Training Manual-piping: Selection And Limitations Of Piping Components
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DOC No. : 29040-PI-UFR-0014
TRAINING MANUAL- PIPING
Uhde India Limited
SELECTION AND LIMITATIONS OF PIPING COMPONENTS
Rev.
: R1
Page
: 1
CONTENTS Page 0.0
Cover Sheet
1
1.0
Pipes and Fittings
2
2.0
Comments on selection and Limitations of Components
2–6
3.0
Piping Joints
6–8
4.0
Fabrication, Assembly and Erection of Process Plant Piping
8 – 11
5.0
Examination , Inspection and Testing
12 - 14
Applicable Revision: R1 Prepared: NNG
Checked: AKB
Approved: RUD
Date: 15.01.2001 First Edition: R0 Prepared: DNL
Date:
Date:
Checked: AKB
Approved: RUD
Date: 14.09.2000 File Name: C- 14
Date: 20.09.2000 Server: PUNE: KUMUS 207
Directory: PUNE: Refer \ Pi \ Training Manual
Date: 31.10.2000 VKO: KUMUS 209
VKO: Refer \ Training Manual
TRAINING MANUAL- PIPING
Uhde India Limited 1.0
SELECTION AND LIMITATIONS OF PIPING COMPONENTS
DOC No. : 29040-PI-UFR-0014 Rev.
: R1
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: 2
PIPE AND FITTINGS: Furnace lap weld ferrous pipe, furnace butt-weld ferrous pipe, spiral-weld ferrous pipe, and fusion-welded steel pipe (made to ASTM A134, A53, Type F, API 5L furnace butt welded and A211) are not permitted for hydrocarbons or other flammable fluids within process unit limits or for hazardous fluids in any location. Non-ferrous pipe made by similar manufacturing process is similarly restricted. The use of bell-and-spigot fittings is limited to water and drainage service. Also, pipe couplings made of cast, malleable, or wrought iron are not permitted for flammable fluids within process limits or hazardous fluids in any area. In addition, they cannot be used for flammable fluids outside process unit limits at design temperatures above 300°F or design pressures above 400 psig.
2.0 COMMENTS ON SELECTION AND LIMITATIONS OF COMPONENTS: th (Refer Ch. C7 - "Process Piping Systems" in Piping Handbook 7 edition by M.L.Nayyar) There are many Code mandated restrictions for the use of fittings, bends, intersections, and valves which are not universally applicable to all process plant services, and such components are not easily codified. Some guides, however, are of value to the designer and are listed: •
Welding fittings are usually preferred to flanged fittings, not only for economic reasons but because the potential for leakage is reduced.
•
Pipe bends are preferred to butt welding elbows for reciprocating compressor suction and discharge piping, vapour relief-valve discharge piping, and piping conveying corrosive fluids (such as acid where turbulence in a fitting may cause excessive corrosion).
•
Bends or dead end tees should be used for piping which conveys pulverized abrasive solids suspended in gas in the dilute phase. Dead end tees (so arranged that the flow will impinge against the dead end) have a longer life than bends in abrasive service and should be used if the system can be designed to accommodate the resulting increase in pressure drop.
•
Bends should be used for dense phase flow of pulverized abrasive solids and for all piping which handles either pulverized or granular solids suspended in liquids or granular solids suspended in gases.
•
If the flow is through a branch into a header (or run pipe) in a piping system which transports pulverized abrasive solids suspended in gas in the dilute phase, a dead end cross (so arranged that the flow will impinge against the dead end) should be used.
•
In services with very high corrosion rates, butt welding fittings with the same inside diameter (ID) as the attached pipe (if not the same, consider taper boring the component with the smaller ID) are preferred to threaded and socket welding fittings.
•
Threaded cast iron fittings should not be used in pressurized process and utility piping.
•
Threaded plugs are preferred to pipe caps for threaded end closures to reduce dead end corrosion problems.
•
In most process plants, internal corrosion is a greater problem than external corrosion. Consequently, it is common practice that all 3/4 in and larger steel and cast iron (and all 2 1/2 in and larger brass) gate, globe, and angle valves (located above grade) be of the outside screw and yoke type.
TRAINING MANUAL- PIPING
Uhde India Limited
SELECTION AND LIMITATIONS OF PIPING COMPONENTS
DOC No. : 29040-PI-UFR-0014 Rev.
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•
Although valves with seal welded or pressure seal bonnets and welding ends are commonly used in steam service, 2 1/2 in and larger valves in process service are usually equipped with flanged ends.
•
Valves operated in full open or block service are generally gate valves. Butterfly valves, ball valves, non-lubricated plug valves, and lubricated plug valves may be considered as possible alternates to gate valves.
•
As a general rule, hand operated throttling valves for services where fine control is not required, and those for control valve bypasses should be globe valves (internal stem and plug preferred) for sizes 2 in and smaller and gate valves for sizes 2 1/2 in and larger. For severe throttling service and where close control is required, a conventional control valve with a hand operator should be used. The only other common application for globe valves in process service is for mixing purposes.
•
Solid-wedge and flexible-wedge gate valves are generally preferred to split and doubledisk valves. Split-wedge and double-disk valves are generally used for clean liquids and noncondensing gases only.
•
Gate valves with Teflon inserts in the seat rings are very satisfactory in liquid butane and propane services.
•
Where choking may occur in blocked connections, a flushing connection should be added between the valve and the process line or equipment. The flushing medium may be oil, gas, or steam (if water can be tolerated in the system.
•
If the pressure differential across a closed gate valve is approximately equal to the pressure rating of the valve, consideration should be given to providing a pressure equalizing bypass around the valve. Consideration should also be given to bypasses for valves in steam lines for warm-up purposes. When bypasses are provided, they should be sized in accordance with the Manufacturers Standardization Society (MSS) of the Valve and Fitting Industry’s standard Practice (SP) MSS SP-45 (bypass and drain connection standard). A gate valve should be provided in the bypass line.
•
Drain or bypass connections may be tapped (or socket welded) into a valve body where necessary to simplify piping or to assure complete drainage.
•
Do not use check valves in vertical lines in which the flow is downward.
•
If a valve is installed with the stem lower than horizontal, the valve bonnet should be provided with a drain.
•
The designer should consider providing gear operators for all 6-in and larger lubricated plug valves and all 14-in and larger gate valves.
•
The use of double block valves should be kept to a minimum. Double block valves, however are required for sample connections and for drains which are connected to a closed drain system. Double block valves or their equivalent should be used where contamination must be prevented.
•
Under certain conditions double block valves are also needed where it is necessary to remove essential equipment from service for cleaning or repairs while the unit continues in operation. However, even in these cases often a single block valve with provisions for blinding will suffice. Such equipment must be provided with a spare, or it must be possible to bypass it temporarily without shutting down the unit. The nature of the fluid, its pressure and temperature, and many other factors must be considered when determining the need for double block valves. Generally, the need for double block valves at equipment should
DOC No. : 29040-PI-UFR-0014
TRAINING MANUAL- PIPING
Uhde India Limited
SELECTION AND LIMITATIONS OF PIPING COMPONENTS
Rev.
: R1
Page
: 4
be considered if the fluid is hazardous or very corrosive or if the fluid is above 500°F. Where double block valves are used, a 3/4-in valve should be installed between the block valves. See FIG.1 FIG.1 BLOCK VALVES
TO RELIEF SYSTEM OR SAFE DISPOSAL
3/4” VALVE
DOUBLE BLOCK AND BLEED Some ball valves and non-lubricated valves, when equipped with a bleeder between the seats, have been satisfactory substitutes for double block valves. Both conventional gate valves with Teflon inserts in the seat rings and flexible-wedge gate valves have also been equipped with a bleeder connection and used in place of double block valves. th
2.1 Selection and limitation of flanges (Refer Ch. C7 – Piping Handbook, 7 Ed.) The Code restricts the use of screwed flanges as it does of any threaded joint. Slip-on flanges must not be used in installations where many large temperature cycles are expected or if the flanges are not insulated. The following statements on flanges are included for the designer’s guidance. •
The use of cast-, nodular-, wrought-, and malleable-iron screwed flanges should be avoided.
