor bolts, vibration meters for excessive fan or motor vibration, motor amp readings, and bearing temperatures. Inspect fan housings for damage and check all air and gas ducts for leakage, expansion problems, and missing insulation. Ash Removal Systems Inspect all piping for leakage and pluggage.

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Boiler Water Circulating Pumps Inspect motor and related piping for leakage. Check the pump suction and discharge pressures. Check and record motor cooling water temperatures. Compare data to normal operating conditions. Note abnormal conditions. Pre-boiler Systems Check all components and piping for leakage. Check all components for any missing insulation.

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INTERNAL INSPECTION – WATER SIDE PRESSURE PARTS The internal inspection requires unit downtime. Lots of maintenance activity is also scheduled during the outage. The internal inspection activity is complex and covers a large work area. This section covers only the water-side pressure parts of an inspection plan. Steam Drum and Internals Examine the steam/water separating equipment. Inspect the turbo separators, both the primary and secondary stages. Look for corrosion, deposits, erosion, missing parts, etc. Examine the condition of the corrugated plate dryers and the return piping. During inspection: 

Check the condition of the seal around the manway door.

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Check the area around the inside of the manway door.

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Check the interior of the drum for corrosion and deposits.

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Check the condition and mounting of the chemical feed pipe, the blowdown pipe, and the feedwater distribution header.

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Check the downcomer nozzles, screens, and vortex eliminators.

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Check all drum internals for wear and fit.

Thoroughly examine the drum liners for cracks. Cracks in the liner will allow boiler water to bypass the steam separation equipment and allow the carryover of suspended solids into the superheater. Lower Waterwall Drums During inspection, crawl through the drum checking for cracks or crack-like indications particularly around nozzle welds and manway access doors. Generally, these cracks are shallow, not much deeper than 1/32". Usually found on the wetted surfaces of the drum is a corrosion indication, which could play a part in promoting a crack penetration. If cracks or crack-like indications are found, determine the depth by a number of spot grindings. Information on the depth together with the specific location of the cracks will permit calculations to be made to determine whether the remaining material thickness is sufficient to meet the requirements of the ASME Boiler Code for New Boiler Design and Construction.

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Potential Cracking Sites

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During inspection, check the screens or strainers located in the drum. These screens prevent foreign material from plugging the orifices. The screens must be intact and firmly secured in place. If any large holes have developed in the screens, recommend that they be replaced. Typical Lower Drum Arrangement

Check the locating pin, orifice clamp, and fastener for deterioration, fit, and tightness. Check for gaps between the orifice adapter and header counter bore. If gaps are found, the adapters may need to be replaced, repositioned, or repaired. Check the diameter of the furnace wall supply tube orifices using "Go/No Go" gages. If an orifice is found to be worn, that is, the opening is enlarged, recommendation should include replacement. The orifice plates assure that each tube circuit gets an adequate flow depending on its location in the furnace. Orifices are numbered for reference and have indexing holes so they cannot be incorrectly placed. Orifices could be either fouled or plugged with deposits, or enlarged by wear or corrosion. If the orifice is fouled, that is, the opening restricted, recommendations include cleaning during the outage (if possible) or replacing. Check the orifice mounting and locating pins, and the clamp and fasteners for signs of deterioration and looseness. Inspect the orifice adapter for signs of bypassing flow. If problems are found, recommendations might include replace, reposition, or repair the adapter.

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Headers To perform an internal examination, remove the handhole inspection ports on the header. Examine the interior for corrosion, deposits, or any other foreign material. Check the area around the handhole for any signs of cracking. Check the handhole port seal. During an external examination, visually check the entire header for corrosion, erosion, etc. Visually check the header nipple welds for signs of cracking. Note cracking and make recommendations for repair.

Header Inspection If the header is insulated or covered with refractory, note the condition.

Also inspect all other welds, especially for different material welds (DMW), near the header. If any cracking is found, determine depth and location, and consult Engineering for recommended repairs. 01/2016

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Inspect the area around each header for signs of potential problems. Inspect the area where a header penetrates a wall or floor for cracks or expansion problems. Check all hanger rods for tightness. Also check condition of hanger rods, clevises, and clevis pins for bowing, overheating, and damage. Hanger rods are made of a tempered material and should not be cut and rewelded. If significantly damaged recommendation should include replacement. The combined circulation units are supplied with orificed waterwall inlet headers that can be internally inspected if the handhole caps are removed. These headers should be checked for cracking, deposits (especially on the orifices), loose marmon clamps, and cracking between the internal partition plates and the ID of the header. Header cleanliness is a must.

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INTERNAL FIRE-SIDE FURNACE INSPECTION The second part of the internal inspection is the fire-side (gas-side) or furnace inspection. Again, this is a large area to inspect, with complex components. This section is divided into component sections. Bottom Hopper Area – PC Boiler The coutant sloped bottom tubes and the bottom ash hopper comprise the lower furnace area. Inspect casing, plates, screens, and the structural condition of expansion and support members. Remove all debris, bottom ash, and water remaining in the hopper enclosures. Examine the water seal trough material and structural condition. Inspect trough for corroded and deteriorated lining and structural support. Look closely at all welds for signs of cracking and indication of expansion problems. Examine the seal plate for indications of corrosion, deterioration, and cracks in the surface. Inspect splash screen for tears and holes in screen material. Examine all support structures for indication of expansion problems. Inspect for signs of corrosion and deteriorating conditions. Inspect drip shield for signs of erosion or corrosion. The attachment welds securing the drip shields to the waterwall tubes should be inspected and dyepenetrant checked, if cracks are suspected, as some tube leaks have been experienced at these welds. Inspect the slope tubes for signs of erosion, corrosion or thermal stress. Problems in this area could be caused by sliding ash and slag, chemical reaction of the ash and moisture, splashing or surging, wave propagation, and flooding during filling. Some possible solutions are to maintain ash hopper normal water level at least 30" below the tubes and have an overflow capable of handling excessive amounts.

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Furnace Seal Inspection

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Lower Combustor – CFB Boiler Maintenance Issues for the Lower Combustor / Hearth Zone are directly related to Unit Operation. 

Improper SA Flow or drop in pressure can result in overheating of the Lower SA Ducts and Start Up Burners.

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Improper PA Flow o

Low flow can cause the Fluid Bed to Slump and ash to enter PA Plenum.

o

High flow can contribute to accelerated erosion of PA nozzles.

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Start Up curve for refractory cure can reduce some refractory spalling repairs.

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Cracks in the Plenum Corners above the header and at sidewall gusset supports due to unit expansion.

Inspection Focal Points 

PA Nozzles –ash pluggage, broken, and erosion

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PA Plenum –ash build up, gusset supports, corners

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FBAC ACV Inlets –Grease Air Ports

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SA Ducts –Overheat damage

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Fuel Chutes –Ceramic Tiles

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Start Up Burners –Erosion, overheating

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Ash Return Vents –Gaps

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SRD Duct Outlets –Refractory and Grease Air

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FBHE Return Ducts –Refractory and FA Nozzles

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Refractory –Spalling of ledges

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Water Walls for erosion and condition of AMSTAR Spray

Lower Dead Air Space Inspection includes the examination of all skin casing, insulation, refractory, seal boxes, tube assemblies, and the structural condition of all expansion and support members, supports, braces, and hanger rods. Examine all support structures for broken welds, disconnected, broken, or bent rods and missing nuts and bolts. 

Check for bent or twisted supports.

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Check all slope tube support buckstays.

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Check all framing supports.

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Examine condition of bottom slope tubes.

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Dead Air Space Support Steel and Hangers

Hanger Disengaged from Support

Visually inspect the dead air space for ash accumulations due to gaps at the slope tube membranes. Also check sidewall casing structure for any indication of defects or cracks.

Damaged Waterwall Slope Tube Large clinker or ash accumulations can build up in the tube assemblies in the top of the furnace and eventually fall, damaging the lower slope tubes and the structural steel inside the lower dead air space, especially near the side wall corners. 01/2016

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Visually inspect the bifurcated tube membranes for cracking near the membrane end at the bottom of the side wall tubes above the bifurcate. Dye-penetrant checking of this area is also recommended if there is any history of tube failures. If tube failures have occurred or cracking is evident, treat the membrane as follows: Contour the ends of the membrane welds, creating a smooth radius. Cut the middle of the membrane back from the end a few inches and drill a hole at the end of the cut. Use a pencil grinder to remove any rough edges from the cut and hole. Examine sidewall seal boxes for cracks, tears, and signs of expansion problems.

Side Waterwall Seal Box Crack Furnace pressure or expansion can cause the slope wall scallop bars to tear adjacent to the sidewall scallop bars. The tear can extend into the side wall tube, causing a failure. Inspect seal plate condition where waterwall downcomers penetrate lagging. Check expansion joints (boots) at the lower strut penetrations.

