TOFD & PA Procedure for 301

PROCEDURE FOR AUTOMATED TOFD & PA INSPECTION OF BUTT WELD JOINTS

SIEVERT ARABIA LIMITED Dammam - Saudi Arabia Tel. 03 8411 846 Fax. 03 8411 812

Document No. SAL-TECH-SOP-TOFD & PA-0102015

PROCEDURE FOR AUTOMATED PA & TOFD INSPECTION OF BUTT WELD JOINTS

Customer Client Contractor Sub-Contractor Project No.

05th December 2015 Page 2 of 49

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SEPCO Electric Power Construction Corporation Saudi Aramco Zamil Steel Industries Sievert Arabia Limited ZS-PE-301-01 To 05

THIS OPERATING PROCEDURE IS CONTROLLED BY THE SIEVERT ARABIA LIMITED AND MAY NOT BE AMENDED, REVISED OR ALTERED IN ANY OTHER WAY WITHOUT THE CONSENT OF THAT COMPANY. THE SIGNATURES BELOW AUTHORISE ALL PAGES OF THIS PROCEDURE FOR USE FROM THE DATE OF APPROVAL SHOWN

ISSUE

REVISION

DATE

REMARKS

1

0

05th Dec 2015

Initial Issue

NAME POSITION

Prepared by Bechan Barai ASNT NDT Level II

Reviewed & Approved by Abdul Habibullah ASNT NDT Level III (195519)

05 th December 2015

05 th December 2015

SIGNATURE DATE

SIEVERT ARABIA LIMITED Dammam - Saudi Arabia Tel. 03 8411 846 Fax. 03 8411 812 PROCEDURE FOR AUTOMATED PA & TOFD INSPECTION OF BUTT WELD JOINTS

Item

Comment


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Resolution


Prepared and reviewed by




05th December 2015

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CONTENTS 1.0

SCOPE: ………………………………………………………………….

6

2.0

PURPOSE: ………………………………………………………………

7

3.0

REFERENCE: …………………………………………………………..

7

4.0

SAFETY: ……………………………………………………………….

8

5.0

PERSONNEL QUALIFICATION: ……………………………………

8

6.0

SURFACE PREPARATION: ………………………………………….

8

7.0

INSPECTION EQUIPMENT AND ACCESSORIES: …………………

9

7.1

ACQUISITION UNIT & SOFTWARE: ………………………………..

9

7.2

SCANNER DETAILS: …………………………………………………...

10

7.3

SEARCH UNIT & WEDGES: ……………………………………….

11

8.0

COMPUTRIZED IMAGING TECHNIQUE: …………………………

12

9.0

COUPLANT: ……………………………………………………………..

12

10.0

CALIBRATION BLOCKS: ………………………………………………

12

11.0

QUALIFICATION BLOCKS: …………………………………………

16

12.0

CALIBRATION: ……...………………………………………………….

19

12.1

EQUIPMENT CALIBRATION: ……………………………………….

19

12.2

ENCODER CALIBRATION: ………………………………………….

23

12.3

VELOCITY & WEDGE DELAY CALIBRATION: ……………………...

23

12.4

SENSITIVITY CALIBRATION: ………………………………………...

25

12.5

TCG CALIBRATION………………………………………………..

26

13.0

CALIBRATION CONFIRMATION: …………………………………….

27

14.0

SCAN PLAN: …………………………………………………………..

28



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15.0

EXAMINATION COVERAGE & SCANNING: ………………………...

28

16.0

RECORDING AND EVALUATION: ……………………………………

30

17.0

ACCEPTANCE CRITERIA: ……………………………………………..

37

18.0

REPORTING: …………………………………………………………….

38

ANNEXURE-1- SCAN PLAN DETAILS……………………………………………….

41



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1.0 SCOPE This procedure describes the requirement and application of automated Time of Flight Diffraction (TOFD) examination for detection and evaluation of discontinuities within weld metal and heat affected zone of weld joints, and TOFD dead zones shall be covered by Phased array method for deaerator. Final inspection shall be after PWHT in general arrangement for deaerator. This procedure, when used in combination with specified scan plan is applicable for single V groove joints configuration and thickness range as per table given below. Work to this procedure will be in compliance with ASME Sec VIII Div 2.This procedure is applicable for both circumferential and longitudinal weld seams. Job no.

Joint No.

Material

Thickness

Joint configuration

Welding Process

301-01

CS1 TO CS11 & LS1 TO LS9

SA 516 Gr 70 N

20,24,25 & 28mm

Single V

SAW + SMAW

301-02 TO 05

CS1 TO CS7 & LS1 TO LS5

SA 516 Gr 70 N

22,24,25 & 28mm

Single V

SAW + SMAW

Fig 1 : Single V Configuration




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2.0 PURPOSE This procedure shall apply to the general aspect of ultrasonic examination of welds using TOFD technique along with Phased array and Omniscan equipment coupled with WeldROVER or HSMT X-03 (in areas inaccessible to WeldROVER Scanner). Main objective of this procedure is to 

Monitor the performance of the equipment used



Set the display and acquisition parameter



Provide details for calibration and sensitivity requirement



Describe the recording criteria



Give the details of the equipment used and extent of volume coverage.

Since the qualification of this procedure is unique to the Omniscan equipment, this procedure is not valid with any other instrument. TOFD Sensitivity to near surface indications may be enhanced by using; higher frequency probes, smaller PCS (Probe Center Separation), Lateral wave straightening or subtraction algorithms.

3.0 REFERENCE The following documents shall be referred in conjunction with this procedure: 

ANSI/ASNT CP-189-2011: ASNT Standard for Qualification and Certification of Nondestructive Testing Personnel.