•
In services with very high corrosion rates, the bore of weld neck flanges should be the same inside diameter as the attached piping (if not the same, consider taper boring the component with the smaller inside diameter).
•
The bore of weld neck orifice flanges should match the inside diameter of the attached pipe.
•
ASME Standard B16.47 for Large Diameter Steel Flanges, governs steel flanges in sizes larger than 24 in. However, the designer must ensure that the flange drilling on such flanges will match that of the equipment to which it is to be attached. MSS-SP-44 Steel Pipeline Flanges & ASME B16.47 - Large Diameter Steel Flanges are also useful standards when using flanges larger than 24 in.
2.2 Selection and Limitations of Blanks In a process plant, blanks are usually required to isolate individual pieces of equipment at shutdown and to block off selected process lines positively at the process unit limits. They are
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TRAINING MANUAL- PIPING
Uhde India Limited
SELECTION AND LIMITATIONS OF PIPING COMPONENTS
DOC No. : 29040-PI-UFR-0014 Rev.
: R1
Page
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also needed during operation wherever positive shutoff is required to prevent leakage of one fluid into another. Blanks should be located in horizontal lines if possible. Blanks should not be used in vertical water and steam lines in climates where danger of freezing exists. Circular handletype blanks can be used for raised face joints in locations where the lines can be sprung easily to permit installation of the blanks. As a rule, this is easily accomplished only in 4-in and smaller lines. Figure-eight-type blanks are used for larger lines and even then, jackscrews may be needed to install the blank. Blanks should be made from a plate specification approved for use in ASME B31.3, of substantially the same chemical composition as the pipe. 2.3 Selection and Limitations of Gaskets Gaskets must be made of materials which are not injuriously affected by the nature of the fluid or its temperature under anticipated operating conditions. Non-metallic gaskets are usually not permitted above 750°F gasket design temperature. Various elastometric gasket materials have very low (200°F) maximum service temperatures. Also, non-metallic gaskets should not be used in non-confining (flat or raised face) flanged joints at gasket design pressuretemperature conditions above the ratings of Class 600 flanges per ASME B16.5, except that for non-flammable, non-toxic service fluids, the limiting ratings can be those of Class 900 flanges. The use of metal or metal non-metallic filled gaskets is not limited as to pressure provided the gasket materials are suitable for maximum fluid temperatures. The American Society of Mechanical Engineers has developed ASME B16.20, a standard covering the dimensions of spiral-wound and double-jacketed gaskets. The spiral-wound gasket covered by ASME B16.20 has been widely used with great success with raised face flanges as a replacement for the ring type joint. 2.4 Selection and Limitations of Flange Facings When Class 125 cast-iron or flat face non-metallic flanges are bolted to Class 150 steel flanges, the 1/16-in raised face on the steel flanges should be removed. If the raised face is removed and a full-face gasket is used, either high-strength carbon-steel bolting or alloy-steel bolting may be used. However, if the face is not removed (or if the face is removed and a ring gasket extending only to the inner edge of the bolt-holes is used), the bolting material may not be of higher strength than carbon steel ASTM A307 Grade B. 2.5 Selection and Limitations of Bolting Carbon-steel machine bolts may be used to make flange connections for bolt metal temperature from -20°F to 400°F inclusive. This restriction is quite conservative with regard to pressure limit. Also, these bolts can be used quite safely to the limits of the Class 300 pressure class as permitted in ASME B16.5 with the use of appropriate gasketing material. The most widely used bolting materials in process plant are ASTM A193 Grade B7 stud bolts with ASTM A194 Grade 2H heavy semifinished hexagonal nuts. These materials are acceptable from -50°F to 1000°F. A number of operating companies use these materials almost exclusively to simplify inventories and reduce the possibility of misapplication of carbon -steel bolting. Carbon-steel bolting may be used with non-metallic gaskets with flanged joints rated Class 300 and lower for bolt metal temperatures at -20°F to 400°F.
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2.6 Selection and Limitations of Strainers (Refer Ch. C7 – Piping Handbook, 7 Ed.) The material for the strainer body (including bolting) should be equal to material specified for the valves in the same service. The screen material generally should be the same as the valve trim (e.g., 11-13 percent chrome or Type 316 stainless steel for most services). The location of permanent strainers (as contrasted to the temporary cone type which is installed at a flanged joint) also merits attention. Centrifugal and reciprocating pumps handling material containing solids should have permanent strainers provided in the suction lines to the pump or in the vessel from which the pump takes suction. The free area of such strainers should not be less than three times the cross-sectional area of the suction line. In addition, permanent strainers or filters should be provided in the piping for the protection of the equipment indicated in Table C 7.8 (Strainer Screen Openings for Equipment Inlet th Piping) of the Piping Handbook 7 Ed. The maximum clear opening for screens in these strainers varies with the application, but it should not exceed the value recommended for the particular type of equipment. The available pressure differential usually determines the minimum clear opening for screens. Permanent strainers should have baskets, which can be flushed clean during operation or easily removed for cleaning. If considerable clogging of strainers is anticipated, the strainers should be of the self-cleaning or duplex type to permit continual flow of clean liquid. 3.0
th
PIPING JOINTS: (Refer Ch. C7 – Piping Handbook, 7 Ed.) The type of piping joint used must be suitable for the pressure temperature conditions and should be selected by giving consideration to joint tightness and mechanical strength under the service conditions (including thermal expansion) and to the nature of the fluid handled with respect to corrosion, erosion, flammability, and toxicity. In general, the number of disassembly joints is minimized; most joints are welded if the material is weldable. Welded piping is used almost exclusively for transporting hydrocarbons and other flammable fluids. Bypass piping, alternate process connections, and auxiliary piping systems such as gland oil, seal oil, lubricating oil, fuel gas, fuel oil, heating or cooling oil, flushing oil, flue gas and blowdown piping, are included. Welded construction is also used for all piping outside process unit limits which is used for the transfer of hydrocarbons or most other process fluids. Piping which is threaded or welded, depending primarily on economic considerations, includes piping, other than specifically mentioned above, in services such as drains, vents, pumpouts, sample connections, and certain instrument leads, which contain process fluids only upon intermittent or occasional use of the piping involved and which are not an integral or essential part of the process system. 3.1 Welded Joints The Code permits welded joints in all instances in which it is possible to qualify welding procedures, welders and welding operators in conformance with the rules of the Code. There are, however, a few minor additional considerations for seal-welded (threaded) and socketwelded joints limited to size NB 2”. For example, the Code cautions against the use of socketwelded construction in cases where severe crevice corrosion or erosion occurs. The Code also states that seal welds may be used to avoid joint leakage but that they shall not be considered as contributing any strength to the joint.
TRAINING MANUAL- PIPING
Uhde India Limited
SELECTION AND LIMITATIONS OF PIPING COMPONENTS
DOC No. : 29040-PI-UFR-0014 Rev.
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3.2 Flanged Joints The number of flanged joints in a piping system is usually determined by maintenance and erection considerations, including sufficient flanged joints for insertion of blanks during shutdown. 3.3 Expanded Joints This type of joint is more commonly used on the piping and tubes for refinery heaters. They are excluded for use in hazardous and toxic services and under severe cyclic conditions. 3.4 Threaded Joints The threading of pipe with a wall thickness less than ASME B36.10M standard wall is not permitted, and the use of threaded joints where severe crevice corrosion or erosion may occur should be avoided. Economics will limit the use of threaded piping to small pipe sizes (2 in and smaller) for most services; however, it is used for most galvanized piping. All pipe threads on piping components must taper pipe threads in accordance with ASME B1.20.1 except the following: •
Pipe threads other than taper pipe threads may be used for piping components, where tightness of the joint depends upon a sealing surface other than the threads and where experience or tests have demonstrated that such threads are suitable for the condition.
•
Couplings, 2 inch and smaller, with straight-tapped pipe threads may be used on piping components with taper pipe threads if the design conditions do not exceed 150 psig or 400°F and if the fluid handled is non-flammable and non-toxic (Category D Fluid Service).
