Abstract: Keywords: AUT, ASNT, Blind Test.

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1 Insight of Blind Test Qualification Process of AUT Mitesh Panchal, Niyant J Mehta and Pemmaraju Raghavendra NDE Department, Heavy Engineering Division, Larsen and Toubro Limited, Hazira, Surat,India niyant.mehta@larsentoubro.com Abstract: The competency of personnel performing Non Destructive Examination (NDE) is most important in all industries to have reliable NDE results. The Competency of NDE personnel is highly dependent on proper training, examinations and experience to perform NDE tasks using the applicable test method or technique. Mainly two types of certification programmes are available worldwide i.e Employer based and Central certification programme such as SNT-TC-1A of ASNT as well as PCN/ISO 9712 of Bi NDT.However for Advanced Ultrasonic Testing (AUT) techniques need stringent requirements of qualification and certification. Blind Test qualifications are introduced in addition to ASME requirements by many international clients to have more competent personnel with respect to AUT techniques. Blind Test are test of personnel, procedure and equipment as well and very tough to clear due to stringent passing criteria. Since there is no proven/time tested database of reliability of AUT is available, every time we apply it to new product and the same technique requires to be validated on a welded mockup block that is similar to actual weld joint. This mockup can be either weld joint with known induced defects or unknown blind blocks with weld joints. Code allows this validation on known mockup, however certain international clients prefer to verify the competence of NDE personnel vide a blind test block.i.e a weld test block (with similar weld joint configuration that of actual weld joint on the job) is supplied to the vendor with induced defects at various zones of welds without disclosing fingerprinting report of the block. The real challenge for NDE personnel is to detect, size and analyze all the flaws induced. Several times in our experience it was observed that these flaws are induced keeping in view of inherent limitations of AUT (TOFD and /or PAUT). The examinations based on these blind test blocks enhance our technique sheet, procedure & personal to be more sensitive towards near surface /close to surface detection as well as through wall height sizing. To meet the above challenges we have framed our training, qualification, certification program in such a way that we can address stringent requirements of Blind Test qualification. This includes rigorous theory and practical training followed by mock up examination.we have successfully cleared all the Blind Test examination conducted by international clients (such as KBR,Jacobs,Exxon Mobil, Shell Global etc..) gaining customer confidence and full satisfaction. Keywords: AUT, ASNT, Blind Test. 1.0 Introduction: ASME requirements for Advanced Ultrasonic Testing (AUT) are generic and provide guideline to have AUT setup including personnel and procedure qualification. Many international client are introducing blind Test in addition to ASME code requirements. Blind tests is a true test of competency for a NDE dept. involves in preparing a procedure/scan plan and applying the same on the block/specimen provided.hence,it encompasses the procedure preparation capabilities, capability of individual with respect to code requirements and hands on practicals including capability of flaw evaluation. Blind Test blocks are made keeping in view of inherent limitation of AUT techniques such as flaws induced at dead zones, multiple flaws induced in same depth plane etc makes the test very tough to clear. They are supplied by the customer in a sealed container to the Vessel fabricator and opened only in presence of customer representative. We understand the technique limitations and introduces additional checks to overcome the same.we develop rigorous training programme

2 which addresses such limitation of techniques including accurate and reliable flaw sizing methods to match code as well as blind test requirements. 2.0 ASME Code and stringent Blind Test requirements regarding AUT: As per ASME only qualified UT personnel trained in the use of the equipment and who have demonstrated the ability to properly acquire examination data, shall conduct production scans. Personnel who analyze and interpret the collected data shall be a Level II or III who have documented training in the use of the equipment and software used.the training and demonstration requirements shall be addressed in the employer s written practice. Written Practice to be made based on SNT-TC-1A 2006 Edition guidelines however the same is silent on requirements for AUT Personnel qualification and Certification. Well defined and structured training programme is mandatory before the blind test qualification. Personnel performing blind test shall have adequate training, experience and certification in the particular test techniques including A scan UT as a prerequisite. The Mandatory appendix IX, article 4 of ASME Sec V provides the requirements of qualification of AUT Procedures. This includes the requirements of demonstration blocks preparation, Qualification data,evaluation and demonstration records. A Demonstration block shall be prepared by welding or provided the acoustic properties are similar, The hot isostatic process (HIP) may be used. The thickness of the demonstration block shall be within 25% of the thickness to be examined.for weld joining of Two different thickness of material, demonstration block shall be made as per thinner of the two thicknesses. The Demonstration block s weld joint geometry shall be representative of the production joint s detail. The demonstration block shall contain minimum three actual planer flaws or three EDM Notches oriented to simulated flaws parallel to the production weld s axis and major groove faces. The flaws shall be located at or adjecant to the block s groove faces as follows: One surface flaw on the side of the block representing the component O.D. surface One surface flaw on the side of the block representing the component I.D. surface One subsurface flaw When the scan plan to be utilized subdivides a weld into multiple examination zones, a minimum of one flaw per zone is required. In addition to the above ASME requirement blind test block contains challenging flaws such as: Flaws oriented transverse to the weld center line Flaws kept in blind zones of TOFD UT Flaws located at HAZ area near to both ID and OD surface Multiple flaws at various depths and locations. Also joint having geometry such as dissimilar thickness weld joints, Nozzle joints with less lip distance etc. requires specific scan plans. Acceptable performance as per ASME requires that the flaws are sized as being equal to or greater than their actual size (i.e., both length and height).however in blind test stringent tolerances are applied. As per ASME all the flaws in the demonstration block are required to be detected however during blind test we come across False Call Rate (FCR) which is marking acceptable indication as repair and vice versa.