Furnace Waterwalls Lower Sidewall Tubes

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Inspect the lower sidewalls, looking for signs of erosion caused by sliding ash. Also examine the area around the lower sootblower openings for erosion. On many units, the lower sidewall tubes at the center point are tied together by a solid plate. Failures have occurred in this area, along the tube membrane, due to fatigue resulting from concentrated areas of thermal stress or corrosion attack, at the high stress concentrations. Inspect this area, looking for signs of fatigue or corrosion. If damage is found, replace the first two or three tubes to either side of the centerline and implement the lower sidewall modification. Furnace Bottom Slope Tubes Inspect waterwall tubes in the coutant bottom for gouges, dents, bowing, and overall damage due to slag falls, slag erosion, or a combination of the two. Erosion (abrasion wear) from tumbling and sliding slag or flyash can wear down the tube surface exposed to the furnace area. When this happens, the tube can fail from excessive thinning or from a minor slag fall rupturing a weakened tube wall. Large sections of slag from the upper furnace can dent the tubes and rupture them at the impact area or cause an overheating failure elsewhere due to restricted flow. Failure can occur in the dead air space side of the tubes, at the steel support lugs. The great force of slag falls can deflect the hopper slope tubes along with the support steel. Inspect for leaks in the sealed membrane. Leaks can result in overheating of the structural support steel in the dead air space. GUIDELINE When evaluating gouges and dents in slope tubing, indentations that reduce the wall thickness below the original Minimum Wall Thickness (MWT) should be considered for repair. Tubing should be considered for replacement when wear or corrosion has reduced wall thickness below original MWT. Individual tubes or tubing panels should be considered for repair or replacement when warpage or bowing has deflected the tube(s) more than 1 tube diameter out of line. Waterwalls Thoroughly inspect all waterwalls. Give particular attention to the following 

Waterwalls around sootblower openings

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Waterwalls around the windbox openings

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Waterwall corners

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Waterwalls in the high heat absorbing areas

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

The extended side walls

Examine waterwalls around sootblower openings for erosion and wear. Inspect the tubes adjacent to the blowers frequently to determine tube wall thickness. Ultrasonic testing equipment and actual measurements can be helpful in determining any tube wastage. If erosion is noted, check the alignment of the blower. The centerline of the swivel tube should be perpendicular to the face of the boiler tubes. Check the distance of the centerline of the cleaning nozzle to the face of the boiler tubes. Inspect the waterwall tube membrane at the sootblower opening. membrane can be relieved with a saw cut through the center.

In some instances, this

Examine the waterwalls in the vicinity of the firing zone for corrosion and wastage. Thoroughly check the walls around the windbox and corners. Adjust coal fineness to prevent coarse coal from reaching the furnace. Maintain equal distribution of coal to all fuel nozzles. Verify by clean airflow distribution testing of the pulverizers and/or coal line mass flow tests. Centerwall On divided furnace units with centerwalls, observe and record the amount and direction of centerwall tube panel bowing. While some panel bowing is acceptable, bowing in excess of several feet out-of-plane may be indicative of operational or structural problems and should be investigated further. Deflection Arch Rear waterwall tubes form the deflection arch, projecting forward at the top of the furnace rear wall and then sloping back underneath the superheater and reheater vertical spaced assemblies. Examine the upper arch for signs of erosion. Flyash/sootblower erosion can cause considerable damage to the tubes and peg fins. Closely inspect arch tubes adjacent to the furnace centerline for evidence of sootblower erosion. Erosion is more prevalent in this area due to the droop of the lance as it is extended into the furnace. Check the entire arch. Depending on unit operation, erosion can occur either on the nose or 3 to 4" above the bend. Eddying of flyash above the bend can result in even wear, problems may be difficult to detect by visual observation. Refractory under the tubes can be eroded away exposing the skin casing, resulting in skin casing cracking and warping. On newer units the upper arch tubes will be of solid membrane design, which in most cases has eliminated skin casing problems. Overheating of upper dead air space support members can also result and can affect the structural integrity of this area. 01/2016

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Examine the rear waterwall hanger tubes for erosion. The backs of the rear waterwall hanger tubes are susceptible to flyash erosion where they penetrate the upper slope of the arch. To prevent damage and subsequent ruptures, these tubes should be shielded at least 4 to 6" up from the arch tubes and extend shields down to the seal box. In some instances, abnormal flue gas velocities under the pendants will erode the front side of the tubes. To prevent damage these tubes should be shielded at least 12" up from the upper arch tubes. Check all penetrations through the arch for indication of seal damage. Check the steam-cooled spacer tubes for erosion where they penetrate the upper arch. Check for extended sidewall movement. Sidewall tubes can move away from the wall by as much as 1 to 1.5" allowing flyash to work its way down and bow the casing. Check clearances between the reheater vertical spaced assemblies and the deflection arch

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Nose Arch Inspection Points

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Location of Wear

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Superheater Assemblies The superheater inspection includes the external examination of all tube assemblies. It also includes the examination of all fluid, steam, and mechanical spacers, tube shields, pad welds, flexible spacers, and band type spacers. To inspect the superheater, erect scaffolding or sufficient sky-climbers must be provided to effectively conduct a thorough examination of all superheater assemblies and support members. Inspect all vertical superheater assemblies for signs of hard ash deposits. If the deposits are significant, recommend removal at this time. Examine each group of assemblies separately, since each group is affected differently by gas flow. Review previous inspection reports, then determine areas of concern. Inspect tube assemblies for any sign of failures in the area of dissimilar metal welds. Variables that can promote this failure are the following: 

High temperature

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Time in service

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Differential expansion

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External loading

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Cycling of unit

Inspect all tube assemblies for any signs of warping, bulging, and swelling, which might be indications of overheating. CRITERIA: If tubes are swelled 2% over specified OD, a sample should be taken for analysis. When measuring tubes, take measurements at least 18 inches from the shop welds or bends. This eliminates the effects of manufacturing processes on the tube dimensions. If problems have occurred in the past, recommend removing a tube sample section and send it to the laboratory for analysis. Conduct wastage surveys in selected sections to assess the tube wall thickness. Document the results to compare to measurements in future outages. Superheater Division Panels Steam-cooled spacer tubes help maintain the alignment of the division panels and minimize panel sway. These spacer tubes bifurcate at the front of the furnace and proceed horizontally across the left and right sides of the division panels. Because of this, wear between spacer tubes and the superheater division panels can be a problem and can cause considerable damage if overlooked during an outage.

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During the inspection, examine all elements and assemblies for any indication of bowing or signs of misalignment. Examine horizontal tubes for misalignment. Broken slip spacers allow horizontal tubes of the division panels to distort and collect slag. Once out of alignment, the weight of additional slag could cause the tubes to sag. Realign any tubes out of alignment and add additional flexible tube ties. Repair any broken flexible tube ties. Consider recommending replacement of any misaligned tubes, which are badly bent. Examine misalignment between flexible tube ties. In these areas, tubes can bow out of alignment mainly due to the differential expansion between the panels. Check for misalignment between the top and middle level of slip spacers. Check for misalignment between the roof tube and the first flexible tie. Realign any bent tubes and add additional tube ties. Examine girdling tubes for misalignment. Tubes bow out of alignment due to tie lugs breaking away at the weld. This can be caused by the vertical differential expansion between the girdling tubes on each side of the panel. Check for broken lugs on each side of the panel. Check for broken connecting straps. Check for wear between the vertical girdling tube and the horizontal tubes of the division panel. Install new tie lugs that allow for vertical expansion between the vertical girdling tubes on each side of the panel. Examine all elements and assemblies for wear. Tube wear between a steam-cooled spacer and the division panel tubes can easily be seen when the tubes are separated using a pry bar. Mark each worn tube so they can easily be identified when repairs are made. Inspect for tube wear between each support lug and the bottom of the steam-cooled spacer. Inspect the steam-cooled spacer tubes where they cross over between panels. Check for wear between the wrapper of a division panel and the spacer tube. Before any repair work is begun, make note of material changes. This information can be found on a unit material diagram. Superheater Division Panel Anchors The front wall anchors for the spacer tubes on radiant reheat units are subjected to severe wear due to furnace pulsations (Figure 28). In general, the superheater division panels move from side to side while the front wall moves from front to rear. The radiant reheat inlet header acts like a buckstay to reduce front wall movement. There is still some movement however, because the front anchors are located between the radiant reheat inlet header and the top of the furnace.

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Superheater Division Panel Anchors Thoroughly inspect the division panel anchors and check the spacer tube roller sleeves. They should be free to rotate, and centered with respect to the offset tube sleeves. There should be a total of 3/8" clearance between the offset sleeves and spacer tube sleeves. Check to see if the collar is rubbing against the offset tube instead of the spacer tube sleeve. Check for correct clearances so as not to cause excessive collar-to-sleeve wear. Check for wear on the spacer tube roller shields. In making recommendations for repair, make note to rotate roller shields so that the non-worn surface would be facing the anchor tube shields. Superheater Platen Assemblies During inspection, examine the fluid-cooled spacer for tube wear. Inspect for wear between the fluid-cooled spacer and the superheater pendant platen tubes on both sides . Check for steam-cooled spacer tube wear. At the front of these assemblies, a steam-cooled spacer tube passes between the first and second tube assemblies. The newer steam-cooled spacer lug consists of a scalloped lug, a spacer lug, and a support lug located between two flexible tube ties. Inspect possible wear areas. Inspect support lugs for thinning due to wear or oxidation. Inspect for spacer lugs that may have come out of the support lugs.