3.5 Flared, Flareless, and Compression Joints Piping joints using flared, flareless, or compression-type tubing fittings may be used within the limitations of applicable standards or specifications. In the absence of such standards or specifications, the engineer shall determine that the type of fitting selected is adequate and safe for the design conditions in accordance with the following requirements: •
The pressure design shall meet the requirements of the code.
•
A suitable quantity of the type and size of fitting to be used shall meet successful performance tests to determine the safety of the joint under simulated or similar service conditions.
•
Fittings and their joints shall be suitable for tubing with which they are to be used.
•
Fitting shall not be used in services which exceed the manufacturer’s maximum pressuretemperature recommendations.
3.6 Caulked Joints The term caulked joints applies to joints of the bell-and-spigot type which are permitted only for water service at pressures suitable for the pipe to which they are applied. Provisions must be made to prevent disengagement of the joints at bends and dead ends and to support lateral reactions produced by branch connections or other causes.
TRAINING MANUAL- PIPING
Uhde India Limited
SELECTION AND LIMITATIONS OF PIPING COMPONENTS
DOC No. : 29040-PI-UFR-0014 Rev.
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3.7 Brazed and Soldered Joints Fillet-brazed or fillet-soldered joints may not be used in process piping, but soldered-type and silver brazed socket-type joints are permitted in non-flammable non-toxic service. The low melting point of brazing alloys shall be considered where possible exposure to fire is involved. 4.0
FABRICATION, ASSEMBLY AND ERECTION OF PROCESS PLANT PIPING: Complete detail and exact requirements which relate to fabrication , assembly and erection of the process piping systems are given in Chapter V of ASME B31.3. Important phases of the Code treatment of these topics are covered briefly below. 4.1 Material for Welding (Refer Clause 328.3) All filler materials must comply with the requirements in Section IX ASME, Boiler and Pressure Vessel Code. If backing rings are used in services where their presence will result in severe corrosion or erosion, it is required that the backing ring be removed after welding and the internal joint ground smooth. 4.2 End Preparation (Refer Clause 328.4) ASME B16.25 provides dimensional standards for weld end bevels. Preferably, the ends of pipe and the edges of plate which are to be formed into pipe should be shaped by machine. Other methods of shaping may be used provided a reasonably smooth surface suitable for welding and free from tears, slag, scale and grease is attained. Oxygen or arc cutting is acceptable only if the cut is reasonably smooth and true and all slag is cleaned from the flame cut surfaces. If piping component ends are machined on the inside for backing rings, such machining must not result in a finished wall thickness, after welding, less than the minimum design thickness plus corrosion and erosion allowances. Generally a root gap of 1/8 in is used for joints (including branch connections) without backing rings, except that where the pipe wall thickness is less than 3/16 in, a 1/16 in root gap is generally used. 4.3 Other Alignment Considerations (Refer Clause 328.4.3) Flange bolt-holes should straddle the established center lines unless other orientation is required to match the flange connections on equipment. Slip-on flanges should be positioned so the distance from the face of the flange to the pipe end is about equal to the nominal pipewall thickness plus 1/8 in. Welding neck orifice flanges should be the same bore as the pipe to which they are attached and must be aligned accurately. Longitudinal seams in adjoining lengths of welded pipe should be staggered and located to clear openings and external attachments. The following restrictions, limitations or guidelines apply to welding of process piping: •
Projection of weld metal into the pipe bore at welded butt joints should not exceed 1/16 in for pipe 8 in and smaller or 1/8 in for larger pipe. Excessive projection on accessible joints should be removed. Welds attaching welding neck orifice flanges to pipe should be ground smooth on the inside.
TRAINING MANUAL- PIPING
Uhde India Limited
SELECTION AND LIMITATIONS OF PIPING COMPONENTS
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•
On ferritic materials to be used below 20°F, the welder’s identification mark should be preferably be made with ink stencil. Steel stamping should be avoided.
•
Welding procedure for fillet welds and seal welds :
The Code does not permit cracks in fillet or seal welds and limits undercutting to 1/32 in for these welds. Fillet welds may vary convex to concave. If seal welding of threaded joints is performed, the Code requires that all exposed threads be covered by the seal weld and that the welding be done by qualified welders. In addition to the Code requirements, it is strongly recommended that (1) threaded joints be made dry (without thread compound), (2) seal welds be at least two-pass (preferably three-pass) welds using a 3/32 in or 1/8 in electrode 1 (5/32 in electrode is acceptable for 2 /2 in and larger pipe size), and (3) valve and union ends be welded by the electric arc process to minimize distortion and ensure that valves be closed during welding. 4.4 Welding Procedure (Refer Clause 328.5) Before welding, all surfaces must be cleaned and free from paint, oil, rust, scale, and other detrimental material. Furthermore, welding is prohibited if there is impingement of any rain, snow, sleet, or high wind on the weld area. The following code requirements apply to girth butt welds and any longitudinal butt weld in a piping component which is not made in accordance with a standard specification: •
If the external surfaces of the two components are not aligned, the girth butt weld must be tapered between the two surfaces.
•
Tack welds, if not made by a qualified welder using the same procedure as the completed weld, must be removed. Tack welds which are not removed should be made with an electrode which is the same as or equivalent to the electrode to be used for the first pass. Tack welds which have cracked must be removed.
•
The types and limitations of imperfection required to be evaluated with various types of examinations are shown in the Code.
4.5 Preparation and Welding Procedure for Welded Branch Connections Branch connections (including specially made integrally reinforced branch connection fittings) which abut the outside surface of the run wall or which are inserted through an opening cut in the run wall must be so arranged as to provide a good fit and be attached by means of fullpenetration groove welds. The recommendations for spacing and location of branch connections contained in Pipe Fabrication Institute (PFI) Standard ES7 should be followed. A good fit must be provided between reinforcing rings and saddles and the parts to which they are attached. When rings and saddles are used, a vent hole is provided (at the side and not at the crotch) in the ring or saddle to reveal leakage in the weld between branch and main run and to provide venting during welding and heat-treating operations. Reinforcing pads should be proportioned so the diameter of a vent hole is not greater than one-third of the pad width. th
4.6 Fabrication Tolerances for Welded Piping (Refer Ch7 – Piping Handbook, 7 Ed.) A widely accepted tolerance on face-to-face and center-to-face dimensions of welding piping is ± 1/8 in (3 mm). As for the location of the flanges, their lateral translation in any direction
TRAINING MANUAL- PIPING
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SELECTION AND LIMITATIONS OF PIPING COMPONENTS
DOC No. : 29040-PI-UFR-0014 Rev.
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from the specified position should not exceed 1/16 in. (1.5 mm). Also the alignment of flanges should not deviate from the specified position, measured across any diameter, by more than 1/32 in. 4.7 Qualification Qualification of the welding procedures to be used and of the performance of welders and welding operators is required to comply with the ASME Boiler and Pressure Vessel Code. Section IX 4.8 Defect Repairs Weld defects which, require repair must be removed. All repair welds must be made with the same welding procedure initially used. 4.9 Bending and Forming Pipe may be bent by any hot or cold method consistent with material characteristics of the pipe being bent and the intended service. It may be bent to any radius which will result in a bend arc surface which is free of cracks and buckles. Hot bending and forming must be done within a temperature range consistent with material characteristics, end use, or heat treatment. It is recommended that hot bends in pipe sizes 1 1 /2 in and larger be packed with high temperature silica sand and that the pipe be uniformly heated before the hot bending operation. When pipe must be threaded before bending, forging, or heat treating, all exposed threaded surfaces should be protected during heat treatment. 4.10 Cleaning after Fabrication Following fabrication, all loose scale, weld spatter, slag, sand and other foreign materials should be removed from the piping. PFI Standard ES5 ( Cleaning of Fabricated Piping) is an acceptable standard for cleaning fabricated piping. Piping should not be painted in the fabricating shop (i.e., before it has been erected and tested). 4.11 Heat Treatment Heat treatment is used to avert or relieve the detrimental effects of high temperature and severe temperature gradient inherent in welding and to relieve the residual stresses created by bending and forming. The welding procedure qualification establishes the necessity for preheating and post-heating welds (and the temperatures and soaking period to be used) in order to restore or obtain the physical properties of the materials (such as strength, ductility, and corrosion resistance) needed to satisfy end use requirements. 4.12 Bolting Procedure for Flanged Joints It is a good practice to apply an antiseize thread compound to the bolts before the nuts are installed. A mixture of graphite and oil is one of the best substances for this purpose. Tightening og bolts should follow usual criss-cross sequential pattern to approximate pre-load seating of the Gasket In bolting joints using spiral-wound gaskets, the gasket should be compressed to about 25 percent of the original thickness. Spiral wound gaskets conforming to API Standard 601 have a 0.125 in thick outside gauge and centering ring. The gasket is seated when it is compressed until the flange faces touch the gauge ring.
