Development of Welding And Testing Technique/s For Dissimilar Metal Welding Of SA-508 Gr-3,class-1 Material With SS-316L. By Khalid Mahmood Pakistan Welding Institute (PWI) PAKISTAN ATOMIC ENERGY COMMISSION (PAEC) PAKISTAN
Scheme of Presentation Introduction Objectives of development work Scheme of execution Experimental work Results and analysis Conclusions 2
Introduction Introduction Dissimilar metal welding: is a specific requirement where a transition in metallurgical interfaces is attained in such a way that the intended mechanical properties are achieved. Dissimilar metal welding presents a number of engineering challenges such as: complex configurations, control of weld microstructure, difference in chemical, physical, mechanical properties, difficulties in testing & inspection techniques etc. 3
SA-508 Cl. 1 Gr-3 is a constructional steel used mainly in the form of forgings for the manufacture of: Reactor Pressure Vessel (RPV), Steam Generator (SG), Pressurizer (PZ) and Introduction Reactor Coolant Pump (RCP) in nuclear power plants. It is specifically needed to weld the safe ends of SS-316 with SA-508 Gr-3, Cl. 1, material during NPP construction phase which in term of welding is called the dissimilar metal welding and is difficult to achieve. 4
Introduction 5
Objectives of Development Work Objective The primary objectives were: Development of welded coupons (for calibration and with known defects) for training/certifications of UT personnel. Development of welding procedure and performance qualifications for dissimilar welds repair and maintenance, if required and allowed. To assess and enhance the capability level for testing and examination of dissimilar welds at PAEC level. 6
Present status of NPPs in Pakistan Total NPPs = 07 Nos. Operational = 04 Nos. Under-construction = 03Nos. Objective 7
Scheme of Execution for Development Work PHASE 1: Collection of relevant information and selection of variables PHASE 2: Preparation of welded coupons. PHASE 3: DT and NDT scheme for prepared coupons and interpretation, discussion and analysis of the obtained results. 8
PHASE 1: Collection of relevant information and selection of variables Welding Coupons: Material And Dimensions: Two (02) coupons were prepared. Plates of SA508 Cl-1, Gr-3 and SA-240 TP 316L were used. Dimensions (each)= 300mm x 300mm x 50mm Welding: Process: Shielded Metal Arc Welding (SMAW) Filler metal: ASME SFA5.11, ENiCrFe-3 (for coupon only) Testing Of Produced Welds: Available information of SNERDI, China (being designer) was taken as reference for all testing and their acceptance criteria. 9
PHASE 2 : Preparation of Welded Coupons (Process Chart) Chemical analysis of base materials Chemical analysis of SA-508 Cutting of SA-508 and SS-316L plates Chemical analysis of SS-316L Inspection of prepared edges of Plates Buttering of SA-508 Plate Applying buttering up to 5-8mm In process hydrogen relievment PT+UT of Buttered plate Completion of buttering up to 30mm Stress relieving after buttering Machining for edge preparation of buttered SA-508 and 316L Plates for welding PT of edge/bevel of buttered plate Welding of plates to produce coupons PT of edge/bevel of SS-316L plate 10
PHASE 2 : Preparation of Welded Coupons (JOINT DESIGN ) Joint design used for the latest NPPs i-e C-3/C-4. SA-508 SS-316L Joint design for the old NPP i-e C-1. 11
PHASE 2 : Preparation of Welded Coupons SA-508 Cl.1, Gr-3 Plate Dimensions =300mmx150mmx50mm Applying Buttering Process: SMAW Filler metal: ASME SFA5.11, ENiCrFe-3, ɸ3.2/4.0mm Currents: 130-140 amps Pre- heating: (min) 150 C Inter-pass temperature: (max) 250 C PWHT: Hydrogen and Stress relieving 12