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Replace spacer and support lugs if required. Type 309 stainless spacer and support lugs should be used for increased alignment and durability. An arrangement utilizing spacer and support lugs on both the top and bottom sides of the steam-cooled spacer tube provides the maximum amount of alignment security. Examine the assemblies for misalignment due to broken flexible tube ties. Realign any bent tubes by placing channel pieces with nuts and bolts on both sides of the assembly to draw the tubes back in place. Replace any broken flexible tube ties and add additional ties as needed. It may be helpful to add a vertical girdling tube similar to those on the superheater division panels to maintain tube alignment at the bottom of the assembly. Examine any misaligned tubes between the flexible tube ties. Misalignment here is most likely due to the differential expansion between dissimilar materials. Expansion problems in this area should be discussed with the manufacturer before taking corrective action. Misaligned tubes in this area are very susceptible to sootblower erosion. Recommend that tubes are realigned and additional flexible ties added, providing they have not been subjected to erosion to the extent they would require tube repair or replacement. Inspect for broken slip spacer and saddle lugs on the lower sections. This would allow tube misalignment and tube-to-tube wear. The outside wrapper tubes on each assembly should be examined for sootblower erosion. Inspect for erosion of the outside wrapper tube in the area of tube metal change. Inspect for missing tube shields or tube shields that have slipped down. If sootblower erosion is a problem in this area, examine the sootblowing system. Check for condensate in the steam blowing system. If condensate is present, check the thermal drain system. Excessive steam pressure can cause rapid erosion. Check that steam pressure and temperature match setpoints. Check frequency of sootblower operation. High concentrations of flyash can also increase the erosion process. Superheater Pendant Spaced Assemblies The superheater pendant spaced assemblies are located directly above the furnace arch. This area is susceptible to deposit buildup, wastage due to the combined effect of gas flows and high flyash concentrations, and tube misalignment. During the inspection, thoroughly examine this area for deposit buildup, abnormal wear or wastage, tube misalignment, slip spacer condition, and support lug condition. Inspect the front and rear steam-cooled spacer tubes at the points where they contact the assembly tube elements. Inspect for missing tube shields. Recommend repair or replacement of broken strap welds. Conduct a wastage survey to assess wall thickness in the leading edges of every 10 assemblies above the long retractable sootblowers and at the rear of the assemblies.

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Examine all flexible tube ties in this area for indications of cracking and broken welds. Flexible ties can come out of alignment due to a restriction in movement, which could be caused by ash accumulation under and between assemblies. Low Temperature Horizontal Superheater Assemblies The low temperature superheater assemblies can be either vertically hung pendant assemblies or banks of horizontal assemblies, depending on boiler design, and are located in the backpass of the boiler above the economizer. The horizontal assemblies are very susceptible to uneven temperatures due to the cooler economizer outlet terminal tubes (horizontal superheater support tubes) passing through the support saddles and causing the adjacent superheater metal surfaces to be subcooled, relative to the rest of the tube surfaces. During the inspection of the horizontal superheater, inspect for superheater tube pairs bowing away from each other due to the uneven temperatures. If the tubes are not breaking away from the saddle support, leave them alone until the next inspection. Check for flyash erosion on the front return bends of the horizontal superheater, especially if the front bends extend above the backpass floor. If this is a problem, recommend installing a method to shield the bends with stainless steel, or install baffles to redistribute the gas flow adjacent to the tube bends. Whether a refractory or metal plate baffle is installed, it should be installed so that the baffle is horizontal and does not slope downwards towards the superheater tubes. This slope will accelerate wear on the tubes as gas and ash sweep downward off the baffle onto the tubes. Check for flyash pluggage between the rows of the horizontal superheater tubes. Check for flyash erosion and pluggage at the rear wall and horizontal superheater assemblies. Reheater Assemblies The reheater inspection includes the external inspection of all tube assemblies. It also includes the examination of all tube shields, pad welds, and mechanical spacers (flexible and band-type). To inspect the reheater, scaffolding must be erected so that a thorough and safe inspection of all reheater assemblies and support members may be conducted. Inspect all vertical spaced reheater assemblies for signs of hard ash deposits. If hard ash deposits are significant, remove them at this time. Examine each group of assemblies separately, since each group is affected differently by gas flow. Review previous inspection reports to determine areas of concern. Inspect tube assemblies for any signs of failures in the area of dissimilar metal welds. Variables that can promote this failure are: 

High temperature



Time in service



Differential expansion

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

External loading



Cycling of unit

Inspect all tube assemblies for any signs of warping, bulging, or swelling, which might be indications of overheating. If problems have occurred in the past, remove a tube sample from a section and send it to the laboratory for analysis. Conduct wastage surveys in selected sections to assess the tube wall thickness. Document the results to compare with previous wastage measurements and what will be taken in future outages. Radiant Reheat Front Wall and Side Walls The radiant reheat front wall and side wall tubes are located in the upper portion of the furnace waterwalls in the area surrounding the superheater division panels. During inspection of this area, check for bowing of the front and sidewall tubes. Realign as necessary. Check for tube swelling due to overheating. Replace tube sections as needed. Check for tube erosion, especially at the lower bends where the tubes go through the wall. Pad weld if needed and install tube shields. Check for tube metal loss due to tube rubbing. If metal loss is found, recommend installing stainless steel tube shields at the points of contact. The tube shields should not be seal welded. Reheater Vertical Spaced Rear Assemblies The reheater vertical spaced rear assemblies are located after the reheater vertical spaced front assemblies at the top of the arch. Install wear strips in crossover tubes where there is contact with the rear waterwall hanger tubes. Check for broken, burned off, or disengaged slip spacers. Reheater Vertical Spaced Front Assemblies The reheater vertical spaced front assemblies are located after the superheater platen assemblies and are suspended above the arch. Check broken or missing slip spacers on the front and rear sides of these assemblies, and note location. Inspect all tube assemblies for signs and magnitude of bowing. Note location and severity. Measure wastage on the leading elements of the assemblies in the area of the long retractable sootblowers and record wastage. Sootblowers normally erode only lead tubes in an assembly (unless out of alignment), but erosion can occur on second, third, or fourth tubes, etc. Appendix D includes samples tables that are used to collect this data. Check for flyash erosion resulting from vertical surface pluggage. This erosion can occur as much as five to six tubes deep in an assembly. One possible cause is high velocity gas erosion, due to the channeling of gases in a vertical section. This can develop when a reheater vertical section 01/2016

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experiences severe pluggage, possibly due to a change to high sodium coal or misalignment of vertical tube assemblies. Sootblowers cut flow path channels through the pluggage, which eventually grow smaller and deeper into the bank. The resulting orifice creates high velocity uneven gas flow distribution that is directed at the inner vertical tubes. Flyash erosion on vertical tubes, resulting from plugged conditions typically exhibit areas of cratered and protruding surfaces quite different from the classical, generally smooth flyash erosion patterns found on screen tubes and rear pass horizontal surfaces. If pluggage occurs during operation, determine the degree of it through the use of observation doors or by an increase in gas side pressure drops, and in some cases by changes in individual tube element steam temperatures. During an inspection, examine closely the vertical sections known to be susceptible to plugging. Failures due to high velocity gas channeling should be reported as flyash erosion and a description of the pluggage and the circumstances should be carefully documented. Check reheater vertical spaced front assemblies and furnace deflection arch for clearances (Figure 30). Inspect condition of tube shields and note locations of missing tube shields. Appendix D includes samples tables that are used to collect this data. Check condition of high crown seals where tubes penetrate the roof. Rear Waterwall Screen Tubes The rear waterwall screen tubes are located behind the rear waterwall hanger tubes. As their name implies, they are formed by the rear waterwall tubes forming the arch and bending upward toward the roof. On some units, a refractory kicker baffle has been installed at the base of the screen tubes to redirect the gas flow entering the horizontal SH and economizer sections. Flyash erosion can also occur on the screen tubes directly above the kicker baffle. If erosion is evident, remove the top 2” of refractory kicker baffle. Recommend exposing any eroded areas and repairing screen tubes as required. Conduct a wastage survey to determine where tube shielding is required. Shield screen tubes with at least 12” of 309 stainless steel, in such a way that the bottom of each shield rests on the remaining refractory kicker baffle. Recommend replacing the upper portion of the refractory kicker baffle so that the bottom of each shield is embedded in the refractory. Further up on the screen tubes, examine welded-tie vibration restraints for evidence of cracking (Figure 31). If cracks are found, recommend repairing the affected tubes. If frequent tube failures at these restraints have been responsible for excessive downtime and/or damage to adjacent tubes, an additional row of vibration restraints may be required above the welded restraints.

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Cracking of Welded Tie Restraints

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Rear Waterwall Hanger Tubes The rear waterwall hanger tubes are located above the deflection arch between front and rear sections of reheater vertical assemblies. The hanger tubes are furnace rear wall tubes, which pass straight upward from the furnace rear wall through the deflection arch upward to the roof. Inspect all existing tube shields and pad welds . Look for cracks in welds, which are an indication of problems resulting from temperature differentials. Inspect the hanger tubes for wastage, especially at the top where they intersect with the roof tubes and at the bottom directly above the slope tubes. If erosion seems uniformly excessive at any point across the hanger tubes, a wastage survey is recommended. The backside of the hanger tubes is susceptible to flyash erosion directly above where they penetrate the arch tubes. The hanger tubes should be shielded anywhere from 4 to 6" from the arch tubes. The shield should extend down to the seal box. In some instances, flyash laden flue gas will flow under the pendant assemblies at higher than normal velocity, eroding the front side of the hanger tubes. The hanger tubes should be shielded up to at least 12" from the arch tubes. Inspect steam-cooled spacer tubes where they pass between hanger tubes. Inspect for wear at contact points with the steam-cooled spacer tubes. Pad weld and install wear strips as required. Examine hanger tubes in proximity of sootblowers. If erosion is evident, shields may be installed, extending 2 to 3" above and below the centerline of the sootblower locations. Closely inspect all welded tie vibration restraints for weld cracking which may be caused by vibration due to combustion gas velocity or stress caused by ash loading. Upper Dead Air Space The upper dead air space is located at the top of the furnace between the furnace arch and the backpass. Inspection includes the examination of all skin casing, insulation, refractory, tubes, and the structural condition of expansion and support members. During unit operation, local temperatures inside the upper dead air space are approximately 800F. If casing leaks develop allowing furnace gases to enter the dead air space, temperatures can approach 1500F. Overheating of structural steel at these excessive temperatures can lead to distortion, loss of structural integrity and possible failure. Visually inspect all supports, braces, and hanger rods for structural integrity. Randomly perform a "tuning" operation on the hanger rods to check structural soundness by tapping the rod with a metal instrument. Examine all support structures for broken welds, bent rods, and missing bolts and nuts. Inspect for bowing due to extreme temperatures. Examine for cracks, oxidation, and deterioration. Determine how severe the problem is and explore possible methods for reducing or eliminating excessive damage.