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DOC No. : 29040-PI-UFR-0014 Rev.
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Steel-to-cast-iron flanged joints must be assembled carefully in order to prevent damage to the cast-iron flange. Both flanges in steel-to-cast-iron flanged joints should be flat faced. These joints should be made up with extreme care, taking up on bolts uniformly after fitting flanges into close parallel and lateral alignment. Flanges which connect piping to mechanical equipment, such as pumps, turbines or compressors, should be fitted up in close parallel and lateral alignment before tightening the bolting. 4.13 Cast-Iron Bell-and Spigot Piping Bell-and-spigot joints in cast-iron piping must be assembled using poured lead or other joint compound suitable for the service. Usually each cast-iron bell-and-spigot joint is packed with hemp, poured full of lead (with a minimum number of pours), then caulked. The depression of lead below the face of the bell, after joint caulking, should not exceed 1/4 in. (Lead wool can be used where it is not permissible to pour lead). 4.14 Threaded Piping Any compound or lubricant used on threads must be suitable for the service conditions and compatible with both the service fluid and the piping materials. Threaded joints which are to be seal welded should be made up without any thread compound. 4.15 Erection of Corrugated Expansion Joints Corrugated expansion joints should be installed as-shipped from the manufacturer or compressed for the cold condition at erection, depending on anticipated direction and magnititude of movement after the pipeline reaches operating temperature. The manufacturer’s recommended total travel should preferably straddle the calculated travel. 4.16 Erection of Valves Valve packing glands should be checked for the quality and quantity of packing, and lubricated plug valves should be provided with proper lubricant. 4.17 Erection of Pipe Supports In addition to the major supports specified by the design drawings, minor supports as found necessary in the field should also be installed to prevent undesirable vibration, sag, lateral movement, and stresses. Spring hangers, including constant-support type, should be checked for proper adjustment of travel and be correctly positioned for the cold condition of erection. 4.18 Cleaning of Lines after Assembly and Erection After completion of erection, scale, dirt, welding electrodes, slag and other foreign material should be removed from the lines. Particular attention should be given to the cleaning of air lines and compressors and blower, pump and turbine inlet piping. Before the initial operation, steam lines to turbines and to steam ends of reciprocating compressors and pumps should be blown down with steam, 100 psig or higher. All practical precautions should be taken to prevent the introduction of foreign matter into pumps, instruments and other equipment. Cleaning may be accomplished by flushing out the lines. Temporary strainers should be used at pumps during flushing operation unless spools or valves can be conveniently dropped out and suitable deflectors provided to prevent refuse from entering the pumps. Consideration should be given in dismantling those lines which cannot be adequately cleaned by flushing.
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EXAMINATION, INSPECTION AND TESTING: (Refer Ch. 7 of Piping Handbook, 7 Ed.) Before initial operation, piping installation should be inspected to the extent necessary to assure compliance with the engineering design and with the material, fabrication, assembly and test requirements of the Code. An employee representative of the owner should be responsible for this inspection. This examiner may delegate performance of any part of the inspection to inspectors who may be employees of his own organization, of an engineering or scientific organization, or of a recognized insurance or inspection company. A non-destructive examination (NDE) plan should be consistent with service severity, incorporating process and mechanical factors. The NDE plan focus should be on those pipelines where failure would produce the most harm to personnel or property. Some issues the designer should consider when developing the NDE plan are as follows: •
Service factors: Corrosivity, toxicity and flammability - hazardous nature of flowing media. The designer should apply a sound NDE program to detect flaws in these dangerous streams.
•
Mechanical factors: Temperature, pressure, cyclic conditions, thermal bending stresses, vibration. Fatigued and highly stressed lines are more likely to fail than low-stressed lines. Detection and removal of flaws can provide additional service life.
5.1 Visual Examination All welds are required to be capable of compliance with the limitations on imperfections specified in the Code for visual examination. Visual examination consists of observation by the inspector of whatever portions of a component or weld exposed to such observation, either during or after manufacture, fabrication, assembly or test. 5.2 Supplementary Types of Examination The following supplementary types of examination are not required unless specified by the engineering design because of special service conditions requiring a high degree of freedom from imperfections. If such examination is specified for a weld, it is only required that the weld examined be repaired, if necessary, so the weld imperfections comply with the limitations in the Code for the type of examination used. If supplementary types of examination are specified, they should be performed after completion of any postheat treatment where required. If any of the following types of examination is specified by the engineering design, it should be performed to the extent as follows: 5.2.1
Magnetic Particle
Magnetic Particle Examination is essentially a surface type examination. An area to be examined by magnetic particle examination can be completely examined or examined on a random sampling basis, as specified. 5.2.2
Random Radiography
X-Ray or gamma-ray radiography may be used. The selection of the method should be dependent upon its adaptability to work being radiographed. When random radiography of welds is specified by the engineering design, it should be done on the number of welds designated. The engineering design shall specify the extent to which each examined weld should be radiographed. Random radiography may also be used for examination of piping components such as valve or fitting to any extent specified by the engineering design.
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100 Percent Radiography
If 100 percent radiography is specified for welds in piping, each weld in the piping shall be completely radiographed. 5.2.4
Hardness Tests
The extent of hardness testing required shall be specified by the engineering design, considering the severity of the service, type of material and other pertinent factors. 5.3 Pressure Tests Before initial operation, piping must be pressure tested to assure leak tightness. If repairs or additions are made following the pressure tests, the affected piping is retested, except that in the case of minor repairs or additions, the owner may waive retest requirements. The pressure test is maintained for a sufficient time, but not less than 10 min, to determine if there are any leaks. Water is commonly used as the test fluid except when there is a possibility of damage due to freezing or if the operating fluid or piping material would be adversely affected by water. If hydrostatic testing is not considered practical, a pneumatic test using air or another nonflammable gas may be substituted. A preliminary air test at not more than 25 psig, is made before hydrostatic test in order to locate major leaks. If pressure tests are conducted at low metal temperatures, the possibility of brittle fracture must be considered. Hydrostatic pressure tests are conducted at 1.5 times nominal design pressure, adjusted for temperature. ASME B 31.3 gives the Formula for temperature correction for Pressure Test as follows: PT
=
Where: PT P ST S
1.5 P ST / S = Minimum Test Gauge Pressure = Internal Design Gauge Pressure = Allowable Stress value at Test Temperature = Allowable Stress value at Design Temperature
Pneumatic tests are conducted at 1.1 times nominal design pressure. 5.4 Test Preparation All joints, including welds, are to be left non-insulated and exposed for examination during the test. If a joint has been previously tested in accordance with the Code, it may be insulated or covered. Piping designed for vapour or gas shall be provided with additional temporary supports, if necessary, to support the weight of the test liquid. Expansion joints shall be provided with temporary restraint, if required, for the additional pressure load under test of shall be isolated from the test. Equipment which is not to be included in the test shall be either disconnected from the piping or isolated by valves or blanks. All pressure gauges, gauge glasses, flow meter pots, liquid level float gauges, and all other pressure parts of instruments, together with the piping connecting the instruments to the main piping, should be included in the hydrostatic test. Relief valves and rupture disks should not be subjected to the pressure test. If a pressure test is to be maintained for a period of time and the test liquid in the system is subject to thermal expansion, precautions must be taken to avoid excessive pressure built up.