ASME Section V Article 4 (2013): Ultrasonic Examination Methods for Welds.



ASME Sec VIII, Division 2 (2013), Rules for Construction of Pressure Vessels.



ASME Section V Article 5 (2013): Ultrasonic Examination Method for Materials.



Sievert Arabia Limited Written Practice SAL/WP/QOP/001/2010



Omniscan Manual



SAEP 1142: Qualification of Non-Saudi Aramco NDT Personnel




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4.0 SAFETY All personnel are responsible for ensuring that they, as well as their fellow employees perform their job in a safe and professional manner, while adhering to the safety guidelines laid out in safety manual SAL-HS-CP-GSE. In addition they will also adhere to any statutory and local safety requirements along with any Client / Project specific safety requirements.

5.0 PERSONNEL QUALIFICATION Personnel performing non-destructive testing to this specification shall be qualified and certified in accordance with employer’s written procedure at Level-II TOFD & PAUT minimum, in addition he shall be trained on Omni scan MX equipment and shall have minimum one year experience in TOFD/PA activities. The personnel shall hold Aramco approval to do this inspection. The personnel who acquire and interpret the PAUT Data shall be participated the demonstration on Qualification block. Data acquisition and analysis shall be performed by a Level II or Level III; however only UT Level III personnel and qualified in TOFD shall perform final examination data package review.

6.0 PREPARATION OF EXAMINATION AREA Surface Preparation: On finished contact surface a minimum area of 150 mm on either side of the weld shall be free from dirt, weld spatters, corrosion product, surface irregularities or foreign matter that might interfere with free movement of the search unit and affects the transmission of ultrasonic vibrations. When the base material or weld surface interferes with the examination, the base material or weld shall be prepared as needed to permit the examination. Surface preparation shall be under the client’s scope. In order to exactly locate the centre line of the weld a scribe line shall be marked at least on one side of the weld.


Document No.

05th December 2015

SAL-TECH-SOP-TOFD & PA-0102015

Page 9 of 49

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Generally it is assumed that parent material has been tested using normal beam for planar flaw e.g. lamination, during various stages of fabrication. If the same not documented then prior to start of the TOFD & PA inspection, the base metal and HAZ area shall be scanned using normal beam probe to locate reflectors that can limit the capability of the TOFD & PA inspection to examine the weld volume.

Weld Identification: Weld joints shall be identified with Weld Seam No. This unique weld numbering system will be recorded as part of the file storage data. On the prepared area for inspection there will be a “zero” reference index and/or position numbers marked on the weld with paint marker arrow indicating the direction of scanning. All circumferential measurement shall be made clockwise from the zero reference position on the weld when looking in the direction of product flow. For vertical long seams scanning shall start from bottom side of the shell towards topside.

7.0 INSPECTION EQUIPMENT AND ACCESSORIES 7.10 ACQUISITION UNIT & SOFTWARE Omniscan MX 16/128 Phased array and TOFD inspection unit (Figure 2 (a)) which can be operated in pulse echo and/or pitch catch mode, shall be used in association to this procedure. Omniscan contains 16 independent pulser/receiver channels. The System is capable of generating the B-Scan, C-Scan, S-Scan display

Figure 2 (a) Omniscan

along with A-scan. Omniscan is equipped with a calibrated stepped gain controls in units of 2 dB or less.

The data storing capabilities of the system requires the use of an external storage device, flash card or USB memory stick. In addition to data storage, the PC will also be used by the dataanalysis personnel for analyzing data subsequent to the completion of data collection. Datadisplay and analysis software (Tomoview 2.7R6 or higher version) compatible to that residing




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on the Omni Scan phased array system shall also be used for data play back. Tomoview 2.7R6 – It is a powerful and versatile package that will be utilized for offline analysis of previous acquired data files.

Figure 2 (b) Data display in Tomoview

7.20SCANNER DETAIL

WeldROVER Weld ROVER (Fig. 2 (c)) is a small and easy to operate one axis encoded, motorized scanner. It can be used on plates and pipe like structures with up to 6 probes (depends on OD/ID of the pipe). Figure 2 (c)WeldRover

HSMT-X03(Fig 2(d)) Scanner is a one axis encoded, semiautomated scanner. This scanner can hold up to 10 probes for either

phased

array or

conventional

UT.

The

basic

configuration is intended for construction welding inspection. In order to be used in more restricted areas, the scanner can also be reconfigured with the provided short frame bars. Figure 2 (d)HSMT-X03





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The Omniscan ultrasonic system will be suitably interfaced with an automatic/semi-automated scanner drive mechanism that moves the probes in one encoded axis. Four industrial strength magnetic wheels make it suitable to move on ferromagnetic materials (used in power plant and petrochemical industries). Mechanical holders are used to ensure that the probe spacing is maintained at a fixed distance. The mechanical holder for the probes shall be equipped with a positional encoder that is synchronized with the sampling A-scan of signals. For WeldROVERMotion controller allows 10 different scan speeds from 5mm/sec to 50mm/sec with a resolution of 2100 steps/mm. For HSMT X-03 resolution of encoder is 12 steps/mm. 7.30 SEARCH UNIT & WEDGES Ultrasonic transducers configurations are specified by the technique used to cover the full volume of the weld. Single element probes used for TOFD shall have crystal diameter between 3mm to 10mm. The probe frequency and diameter of the search unit will be determined

Figure 2 (f) TOFD Probes & Wedges

by the pertinent parameters for the approved technique. Square or rectangular transducers of equivalent size and frequency may also be used.Probes shall be mounted on a wedge of suitable material and refracting angle as to be compatible to provide required beam steering. Nominal refracting wedgeangle should be 45o, 60o and 70o. Wedges shall have a provision for irrigation hole to provide uniform couplant for scanning. Table provides recommended search unit parameter for TOFD inspection in the specified thickness range……. Thickness t (mm)