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Examine all hanger rods and support structures for integrity. Broken, missing or loose clevis pins and rods must be replaced and properly tensioned. Inspect rods for elongation due to high temperatures. Examine all turnbuckles for cracked, missing, or weakened assemblies. Visually inspect all casing structures for any indication of defects. Check for loose waterwall hangers. Inspect for loose floor hangers that extend from the backpass extended sidewalls. Inspect for bent center row hangers. Inspect for loose horizontal buckstay bolts. Examine seal boxes. Inspect for cracks, tears, and signs of expansion problems. Examine casing for indication of warping due to overheating. Inspect all support buckstays for indication of bulging, twisting, and cracks. Examine the condition of the refractory around the peg finned bifurcated tube assemblies. Missing and deteriorated refractory and insulation material can cause erosion, overheating problems, and heavy flyash buildup in this area. Remember that support structures are designed for a predicted load and stress. Any amount of skin casing expansion that is greater than the tube expansion must be absorbed by the expansion joint that runs from left to right. Recommend repairing. Details are in Appendix G Reduce sootblowing frequency and pressure if frequent tube erosion or refractory and casing damage is evident. Recommend installing shields on the furnace side between the tubes, on top of peg fins. On newer units, the rear waterwall upper arch will have a solid membrane between the tubes instead of peg fins, which in most cases has eliminated the skin casing problems. Inspect for structural damage at the roof of the dead air space. Reheater front vertical spaced assemblies are located above the tubes forming the roof of the dead air space. Structural steel damage occurs when flyash builds up under these assemblies which expand downward. The tube assemblies push on the ash, which in turn pushes on the roof tubes and structural steel under them. This flyash restriction can cause roof tube and reheater damage in addition to the structural steel damage. If necessary, recommend installing sootblowers in this area to minimize ash buildup. Furnace Roof Tubes From inside the furnace, conduct a visual inspection of furnace roof tubes. List discrepancies on a diagram showing plan view of the superheater and reheater assemblies (Figure 33). Inspect refractory condition, noting any missing refractory. Inspect for sagging roof tubes, paying particular attention to sidewalls. Check for worn or burned peg fins and missing refractory at the steam-cooled spacer penetrations. Continue the inspection inside of the penthouse, especially where sagging roof tubes or missing refractory are observed. Check for skin casing overheating, deformation, or cracks. Inspect for cracks in the seals around the superheater and reheater pendant assembly tubes where they pass up through the roof tubes. 01/2016

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Economizer The economizer is located behind the rear low temperature horizontal superheater in the lower section of the boiler backpass. The economizer is a bare tube, arranged in-line unit. Inspect each of the banks of the economizer for polishing, tube alignment, and pluggage (Figure 34). If erosion is a problem, consider recommending the installation of tube shields. Check front and rear return bends and bare tube surfaces for metal wastage. Ultrasonic testing of tubes is recommended when heavy polishing or erosion is evident. Inspect for polishing around sootblower openings. Check clearance between tube bends and the backpass walls, and between headers and sidewalls. Examine all economizer support tubes. Check for tube misalignment. Check for tube erosion due to flyash and gas flow. Inspect material condition of tube shields. Check for wear resulting from metal-to-metal contact between the vertical support tubes and horizontal economizer tubes. Inspect all elements for possible pluggage problems and investigate material condition of elements covered with ash. Check for flyash/sootblower erosion of tube bundle support hangers. Inspect for broken support straps. Install additional straps as required. Pull up any elements that may have sagged due to broken straps. Check for gouging between hanger supports and tubes. Examine all wire mesh and refractory baffles and the tube surface condition under the baffled area. Inspect expanded metal screens for tears, holes or missing sections. Inspect refractory baffle condition noting missing, eroded, or crumbling sections. Inspect for tube wastage where the refractory ends. In some instances where the tube return bends may be coated with Super 3000, inspect for deterioration of refractory especially after water washing this section. Inspect for gaps behind baffles at sidewalls. Increased gas velocities can polish the side wall tubes. If any gaps are found, recommend installing mesh and filling with Super 3000 refractory.

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Economizer Inspection

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Examine condition of refractory at sidewall tubes and recommend repair as necessary. Examine all header assemblies for metal wastage due to erosion. Outside diameter measurements will indicate wear patterns. Inspect welds around tube nipples and headers for cracks. Install erosion shields if necessary. Examine the economizer ash hopper for structural defects. Inspect support steel and hopper ductwork for signs of overheating and erosion to the refractory layer. Examine hopper for buckling and cracks due to expansion problems. High temperatures at the hoppers can usually be traced back to high temperature gases bypassing the economizer assemblies. Inspect circumferential welds on the economizer inlet header. Check for stress corrosion fatigue cracking at inlet tubes. Penthouse The penthouse is dead air space located on top of the unit. It houses all of the headers, which are located in this area, along with the steam drum. The amount of ash accumulations in the penthouse dictates whether or not removal is necessary before, during, or after the inspection. If the ash is uniform in depth, it should be removed prior to inspection. If repairs are required, remove the ash before or during the outage. If small individual piles of ash are present, inspect the penthouse before ash is removed (individualized piles of ash indicate areas of possible casing leaks). Exercise care while vacuuming; the ash will retain heat for a longer period of time than that required for cooling the boiler. Inspect the penthouse casing structure for any indications of problems. Cracking is the most likely problem encountered. Check for cracks in the casing panels that may occur at the transition points, at the junction of tube assemblies, or at the high crown seals. Recommend repairing large cracks by grinding out the crack and welding a casing patch in place. Repair small cracks by welding. Inspect the floor area for cracked or missing refractory. Recommend repairing missing refractory by patching. Inspect all supports, braces, and hanger rods for structural integrity. Check all supports for broken welds, cracks, bent rods, missing nuts or bolts, and for any bowing or any other signs of misalignment. Check hanger rods for proper tension. Also check for missing or loose clevis pins and the condition of the hanger rod turnbuckles. Inspect all pipe braces, supports, saddles, and hangers. Visually examine all headers located in the penthouse. Selectively check header tube root nipples. If any problems are found or suspected, check all nipples on that header. Magnetic particle method would work very well in finding cracks.

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Check the condition of the insulation material on all high temperature headers in this area. Look for deteriorated or missing insulation along the walls and roof. Check the condition of all expansion joints in the penthouse area. Look for signs of expansion problems. Thermocouples might be installed on some headers or tubes in the penthouse. Check the condition of these thermocouples and associated wiring. Exercise caution so as not to damage any of these thermocouples. Observation Ports and Access Doors Inspect observation ports and note condition of spring grips, latch pins, gaskets, liners, and door opening refractory. Inspect the refractory material around openings in the observation door. Inspect for slag buildup that can obstruct the view from an observation port. In areas where tube assemblies are protected by refractory, check for any indications of problems. Examine refractory material for cracks, erosion, and missing sections. Inspect access doors and note condition of refractory around opening.

Example of Observation Port Inspection

Desuperheater The purpose of the desuperheater is to control steam temperature through the use of cool tempering water. Desuperheaters are installed in both the superheater and reheater circuits.

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The typical in-line desuperheater consists of a shell, liner, and spray nozzle assembly. The shell acts as housing. The spray nozzle assembly introduces the tempering water. The liner protects the shell from thermal shock when the relatively cold tempering water is injected into the steam system. Conduct superheater desuperheater liner inspections every three years. This inspection is accomplished by inserting a boroscope through one of the penetrating screw holes. Examine the liner for any gross deformations. Examine the spray nozzles for any enlargement of the nozzle holes. If extensive wastage is found, replace the spray nozzle. Examine the hole in the liner where the penetrating positioning screw has been removed and measure the hole for elongation. Without wear, the hole should be 1.06", +0.016", - 0.00" in diameter. Record any elongation and the direction with relation to the run of pipe. If the hole has elongated 1/2" longitudinally or is within 1/4" of the edge of the reinforcing ring, recommend replacing the liner. If inspection shows the liner to be in good condition, replace the penetrating screw through the liner, and seal weld the screw to the pipe. The reheater desuperheater liners are not subjected to the temperature differentials seen in the superheater desuperheater and therefore do not usually require inspections as often. Steam Cooled Enclosure (Backpass) The backpass wall and roof sections are formed by the backpass side wall tubes at front, backpass side wall tubes at rear, backpass front wall tubes, backpass front wall screen tubes, backpass roof tubes, backpass rear wall tubes and the backpass lower rear wall tubes of the vertical gas pass. The superheater tubes going to the backpass area from the "back pass at roof inlet header" form the furnace front roof tubes (above the furnace) and furnace rear roof tubes (above the arch). The most common problem found is erosion. Both sootblower and flyash erosion are often found on the backpass wall tubes (Figure 38). Sootblower erosion is commonly found along the paths of the sootblower lance. The tubes on the front steam-cooled wall seem to have this problem most often. Flyash erosion is commonly noted along the sidewalls and at the base of the walls, especially on tubes that are out of alignment. The backpass wall tubes should be inspected for overheating. Typical signs include swelling, discoloration, circumferential or longitudinal cracks, and other problems. Also, inspect the backpass walls for bowing, conditions of damaged refractory and casing.