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5.5 Pneumatic Testing If piping is tested pneumatically, the test pressure is set at 110 percent of the design pressure. Pneumatic tests include a preliminary check at not more than 25 psig; the pressure is then increased gradually in steps providing sufficient time to allow the piping to equalize strains during test and to check for leaks. 5.6 Test Records Records must be made of the tests, including date of test, identification of piping tested, test fluids, test pressure and approval by inspector.
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CONTENTS Page 0.0
Cover Sheet
1
1.0
Pipes and Fittings
2
2.0
Comments on selection and Limitations of Components
2–6
3.0
Piping Joints
6–8
4.0
Fabrication, Assembly and Erection of Process Plant Piping
8 – 11
5.0
Examination , Inspection and Testing
12 - 14
Applicable Revision: R1 Prepared: NNG
Checked: AKB
Approved: RUD
Date: 15.01.2001 First Edition: R0 Prepared: DNL
Date:
Date:
Checked: AKB
Approved: RUD
Date: 14.09.2000 File Name: C- 14
Date: 20.09.2000 Server: PUNE: KUMUS 207
Directory: PUNE: Refer \ Pi \ Training Manual
Date: 31.10.2000 VKO: KUMUS 209
VKO: Refer \ Training Manual
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PIPE AND FITTINGS: Furnace lap weld ferrous pipe, furnace butt-weld ferrous pipe, spiral-weld ferrous pipe, and fusion-welded steel pipe (made to ASTM A134, A53, Type F, API 5L furnace butt welded and A211) are not permitted for hydrocarbons or other flammable fluids within process unit limits or for hazardous fluids in any location. Non-ferrous pipe made by similar manufacturing process is similarly restricted. The use of bell-and-spigot fittings is limited to water and drainage service. Also, pipe couplings made of cast, malleable, or wrought iron are not permitted for flammable fluids within process limits or hazardous fluids in any area. In addition, they cannot be used for flammable fluids outside process unit limits at design temperatures above 300°F or design pressures above 400 psig.
2.0 COMMENTS ON SELECTION AND LIMITATIONS OF COMPONENTS: th (Refer Ch. C7 - "Process Piping Systems" in Piping Handbook 7 edition by M.L.Nayyar) There are many Code mandated restrictions for the use of fittings, bends, intersections, and valves which are not universally applicable to all process plant services, and such components are not easily codified. Some guides, however, are of value to the designer and are listed: •
Welding fittings are usually preferred to flanged fittings, not only for economic reasons but because the potential for leakage is reduced.
•
Pipe bends are preferred to butt welding elbows for reciprocating compressor suction and discharge piping, vapour relief-valve discharge piping, and piping conveying corrosive fluids (such as acid where turbulence in a fitting may cause excessive corrosion).
•
Bends or dead end tees should be used for piping which conveys pulverized abrasive solids suspended in gas in the dilute phase. Dead end tees (so arranged that the flow will impinge against the dead end) have a longer life than bends in abrasive service and should be used if the system can be designed to accommodate the resulting increase in pressure drop.
•
Bends should be used for dense phase flow of pulverized abrasive solids and for all piping which handles either pulverized or granular solids suspended in liquids or granular solids suspended in gases.
•
If the flow is through a branch into a header (or run pipe) in a piping system which transports pulverized abrasive solids suspended in gas in the dilute phase, a dead end cross (so arranged that the flow will impinge against the dead end) should be used.
•
In services with very high corrosion rates, butt welding fittings with the same inside diameter (ID) as the attached pipe (if not the same, consider taper boring the component with the smaller ID) are preferred to threaded and socket welding fittings.
•
Threaded cast iron fittings should not be used in pressurized process and utility piping.
•
Threaded plugs are preferred to pipe caps for threaded end closures to reduce dead end corrosion problems.
•
In most process plants, internal corrosion is a greater problem than external corrosion. Consequently, it is common practice that all 3/4 in and larger steel and cast iron (and all 2 1/2 in and larger brass) gate, globe, and angle valves (located above grade) be of the outside screw and yoke type.
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•
Although valves with seal welded or pressure seal bonnets and welding ends are commonly used in steam service, 2 1/2 in and larger valves in process service are usually equipped with flanged ends.
•
Valves operated in full open or block service are generally gate valves. Butterfly valves, ball valves, non-lubricated plug valves, and lubricated plug valves may be considered as possible alternates to gate valves.
•
As a general rule, hand operated throttling valves for services where fine control is not required, and those for control valve bypasses should be globe valves (internal stem and plug preferred) for sizes 2 in and smaller and gate valves for sizes 2 1/2 in and larger. For severe throttling service and where close control is required, a conventional control valve with a hand operator should be used. The only other common application for globe valves in process service is for mixing purposes.
•
Solid-wedge and flexible-wedge gate valves are generally preferred to split and doubledisk valves. Split-wedge and double-disk valves are generally used for clean liquids and noncondensing gases only.
•
Gate valves with Teflon inserts in the seat rings are very satisfactory in liquid butane and propane services.
•
Where choking may occur in blocked connections, a flushing connection should be added between the valve and the process line or equipment. The flushing medium may be oil, gas, or steam (if water can be tolerated in the system.
•
If the pressure differential across a closed gate valve is approximately equal to the pressure rating of the valve, consideration should be given to providing a pressure equalizing bypass around the valve. Consideration should also be given to bypasses for valves in steam lines for warm-up purposes. When bypasses are provided, they should be sized in accordance with the Manufacturers Standardization Society (MSS) of the Valve and Fitting Industry’s standard Practice (SP) MSS SP-45 (bypass and drain connection standard). A gate valve should be provided in the bypass line.
•
Drain or bypass connections may be tapped (or socket welded) into a valve body where necessary to simplify piping or to assure complete drainage.
•
Do not use check valves in vertical lines in which the flow is downward.
•
If a valve is installed with the stem lower than horizontal, the valve bonnet should be provided with a drain.
•
The designer should consider providing gear operators for all 6-in and larger lubricated plug valves and all 14-in and larger gate valves.
•
The use of double block valves should be kept to a minimum. Double block valves, however are required for sample connections and for drains which are connected to a closed drain system. Double block valves or their equivalent should be used where contamination must be prevented.
•
Under certain conditions double block valves are also needed where it is necessary to remove essential equipment from service for cleaning or repairs while the unit continues in operation. However, even in these cases often a single block valve with provisions for blinding will suffice. Such equipment must be provided with a spare, or it must be possible to bypass it temporarily without shutting down the unit. The nature of the fluid, its pressure and temperature, and many other factors must be considered when determining the need for double block valves. Generally, the need for double block valves at equipment should
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be considered if the fluid is hazardous or very corrosive or if the fluid is above 500°F. Where double block valves are used, a 3/4-in valve should be installed between the block valves. See FIG.1 FIG.1 BLOCK VALVES
TO RELIEF SYSTEM OR SAFE DISPOSAL
3/4” VALVE
DOUBLE BLOCK AND BLEED Some ball valves and non-lubricated valves, when equipped with a bleeder between the seats, have been satisfactory substitutes for double block valves. Both conventional gate valves with Teflon inserts in the seat rings and flexible-wedge gate valves have also been equipped with a bleeder connection and used in place of double block valves. th
2.1 Selection and limitation of flanges (Refer Ch. C7 – Piping Handbook, 7 Ed.) The Code restricts the use of screwed flanges as it does of any threaded joint. Slip-on flanges must not be used in installations where many large temperature cycles are expected or if the flanges are not insulated. The following statements on flanges are included for the designer’s guidance. •
The use of cast-, nodular-, wrought-, and malleable-iron screwed flanges should be avoided.
•
In services with very high corrosion rates, the bore of weld neck flanges should be the same inside diameter as the attached piping (if not the same, consider taper boring the component with the smaller inside diameter).
•
The bore of weld neck orifice flanges should match the inside diameter of the attached pipe.
