Qhse P11 Ti Jp05 Ut-gen-ultrasonic Inspection Rev

Job Procedure for Analysis of MFL inspection Result Using Ultrasonic method

Document No:

QHSE P11 TI JP05 UT-Gen

Rev

01

Issue Date

Prepared by:

Reviewed by:

Approved by:

Name & Signature: Amal Sasi

Name & Signature: Rajesh.P.K

Name & Signature: Nisanth

Date: 25-02-2016

Date:01-03-2016

Date:02-03-2016

02 March 2016

Job Procedure for Analysis of MFL inspection Result Using Ultrasonic method CONTENTS

Section

Description

Page No.

Amendment Record

3

1.0

Scope

4

2.0

Limitations

4

2.0

References

4

4.0

Definitions

4

5.0

Prerequisites

6

6.0

Equipment required

6

7.0

Personnel

7

8.0

Preparation

7

9.0

Calibration

7

10.0

Plate thickness verification

8

11.0

Confirmation

9

12.0

Reporting

9

QHSE P11 TI JP05 UT-Gen /Procedure Analysis of MFL inspection Result Using Ultrasonic method-Rev No: 01-Date: 02 March 2016

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Job Procedure for Analysis of MFL inspection Result Using Ultrasonic method

1. Amendment Record Revision No.

01

Date of Amendment

02 March 2016

Section / Checklist Amended

All

Name Amendment Details Overall formatting and old Procedure Reference No. Aries/ANDT-UTM-01 changed to new number QHSE P11 TI JP05 UT-Gen

Reviewed

Approved

Rajesh.P.K

Nisanth

Rajesh.P.K

Nisanth

Amendment as per latest Written practise QHSE/P11/CNDT/WP/01Rev-09 00

04 July 2013

All

Initial Issue

QHSE P11 TI JP05 UT-Gen /Procedure Analysis of MFL inspection Result Using Ultrasonic method-Rev No: 01-Date: 02 March 2016

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Job Procedure for Analysis of MFL inspection Result Using Ultrasonic method 1.

Scope This procedure describes the requirements for locating and assessing the depth of under floor corrosion pitting using the Ultrasonic A-scan method with a 10 mm dia 0° twin crystal probe to confirm the results of (MFL) inspection of Bulk Liquid Storage Tank Floors

2.

Limitations The sensitivity of the method varies with surface roughness of the scanning surface. Severe top surface pitting may prevent satisfactory inspection by ultrasonics. As with all inspection methods the effectiveness of inspection is affected by the cleanliness and preparation of the floor. In particular, debris and loose corrosion products may prevent adequate coupling of sound into the material. The Twin crystal probes will not necessarily identify isolated pitting which is detected by MFL scanning due to the physical limitations of UT A scan technique with a 10 mm dia probe Floors coated with fibre-glass and rubber cannot normally be inspected using this method.

3.

References

The following documents shall be referred to in conjunction with this procedure: API Std. 650, API Std. 620, API Std. 653, EEMUA Std. 154,

Welded Steel Tanks for Oil Storage Welded Steel Storage Tanks Inspection and Repair of Storage Tanks Guidance to owners on demolition of Vertical steel Storage Tanks EEMUA Std. 159, Guide to the Inspection, Maintenance and repair of Above ground vertical cylindrical steel storage tanks UK HSE report 481, Recommended practice for magnetic flux leakage Inspection of atmospheric storage tank inspection

QHSE/P11/ CNDT/WP/01Rev-09

4.0

Recommended Practice for personnel Qualification and Certification in Nondestructive Testing.

Definitions A-scan display

This refers to the use of a Liquid Crystal Display (LCD) panel to display ultrasonic signals as vertical deflections of a horizontal time scale.

QHSE P11 TI JP05 UT-Gen /Procedure Analysis of MFL inspection Result Using Ultrasonic method-Rev No: 01-Date: 02 March 2016

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Job Procedure for Analysis of MFL inspection Result Using Ultrasonic method Time base

The horizontal scale on the LCD that is calibrated in time ( sec) or material thickness units. The scale usually has ten equal major divisions

Vertical scale

The vertical scale on the display represents the amplitude of the ultrasonic signal and is normally described as a percentage of Full Screen Height (FSH).