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Backpass Inspection

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INTERNAL INSPECTION – WINDBOXES General Description – PC Boiler The windbox area is not a pressure part, but is a significant part of the furnace inspection. Before making the initial examination of the windbox assemblies, a review of the windbox arrangement drawing should be made to determine the windbox concept, fuel and auxiliary air compartment arrangement, warm-up fuel arrangement, intended method of support of components, furnace and windbox expansion values, and expansion provisions. The basic functions of all burners of fossil fuels are to provide the time, temperature and turbulence to unite the fuel with air and convert the potential chemical energy of the fuel to a more usable form, heat energy. In order to accomplish the process safely and efficiently, manufacturers have devised many arrangements of ignition, atomization and fuel-air mixing. In spite of state of the art improvements to make burners safer and more efficient and extensive standardization, each burner on a given steam generator seems to perform differently from supposedly identical installations on other steam generators. We consider fuel burning a combination of science and art. Tangential firing differs in concept from the wall burners in that the furnace itself is the burner. The corner mounted nozzles serve only to inject fuel and air into the furnace in layers and at firing angles that will promote mixing and burning in the furnace. Oil burning is most efficient with wide open fuel air dampers and a high windbox-to-furnace differential pressure. This is accomplished by throttling the auxiliary air dampers. Gas and coal are efficiently burned with throttled or modulated fuel air dampers and lower windbox to-furnace differential pressures. Design Features The following are general design information for tangential firing from furnace corners on fielderected and modular units: Fuel suitability - natural gas, waste gases, fuel oils (coal is not covered in this guidebook) Design turndown ratio - 10 to 1, depending on fuel capability Oil atomization capabilities - steam or air, wide-range mechanical, straight mechanical Primary air used for coal transport only Secondary air (all fuels) splits into fuel air and auxiliary air. Air enters furnace in tangential layers and can be distributed behind the fuel or parallel to the fuel stream as necessary. The fuel air dampers are positioned as a function of elevation loading. The auxiliary air dampers control windbox-to-furnace delta-P.

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Minimum excess air 15 percent on oil* 10 percent on natural gas* *For improved efficiency and lower emissions, special firing equipment is available, but must be used in combination with sophisticated controls and careful load regulation. In recent years environmental regulations have generated a need to burn fuel oils at very low excess air. In many cases this has required changes to diffusers, air nozzles and oil gun tips. Each case must be approached separately, but tangential firing has the capability of being operated at less than 3 percent excess air, providing plant instrumentation is suitable to control the process, and operators and maintenance personnel are trained and motivated to follow more stringent practices than for higher excess air firing. Low excess air firing requires: 1. Accurate, low maintenance, high reliability excess oxygen monitoring equipment. 2. Controls must be kept tuned and in automatic operation. 3. Secondary air dampers must be carefully set to be at equal positions at the same elevation at all four corners. Depending on individual firing conditions, the upper or lower auxiliary damper may have to be pinned or biased open to clear up smoky furnaces. 4. Fuel flows at each corner must be as equal as possible on an elevation basis. With oil firing this means monitoring burner tip orifices for erosion and separating worn tips within wear groups on the unit at any one time. The following is suggested standard for tip wear: Effective Flow Classification New

0 to 3

A

3 to 5

B

5 to 7

C

7 to 10

Increase, Percent*

*Effective flow increase is approximately equal to the percent increase of the orifice tip diameter squared. Discard all tips worn greater than 10 percent flow increase.

Windbox Arrangement – PC Boiler 01/2016

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There is a vertical windbox assembly in each of the corners of the furnace. A typical windbox assembly is divided into compartments for the admission of fuel and secondary air into the furnace Coal compartments contain coal nozzles and also admit "fuel air" into the furnace. The term "fuel air" is applied to that portion of secondary air that is supplied to a fuel compartment. Auxiliary air compartments admit "auxiliary air" into the furnace. The term "auxiliary air" is applied to that portion of secondary air that is supplied to the auxiliary air compartments. Oil or gas compartments contain oil guns or gas nozzles for warm-up or load carrying duty. When oil guns or gas nozzles are not in service, these compartments may function as auxiliary air compartments. The uppermost air compartments in some installations are termed the "overfire air" compartments. The term "overfire air" is applied to that portion of secondary air that is supplied above the fire. This air is used to control the formation of nitrogen oxides (NOx). Located inside each air, coal, and oil compartment (>18” wide) are turning vanes, which direct the air around the corner from the windbox damper section into the furnace. The turning vanes impose a streamlined, even distribution of air to each air, coal, or oil nozzle. Partition plates form the top and bottom of each compartment.

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Windbox Arrangement

Coal Compartment – PC Boiler 01/2016

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Inside each coal compartment is a stationary nozzle and a tilting nozzle, which is also called a nozzle tip or bucket. The stationary nozzle is supported at one end by the windbox panels and at the other end by support plates bolted to the sides of the nozzle. The tilting coal nozzle tips pivot on pins attached to the stationary nozzle. The tilting coal nozzle tips can be tilted upward and downward 25 from horizontal. “Splitter plates” in the nozzle tip direct the flow of primary air and coal into the furnace as the nozzle tip is tilted from horizontal. A seal plate pivots as required with the nozzle tip to close any gap that forms between the nozzle tip and the stationary nozzle as the nozzle tip is tilted up or down. One design of stationary coal nozzle for high-turndown applications is provided with an internal horizontal splitter plate that separates the primary air/coal stream into a fuel rich and a fuel lean stream. This ensures that the proper air/coal ratios required for combustion are available over a greater unit load range. The nozzle tip itself contains diverging corrugated splitter plates and air deflectors. The irregularly "v" shaped bluff body diffuser induces turbulence to the discharging air/coal stream. In addition, it creates a low-pressure zone, which causes a high recirculation pattern to form. These features promote a more stable ignition point over wide load ranges. Oil Gun Compartment – PC Boiler The corner windbox may also contain oil gun assemblies. The oil guns, along with eddy plate side ignitors, may be used for warm-up of the boiler. The oil guns may also be used for load carrying and to provide the ignition energy needed to light off pulverized coal at adjacent elevations. The oil may also be utilized to provide stabilization for the coal fires at low boiler loads. Each oil gun compartment contains a tilting nozzle mounted on pins inside the windbox frame. A tilt adjusting mechanism, similar to the design of the air and coal compartments, links the tilting nozzle tip to the main tilt linkage. The nozzle is fitted with a vane diffuser for directing the air around the oil gun tip in a circular motion to create a recirculation zone for proper oil ignition. Natural Gas Compartment – PC Boiler Natural gas nozzles may also be provided as a warm-up or alternate main fuel source. They may be installed in a compartment either alone or with an oil gun. The natural gas burners consist of rigid piping supplying gas into wide flat nozzle assemblies located directly behind the tilting windbox nozzle tips. The gas nozzle tip is secured into brackets or guides on the sides of the windbox compartment. Flame Scanners – PC Boiler 01/2016

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Flame scanners are generally located in compartments between the main fuel elevations (coal or oil) for monitoring fireball stability. Filtered cooling air is delivered to the flame scanners through an air system consisting of the scanner cooling air fans, filters, and dampers. Cooling air is supplied to each scanner assembly through the scanner cooling air header located adjacent to the windbox. Windbox Dampers – PC Boiler Dampers at the inlet to each windbox compartment proportion the air depending on use, unit load, and feeder speed. One damper blade in each compartment is driven. The damper blades in each compartment are connected by linkage so that they all move together. Each damper should have a position indicating slot or bar on the end of the damper shaft, which is visible from the outside of the windbox. The slot or bar is parallel to the driven damper blade, and shows the exact position of the damper blades. Tilting Mechanism – PC Boiler The fuel and air nozzles are positioned by either electric motor drives or pneumatic tilt drive cylinders. Although there is one tilt drive for each windbox corner, the tilt drives are controlled so that the nozzles at all corner windboxes are always at the same tilt angle. Each corner elevation tilt indicator is equipped with a position indicator, a manual locking pin, a shear pin, and a spring-loaded locking pin. The fuel nozzles can typically tilt through a 50 range, 25 up and 25 down. The oil nozzles can typically tilt through a 60range, 30 upward and 30 downward from the horizontal. The auxiliary air nozzles can typically tilt through a 60 range, 30 upward and 30 downward from horizontal. Low Nox Concentric Firing Systems (LNCFSTM) – PC Boiler Tangential firing systems that have been modified for Low NOx operation may include the following additional features

Modified coal nozzle tips (“Flame Attachment”) - a design to create zones of recirculation for ignition stability nearer to the nozzle tip.

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Separated Over Fire Air (SOFA) registers - smaller windboxes located above the main windboxes to provide a significant amount of the secondary air staging. Fixed Offset “CFS” air nozzle tips - air nozzle tips constructed to direct a portion of the air into the furnace along a line that is offset from the main fuel. When required, these are utilized only in the main windboxes. Horizontally (“Yaw”) adjustable air nozzle tips - air nozzle tips that are adjustable for the amount of horizontal offset of the air introduction to the furnace. These may be utilized in the main windbox and in the SOFA registers These components are arranged in a fashion similar to traditional tangential firing equipment. However, they incorporate the latest standards for durability. The Low NOx Concentric Firing System (LNCFSTM) maximizes the NOx reduction capabilities of existing tangential firing systems while minimizing unit modifications. An LNCFS uses a combination of techniques to reduce NOx. These are "bulk furnace staging", “local combustion air staging”, and "early controlled coal devolatilization." Bulk furnace staging takes a portion of the combustion air, which is introduced at the fuel-burning zone, and diverts it to retard air and fuel mixing. With conventional tangential firing, the introduction of excess combustion air during the early stages of coal devolatilization contributes significantly to the formation of NOx. The LNCFS maximizes the bulk staging concept by using both separated overfire air and concentric firing. Local combustion air staging is produced by introducing a portion of the secondary air, called overfire air, above the primary firing zone. This is accomplished by utilizing a separated overfire air (SOFA) windbox, which is installed above each corner windbox. The concentric firing system utilizes a re-direction of the secondary (auxiliary) air, which is admitted in the main firing zone, diverting it away from the coal stream. In this manner, combustion stoichiometry is reduced by preventing the fuel stream from entraining with the air stream during the initial stages of combustion. Fuel nitrogen conversion is reduced, while maintaining appropriate oxidizing conditions along the furnace walls. The introduction of air in the concentric firing circle is accomplished with installation of concentric (CFS) air nozzles. Early controlled coal devolatilization utilizes the technique of early fuel ignition. Initiating the combustion point at a close distance to the fuel nozzle produces a stable volatile flame that is more easily controlled under sub-stoichiometric firing conditions. A specially designed coal nozzle is used to promote a strong primary flame.