•
ASME Standard B16.47 for Large Diameter Steel Flanges, governs steel flanges in sizes larger than 24 in. However, the designer must ensure that the flange drilling on such flanges will match that of the equipment to which it is to be attached. MSS-SP-44 Steel Pipeline Flanges & ASME B16.47 - Large Diameter Steel Flanges are also useful standards when using flanges larger than 24 in.
2.2 Selection and Limitations of Blanks In a process plant, blanks are usually required to isolate individual pieces of equipment at shutdown and to block off selected process lines positively at the process unit limits. They are
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also needed during operation wherever positive shutoff is required to prevent leakage of one fluid into another. Blanks should be located in horizontal lines if possible. Blanks should not be used in vertical water and steam lines in climates where danger of freezing exists. Circular handletype blanks can be used for raised face joints in locations where the lines can be sprung easily to permit installation of the blanks. As a rule, this is easily accomplished only in 4-in and smaller lines. Figure-eight-type blanks are used for larger lines and even then, jackscrews may be needed to install the blank. Blanks should be made from a plate specification approved for use in ASME B31.3, of substantially the same chemical composition as the pipe. 2.3 Selection and Limitations of Gaskets Gaskets must be made of materials which are not injuriously affected by the nature of the fluid or its temperature under anticipated operating conditions. Non-metallic gaskets are usually not permitted above 750°F gasket design temperature. Various elastometric gasket materials have very low (200°F) maximum service temperatures. Also, non-metallic gaskets should not be used in non-confining (flat or raised face) flanged joints at gasket design pressuretemperature conditions above the ratings of Class 600 flanges per ASME B16.5, except that for non-flammable, non-toxic service fluids, the limiting ratings can be those of Class 900 flanges. The use of metal or metal non-metallic filled gaskets is not limited as to pressure provided the gasket materials are suitable for maximum fluid temperatures. The American Society of Mechanical Engineers has developed ASME B16.20, a standard covering the dimensions of spiral-wound and double-jacketed gaskets. The spiral-wound gasket covered by ASME B16.20 has been widely used with great success with raised face flanges as a replacement for the ring type joint. 2.4 Selection and Limitations of Flange Facings When Class 125 cast-iron or flat face non-metallic flanges are bolted to Class 150 steel flanges, the 1/16-in raised face on the steel flanges should be removed. If the raised face is removed and a full-face gasket is used, either high-strength carbon-steel bolting or alloy-steel bolting may be used. However, if the face is not removed (or if the face is removed and a ring gasket extending only to the inner edge of the bolt-holes is used), the bolting material may not be of higher strength than carbon steel ASTM A307 Grade B. 2.5 Selection and Limitations of Bolting Carbon-steel machine bolts may be used to make flange connections for bolt metal temperature from -20°F to 400°F inclusive. This restriction is quite conservative with regard to pressure limit. Also, these bolts can be used quite safely to the limits of the Class 300 pressure class as permitted in ASME B16.5 with the use of appropriate gasketing material. The most widely used bolting materials in process plant are ASTM A193 Grade B7 stud bolts with ASTM A194 Grade 2H heavy semifinished hexagonal nuts. These materials are acceptable from -50°F to 1000°F. A number of operating companies use these materials almost exclusively to simplify inventories and reduce the possibility of misapplication of carbon -steel bolting. Carbon-steel bolting may be used with non-metallic gaskets with flanged joints rated Class 300 and lower for bolt metal temperatures at -20°F to 400°F.
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2.6 Selection and Limitations of Strainers (Refer Ch. C7 – Piping Handbook, 7 Ed.) The material for the strainer body (including bolting) should be equal to material specified for the valves in the same service. The screen material generally should be the same as the valve trim (e.g., 11-13 percent chrome or Type 316 stainless steel for most services). The location of permanent strainers (as contrasted to the temporary cone type which is installed at a flanged joint) also merits attention. Centrifugal and reciprocating pumps handling material containing solids should have permanent strainers provided in the suction lines to the pump or in the vessel from which the pump takes suction. The free area of such strainers should not be less than three times the cross-sectional area of the suction line. In addition, permanent strainers or filters should be provided in the piping for the protection of the equipment indicated in Table C 7.8 (Strainer Screen Openings for Equipment Inlet th Piping) of the Piping Handbook 7 Ed. The maximum clear opening for screens in these strainers varies with the application, but it should not exceed the value recommended for the particular type of equipment. The available pressure differential usually determines the minimum clear opening for screens. Permanent strainers should have baskets, which can be flushed clean during operation or easily removed for cleaning. If considerable clogging of strainers is anticipated, the strainers should be of the self-cleaning or duplex type to permit continual flow of clean liquid. 3.0
th
PIPING JOINTS: (Refer Ch. C7 – Piping Handbook, 7 Ed.) The type of piping joint used must be suitable for the pressure temperature conditions and should be selected by giving consideration to joint tightness and mechanical strength under the service conditions (including thermal expansion) and to the nature of the fluid handled with respect to corrosion, erosion, flammability, and toxicity. In general, the number of disassembly joints is minimized; most joints are welded if the material is weldable. Welded piping is used almost exclusively for transporting hydrocarbons and other flammable fluids. Bypass piping, alternate process connections, and auxiliary piping systems such as gland oil, seal oil, lubricating oil, fuel gas, fuel oil, heating or cooling oil, flushing oil, flue gas and blowdown piping, are included. Welded construction is also used for all piping outside process unit limits which is used for the transfer of hydrocarbons or most other process fluids. Piping which is threaded or welded, depending primarily on economic considerations, includes piping, other than specifically mentioned above, in services such as drains, vents, pumpouts, sample connections, and certain instrument leads, which contain process fluids only upon intermittent or occasional use of the piping involved and which are not an integral or essential part of the process system. 3.1 Welded Joints The Code permits welded joints in all instances in which it is possible to qualify welding procedures, welders and welding operators in conformance with the rules of the Code. There are, however, a few minor additional considerations for seal-welded (threaded) and socketwelded joints limited to size NB 2”. For example, the Code cautions against the use of socketwelded construction in cases where severe crevice corrosion or erosion occurs. The Code also states that seal welds may be used to avoid joint leakage but that they shall not be considered as contributing any strength to the joint.
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3.2 Flanged Joints The number of flanged joints in a piping system is usually determined by maintenance and erection considerations, including sufficient flanged joints for insertion of blanks during shutdown. 3.3 Expanded Joints This type of joint is more commonly used on the piping and tubes for refinery heaters. They are excluded for use in hazardous and toxic services and under severe cyclic conditions. 3.4 Threaded Joints The threading of pipe with a wall thickness less than ASME B36.10M standard wall is not permitted, and the use of threaded joints where severe crevice corrosion or erosion may occur should be avoided. Economics will limit the use of threaded piping to small pipe sizes (2 in and smaller) for most services; however, it is used for most galvanized piping. All pipe threads on piping components must taper pipe threads in accordance with ASME B1.20.1 except the following: •
Pipe threads other than taper pipe threads may be used for piping components, where tightness of the joint depends upon a sealing surface other than the threads and where experience or tests have demonstrated that such threads are suitable for the condition.
•
Couplings, 2 inch and smaller, with straight-tapped pipe threads may be used on piping components with taper pipe threads if the design conditions do not exceed 150 psig or 400°F and if the fluid handled is non-flammable and non-toxic (Category D Fluid Service).
3.5 Flared, Flareless, and Compression Joints Piping joints using flared, flareless, or compression-type tubing fittings may be used within the limitations of applicable standards or specifications. In the absence of such standards or specifications, the engineer shall determine that the type of fitting selected is adequate and safe for the design conditions in accordance with the following requirements: •
The pressure design shall meet the requirements of the code.
•
A suitable quantity of the type and size of fitting to be used shall meet successful performance tests to determine the safety of the joint under simulated or similar service conditions.
•
Fittings and their joints shall be suitable for tubing with which they are to be used.
•
Fitting shall not be used in services which exceed the manufacturer’s maximum pressuretemperature recommendations.