Hole Dia (mm)

20 to < 25

2.5

Number Depthof range TOFD (mm) set-ups

1 25 to < 28

3

0-t

Frequency (MHz)

5-10

Wedgeangle

50-70

Element – size (mm)

3-6

Beam intersection

2/3t

As per the Scan plan, TOFD probe and Wedge Details Transducer Type: C543-SM, C563-SM Wedge Type: ST160L-IHC, ST1-70LIHC





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This procedure uses the following probes and wedges for Phased Array PA Probe

Frequency

Number of Elements

Active Aperture

Elevation

Element Size

Supportive Wedge

5L64 A2

5 MHz

64

38.4 mm

10 mm

0.60 mm

SA2 N55S IHC

5L32 A5

5 MHz

32

19.2 mm

10 mm

0.60mm

SA5 N55S IHC

8.0COMPUTRIZED IMAGING TECHNIQUE The major attribute of Computerized Imaging Techniques (CITs) is their effectiveness when used to characterize and evaluate indications: however, CITs may also be used to perform the basic scanning functions required for flaw detection. Computer-processed data analysis and display techniques are used in conjunction with automatic or semi-automatic scanning mechanisms to produce two – dimensional images of flaws, which provide an enhanced capability of examining critical components and structures. Computer processes may be used to quantitatively evaluate the type, size, shape, location and orientation of flaws detected by ultrasonic examination or other NDE methods. Phased array ultrasonic examination is one of the computerized imaging techniques.

9.0 COUPLANT Acoustic coupling shall be obtained by using a medium (oil, grease, cellulose, water) suitable for the purpose. Temperature of the part to be scanned shall be taken into considerations while selecting the couplant. An environmentally safe wetting agent, such as water (up to 50oC) will be required to promote acoustic coupling, however, no residue will remain on the work-piece surface after the water has been evaporated. During examination same couplant shall be used as during calibration.

10.0 CALIBRATION BLOCK The inspection system shall be calibrated using standard calibration blocks and reference blocks. The calibration block material shall be, a nozzle dropout from the component or a component



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prolongation or material of the same specification product form. The calibration block shall receive the same heat treatment as the part to be tested. The surface of the calibration, at no time shall be inferior to that of the component. When the component material to be examined is clad, the block shall be clad by the same welding process as the production part. Two Cal blocks shall be used to scan different thickness varies from 20mm to 28mm. alternatively, a thicker block may be utilized provided reflector size is based on the thickness to be examined and an adequate number of SDH’s exist to comply with basic calibration block.



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The basic calibration block configuration and reflector shall be as shown in figure 3 & 4

Fig 3: 24 mm thick calibration block



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Fig 4 : 28 mm calibration block

Note : 1) All dimensions are in mm. 2) Runner plates shall be attached after drilling and notch preparation. 3) Notch width shall be 3mm Tolerance on hole dia. Shall be +/- 0.8mm and tolerance on location through the block thickness shall be +/- 3mm




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11.0 QUALIFICATION BLOCKS Qualification block shall be prepared from the same product form and material specification or equivalent P-numbers. In case of dissimilar metal welds the material selection shall be based on the side of the weld from which the examination will be conducted. If examination will be conducted from both sides, calibration reflectors shall be provided in both the materials. Prior to the fabrication the block material shall be completely examined with straight beam search unit. When the component material is clad, the block shall be clad by the same welding procedure as the production part. Qualification block shall be prepared by welding or HIP provided the acoustic properties are similar and shall receive the same heat treatment as the part to be tested. Block’s weld geometry shall be representative of production joint. The qualification block shall be within ±25% of the thickness to be examined. For welds joining two different thickness of material, demo block thickness shall be based on thinner of the two materials. The qualification block shall contain a minimum of three flaws parallel to the production weld axis as follows— 1.

One surface flaw on the OD surface

2.

One surface flaw on the ID surface

3.

One subsurface flaw

In case the block can be flipped during UT examination then one flaw may represent both ID and OD surfaces. When due to obstruction the weld examination can only be performed from one side of the weld axis, the qualification block shall contain two sets of flaws, one set on each side of the weld axis. Flaw size shall be based on the qualification block thickness and shall be no longer than that specified by Referencing code Section. For this work flaw size is based on Maximum acceptable flaw height for material thickness as per ASME SECTION VIII DIVISION 2



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Qualification block shall be scanned and the qualification data saved as per the procedure and shall be available to the inspector. Flaws shall be sized and categorized in accordance with the written procedure being qualified. Automated and semi-automated acceptance performance criteria is defined as the detection of all the flaws in the demonstration block and a) Recorded responses or imaged lengths, as applicable, exceed the specified evaluation criteria of the procedure b) The flaws are sized as being equal to or greater than their actual size (i.e., both length and height) c) The flaws are properly categorized (i.e., surface or subsurface) Supplemental manual technique(s) (For Transverse Reflectors) acceptable performance criteria is defined as the demonstration block’s flaws being a) Sized as being equal to or greater than their actual size (i.e., both length and height) b) Properly categorized (i.e., surface or subsurface) Demonstration Block Record The following information shall be recorded: a) The information specified by the procedure being qualified b) Demonstration block thickness, joint geometry including any cladding or weld overlays, and flaw data [i.e., position in block, size (length and height)], separation distance to nearest surface, category (surface or subsurface) c) Scanning sensitivity and search unit travel speed d) Qualification scan data e) Flaw sizing data [same information as flaw data in]