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LNCFS Firing System An unmodified “standard” windbox arrangement is listed in the first column. As the table shows, the differences in types of Low Nox windboxes are the choices and combinations of close coupled or separated over fire air compartments. The selection of an LNCFS I, LNCFS II, LNCFS III or TFS 2000 windbox arrangement is based on the required reduction in NOx formation and the furnace geometry which determines space available for these modifications.

LNCFS common terms and components – PC Boiler LNCFS A retrofit package designed to reduce NOx from pulverized coal units without replacing the existing windbox structures. Generally speaking, LNCFS will utilize new auxiliary air nozzle tips (CFS), new fuel nozzle tips, and one of three different methods of applying OFA. All the components of the LNCFS are designed to withhold air temporarily and at different times during the history of coal particle combustion within the furnace. TFS 2000 01/2016

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Coal firing system is designed for minimum total emissions. Techniques employed to reduce NOx formation, such as sub-stoichiometric primary zone combustion, staging of fuel and air mixing, reduced excess air, and lower heat release rates, are all aimed at controlling the combustion rate and reducing peak flame temperatures. Since these conditions may increase the potential for CO, hydrocarbons, and increased unburned carbon emissions, a balance among these opposing factors is achieved through an integrated firing system that combines finer coal pulverization with advanced fuel admission assemblies and in-furnace air staging utilizing multiple air injection levels. P2 Coal Nozzles The P2 coal nozzle tip assembly utilizes specific design features to guard against tip deterioration and nozzle pluggage. The new tip is provided with a rounded corner design to decrease air turbulence in the tip’s corners and reduce recirculation and deposition of coal and coke. It was developed specifically for the demands of burner modifications for Phase 2 of the Clean Air Act of 1990. Aerotip Flame Front Control Coal Nozzle Tips Aerotip coal nozzle tips are a one-piece fabricated coal nozzle tip. They utilize design features to guard against tip deterioration and nozzle pluggage. To minimize high temperature oxidation, these coal nozzle tips utilize an erosion resistant material that offers a superb high temperature oxidation resistance. Nozzle tip shroud wall thickness is a minimum of 3/8" to resist warpage as well as erosion from the coal stream. In addition, the interior walls of the tip as well as all leading edges of the nozzle tip incorporate a weld overlay hardfacing material for increased erosion resistance. To help prevent coal nozzle/tip pluggage, the stationary coal nozzle choke area is designed to maintain proper coal stream discharge velocities based on fuel line velocities. In addition, the coal nozzle tip utilizes internal splitter plates designed to better control fuel air, especially during tilted conditions. By more effectively controlling fuel air, a more stable flame front position can be maintained over the entire tip tilt range. Crotch Cooling Crotch cooling consists of an air deflector assembly at the extreme top and bottom of each windbox to direct airflow adjacent to the refractory lined crotch areas of the bent waterwall tubes. This improves the cooling of this area as well as controlling the buildup of slag in this area. Both of these actions serve to increase the reliability and longevity of this refractory material. The windbox is partitioned through the damper box to ensure continuous airflow through the crotch air deflectors (no damper control of this airflow).

Air Restriction Blocks

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BOILER INSPECTION GUIDELINE

Air restriction blocks are used above and below coal nozzle tips to accommodate the reduced area nozzle tips. Tip area sizing has been based the best airflow velocities for stable ignition low NOx firing conditions. CFS Tips In the auxiliary air compartments, some special effects can be generated by the design of the air nozzle tip. One specialized auxiliary air nozzle tip is called a CFS tip, which directs air away from the adjacent fuel toward the waterwall. This simultaneously withholds auxiliary air from the adjacent fuel and provides more O2 in the waterwall area that enhances slagging patterns. CCOFA Close-Coupled Overfire Air, is that part of the main windbox where the top air comes out. The original arrangement had OFA, overfire air. After the top two coal elevations were positioned (coupled) closer together, the larger top OFA compartment becomes known as the CCOFA. SOFA Separated Overfire Air refers to air registers that bias combustion air above and away from the main burner zone. These air registers are physically separate from and above the main windbox. External Burner Corner Examination – PC Boiler The following items are general in scope and should be expanded by referring to contract specific drawings or prior unit inspections. Fuel Piping Check piping at windbox for proper support. Check oil piping at windbox for proper mounting and installation. Hoses must allow for cubical expansion of windbox and for travel of retracting mechanism. Hoses must be mounted to operate free of twist or bind, and shall be erected in accordance with standard hose arrangement drawings. Check gas piping hoses at windbox. The mounting must allow for cubical expansion of unit, and hoses must operate free of twist or bind. Yaw Indicator Check the actual position of each air nozzle tip and compare to the plant documentation for the required position. Check that the locking pin is securely in place.

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BOILER INSPECTION GUIDELINE

Yaw Indicator Tilt Mechanism (external) Inspect tilt linkage to insure components are in good condition and there is no interference with other components, building steel, platforms, piping, etc. Inspect indicator and pointer for proper relationship with tilting nozzles. Compare the indicator to both local and remote position indicators of the driving unit or controller. Inspect constant spring supports, if applicable, to insure proper functioning when tilts are actuated. Insulation and Casing Check appearance for any major defects or damage. Make certain brackets for conduit or instrument tubing do not interfere with expansion movements of floating casing. Make certain all removable panels are bolted for tight seal against windbox pressure.

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BOILER INSPECTION GUIDELINE

Clearances Clearance must be provided for removal of oil guns for cleaning. Inspect coal piping at windbox to insure adequate clearance for removal of coal nozzles for maintenance purposes. Where handrails are mandatory, removable sections may be utilized. Damper bearings During NOx retrofits new damper bearings may be installed in both the main windbox and SOFA windboxes. The new style are graphite self aligning bearings. Refer to Figure 46. This damper bearing shaft design can tolerate both dust and temperature, which in the past has caused secondary air dampers to stick. Maintenance history has proven that minimal repair is required on Graphite self-aligning bearings, however it is inevitable that even the Graphite material will eventually wear out. If it is found that the damper shaft has lateral movement to the point where the shaft sticks, and the seal washer is opened and allowing dust to pack in and around the graphite bushing, replace the bushing, spring seal and gasket. Tighten the four bolts firmly when rebuilding. Tighten the keyless bushing (transverse torque component) to 125 ft/lbs to lock the lever arm firmly in place. Never pin or lubricate any part of the keyless bushing. This will result in slipping between the shaft and lever.

Damper Shaft Graphite Bearing

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BOILER INSPECTION GUIDELINE

Internal Burner Corner Examination – PC Boiler A proportional check should be made of each windbox and nozzle assembly internally. Set tilts on"0" per indicator on drive mechanism outside the windbox. All adjustable nozzle tips should be horizontal +0 degrees. If necessary, adjustment may be made at the bellcrank. Check clearances between the nozzle tips and the compartment plates. This clearance should be 3/8" minimum. Check clearances between the side of the nozzle tips and the vertical channels or angles. This clearance should also be 3/8" minimum. Examine all linkages to insure that they are in good condition and that there is no interference with other internal components. Set tilts on +5o and recheck the horizontal clearance and then on -5o and recheck. Horizontal clearances at this time should be 1/4" minimum. Set tilts to +30o as indicated on the position indicator. Check actual tilt angle of nozzle tips. Indicated versus actual should be within +1-1/2 degrees. Repeat at -30o. At extreme tilt positions, nozzle tips shall not touch each other. In oil compartments check location of diffuser cone. Refer to unit Instruction Manual for exact dimensions. Insert oil gun to firing position and clamp. Distance from face of diffuser cone back to the oil gun cap should be as per unit Instruction Manual. Examine ignitor horn and eddy plate assembly. From inside the secondary air connecting duct, examine and operate dampers in each compartment. Check for broken welds--blade to shaft. Inspect and correct any linkage that may have been damaged in shipping and handling. Check installation of turning vanes, welding and completeness of vanes. Inspect joint between air connecting duct and windbox damper frame. This joint must be seal welded inside the duct to preclude air and dust leakage into boiler room. Make sure each compartment is clean and free of weld rods, scrap metal, tools, etc. Windbox Nozzle Tip Field Adjustments – PC Boiler NOTE: Adjustment and verification of the windbox nozzle tip tilt system should be carried out with the windbox in the vertical position. Set external direct drive tilt mechanism indicators at 0 degrees. per indicator scale.