3.6 Caulked Joints The term caulked joints applies to joints of the bell-and-spigot type which are permitted only for water service at pressures suitable for the pipe to which they are applied. Provisions must be made to prevent disengagement of the joints at bends and dead ends and to support lateral reactions produced by branch connections or other causes.
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3.7 Brazed and Soldered Joints Fillet-brazed or fillet-soldered joints may not be used in process piping, but soldered-type and silver brazed socket-type joints are permitted in non-flammable non-toxic service. The low melting point of brazing alloys shall be considered where possible exposure to fire is involved. 4.0
FABRICATION, ASSEMBLY AND ERECTION OF PROCESS PLANT PIPING: Complete detail and exact requirements which relate to fabrication , assembly and erection of the process piping systems are given in Chapter V of ASME B31.3. Important phases of the Code treatment of these topics are covered briefly below. 4.1 Material for Welding (Refer Clause 328.3) All filler materials must comply with the requirements in Section IX ASME, Boiler and Pressure Vessel Code. If backing rings are used in services where their presence will result in severe corrosion or erosion, it is required that the backing ring be removed after welding and the internal joint ground smooth. 4.2 End Preparation (Refer Clause 328.4) ASME B16.25 provides dimensional standards for weld end bevels. Preferably, the ends of pipe and the edges of plate which are to be formed into pipe should be shaped by machine. Other methods of shaping may be used provided a reasonably smooth surface suitable for welding and free from tears, slag, scale and grease is attained. Oxygen or arc cutting is acceptable only if the cut is reasonably smooth and true and all slag is cleaned from the flame cut surfaces. If piping component ends are machined on the inside for backing rings, such machining must not result in a finished wall thickness, after welding, less than the minimum design thickness plus corrosion and erosion allowances. Generally a root gap of 1/8 in is used for joints (including branch connections) without backing rings, except that where the pipe wall thickness is less than 3/16 in, a 1/16 in root gap is generally used. 4.3 Other Alignment Considerations (Refer Clause 328.4.3) Flange bolt-holes should straddle the established center lines unless other orientation is required to match the flange connections on equipment. Slip-on flanges should be positioned so the distance from the face of the flange to the pipe end is about equal to the nominal pipewall thickness plus 1/8 in. Welding neck orifice flanges should be the same bore as the pipe to which they are attached and must be aligned accurately. Longitudinal seams in adjoining lengths of welded pipe should be staggered and located to clear openings and external attachments. The following restrictions, limitations or guidelines apply to welding of process piping: •
Projection of weld metal into the pipe bore at welded butt joints should not exceed 1/16 in for pipe 8 in and smaller or 1/8 in for larger pipe. Excessive projection on accessible joints should be removed. Welds attaching welding neck orifice flanges to pipe should be ground smooth on the inside.
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•
On ferritic materials to be used below 20°F, the welder’s identification mark should be preferably be made with ink stencil. Steel stamping should be avoided.
•
Welding procedure for fillet welds and seal welds :
The Code does not permit cracks in fillet or seal welds and limits undercutting to 1/32 in for these welds. Fillet welds may vary convex to concave. If seal welding of threaded joints is performed, the Code requires that all exposed threads be covered by the seal weld and that the welding be done by qualified welders. In addition to the Code requirements, it is strongly recommended that (1) threaded joints be made dry (without thread compound), (2) seal welds be at least two-pass (preferably three-pass) welds using a 3/32 in or 1/8 in electrode 1 (5/32 in electrode is acceptable for 2 /2 in and larger pipe size), and (3) valve and union ends be welded by the electric arc process to minimize distortion and ensure that valves be closed during welding. 4.4 Welding Procedure (Refer Clause 328.5) Before welding, all surfaces must be cleaned and free from paint, oil, rust, scale, and other detrimental material. Furthermore, welding is prohibited if there is impingement of any rain, snow, sleet, or high wind on the weld area. The following code requirements apply to girth butt welds and any longitudinal butt weld in a piping component which is not made in accordance with a standard specification: •
If the external surfaces of the two components are not aligned, the girth butt weld must be tapered between the two surfaces.
•
Tack welds, if not made by a qualified welder using the same procedure as the completed weld, must be removed. Tack welds which are not removed should be made with an electrode which is the same as or equivalent to the electrode to be used for the first pass. Tack welds which have cracked must be removed.
•
The types and limitations of imperfection required to be evaluated with various types of examinations are shown in the Code.
4.5 Preparation and Welding Procedure for Welded Branch Connections Branch connections (including specially made integrally reinforced branch connection fittings) which abut the outside surface of the run wall or which are inserted through an opening cut in the run wall must be so arranged as to provide a good fit and be attached by means of fullpenetration groove welds. The recommendations for spacing and location of branch connections contained in Pipe Fabrication Institute (PFI) Standard ES7 should be followed. A good fit must be provided between reinforcing rings and saddles and the parts to which they are attached. When rings and saddles are used, a vent hole is provided (at the side and not at the crotch) in the ring or saddle to reveal leakage in the weld between branch and main run and to provide venting during welding and heat-treating operations. Reinforcing pads should be proportioned so the diameter of a vent hole is not greater than one-third of the pad width. th
4.6 Fabrication Tolerances for Welded Piping (Refer Ch7 – Piping Handbook, 7 Ed.) A widely accepted tolerance on face-to-face and center-to-face dimensions of welding piping is ± 1/8 in (3 mm). As for the location of the flanges, their lateral translation in any direction
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from the specified position should not exceed 1/16 in. (1.5 mm). Also the alignment of flanges should not deviate from the specified position, measured across any diameter, by more than 1/32 in. 4.7 Qualification Qualification of the welding procedures to be used and of the performance of welders and welding operators is required to comply with the ASME Boiler and Pressure Vessel Code. Section IX 4.8 Defect Repairs Weld defects which, require repair must be removed. All repair welds must be made with the same welding procedure initially used. 4.9 Bending and Forming Pipe may be bent by any hot or cold method consistent with material characteristics of the pipe being bent and the intended service. It may be bent to any radius which will result in a bend arc surface which is free of cracks and buckles. Hot bending and forming must be done within a temperature range consistent with material characteristics, end use, or heat treatment. It is recommended that hot bends in pipe sizes 1 1 /2 in and larger be packed with high temperature silica sand and that the pipe be uniformly heated before the hot bending operation. When pipe must be threaded before bending, forging, or heat treating, all exposed threaded surfaces should be protected during heat treatment. 4.10 Cleaning after Fabrication Following fabrication, all loose scale, weld spatter, slag, sand and other foreign materials should be removed from the piping. PFI Standard ES5 ( Cleaning of Fabricated Piping) is an acceptable standard for cleaning fabricated piping. Piping should not be painted in the fabricating shop (i.e., before it has been erected and tested). 4.11 Heat Treatment Heat treatment is used to avert or relieve the detrimental effects of high temperature and severe temperature gradient inherent in welding and to relieve the residual stresses created by bending and forming. The welding procedure qualification establishes the necessity for preheating and post-heating welds (and the temperatures and soaking period to be used) in order to restore or obtain the physical properties of the materials (such as strength, ductility, and corrosion resistance) needed to satisfy end use requirements. 4.12 Bolting Procedure for Flanged Joints It is a good practice to apply an antiseize thread compound to the bolts before the nuts are installed. A mixture of graphite and oil is one of the best substances for this purpose. Tightening og bolts should follow usual criss-cross sequential pattern to approximate pre-load seating of the Gasket In bolting joints using spiral-wound gaskets, the gasket should be compressed to about 25 percent of the original thickness. Spiral wound gaskets conforming to API Standard 601 have a 0.125 in thick outside gauge and centering ring. The gasket is seated when it is compressed until the flange faces touch the gauge ring.
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Uhde India Limited
SELECTION AND LIMITATIONS OF PIPING COMPONENTS
DOC No. : 29040-PI-UFR-0014 Rev.