The basic qualification block configuration and reflector shall be as shown below. Notch width shall be 3 mm. All dimensions are in mm. Runner plates shall be attached after notch preparation



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Fig 5 : 24 mm Single V Qualification block

Fig 6 : 28 mm Single V Qualification block




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12.0 CALIBRATION 12.10 EQUIPMENT CALIBRATION Due to the digital control nature of TOFD& PA instruments and also due to the fact that multiple pulser and receivers are used, instruments are subject to screen height and amplitude control linearity checks. Linearity checks shall be as per section T-461.1 & 461.2 (Mandatory appendix I & II) of ASME Section V, Article 4. The results of these checks are recorded in the ultrasonic instrument linearity forms and are kept as a part of the inspection record. OR Linearity checks may be performed as per manufacturer’s standard practice. In this case a template of verification sheet or a mention regarding manufacturer calibration shall be provided. Instrument linearity checks are conducted on a twelve month cycle. Prior to the start of shift operator need to carry out an element check and ensure that probe is in working condition and ensure that no more than 10% of elements are inactive and no two adjacent elements are inactive. Ensure the proper couplant between the probe and wedge. Once data is collected make sure that data missing lines do not exceed the allowable limit.

12.1.1 DISPLAY HEIGHT LINEARITY 1) With the phased array instrument connected to a probe (shear or longitudinal) and coupled to any block that will produce two signals as shown in fig.7 adjust the probe such that the amplitude of the two signals are at 80% and 40% of the display screen height.

Display Height Linearity

Fig 7: A-Scan display for display height linearity




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2) Increase the gain using the receiver gain adjustment to obtain 100% of full screen height of the larger response. The height of the lower response is recorded at this gain setting as a percentage of full screen height. 3) The height of the higher response is reduced in 10% steps to 10% of full screen height and the height of the second response is recorded for each step. 4) Return the larger signal to 80% to ensure that the smaller signal has not drifted from its original 40% level due to coupling variation. Repeat the test if variation of the second signal is greater than 41% or less than 39% FSH. 5) For an acceptable tolerance, the response from the two reflectors should bear a 2 to 1 relationship to within ±3% of full screen height throughout the range 10% to 100% (99% if 100% is saturation) of full screen height. 6) The results are recorded on an instrument linearity form.

12.1.2 AMPLITUDE CONTROL LINEARITY 1) A 16/64 phased-array instrument has 16 pulsers and receivers that are used to address up to 64 elements. Each of the pulser-receiver components is checked to determine the linearity of the instrument amplification capabilities. 2) Select a flat (normal incidence) linear array phased-array probe having at least as many elements as the phased-array ultrasonic instrument has pulsers. 3) Using this probe, configure the phased-array ultrasonic instruments to have an electronic raster scan. Each focal law will consist of one element and the scan will start at element number 1 and end at the element number that corresponds to the number of pulsers in the phased-array instruments. 4) Couple the probe to a suitable surface to obtain a pulse-echo response from each focal law. The backwall echo from the 25 mm thickness of the IIW block or the backwall from the 20mm thickness of the custom linearity block provides the suitable target option. 5) Select channel of the pulser-receivers of the phased-array instrument. Using the A-scan display, monitor the response from the selected target. Adjust the gain to bring the singal to 40% screen height. This is illustrated in fig.8




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Fig 8: A-Scan Display of Backwall Echo on channel 1 of a phased-Array Instrument 6) Add gain to the receiver in the increments of 1 dB, then 2 dB, then 4 dB then 6 dB. Remove the gain added after each increment to ensure that the signal has returned to 40% display height. Record the actual height of the signal as a percentage of the display height. 7) Adjust the signal to 100% display height, remove 6-dB gain and record the actual height of the signal as a percentage of the display height. 8) Signal amplitudes should fall within a range of ±3% of the display height required in the allowed height range of Table 9) Repeat the sequence from 5 to 7 for all other pulser-receiver channels. 12.1.3 TIME-BASE LINEARITY (HORIZONTAL LINEARITY) 1) Configure the phased array instrument to display an A-scan presentation. 2) Select any compression wave probe and configure the phased-array instrument to display a range suitable to obtain at least ten multiple back reflections from a block of a known thickness. The 25-mm wall thickness of the IIW block is a convenient option for this test. 3) Set the phased-array instrument analog-to-digital conversion rate to at least 80 MHz. 4) With the probe coupled to the block and the A-scan displaying 10 clearly defined multiple as illustrated in fig.9



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Fig 9: Horizontal Linearity A-Scan 5) The display software is used to assess the interval between adjacent backwall signals. 6) Acoustic velocity of the test block, determined using the methods described in E 494, is entered into the display software and the display configured to read out in distance (thickness). 7) Using

the reference and measurement cursors determine the interval between each

multiple and record the interval of the first 10 multiples 8) Acceptable linearity may be established by an error tolerance based on the analog-todigital conversion rate converted to a distance equivalent. For example, at 100 MHz each sample of the timebase is 10 ns. For steel at 5900 m/s each sample along the timebase (10 ns) in pulse-echo mode represents 30 µm. A tolerance of ±3 timing samples should be achievable by most analog-to –digital systems. Some allowance should be made for velocity determination error (~ 1%). Typically the errors on the multiples should not exceed ±0.5 mm for a steel plate. 12.1.4 PHASED-ARRAY ELEMENT ACTIVITY VERIFICATION 1) The Phased Array probe shall be checked to determine that all elements of the phased array probe are active and of uniform acoustic energy. Because, during operation in a timed

normal

sequence, each of the elements is addressed by a separate

pulser and receiver, a method from element to element and any differences are




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attributable to the probe itself. To ensure channel is selected to address each element. 2) Any Phased Array Probe that has greater than 25% defective element of the usable aperture should be replaced with a new probe.