PHASE 2 : Preparation of Welded Coupon Inconel Buttering SA-508 plate SA-508 Buttered Plate Prepared edge of buttered SA-508 Plate 13
PHASE 2 : Preparation of Welded Coupon SS-316L Beveled Plate SA-508 plate Fit up of buttered SA-508 and SS-316L Plate SS-316L plate 14
PHASE 2 : Preparation of Welded Coupons With single-u joint design (for NDT+DT) With Double-U joint design (for UT reference block) 15
PHASE 3 : Testing Scheme* for welded Non-Destructive Testing (NDT) Description 100% PT, 100%RT, 100%UT Destructive Testing (DT) Description Chemical Analysis Coupons Tensile Testing (02 specimens at each Temperature) At RT At 350 C Guided Bend Testing (04 specimens) Impact testing (03 specimens each from SA508 and weld regions) At RT At -10 C IGC Testing (specimens from buttering and inconel weld/ss-316l interface region) Metallographic Examination Micro-examination *Available information of SNERDI, China was taken as reference for all testing and their acceptance. 16
PHASE 3 : Non Destructive Testing (NDT) Results Test Area of interest Results Remarks Dye Penetrant Testing (PT) Radiography Testing (RT) Weld+buttering +HAZs Weld+buttering +HAZs Acceptable Acceptable Facility available at PAEC Both tests were performed at NCNDT, PAEC. Dye Penetrate Test Radiography Test 17
PHASE 3 : Non Destructive Testing (NDT) Results Ultrasonic Testing (UT) Manual Pulsed echo technique was adopted for calibration and scanning of produced DMWs by using: 45 and 60 Longitudinal probes with frequency 2MHz. Calibration work has been completed with required sensitivity. Weld was scanned and two acceptable inclusions) were found. discontinuities (slag 18
PHASE 3 : Destructive Testing (DT) Specimens slicing of welded coupon: Slicing to obtain samples for different tests was carried out at PWI with band saw. Diagram shows the location of different samples and their locations are according to SNERDI designer specifications & ASME section IX code QW-463.1 (b). 19
PHASE 3 : Results of Destructive Testing (DT) Chemical Analysis: Chemical analysis of buttering and weld was done by technique called spark emission method at PWI, PAEC. Elements C Si Mn P S Cr Fe Nb Ni Others weld 0.027 0.60 5.60 0.0055 0.011 16.51 7.82 1.84 67.1 Bal. Buttering 0.027 0.61 6.29 0.0047 0.011 15.11 6.93 1.51 69.0 Bal. Acceptance criteria 0.10 1.0 5-9.5 0.03 0.015 13-17 10 1-2.5 Bal. 0.50 All elements were found in acceptable range. 20
PHASE 3 : Results of Destructive Testing Tensile Test: At Room Temperature (RT/20 C). At 350 C. (DT) Two samples for each case were tested. Tensile test samples were machined according to ASME section IX code QW 462.1 (c) for room temperature and QW 462.1 (d) for 350 C. Samples were tested as per ASME section IX code QW-150. Reduced Section Flat Tensile Samples Reduced Section Rounded Tensile Samples 21
PHASE 3 : Results of Destructive Testing (DT) Tensile Test: UTM with tensile flat sample Tested flat reduced section samples Tested rounded reduced section samples 22
PHASE 3 : Results of Destructive Testing Tensile Test Results: Temperature ( C) Room temp. 350 C Sample No Sample Description Dimensions (mm) Area (mm) 2 (DT) Ultimate Tensile Strength (MPa) Yield Strength (MPa) TT-3 19*19 361 585 350 TT-2 21*19 399 595 355 TT-1 ǿ 12.7 126.7 450 260 TT-4 ǿ 12.6 124.7 495 295 Remarks Broken from SS316L Broken from SS316L Broken from SS316L Broken from SS316L Acceptance criteria: Filler type Testing temp. Tensile Strength Yield strength % Elongation ( C) (MPa) (MPa) (A) ENiCrFe-3 RT 550 314 30 ENiCrFe-3 350 425 167 30 The samples were in acceptable range. 23