: R1
Page
: 11
Steel-to-cast-iron flanged joints must be assembled carefully in order to prevent damage to the cast-iron flange. Both flanges in steel-to-cast-iron flanged joints should be flat faced. These joints should be made up with extreme care, taking up on bolts uniformly after fitting flanges into close parallel and lateral alignment. Flanges which connect piping to mechanical equipment, such as pumps, turbines or compressors, should be fitted up in close parallel and lateral alignment before tightening the bolting. 4.13 Cast-Iron Bell-and Spigot Piping Bell-and-spigot joints in cast-iron piping must be assembled using poured lead or other joint compound suitable for the service. Usually each cast-iron bell-and-spigot joint is packed with hemp, poured full of lead (with a minimum number of pours), then caulked. The depression of lead below the face of the bell, after joint caulking, should not exceed 1/4 in. (Lead wool can be used where it is not permissible to pour lead). 4.14 Threaded Piping Any compound or lubricant used on threads must be suitable for the service conditions and compatible with both the service fluid and the piping materials. Threaded joints which are to be seal welded should be made up without any thread compound. 4.15 Erection of Corrugated Expansion Joints Corrugated expansion joints should be installed as-shipped from the manufacturer or compressed for the cold condition at erection, depending on anticipated direction and magnititude of movement after the pipeline reaches operating temperature. The manufacturer’s recommended total travel should preferably straddle the calculated travel. 4.16 Erection of Valves Valve packing glands should be checked for the quality and quantity of packing, and lubricated plug valves should be provided with proper lubricant. 4.17 Erection of Pipe Supports In addition to the major supports specified by the design drawings, minor supports as found necessary in the field should also be installed to prevent undesirable vibration, sag, lateral movement, and stresses. Spring hangers, including constant-support type, should be checked for proper adjustment of travel and be correctly positioned for the cold condition of erection. 4.18 Cleaning of Lines after Assembly and Erection After completion of erection, scale, dirt, welding electrodes, slag and other foreign material should be removed from the lines. Particular attention should be given to the cleaning of air lines and compressors and blower, pump and turbine inlet piping. Before the initial operation, steam lines to turbines and to steam ends of reciprocating compressors and pumps should be blown down with steam, 100 psig or higher. All practical precautions should be taken to prevent the introduction of foreign matter into pumps, instruments and other equipment. Cleaning may be accomplished by flushing out the lines. Temporary strainers should be used at pumps during flushing operation unless spools or valves can be conveniently dropped out and suitable deflectors provided to prevent refuse from entering the pumps. Consideration should be given in dismantling those lines which cannot be adequately cleaned by flushing.
TRAINING MANUAL- PIPING
Uhde India Limited 5.0
SELECTION AND LIMITATIONS OF PIPING COMPONENTS
DOC No. : 29040-PI-UFR-0014 Rev.
: R1
Page
: 12 th
EXAMINATION, INSPECTION AND TESTING: (Refer Ch. 7 of Piping Handbook, 7 Ed.) Before initial operation, piping installation should be inspected to the extent necessary to assure compliance with the engineering design and with the material, fabrication, assembly and test requirements of the Code. An employee representative of the owner should be responsible for this inspection. This examiner may delegate performance of any part of the inspection to inspectors who may be employees of his own organization, of an engineering or scientific organization, or of a recognized insurance or inspection company. A non-destructive examination (NDE) plan should be consistent with service severity, incorporating process and mechanical factors. The NDE plan focus should be on those pipelines where failure would produce the most harm to personnel or property. Some issues the designer should consider when developing the NDE plan are as follows: •
Service factors: Corrosivity, toxicity and flammability - hazardous nature of flowing media. The designer should apply a sound NDE program to detect flaws in these dangerous streams.
•
Mechanical factors: Temperature, pressure, cyclic conditions, thermal bending stresses, vibration. Fatigued and highly stressed lines are more likely to fail than low-stressed lines. Detection and removal of flaws can provide additional service life.
5.1 Visual Examination All welds are required to be capable of compliance with the limitations on imperfections specified in the Code for visual examination. Visual examination consists of observation by the inspector of whatever portions of a component or weld exposed to such observation, either during or after manufacture, fabrication, assembly or test. 5.2 Supplementary Types of Examination The following supplementary types of examination are not required unless specified by the engineering design because of special service conditions requiring a high degree of freedom from imperfections. If such examination is specified for a weld, it is only required that the weld examined be repaired, if necessary, so the weld imperfections comply with the limitations in the Code for the type of examination used. If supplementary types of examination are specified, they should be performed after completion of any postheat treatment where required. If any of the following types of examination is specified by the engineering design, it should be performed to the extent as follows: 5.2.1
Magnetic Particle
Magnetic Particle Examination is essentially a surface type examination. An area to be examined by magnetic particle examination can be completely examined or examined on a random sampling basis, as specified. 5.2.2
Random Radiography
X-Ray or gamma-ray radiography may be used. The selection of the method should be dependent upon its adaptability to work being radiographed. When random radiography of welds is specified by the engineering design, it should be done on the number of welds designated. The engineering design shall specify the extent to which each examined weld should be radiographed. Random radiography may also be used for examination of piping components such as valve or fitting to any extent specified by the engineering design.
TRAINING MANUAL- PIPING SELECTION AND LIMITATIONS OF PIPING COMPONENTS
Uhde India Limited 5.2.3
DOC No. : 29040-PI-UFR-0014 Rev.
: R1
Page
: 13
100 Percent Radiography
If 100 percent radiography is specified for welds in piping, each weld in the piping shall be completely radiographed. 5.2.4
Hardness Tests
The extent of hardness testing required shall be specified by the engineering design, considering the severity of the service, type of material and other pertinent factors. 5.3 Pressure Tests Before initial operation, piping must be pressure tested to assure leak tightness. If repairs or additions are made following the pressure tests, the affected piping is retested, except that in the case of minor repairs or additions, the owner may waive retest requirements. The pressure test is maintained for a sufficient time, but not less than 10 min, to determine if there are any leaks. Water is commonly used as the test fluid except when there is a possibility of damage due to freezing or if the operating fluid or piping material would be adversely affected by water. If hydrostatic testing is not considered practical, a pneumatic test using air or another nonflammable gas may be substituted. A preliminary air test at not more than 25 psig, is made before hydrostatic test in order to locate major leaks. If pressure tests are conducted at low metal temperatures, the possibility of brittle fracture must be considered. Hydrostatic pressure tests are conducted at 1.5 times nominal design pressure, adjusted for temperature. ASME B 31.3 gives the Formula for temperature correction for Pressure Test as follows: PT
=
Where: PT P ST S
1.5 P ST / S = Minimum Test Gauge Pressure = Internal Design Gauge Pressure = Allowable Stress value at Test Temperature = Allowable Stress value at Design Temperature
Pneumatic tests are conducted at 1.1 times nominal design pressure. 5.4 Test Preparation All joints, including welds, are to be left non-insulated and exposed for examination during the test. If a joint has been previously tested in accordance with the Code, it may be insulated or covered. Piping designed for vapour or gas shall be provided with additional temporary supports, if necessary, to support the weight of the test liquid. Expansion joints shall be provided with temporary restraint, if required, for the additional pressure load under test of shall be isolated from the test. Equipment which is not to be included in the test shall be either disconnected from the piping or isolated by valves or blanks. All pressure gauges, gauge glasses, flow meter pots, liquid level float gauges, and all other pressure parts of instruments, together with the piping connecting the instruments to the main piping, should be included in the hydrostatic test. Relief valves and rupture disks should not be subjected to the pressure test. If a pressure test is to be maintained for a period of time and the test liquid in the system is subject to thermal expansion, precautions must be taken to avoid excessive pressure built up.
TRAINING MANUAL- PIPING
Uhde India Limited
SELECTION AND LIMITATIONS OF PIPING COMPONENTS
DOC No. : 29040-PI-UFR-0014 Rev.
: R1
Page
: 14
5.5 Pneumatic Testing If piping is tested pneumatically, the test pressure is set at 110 percent of the design pressure. Pneumatic tests include a preliminary check at not more than 25 psig; the pressure is then increased gradually in steps providing sufficient time to allow the piping to equalize strains during test and to check for leaks. 5.6 Test Records Records must be made of the tests, including date of test, identification of piping tested, test fluids, test pressure and approval by inspector.
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