Fig 10: Continuity Display for Phased-Array Instrument or Cable

12.2 ENCODER CALIBRATION The encoder shall be connected to the Omni Scan equipment and the calibration wizard shall be used to calibrate the encoder. Through the menu wizard set up, all the parameters are fed and the encoder is made to scroll on a pre-determined known length from initial position, press calibrate, get the calibration done. Encoder calibration shall be confirmed by moving a minimum distance of 500mm and the distance displayed being ±1% of the actual distance moved. Encoder calibration shall be carried out prior to the first use and not to exceed one month.

12.3 VELOCITY & WEDGE DELAY CALIBRATION For contact examinations the temperature differential between the calibration block and examination surface shall be within 14o C.



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TOFD After initial UT parameter and PCS setting for the given weld configuration and weld thickness, an inspection pass is performed on the calibration block and a location is chosen in the B-scan image by choosing the data cursor, where the lateral wave and Back wall signal is seen. The velocity and wedge delay calibration is performed by choosing the ultrasound reference cursor (Ur) on the lateral wave and place the TOFD (Tr) value as “0”. Place the ultrasound measurement cursor (Um) on the phase reversal amplitude of the back wall signal and place the TOFD (Tm) value “part thickness”. Accept calibration and the TOFD calibration shows the value of the part thickness in the B-scan display. In case, if the part is divided into multiple zones where back wall or lateral wave or both may not be available, calibration can be performed using SDH’s at known depth. Phased Array Compensation for delay in the wedge is required so as to ensure that indications detected are poisoned correctly. The wedge delay calibration shall be carried out for both linear scan and as well as sectorial scan. The velocity & wedge delay calibration can be carried out in sound path (using 50mm, 100mm radius of V1 block) mode or true depth (using SDH’s) mode with known reflector having fixed sound path or depth respectively. Peak up this signal from the calibration reflector and scan the phased array probe backwards through all the different angles or focal laws. Scan forward over the calibration reflector through all the refracted angles of focal laws. When the signal for all angles and focal laws lies within the threshold, Omniscan system dynamically adjusts delay setting to correctly indicate radius (depth). Figure (11) shows the screen display during wedge delay calibration.

Figure 11: Wedge delay calibration



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12.4SENSITIVITY CALIBRATION TOFD The maximum diffraction efficiency occurs when the included angle is about 120o the probes should be arranged such that beam centre lines intersect at about this angle (approximately at 2/3 of the zone thickness). The time window and PCS shall be set to those values that will be used in subsequent examination. The time window should start at least 1µs prior to the time of arrival of the lateral wave, and should at least be extended up to the first back wall echo with allowance for thickness and mismatch variation. Useful data can be obtained from mode converted signals so it is recommended that the time window recorded also includes the time of arrival of the first mode converted backwall echo signal. Sensitivity calibration shall be performed on the calibration block or on the test object itself. Set the TOFD probes on the surface to be utilized for calibration and set the gain control so that the lateral wave amplitude is from 40% to 90% of the full screen height(FSH) and the noise (grass) level is less than 5% to 10% FSH. This is the reference sensitivity. For multiple zone examinations when the lateral wave is not displayed, or barely discernible, set the gain control based solely on the noise (grass) level. Phased Array Variation between electronics of pulsers and receivers and variation between probe elements results in small gain variation from one focal law to the next. Also the variation in path distance in both wedge and steel will result in some focal laws requiring more gain. So to compensate for this Omniscan shall be calibrated for sensitivity, which can be carried out dynamically. The sensitivity calibration shall provide the required gain adjustments for each refracted angle and sound path used. Select a calibration reflector, which is within the zone of material to be examined. Peak up this signal from the calibration reflector and scan the phased array probe backwards through all the different angles or focal laws. Scan forward over the calibration reflector through all the refracted angles of focal laws. The Omniscan System calculates the required gain needed at each focal law to adjust the amount of gain required to obtain the sensitivity.



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Figure 12 illustrates the example of special screen feature used to ensure the sensitivity (amplitude response) from each focal law. All focal laws provide a uniform amplitude response to the calibration reflector. As the operator moves the probe back and forth over a calibration reference reflector, unit software automatically adjusts gain to the prescribed amplitude 80% with +5% tolerance limit. The horizontal scale is the virtual probe aperture (VPA) which defines the group of elements i.e. focal law that is sequenced in the scan. These focal laws are either linear or sectorial depending on whether E-scan of S-scans is being calibrated.

Figure 12: Sensitivity Calibration (S-Scan)

12.5 TCG CALIBRATION Time corrected gain calibration shall be applied to compensate for attenuation in the material for the sound paths used during calibration and examination. Generally Phased array inspection is being done in full skip so in order to compensate for the attenuation; calibration shall be performed as per the plan shown below (Fig 13). To obtain the TCG calibration, peak the signal from the respective SDH’s and adjust the gain to obtain 80% of amplitude from the reflector. Place the phased array probe perpendicular to the SDH’s axis. Move the phased array probe forward and backward to equal the amplitude for all the focal laws and angles and plot the first point. The same process is repeated to set the response from each reflector




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for each focal law at 80% FSH. Omniscan uses the gain compensation required due to attenuation in the sound travel and adjust the gain for all focal laws/angles. Once all the points are picked the TCG can be accepted. TCG calibration has to be carried out for all scan plans in a multi group option while using phased array probe. The examination system calibration shall be stored in the Omni scan System with electronic memory, on an external chip or data storage device. This calibration may be used at a later date provided that the system calibration is verified prior to the examination. A complete ultrasonic system calibration shall be performed at least once prior to the examination.