The above requirements shall be addressed properly during blind test to avoid missing of flaws, improper sizing and characterization of flaws, wrong indication marking (FCR) etc.

3 The above requirements shall be addressed properly during blind test to avoid missing of flaws, improper sizing and characterization of flaws, wrong indication marking (FCR) etc. thus disqualifying the Blind Test. 3.0 Learnings and its implementation based on Blind Test: We study,learn and implement many learnings from the blind test and some of them are listed below.we done brainstorming and lots of experiments and its validation before implementing the same. 3.1 Training, qualification and certification of NDE personnel: Based on experience of blind test, we have made specific training programme for our Level II operators which include theory and Practical of particular AUT technique. We have library of qualification block made for thickness range between 22 mm to 450 mm with various joint geometries and material. We also developed a library of flaw images which can be referred while characterization of a flaw. A trainee is subjected to mock up AUT examination on various qualification blocks.level III is comparing the result with fingerprinting report of the block and giving feedback to the trainee regarding selection of scan plan,equipment and apparatus, parameter setting,data acquisition, image evaluation and Report preperation.particularly for flaw evaluation, a trainee is subjected to many reference images having artificial flaws, conditions like improper parameter settings, images showing mode converted signals, images showing multiple flaws etc. Trainee also learn usage of advance software tools such as lateral wave removal, backwall removal, SAFT (synthetic Focusing Aperture Technique), mode converted parabola etc. In this process trainee gains experience and confidence to face the blind test examination. Our Written Practice is made incorporating SNT TC 1A 2006 as well as 2011 Edition although 2006 edition is only applicalble.detailed syllabus for AUT techniques are tailor made and mentioned in our Written Practice.We specified training hours and annual practical verification of our Level I/II personnel performing AUT as per SNT TC 1A 2011 edition. 3.2 Specific scan plan to get length of transverse flaws: Transverse flaws may go undetected in D scan (non-parallel scan) hence we perform TOFD transverse B scan (parallel scan) on a weld to detect such flaws as shown in Fig.1 Fracture mechanics based acceptance criteria require indication length and height. While doing TOFD, any indication oriented transverse to the weld will give height dimension however length dimension cannot be captured. To overcome such limitation we find out lenght of such indication by applying a pulse echo A scan, PAUT or by transverse D-scan of TOFD. API 934 Appendix A can be followed as a guideline to detect the flaws oriented transverse to the weld. A sketch of TOFD transverse D scan is shown in Fig.1. Fig.1: TOFD UT image of transverse indication, Schematic of transverse B scan and transverse D scan.

3.3 Specific probe selection for improved near surface detection and resolution: Flaws kept in blind zones of TOFD UT may be missed if selection of probe is not appropriate.

detection. 70 deg. 5 Mhz with 6 mm dia probe having dead zone of 5-6 mm (refer Fig 2 a) whereas 70 deg 10 Mhz, 3 mm dia probe is having dead zone of only 2-3 mm.

Fig 2a: 70 deg, 5 Mhz 6 mm dia Fig 2b: 70 deg, 10 Mhz 3 mm dia We also incorporated use of creep wave and PAUT techniques to detect surface flaws which are open to surface or 2-3 mm below

4 Advanced simulation software and its use on dissimilar thickness joints: We have improved our procedures and scan plans considering the requirements of blind test.

4 3.3 Specific probe selection for improved near surface detection and resolution: Flaws kept in blind zones of TOFD UT may be missed if selection of probe is not appropriate. After carrying out various trials with combinations of different probes with different diameter and frequencies we finalized 10 Mhz, 3 mm Dia TOFD probe for improved near surface detection. 70 deg. 5 Mhz with 6 mm dia probe having dead zone of 5-6 mm (refer Fig 2 a) whereas 70 deg 10 Mhz, 3 mm dia probe is having dead zone of only 2-3 mm. Due to the same we could find out bottom tip of the surface indications as shown in fig 2b. Fig 2a: 70 deg, 5 Mhz 6 mm dia Fig 2b: 70 deg, 10 Mhz 3 mm dia We also incorporated use of creep wave and PAUT techniques to detect surface flaws which are open to surface or 2-3 mm below the surface in blind zones while performing TOFD UT.(Refer Fig 3a and 3b) Fig 3a: Scan plan including Creepwave and PAUT Fig 3b: Image showing Creepwave and PAUT alingwith TOFD 3.4 Advanced simulation software and its use on dissimilar thickness joints: We have improved our procedures and scan plans considering the requirements of blind test.we use advance AUT simulation softwares i.e Eclipse Scientific beam tool USA,BSP by MJ inspection Malaysia etc.for dissimilar thickness weld joints,based on scan plan software input, we use separate PCS for each probe as well as separate angle as per the taper angle with offset scanning to cover the full weld with adequate sensitivity at each zone (Refer Fig 4a).