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To verify the windbox is vertical and plumb, the reference marks on the windbox frame or the front flange surface of the throat frame should be confirmed with a level. Adjustable nozzle tips directly connected to the tilt drive mechanism by the horizontal reach-rod should be in the horizontal position (relative to the windbox frame) within ± 2 degrees. Use the measurement reference points clearly marked on both the windbox and the nozzle tip by the fabricator for a level check. Any necessary adjustments to the driving nozzle may be made at the threaded end of the reach-rod (at the bell crank). Adjustable nozzle tips in the air/oil/gas compartments which are interconnected with the driving nozzle tip by means of vertical bars can be off from each other by as much as ±2degrees. All adjustable nozzle tips should be properly centered within each compartment to provide at least 1/2" clearance between the tips and the windbox frame. All coal nozzle assemblies should be properly centered within each coal compartment to provide equal clearances between the coal nozzle tip and the adjacent partition plates. The min. clearance should be 1/2". both of the coal nozzle assembly supports should be firmly resting on the partition plate. If this condition is not met, excessive external loading by the fuel piping may be distorting the arrangement of the assembly within the compartment. Examine all linkages to ensure that they are in good condition and that there is no interference between other internal components. Inspect the clearances around the vertical nozzle tip connecting links and the internal connecting bars, particularly where they pass through the slots in the partition plates. there should be no less than 1/4" clearance around these items at any point throughout the ± 30 degree tilt range. Tilts should be moved +5 degrees to -5 degrees and then back to 0 (zero) degrees. The clearance between the partition plates and the nozzle tips should then be rechecked. the minimum clearance should be 1/2". Stroke the tilts between +30 degrees. and -30 degrees through component inspection, look and listen for anything unusual that may indicate interference. Note that in the extreme positions of the tilt range the actual tip position may be off from the indicated position by as much as ± 2 degrees. Lubricating Windbox Internal Components – PC Boiler Lubricant should be applied during field windbox overhauls. Link pins, stationary pins for bellcranks (requires removal of bellcranks if it does not contain graphite sleeved bearings) and other accessible pivots should be lubricated according to the unit instruction manual.

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BOILER INSPECTION GUIDELINE

Fluidized Bed Ash Cooler – CFB Boiler Check the Function – Combustor bottom ash flows by an ash flow control valve to the FBAC and is cooled by fluidization of the ash particles that creates a flow of ash between the tubes of each pressure part assembly. The bottom ash is cooled from 1700 degrees F to approximately 350 degrees F. The FBAC has two sectioned compartments that are called the High Pressure and the Low-Pressure Compartments. The water flow thru the high-pressure tubes is located between the boiler feed pump discharge and the economizer. The water flow in the Low Pressure is cooling water. A vent or series of vents return some ash flow back to the combustor transported by fluidization air. The vents allow filling of the ash cooler with an inventory of ash so the DCS can perform a desired control scheme. FBAC Gravel Screws remove top size bottom ash particles from the floor of the FBAC. Instrumentation to the DCS for ash cooler operation includes lower bed ash temperatures, chamber pressures for inventory indication, main vent temperature, waterside differential temperature and final outlet ash temperature. Upgraded versions of the FBAC gravel screws include VFD or speed control of the bottom ash screws from the control room to allow control of the FBAC chamber pressures. Chamber pressure (ash inventory) to ash temperature relationship. Excessive fluidizing air to pressure part erosion relationship. Sintering and DE fluidization conditions. Charge FBAC with bottom ash prior to start up. Ash velocity range during operation is 2 –2.5 fps. Inspection 

Visual/UT inspections of all the HP and LP assemblies



Spread the assemblies apart to allow access for inspection.



UT worn thru Amstar Coating Areas.



Inspect the nozzles for erosion of casting-go no go gauges.



Rotate nozzles depending on erosion location or pattern.



Inspect refractory condition.



Copper Sulfate for Amstar Coated Tube Replacement



Inspect stainless cast handcuffs for cracking/replacement.



Handcuff bolt torque procedure. •Determine worn tubes to be shielded or replaced.

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CFB Cyclones – CFB Boiler CFB Cyclones - Centrifugal path recycle cyclones are designed to remove about 99% of the solids entrained by the gas. Vortex Finder - in the top of the cone has a narrow laminar flow stream that allows only 1% of the ash out the backend, but 100% of the gases of combustion do exit. Key Components 





Inlet Duct o

Ammonia Injection Grid (AIG)

o

Expansion Joint

Outlet Duct o

AIG

o

Expansion Joint

Cyclone Body o

Expansion Joints

o

Grease Air Nozzles

o

Vortex Finder

Inspection Items 

AIG –Plugged nozzles, overheated lances



Refractory Walls –Missing sections of refractory



Expansion Joint –Slag buildup



Vortex Finder –Cracked welds/missing, misaligned assembly

Siphon Seal Pots – CFB Boiler Function – Siphon Seal Pots - Allow the Cyclones to fluctuate in reserve level to store the surplus ash during transitional periods. Heat transfer has three options for managing thermal inventory. 

Return directly to the furnace and enrich the fluidized bed fire. Transits through SRDs(Solids Return Ducts).



Momentarily fill the lower half of the cyclone as excessive flow is exiting the top of the furnace.

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

Pass through the FBHEs (Fluidized Bed Heat Exchangers) to reduce heat returned to the fire in the bubbling bed. Flow is controlled by ACVs (Ash Control Valves).

Operating checks 

Normal Operating Static Pressure range will increase to ~40” –80” wg. At 100” wg, operator needs to watch closely for further increases in pressure. At 120” wg, there is possible pluggage that will require action. Commissioning engineers must field test actual alarm set points.



Low pressure suggest that fluidizing air flow is being lost.



High pressures (>100” wg.) suggest that the seal is plugging.



Fluidizing Air and Grease Air help to keep the ash flowing through the Siphon Seal Pots, ACVs, and SRDs.

Key Inspection Points 





Siphon Seal Pots o

Refractory

o

Fluidized Air Nozzles

o

ACV Plug Refractory Seat

o

Grease Air Ports

o

Seal Pot Support Beams (recently discovered during Spring 2012 Outage)

Ash Control Valves o

Plug condition

o

Plug Shaft

o

Bonnet

o

Anti-Rotation Key

SRDs o

Expansion Joints: packing of ash can lead to fire in joint

o

Refractory

o

Grease Air Ports



SRD Outlet into Lower Combustor



Refractory Repairs

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Most Major Maintenance Issues for the Siphon Seal Pots/ ACVs/ SRDs are directly related to Unit Operation. Improper FA Flow or Grease Air Flow can result in plugging and pressure problems within the Seal Pots. Improper Ash Removal from the SRD Expansion Joints can lead to dangerous situations around the Seal Pots and SRD Expansion Joints. Start Up curve for refractory cure can reduce some refractory spalling repairs. Properly trained and disciplined operators can prevent most maintenance issues on CFBs from becoming major outage projects. CFB Boiler Fluidized Bed Heat Exchanger Inspection Focal Points 

FA Nozzles



ash pluggage, broken, and erosion



Handcuff Castings -Bumper Pads



Refractory



Spalling around tube penetrations, jacking of inlet wall penetrations, and seams of floor, sidewalls, roof, and inlet duct

PRE-OUTAGE WALKDOWN CHECKLIST

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This checklist is designed to prompt the inspector to methodically observe all components during an inspection and to record abnormal data. The data will later be used to evaluate the unit’s condition. Having a method to the madness of combing a unit from top to bottom adds value to the routine. Flexibility to roam off course when necessary, knowing the checklist will get you back on track or remind you which areas were missed. Note taking is made simple when the item is already listed, all you have to do is circle a “problem area” in the data-to-collect column and describe what you see. The checklist coaches the inspector to look at areas that might otherwise be missed. Sort the list so that the sequence is similar to the actual walkdown. Format the document as a landscape page and make the “note” column larger. Highlight areas that are known “problem areas” of the unit being inspected.

AREA & INSPECTION CRITERIA

DATA TO COLLECT

Boiler Support Boiler hanger rods

Abnormal or loose hanger rods, integrity

Variable load and constant load spring hangers

Bottomed-out spring hangers, loading

All vertical and horizontal buckstays

Warpage or misalignment

All buckstay stirrups, bolts, nuts, and washers

Integrity, abnormal condition

Expansion trams (boiler is hot)

Readings at reference points

Safety Valves Stem or packing

Leakage

Drip pan

Pluggage

Area between the safety valve and vent piping

Binding or interference

Structural Steel Structural steel for boiler or auxiliary equipment

Interference

Grating and walkways

Missing or loose sections

Handrails

Missing or broken sections

Insulation and Lagging

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BOILER INSPECTION GUIDELINE

Insulated Areas

Missing Insulation, discoloration, signs of leakage

Duct insulation in areas of expansion joints

Signs of buckling, leakage

Insulation in areas around sootblowers, and access doors

inspection

ports, Missing or damaged insulation

Poured refractory for damage

Abnormal condition

Sootblowers and Furnace Probe Local and remote operation by cycling each sootblower Failure to operate through its operating sequence Sootblower supply lines, valves, and swivel tubes

Steam leakage

Sootblower wall box

Damage

Drive mechanism on all sootblowers

Damage, interference

Cranks and tools to retract a sootblower which has Available stopped in the "advanced" position Movement of air heater sootblower swivel mechanism

Interference

Furnace temperature probe

Damage

Ignitors Operate each ignitor

Lamp status, ignitor failure

Electrical cables, oil, gas, and air supply lines

Damage, interference

Tilting Tangential Firing System Fuel and Air Nozzles

Degree of tilt

All overfire air nozzles

Degree of tilt

All corners within 5° of each other

Excess tilt

All coal piping entering the windbox (especially at Wear, damage, leakage elbows or couplings) Fuel pipe hangers

Damage, loose

All windbox air dampers

Position per scribe mark on damper shaft

Compare All dampers on the same elevation

Dampers not in same position

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BOILER INSPECTION GUIDELINE

Windbox and related duct work

Leakage

Oil Guns All oil and steam or air lines

Leakage

All related piping and valves

Leakage, damage

Oil gun advance and retract mechanism

Failure to operate

Spare oil guns

Dirty, not stored

Coal Piping Coal pipes

Indication of wear

Coal pipe couplings

Sign of leakage

Coal pipe constant load spring hangers

Expansion problems, loading

Coal Feeders - Gravimetric Tension pulley

Position

Feeder belt

Tracking

Feeder housing (with stands 100 psig spike)

Integrity, pressure damage

Observation windows and Doors

Broken, will not close

Coal Feeders – C-E Volumetric Drive clutch assembly

Wear or damage

Hinged leveling gate lever

Movement

Feeder housing.