Figure 13: PA Calibration Using SDH’s 13.0 CALIBRATION CONFIRMATION A system calibration confirmation shall be used to verify sensitivity at the start and finish of each examination using the appropriate calibration block. The sensitivity control settings are adjusted to match those recorded for reference sensitivity. The search unit is positioned to detect the first and last point on the TCG using the reference reflectors. The examination deemed to be void if any point on the TCG decreased by 20% or 2dB of its amplitude. All inspection since last valid calibration needs to be rescanned. If the sensitivity has increased all recorded indications since last valid calibration or calibration check shall be reexamined and there values shall be changed on data sheet. Any change in search unit, wedge and ultrasonic instrument cause for a new calibration. For confirmation of TOFD calibrations; scan the calibration block at the reference sensitivity level with SDH’s at the centre of the pair of probes. The SDH responses from the required zone shall be a minimum 6dB above the grain noise and shall be apparent in the resulting digitized grayscale display.




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14.0SCAN PLAN A documented examination strategy shall be provided showing search unit placement and movement that provides a standardized and repeatable methodology for the examination. Scan plan shall include beam angles and direction with respect to the weld axis reference point, weld geometry and number of zones. Scan plan provides clear view of scanning, helping to clearly convey weld coverage, HAZ coverage and probe position, in addition to critical dimensions. The beamset parameters dialog displays a visual representation of the transducer elements that are used to form the beamset. Varying the focus of the beam is the capability of TOFD &PAinstrument, but generally focusing is not the norm for weld inspection. Beam spread visualization allows you to more accurately see the beam coverage and near field visualization ensures that any focusing being performed is within the near field. True Depth, Projection and Half Path focus types can be visualized in the workspace and documented as a technique report. These all is achieved with the help of ESbeam software tool. The scan plan for inspection of full volume of given weld geometry and thickness are given in Annexure: 1

Note: Scan plan given below may require modification based on the actual field conditions to achieve optimum inspection results. Such improvements are applicable provided it has been demonstrated successfully on the qualification block.

15.0 EXAMINATION COVERAGE & SCANNING The ultrasonic examination area shall include the volume of the weld plus the lesser of 25mm or thickness on each side of the weld or Alternatively, examination volume may be reduced to include the actual heat affected zone (HAZ) plus 6 mm (1/4 in.) of base material beyond the heat affected zone on each side of the weld provided the following requirements are met: 1) The extent of the weld HAZ is measured and documented during the weld qualification process; and



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2) The ultrasonic transducer positioning and scanning device is controlled using a reference mark (paint or low stress stamp adjacent to the weld)

to ensure that the actual HAZ

plus an additional 6 mm (0.25 in.) of base metal is examined. The required volume of the base material and weld to be examined shall be scanned from outer surface/inner surface using a linear scanning technique with encoder.The level of gain used for scanning shall be appropriate for the configuration being examined and shall be capable of detecting the calibration reflectors at the maximum scanning speed. Each linear scan shall be parallel to the weld axis and at a constant standoff distance with the beam oriented perpendicular to the weld axis from the zero datum point. Scanning mechanisms shall be used to maintain a constant distance and alignment between the index points of the two probes. Scanning mechanisms can either be motor or manually driven with encoder. They shall be guided by means of a suitable guiding mechanism (steel band, belt, automatic track following systems, guiding wheels etc.). Guiding accuracy with respect to the centre of a reference line (e.g. the centre line of a weld) should be kept within a tolerance of ±10 % of the probe index point separation. The scan plan shall demonstrate by plotting or with using a computer simulation the appropriate examination angles for zones at different depth. This scan plan shall be documented to show that the examination volume was examined. This scan plan shall be a part of the final examination report. More than one line scan may be required to ensure complete coverage of the weld and heat affected zone. Transverse defects can be identified with manual UT. Prior to scanning, calibration data shall be recorded and stored. The Restricted access welds like T-Joints shall have to be dressed for its weld cap and examined. During inspection over this dressed weld surface, if data acquisition is not acceptable due to missing data lines, then the weld cap shall be removed for inspection. A maximum sampling of 1mm shall be set for and be used between A-scans collected for thickness up to 50mm. A 2mm resolution can be used for thicknesses more than 50mm. Scanning speed shall not exceed 150 mm/sec. Scanning speed will be limited by mechanical ability to maintain acoustic coupling and by the system’s electronic ability to ensure full




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wave forms are captured without missing data points. Scanning speed shall not exceed that qualified. Missing of data lines shall not exceed 5% of the total acquisition with adjacent data shall not be missed. Omni Scan equipment has the capability of rewriting the data while observed loss of data. The encoder is retrieved back to home position whenever data is missed. Missing data is represented by black lines in the display. Between two consecutive scans there should be an overlap of 50 mm. Repaired weld area shall be rescanned with an overlap of minimum 50mm at the start and end of the scan.

16.0 RECORDING AND EVALUATION A scan data shall be recorded for the area of interest in an unprocessed form with no thresholding at a minimum digitization rate of five times the examination frequency and recording increment of a maximum of 1mm for material less than 50mm thick and 2mm for material having thickness greater than 50mm. Calibration check data shall also be recorded. Only Trained Level II - UT operators with hands on training Omni Scan shall calibrate and carry out UT inspection. Only personnel certified Level II or III in Ultrasonic testing along with knowledge of phased array and Omni Scan equipment shall evaluate the results of ultrasonic examinations for acceptance. For amplitude base technique, the location, amplitude and extent of all reflectors that produces a response greater than 20% of the reference level shall be investigated. For non-distance amplitude based techniques (TOFD), all indication images that have indicated lengths greater than the following shall be evaluated in terms of the acceptance criteria of the referencing code section: a) 0.15 in. (4 mm) for welds in material equal to or less than 1½ in. (38 mm) thick b) 0.20 in. ( 5 mm) for welds in material greater than 1½ in. (38 mm) thick but less than 4 in. (100 mm) For welds joining two different thickness of material, material thickness shall be based on the thinner of the two material.