3.5 Scan plan with Focus scan and Offset scans: We added focus scans and offset scans in our scan plan to address accurate detection and sizing of the flaws which are located at HAZ area.

(refer fig. 5a & b) 45 deg scan showing No indication 60 deg focused scan showing indication Fig 4a: Scan plan for dissimilar thickness weld joint.

5 3.5 Scan plan with Focus scan and Offset scans: We added focus scans and offset scans in our scan plan to address accurate detection and sizing of the flaws which are located at HAZ area. (Refer Fig 4b) It also helps to separate out multiple indications. We utilize B scan to find out location of indications thus finalizing that they are in same depth plane or in different depth plane.(refer fig. 5a & b) 45 deg scan showing No indication 60 deg focused scan showing indication Fig 4a: Scan plan for dissimilar thickness weld joint. Fig 4b: Focus scan Fig 5a: Schematic showing B scan Fig 5 b: TOFD UT image of B scan 3.6 Control on index (Y axis) offset errors in TOFD/PAUT: Index Offset (Y axis) errors in PAUT may lead to missing of indications and the same is addressed by usage of circular rings with magnet. Similarly for TOFD UT offset during scanning may result in missing indications. The same is addressed by implementing center line marking and tracking the same by laser tracker.(refer Fig 8a,6a and b respectively)

Fig 6a : PAUT scanning using circular Rings Fig 6b: TOFD/PAUT Auto scanner with Laser

7 Control on oversizing of surface flaws in PAUT: There is a tendency of oversizing

To address this issue we implement maximum amplitude technique in stead of 6 db Drop

7) Fig 7: Scan plan of PAUT showing surface indication and its image on PAUT screen 3.

distance is also very important with respect to blind test qualification.

6 Fig 6a : PAUT scanning using circular Rings Fig 6b: TOFD/PAUT Auto scanner with Laser Tracker 3.7 Control on oversizing of surface flaws in PAUT: There is a tendency of oversizing surface flaws in PAUT which are found in full skip scanning. To address this issue we implement maximum amplitude technique in stead of 6 db Drop method for sizing the indications.(refer Fig. 7) Fig 7: Scan plan of PAUT showing surface indication and its image on PAUT screen 3.8 Control on Scan (X axis) error due to encoder: Encoder which records the scanning distance is also very important with respect to blind test qualification. Each indication in the blind test block is located at distinct location from datum point or reference mark. If the scan surface distance (X value) from datum point is wrongly marked, indication may be considered as missed. To avoid such situation, encoder shall be always calibrated before starting AUT blind test examination.(refer Fig 8 a and b) Fig 8a: Schematic showing scan directions Fig.8b: TOFD UT Image showing Shift in X value due to encoder error.

7 We design our qualification blocks keeping in view of the entire above blind test requirements. We keep stringent performance evaluation criteria to match the requirements of blind tests. We allow stringent tolerances in sizing of defects.undersizing of indications are not acceptable. Also identifying and reporting Falls Indication i.e. Falls Call Rate (FCR) are not acceptable. Conclusion: The paper has attempted to bring to the notice that the study and experience gained from blind test can be helpful to enhance the competency of personnel performing AUT and continual improvement in AUT procedures. We could successfully clear Blind test examinations more than 7 times, which was conducted by different international clients. References: [1] American Society of Mechanical Engineers, Boiler and Pressure Vessel Code, Section VIII & Sec V,2010 Edition 2011a addenda. [2] American Society of Mechanical Engineers, Boiler and Pressure Vessel Code, Section VIII, Division 2, Part 7, 2011a addenda. [3] P. Raghavendra, Niyant Mehta, G.D.Acharya, Ajit Anupam, Replacement of Radiography Testing of Nozzle to Shell Butt Joints of Pressure Vessels by Phased Array Ultrasonic Testing Technique, NDE Conference, Chennai, [4] P.Raghavendra,Niyant Mehta,Girish Namboodiri,M.M.Makwana Limitation of AUT s Mandatory Requirements of Codes, NDE Conference,Delhi,2012.

In house process development for making blind test competent NDE personnel

In house process development for making blind test competent NDE personnel G. Selvakumar, Sanath Thampi, Niyant J Mehta, Pratik Patel, Pemmaraju Raghavendra More info about this article: http://www.ndt.net/?id=22331