PHASE 3 : Results of Destructive Testing Guided Bend Test: (DT) Bend test samples were machined according to ASME section IX code QW 462.2. Four samples were tested as per ASME section IX code QW 160. The type of bend was transverse side bend. Side bend test samples 24
PHASE 3 : Results of Destructive Testing Guided Bend Test: (DT) UTM with side bend sample Side bend tested samples Side bend tested samples 25
PHASE 3 : Results of Destructive Testing Guided Bend Test: Acceptance criteria for Bend test is: (DT) Type of Bend Angle of Bend Max. opening no. Max. opening length Side Bend 180 2 3mm Results of bend test are shown below. Sample No SB-1 SB-2 SB-3 SB-4 Type of Bend Side Bend Side Bend Side Bend Side Bend Size Angle of Observation Status (mm) Bend 240*45*10 180 Opening 3mm Accepted 240*45*10 180 Opening 3mm Accepted 240*45*9.5 180 Opening 3mm Accepted 240*45*10 180 Opening 3mm Accepted 26
PHASE 3 : Results of Destructive Testing Impact Test: Impact test samples were machined according to ASTM E23. Six samples were taken from HAZ of SA-508 and weld regions. Three samples form each region were tested at: Room temperature -10 C. (DT) The acceptance criteria was that energy absorbed should be 71J and lateral expansion should be 0.8mm. Impact test samples (for Ref.) 27
PHASE 3 : Results of Destructive Testing (DT) Impact Test: Impact tested samples at room temp. Impact tested samples at -10 C. 28
PHASE 3 : Results of Destructive Testing Impact Test Results: (DT) Temperature ( C) Room temp. Sample No Region Notch Type Energy Absorbed (J) Lateral Exp. (mm) 1 weld V 120 3.91 2 weld V 116 4.16 3 weld V 115 3.53 11 HAZ (SA-508) V 164 4.24 12 HAZ (SA-508) V 126 4.4 13 HAZ (SA-508) V 129 4.3-10 C 4 weld V 131 3.91 5 weld V 120 3.78 6 weld V 130 4.11 14 HAZ (SA-508) V 128 4.54 15 HAZ (SA-508) V 124 4.24 16 HAZ (SA-508) V 127 4.54 All samples were in acceptable range of absorbed energy and lateral expansion at RT and -10 C. 29
PHASE 3 : Results of Destructive Testing (DT) IGC Results: ASTM A262 Practice-E was used for testing. No cracking/opening was observed at required magnification even after bending of sensitized samples. 30
PHASE 3 : Results of Destructive Testing (DT) Metallographic examination: Metallographic examination was performed at NCNDT, PAEC. Regions of interest were weld, buttering, HAZ (SA-508), HAZ (SS-316L) Base metal SA-508 and SS-316L. 31
PHASE 3 : Results of Destructive Testing (DT) Metallographic examination: The acceptance criteria and results for metallographic examination are: Type of Region Type of structure Result Base Metal SA-508 Tempered Bainite No abnormality was Base Metal SS-316L Austenite + few carbide observed against the HAZ (SA-508) Tempered Bainite required microstructure. HAZ (SS-316L) Austenite + few carbide Weld Austenite + few carbide Buttering Austenite + few carbide 32
Problems faced: Non-availability of material/s, particularly SA508, for development on DMWs. Very limited access to technology for development of welding coupons and training of NDT personnel on DMWs (SA508/SS316). Specific UT procedure and probes were not available at local level for scanning of these welds. Positive outcomes: Acceptable results of Destructive testing (DT) proved that weld produced was of required quality from strength, ductility, toughness and corrosion resistance point of view. Same variables can be adopted for welding qualifications in future. After confidence in manual scanning of these welds using pulse echo technique, a dedicated team of NCNDT personnel is still working for skill enhancement by using TOFD and PAUT techniques. Future course of action: Conclusions More welded coupons even with known welding defects will be prepared for training of welding and NDT teams by PWI. 33
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