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Non Relevant Indications Signals which are determined to originate from metallurgical discontinuities (such as cladding to base material interface) and/or geometrical features (such as weld reinforcement or root geometry) may be classified as geometric indication. Such reflectors are not characterized as indications nor compared with allowable indication standard. The presence of geometric reflectors is confirmed either by reviewing the fabrication drawing of the weld preparation or by plotting the reflectors co-ordinates or by supplemental inspection (PT or MT) result. In addition to reporting indications, area of restricted access which cannot be scanned shall be recorded and reported.

Relevant Indications Signals that are determined to result from welding flaws will be assessed according to the acceptance criteria in ASME Sec VIII Div2.For PA, flaw sizing shall be performed using -6 dB Drop technique. Flaw length parallel to the surface can be measured from the distance encoded D- or C-scan images using amplitude drop techniques by placing vertical cursors on the extents of the flaw displayed on the D- or C- scan display. Flaw height normal to the surface can be measured from the B-, E-, or S-scan images using amplitude drop techniques. Using amplitude drop techniques, the horizontal cursors are placed on the displayed flaws upper and lower extents. For TOFD, flaw lengths parallel to the surface can be measured from the TOFD image by fitting hyperbolic cursors to the ends of the flaws. Flaw height perpendicular to the surface can be measured from the TOFD image by fitting cursors on the top and bottom tip signals. A sizing procedure qualified by performance demonstration will be used to assess all indications interpreted to be flaws. TomoView software should be used for further processing (e.g. lateral wave synchronization, lateral wave removal and to apply soft gains) which enhances the interpretation of the discontinuities. Size & Category Dimensions of the flaw shall be determined by rectangle that fully contains the area of the flaw. Length of the flaw is the dimension of the rectangle parallel to pressure retaining surface, and




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the height of the flaw is the dimension of rectangle perpendicular to the pressure retaining surface. Flaws shall be characterized as being surface or subsurface based on their separation from the nearest component surface: 1.

If space is equal to or less than one half of the height of the flaw than flaw shall be categorized as surface flaw.

2. If space is greater than one half of the height of the flaw than flaw shall be categorized as subsurface flaw.

Surface Indications

Sub Surface Indication

S
S>a

Figure 14: Classification of Surface & Sub surface Indications Flaws shall be evaluated for acceptance using the applicable criteria for the respective thickness, with the following additional requirements-Flaws identified as surface flaws during the UT examination may or may not be surface connected. Therefore, unless the UT data analysis confirms that the flaw is not surface connected, it shall be considered surface connected or a



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flaw open to the surface, and is unacceptable unless surface examination is performed. If the flaw is surface connected, the requirements above still apply. However, in no case shall the flaw exceed the acceptance criteria in this Division for the material employed. Acceptance surface examination techniques are as follows: (1)

Magnetic particle examination (MT) in accordance with ASME 2013 SECTION VIII,

DIVISION 2 paragraph 7.5.6 (2)

Liquid penetrant examination (PT) in accordance with ASME 2013 SECTION

VIII,

DIVISION 2 paragraph 7.5.7

Figure 15: Multiple Planar Flaws Oriented in a Plane Normal to the Pressure Retaining Surface



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i.

Discontinuous flaws shall be considered a singular planar flaw if the distance between adjacent flaws is equal to or less than the dimension S as shown in Figure (15).

ii.

Discontinuous flaws that are oriented primarily in parallel planes shall be considered a singular planar flaw if the distance between the adjacent planes is equal to or less than 13 mm. (see Figure 16).

iii.

Discontinuous flaws that are coplanar and nonaligned in the through-wall thickness direction of the component shall be considered a singular planar flaw if the distance between adjacent flaws is equal to or less than S as shown in Figure 17.

iv.

For Subsurface Flaws the flaw length shall not exceed 4t.

Figure 16: Surface and Subsurface Flaws



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Figure 17: Non-Aligned Coplanar Flaws in a Plane Normal to the Pressure Retaining Surface



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Flaw sizing technique for PA Flaw sizing can be performed using a -6 dB Drop, amplitude drop techniques Flaw Length. Flaw lengths parallel to thesurface can be measured from the distance encoded DorC-scan images using amplitude drop techniques by placingthe vertical cursors on the extents of the flaw displayedon the D- or C-scan display.

Sample Scan image Showing Flaw Length Sizing Using Amplitude Drop Technique Flaw Height Flaw height normal to the surfacecan be measured from the B-, E-, or S-scan images using amplitude drop Using amplitude drop techniques, the horizontalcursors are placed on the displayed flaws upper and lowerextents.

Sample Scan image Showing Flaw Height Sizing Using Amplitude Drop Technique


Document No.

05th December 2015



Page 37 of 49

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17.0 ACCEPTANCE CRIETERIA Results of weld inspections to this procedure shall be compared to the requirement of acceptance criteria as defined in ASME Sec VIII Div 2.