Sensitivity The adjustment of gain in the receiver amplifier to achieve repeatable signal amplitude during calibration in order to ensure that reflections from corrosion pits will be detected. Basic Calibration The process of adjusting the time base range to represent a known thickness of the material to be tested. Calibration shall be performed on a calibration nominal floor thickness. Transfer Correction The transfer correction is the correction in difference to dB to be added or detected depending upon the surface roughness of the calibration block with respect to the roughness of the proposed surface are of the plate to be scanned. Twin crystal probe An ultrasonic transducer containing separate transmit and receive crystals acoustically isolated to allow echoes to be displayed from reflectors close to the scanning surface. Couplant

Oil, grease, water or wallpaper paste used to exclude air between the transducer and test surface.

Annular plates

Plates around the periphery of the tank that are welded to the shell and overlap the floor plates. Annular plates are often thicker than the floor plates.

Sketch plates

Plates around the periphery of the tank welded to the shell and are overlapped by the floor plates. Sketch plates are usually the same thickness as the floor plates.

Floor plates

The main part of the floor. Floor plates are mostly rectangular.

Man way

The access point for inspection.

Sump

A depression in the floor to collect water etc. The sump cannot normally be inspected using MFL and may be examined using UT.

QHSE P11 TI JP05 UT-Gen /Procedure Analysis of MFL inspection Result Using Ultrasonic method-Rev No: 01-Date: 02 March 2016

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Job Procedure for Analysis of MFL inspection Result Using Ultrasonic method

5.0

Tank datum

An imaginary point outside the tank from which the orientation of the plate layout, man ways and roof access stairways can be defined. By convention the tank datum is usually the bottom left corner of a square containing the tank.

Plate reference

The corner of the plate from which corrosion indications are measured and usually the corner from which scanning is commenced.

Plate orientation

Plates are defined as ‘vertical’ or ‘horizontal’ with respect to the tank datum.

Row number

The plates are considered to be in rows numbered from top to bottom with respect to the tank datum.

Plate number

The plates in each row are numbered from left to right with respect to the tank datum.

Reporting Level

A percentage loss or minimum remaining wall thickness value agreed with the client. Pitting equal to or above this value shall be included in the report

Prerequisites

Before commencing a tank floor inspection with the Floormap scanner, the operator should ensure the following information is available: a)

Floor plate and annular plate thickness.

b)

Floor coating thickness and coating material.

c)

General condition of the top surface for cleanliness and pitting.

Presence of heater coils or other obstruction e) Minimum pit depth to be detected (as a percentage of floor thickness).

6.0

f)

Floor plate numbering system to be used.

g) h)

Name and contact details of client’s site representative. Safety requirements (breathing apparatus, hot work permit system etc).

Equipment required a) b) c)

An A-scan flaw detector with an operating frequency range that includes 5 MHz. Appropriate calibration block. A suitable ultrasonic couplant.

QHSE P11 TI JP05 UT-Gen /Procedure Analysis of MFL inspection Result Using Ultrasonic method-Rev No: 01-Date: 02 March 2016

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Job Procedure for Analysis of MFL inspection Result Using Ultrasonic method d) e) f) g) h) i) 7.0

A 10 mm diameter 5 MHz twin crystal probe and connecting leads. Approved lighting system. Approved generator for lights. Coveralls, Hardhats and safety footwear. Approved Breathing apparatus if required. Other safety equipment as may be required by the contract.

Personnel The individual carrying out the Ultrasonic cross checking shall be trained and certified to a minimum of ASNT level 1 in the use of A-scan equipment for corrosion detection and thickness measurement. All personnel involved in the inspection shall have attended appropriate safety training including confined space and breathing apparatus training where relevant.

8.0

Preparation a)

b)

c)

d) e)

9.0

The tank floor shall be clean and free from loose debris. If necessary each plate shall be swept prior to scanning. It is not normally necessary to grit blast the floor in order to carry out a satisfactory UT inspection. The team leader shall ensure that appropriate work permits have been issued, that the required safety personnel are in position and that the client’s site representative is aware of the times that the team shall be in the tank. Adequate lighting shall be installed and positioned for the inspection.

The floor plates and annular plates shall be numbered in accordance with the agreed numbering system using a suitable paint marker. The team leader shall conduct a visual examination of the floor to assess the cleanliness and degree of top surface corrosion present. If the surface condition for either of the above reasons is considered to reduce the sensitivity of the inspection, the leader shall draw this to the attention of the client’s site representative.