Integrity

Drive motor and gear reducer

Noises, poor lubrication

Pulverizers Mill foundation

Cracks

Gear case oil

Level, temperature, leakage

Examine the material being rejected from the mill (sign Excessive coal of worn or improperly adjusted mill internals). Three journal assemblies

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Movement uniformity

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BOILER INSPECTION GUIDELINE

Separator body

Coal Leakage

Classifier

Do settings match

Mill motor, filters and foundation

Wear, damage

Exhauster type mills: exhauster casing, foundation, and Wear, damage bearing assembly Pulverizer gear housing and exhauster bearing housing

Noise or vibration

Pressurized pulverizers: gear case and journal seal air Leakage or crimped lines systems Air Preheaters Upper/lower bearing assemblies.

Wear or Damage

Oil

Level, leakage

Air preheater seals

Loud noise

Drive motor and gear reducer

Signs of oil leakage

Air preheater sootblowers

Failure to Operate

Boiler Water Circulating Pumps Motor and related piping

Leakage

Pump suction and discharge

Log pressures

Motor cooling water

Log temperatures

Compare data to normal operating conditions.

Abnormal conditions

Fans/Air and Gas Ducts Foundation bolts

Crack or loose

Motor (use vibration meter)

Excess vibration, log amps and bearing temperature

Fan housings, air and gas ducts

Damage, missing insulation, expansion problems

Ash Removal Systems All piping

Leakage, pluggage

Fuel Handling Systems

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leaks,

BOILER INSPECTION GUIDELINE

All coal handling systems

Excessive spillage, accumulation

Oil and Gas piping

Leakage

Pre-boiler Systems All components and piping

Leakage, missing insulation

BOILER INSPECTION FORM – CHECKLIST LOWER FURNACE AREA LOWER DEAD AIR SPACES Membrane cracks – Especially membrane ends Hanger rods Hanger pins Buckstay alignment Buckstay connections to front/rear wall and side walls Buckstay deformation Seal boxes – leaks/cracks Drain piping supports/welds Enclosure support steel (gussets front/rear wall) LOWER SPHERE/HEADERS/DRUMS Door hinges Door alignment Door sealing surfaces Orifice mounting hardware Strainers/screens Internal surface deposits Backing rings Drain piping connection

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BOILER INSPECTION GUIDELINE

BOTTOM ASH HOPPERS Bottom sluice nozzles Weir water headers COUTANT UNDERSIDE OF SLOPE Scallop bar cracks at seal plate Drip screens Drip screen support bar Membrane cracks Tube surface cracks COUTANT TOP SIDE SLOPE General deformation of tubes Impact damage to individual tubes Membrane cracks at junction of front/rear wall and side wall tubes Membrane cracks top and bottom off set tubes at centerwall Off set tubes around water cooled doors Sliding ash erosion of side wall tubes at front/rear wall Sliding ash erosion at upper bend of Coutant Corrosion in centerwall seal box area Wear bar (cracks, weld, wear) MID FURNACE AREA LOWER SOOTBLOWER ELEVATION (TYPICAL AT ALL ELEVATION) Membrane cracks at off set tubes Seal box refractory Seal box wall sleeve Tube erosion Lance tubes cracks

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BOILER INSPECTION GUIDELINE

Lance tube nozzles Lance tube alignment and depth and cleaning radius Corner tube erosion Lance tube rub damage BURNER ZONE Clean upper/lower crotch area Membrane cracking at upper/lower crotch Eroded/corroded tubes at upper/lower crotch Membrane cracks in ignitor off set tubes Overheating in ignitor off set tubes Ignitor components Fly ash erosion of wall tubes in coal nozzle tip area Burner tip alignment Burner tip linkage Burner tip condition – Overheating, erosion, broken welds, warpage, etc. Coal Nozzle – Erosion of nozzle, burner gate, inlet elbow Auxiliary air tip alignment Auxiliary tip linkage Auxiliary air tip condition Flame scanner guide tube SOFA tips SOFA tilt linkage SOFA alignment SOFA support frame work CENTERWALL Panel to panel rub

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BOILER INSPECTION GUIDELINE

Fatigue/corrosion in seal box Hanger springs Panel alignment/distortion Sliding ash erosion – penetrate at front/rear wall Sliding ash erosion at lower bends Membrane cracks Rub damage at upper rear wall arch penetration WATERWALLS Clean selected areas based on history and characteristics of unit design Corrosion Erosion Discoloration Swelling/blisters Deformation Membrane conditions Tube surface condition – cracks/pock marks etc Rear wall outlet header tube nipples (cracks at nipple to header and field welds) UPPER FURNACE AREA RADIANT WALLS Stitch welds Alignment Tie welds Clean tube surface for evaluation DRUMS Feed pipe, Continuous blowpipe, & Chemical feed pipe including support brackets and “U” bolts Downcomer perforated screen box

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BOILER INSPECTION GUIDELINE

Primary separators including secondary separators and attachment bolts Internal shroud and separator baffles Corrugated Plate Dryer box and attachment bolts Drain (drip) pipes Door hinges and hardware Door alignment Door sealing surfaces Debris UPPER FURNACE ARCH Sootblower erosion Slag erosion Off set tube membranes at screen/hanger tube openings Rear wall outlet header tube nipples Membrane/peg fin cracks Coatings Refractory SCREEN TUBES/HANGER TUBES Fly ash erosion on leading side at arch Sootblower erosion Corrosion in seal box areas Loose tubes ROOF TUBES Sagging roof tubes Peg fins/ Refractory Rubs from adjacent assemblies UPPER DEAD AIR SPACE ENCLOSURE

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BOILER INSPECTION GUIDELINE

Hanger rods Structural steel Seal boxes (sidewalls, hanger tubes, headers) Membrane cracks (below rear outlet header, extended side wall) Drain line connections Buckstay connections to rear wall RETRACT SOOTBLOWER OPENINGS/TEMPERATURE PROBE Membrane cracks at off set tubes Seal box wall sleeve Tube erosion Lance tube cracks Lance tube nozzle Lance tube alignment Lance tube rub damage Seal box cracking/leaks/deterioration/seal box refractory Inserted alignment CONVECTION PASS AREA EXTENDED SIDE WALLS AND BACKPASS WALLS Mechanical rubs from horizontal surface (economizer/SH/RH) Fly ash erosion (screen tubes and hanger tubes) Erosion at any gas deflection baffle (sootblower/fly ash) Membrane conditions – solid or peg fin Off set tubes at boiler access doors (Fly ash erosion, peg fin cracks, etc.) Refractory at boiler access door off set tubes Mill board at access doors GAS TOUCHED HEADERS

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BOILER INSPECTION GUIDELINE

Erosion (Fly ash/sootblower) Nipple alignment Nipple welds Header Supports Overheating/Swelling/Blisters Discoloration OD measurements, shear wave, UT, MT, PT, replication Internal inspection Header Distortion ECONOMIZER Pluggage Platenizing Alignments Sootblower erosion at hangers Fly ash erosion (Fin tube, Hangers and alignment straps) Connection between hanger tube and assembly tube Hanger tubes/straps Gas distribution baffle conditions Erosion throughout the bundles (spread or lift bundle for inspection) Cracking at fin ends GAS OUTLET DUCT Expansion joints Structural steel trusses/struts Overheated duct work Fly ash erosion Economizer hoppers (Pluggage cracks erosion) HIGH TEMPERATURE SURFACE AREAS

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BOILER INSPECTION GUIDELINE

PENDANT SUPERHEATER & REHEATER SURFACES Slag accumulation Tube deformation within an assembly Sootblower erosion Fly ash erosion Flex tie rubs Fluid cooled spacer rubs Mechanical rubs from other tubes or supports Clean selected area for surface evaluation Take wall thickness readings at selected sites Take OD readings at selected locations on tube which operate in the creep range Inspect tube for swelling, discoloration or blisters Observe and record general alignment of assemblies Shields HORIZONTAL SUPERHEATER & REHEATER SURFACES Hanger support system Slag accumulation Tube deformation within an assembly Sootblower erosion Fly ash erosion Flex tie rubs Mechanical rubs from other tubes or supports Clean selected areas for surface evaluation Take wall thickness readings at selected sites Take OD readings at selected locations on tube which operate in the creep range Inspect tube for swelling, discoloration or blisters

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Observe and record general alignment of assemblies Shields PENTHOUSE HIGH TEMPERATURE HEADERS Discoloration Scale NDE evaluation (OD,MT,PT,X-ray, shear wave, bore scope, replications) Nipples (welds, discoloration, scale, OD, wall thickness, misalignment) Supports (hanger rods, U-bolts, etc.) High Crown seal LOW TEMPERATURE HEADERS Discoloration Scale Nipples (welds, discoloration, scale, OD, wall thickness, misalignment) Supports (hanger rods, U-bolts, etc.) High Crown seal CASING Cracks Overheating HANGER RODS Looseness Missing clevis pin lock wires Broken components Special case – on divided furnace be sure centerwall rear hanger is not insulated with hot reheat outlet headers LINKS

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BOILER INSPECTION GUIDELINE

Discoloration Scale Supports (hanger rods, U-bolts, etc.) Vent piping connections NDE evaluation (OD, MT, PT, X-ray, shear wave, bore scope, replications) DESUPERHEATERS Discoloration Scale Supports (hanger rods, U-bolts, etc.) NDE evaluation of alignment and positioning pins (MT, PT, X-ray, bore scope) Spray Nozzle

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