Flaw Acceptance Criteria for ½ Inch (13mm) to less than 1 inch (25mm) Thick Weld

a/t

L

Surface Flaw

≤ 0.087

≤ 0.25 In. (6.4mm)

Sub Surface Flaw

≤ 0.143

≤ .025 In (6.4mm)

GENERAL NOTES: (a) The parameter t is the thickness of the weld excluding any allowable reinforcement, and the parameter l is the length of the flaw. For a butt weld joining two members having different thickness at the weld, t is the thinner of these two thicknesses. If a full penetration weld includes a fillet weld, then the thickness of the throat of the fillet weld shall be included in t . (b) A subsurface indication shall be considered as a surface flaw if the separation (S in Figure 13) of the indication from the nearest surface of the component is equal to or less than half the through dimension (2d in Figure 14) of the subsurface indication. (c) The acceptance limits specified here are based upon workmanship considerations and are not necessarily intended for use in evaluating flaws identified after the vessel has gone into service. (d) The length (l) of the flaw shall be drawn parallel to the inside pressure-retaining surface of the component. (e) The depth of the flaw shall be drawn normal to the inside pressure retaining surface and shall be denoted as “a” for a surface flaw or “2a” for a subsurface flaw.



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Flaw Acceptance Criteria for 25mm to 64mm Thick Weld

GENERAL NOTES: (a) The parameter t is the thickness of the weld excluding any allowable reinforcement, and the parameter l is the length of the flaw. For a butt weld joining two members having different thickness at the weld, t is the thinner of these two thicknesses. If a full penetration weld includes a fillet weld, then the thickness of the throat of the fillet weld shall be included in t . (b) A subsurface indication shall be considered as a surface flaw if the separation (S in Figure 10) of the indication from the nearest surface of the component is equal to or less than half the through dimension (2d in Figure 14) of the subsurface indication. (c) The acceptance limits specified here are based upon workmanship considerations and are not necessarily intended for use in evaluating flaws identified after the vessel has gone into service. (d) For intermediate flaw aspect ratio a/l and thickness t (64 mm (2 ½ in.) < t < 100 mm (4 in.)), linear interpolation is permissible. (e) If the acceptance criteria in this table results in a flaw length, l , less than 6.4 mm (0.25 in.), a value of 6.4 mm (0.25 in.) may be used. (f) For materials exceeding 655 MPa (95 ksi) ultimate tensile strength, the use of this table is limited to a thickness of 200 mm (8 in.).

18.0 REPORTING The following data shall be reported in the final report a. Procedure identification and revision.




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b. Instrument Identification including manufacturer’s serial number. c. Transducer type, serial number, angle and frequency. d. Cables used, type and length. e. Probe center spacing (PCS), Data sampling spacing. f. Couplant used g. Special equipment when used (search units, wedges, shoes, automatic scanning equipment, recording equipment etc) h. Computerized programmed identification and revision when used i. Calibrations block identification. j. Instrument reference level gain and, if used damping and reject settings. k. Calibration data including reference reflectors, indication amplitude and distance reading. l. Data correlating simulation blocks and electronic simulator, when used, with initial calibration. m. Identification and location of weld or volume scanned. n. Surface condition. o. Record of indications identified to be rejected. p. Areas of restricted access or inaccessible welds. q. Examination personnel identity and when required by referencing code section, qualification level. r. Date and time examinations were performed.



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REPORT FORMAT (SAMPLE)


Document No.




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Annexure: 1 SCAN PLAN DETAILS Surface of scanning : OD




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Surface of scanning : ID

Note:- scanning from ID surface shall be done when scanning from OD surface is not possible.




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SURFACE OF SCANNING : OD Scan Plan for 301-01 : CS1 & CS5 Thickness:25-20MM SHELL-DISH (A2 & A5)

Scan Plan for 301-01 : CS2 TO CS4 & LS1 TO LS4 & 301-02 TO 05 : CS2 & LS1 TO LS2 Thickness: 25MM SHELL-SHELL



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Scan Plan for 301-01 : CS6 & 301-02 TO 05 : CS4 Thickness:28-28MM SHELL-DISH (A2 & A5)

Scan Plan for 301-01 : CS7 TO CS10 & LS5 TO LS9 & 301-02 TO 05 : CS5, CS6 & LS3 TO LS5 Thickness:28MM SHELL-SHELL



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Scan Plan for 301-01 : CS11 & 301-02 TO 05 : CS7 Thickness:28-24MM SHELL-DISH (A2 & A5)

Scan Plan for 301-02 TO 05 : CS1 & CS3 Thickness:25-22MM SHELL-DISH (A2 & A5)




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SURFACE OF SCANNING : ID Scan Plan for 301-01 : CS1 & CS5 Thickness:25-20MM SHELL-DISH (A2 & A5)

Scan Plan for 301-01 : CS2 TO CS4 & LS1 TO LS4 & 301-02 TO 05 : CS2 & LS1 TO LS2 Thickness:25MM SHELL-SHELL



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Scan Plan for 301-01: CS6 & 301-02 TO 05 : CS4 Thickness:28-28MM SHELL-DISH (A2 & A5)

Scan Plan for 301-01: CS7 TO CS10 & LS5 TO LS9 & 301-02 TO 05: CS5, CS6 & LS3 TO LS5 Thickness:28MM SHELL-SHELL



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Scan Plan for 301-01 : CS11 & 301-02 TO 05 : CS7 Thickness: 28-24MM SHELL-DISH (A2 & A5)

Scan Plan for 301-02 TO 05 : CS1 & CS3 Thickness: 25-22MM SHELL-DISH (A2 & A5)



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Transverse Scanning

The angle beam shall be directed essentially parallelto the weld axis. The search unit shall be manipulatedso that the ultrasonic energy passes through the requiredvolume of weld and adjacent base material. The searchunit shall be rotated 180 deg and the examination repeated. If the weld cap is not machined or ground flat, theexamination shall be performed from the base metal onboth sides of the weld cap in both weld axis directions.

TOFD & PA Procedure for 301

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