Calibration Calibration shall be carried out using a calibration block of appropriate thickness for the Basic Calibration. Transfer correction shall be carried out near to the marked area to be examined at a position having similar surface condition to the marked area. Switch on the unit. Carry out the basic calibration to set a time base range of 25 mm full scale or a multiple of 25 mm that ensures at least two back wall echoes can be displayed. Adjust the gain control to a sensitivity that puts the amplitude of the 2nd back wall echo at 80% FSH. Apply couplant to at least 5 locations on the main floor plates and 5 locations on the annular plates.

QHSE P11 TI JP05 UT-Gen /Procedure Analysis of MFL inspection Result Using Ultrasonic method-Rev No: 01-Date: 02 March 2016

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Job Procedure for Analysis of MFL inspection Result Using Ultrasonic method Apply the probe to each of these locations and adjust the amplitude of the 2 nd back wall echo to be measured to 80% FSH and note the material thickness indicated. The results of the readings taken above shall be used to determine the nominal thickness of the main floor and the annular plates. Any reading that is significantly below the other four shall be discounted from the nominal thickness determination but the position marked as a potential corrosion site.

10.0 Plate thickness verification a)

Apply couplant to the area marked according to MFL results and to an adjacent unmarked area of similar surface condition.

b)

Place the probe on the unmarked area and check that the thickness indicated is equal to the nominal thickness. If it is not equal locate another position that is equal.

c)

Obtain three back wall echoes at this position and adjust the time base range to display these at 3, 6 and 9 main divisions on the time base.

d)

Adjust the gain so that the amplitude of the third back wall echo is at 80% FSH.

e)

Place the probe in the marked area and perform a raster scan over the area with a pitch of approximately 6 mm and maintain a steady scan speed.

f)

The dynamic signal pattern at the pit location(s) will move to the left of the display and decrease in amplitude.

g)

The dynamic signal pattern for poor coupling conditions will collapse in amplitude without moving to the left.

h)

The dynamic signal pattern in the presence of top surface roughness will fluctuate in amplitude with minor movement left and/or right.

i)

Where dynamic signal pattern (f) above is noted, the probe movement should be gradually reduced until the position of maximum effect is reached.

j)

At this position it is likely that signal amplitude will be relatively small especially if conical pitting is present. To ensure that the minimum wall thickness is displayed the gain should be increased so that the first back wall

k)

echo is at 80% FSH and the remaining wall estimated by the position of the first back wall echo as a percentage of ‘3’ multiplied by the nominal wall thickness. For example, if the first back wall echo is at 2 divisions along the time base and the nominal thickness 6 mm, the remaining wall would be 67% times 6 mm = 4 mm.

l)

If a more accurate result is required, the spot should be marked, the basic calibration resumed, and the thickness measured from that calibration.

QHSE P11 TI JP05 UT-Gen /Procedure Analysis of MFL inspection Result Using Ultrasonic method-Rev No: 01-Date: 02 March 2016

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Job Procedure for Analysis of MFL inspection Result Using Ultrasonic method m)

When adjusting the gain for clauses (j) or (k) above care should be taken to ensure that at high gain levels, cross talk between the two crystals is not mistaken for the first back wall echo. Back wall echoes will be equally spaced across the time base.

11.0 Confirmation 11.1

The remaining portion of the MFL marked areas should be examined, as at Clause 10 herein in case more than one area of concern is present.

11.2

All areas marked for confirmation shall be examined in accordance with clause 10.0 above.

12.0

Reporting

12.1

The results of the ultrasonic examination shall be recorded and reported to the team leader for comparison with the MFL results major discrepancies between MFL & UT results may indicate that the permeability of the tank floor is not the same as that of the MFL calibration plate and require further action.

12.2

The co-ordinates of all pitting equal to or greater than the reporting level for each plate together with the percentage loss or remaining wall thickness shall be shown on a diagram for each plate inspected by UT.

12.3

In MFL auto mapping mode the information at 12.2 is generated automatically and displayed in colour coded pixels.

12.4

Results from areas that have been inspected only by Ultrasonics shall also be inserted manually into the Mapping Mode reports for ease of reference.

QHSE P11 TI JP05 UT-Gen /Procedure Analysis of MFL inspection Result Using Ultrasonic method-Rev No: 01-Date: 02 March 2016

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