REPORT ON ROOT CAUSE ANALYSIS & CORRECTIVE ACTION FOR LEAKAGE IN WELD JOINT

Transcription

1 REPORT ON ROOT CAUSE ANALYSIS & CORRECTIVE ACTION FOR LEAKAGE IN WELD JOINT Team Members: S. Rangaprasad Sr.DGM, Manufacturing M.K. Baranidharan DGM, Quality control M Gunasekaran DGM, Quality Assurance E Kallathieppan AGM, Manufacturing Raja Chacko Manager, Quality Control S. Suriyanarayanan- Manager, Design S.Pradeep Welding Engineer S.M. Balaji Sr. Engineer Quality Control Date: 07-JULY-2015 Ref: Customer Complaint No: LT Dated: 01-JUN-2015 Page 1 of 10

2 CONTENTS CONTENTS 1) Background 2) Preliminary Analysis & Interim Containment Action a) Verifications at L&T Valves Factory b) Verifications during assembly c) Correction at site 3) Root Cause Analysis a) Problem Description b) Sequence of events c) Cause and Effect Diagram d) Significant Causes e) Why- Why analysis 4) Corrective action Page 2 of 10

3 1.0 Background Observations: Weld leak Valve Body and pipe joint(refer image) in 6"2500SPL GATE WC6 T5 BW IBR PRVBT ACT BPM during commissioning. Page 3 of 10

4 Supplied Valve Details: 2 Valves of 6"2500SPL GATE WC6 T5 BW IBR PRVBT ACT BPM supplied to Rajpura boiler 1 No each to Unit 1 & Unit 2. Complaint received in valve supplied to Unit 1 &2. Project Valve Type Rajpura Boiler Gate Valve size 6 Class Material Quantity Main valve serial no Tag number 2500SPL WC6 2 No s C & C HCB01AA001 & 02HCB01AA001 Customer P.O LMB/F04/ /JPS(U-1&2) / 164 L&T Valves Sale Order Bypass valve /9770 & /6670 DN20 CL 2500 SPL F22 T-Globe valve (By pass) Pipe detail 3/4 P22 SCH XXS Pipe 2. Preliminary Analysis & Interim Containment Action: a) Verifications at L&T Valves Factory The following documents were verified and found in order: Page 4 of 10 Valve test reports (Quality dossiers) Pre Dispatch Inspection Report Final inspection report Internal valve test report Valve Assembly Record Receiving Inspection Reports

5 Material test certificate from BOF suppliers Review of Gear Unit Test Certificate We have verified the Quality records of the following manufacturing stages 1) Valve serial no: C / C Body Heat no: B12467 / B Foundry: Ultimate Alloys. 2) ANSI area coverage done in the Body casting & found accepted (RT No: UA / UA12-577) 3) 3/4 pipe received & found meeting the material specification(supplier: Sumitomo metal, Japan) 4) Test certificate, Valve test report made 5) Welding done as per approved WPS. Preheating, PWHT done as per approved procedures 6) DP test carried on the weld surface and found no significant indication noticed. 7) Pressure test done as per approved GAD & witnessed by LMB TPI Valve Serial No C ) SCN (Stores Credit Note) done after inspection at per L&T procedures & valves were cleared to painting. Before dispatch (PDI) inspection carried out & cleared. 2.0 Correction: Proposed to remove the defective weld portion at leak area up to pipe wall thickness and perform welding as per approved WPS. On completion of repair weld, PWHT of weld joint & NDE-PT shall be carried out on the surface of the weld. Page 5 of 10

6 3.0 Root Cause Analysis: a) Problem Description DESCRIPTION AREA DESCRIPTION What object has the defect Gate Valve WHAT What is the defect? Weld Leak WHERE Where specifically on the valve do you see the defect? Where geographically is the object observed? First seen - By the customer? Leakage thro weld joint (Leakage noticed inbetween Body & pipe weld joint) At customer site Rajpura, Punjab. Yes WHEN HOW BIG Similar Parts When seen since? When is the observation seen in the valve- while site, operation (i.e. when the valve is used)? When is the observation seen in the life of the object?(eg. when new or after few years of service) How many objects have noticed this observation? How many/much observation(s) per object While operation After the 6 month service Two valve One Page 6 of 10

7 CAUSE AND EFFECT DIAGRAM - DEFINE & VERIFY ROOT CAUSE METHODS/PROCESSES MACHINE Improper surface cleaning (scale/oily surface) Preheat & Post heat ment cycle not done as per approved procedure Unqualified welder Lack of Awareness on WPS/PQR Ammeter & voltmeter used in welding machine not calibrated Visual inspection of weld joints not done Inspection NDE method not performed Unapproved welding consumables used interpass temperature not maintained properly Leakage thro weld joint between Body & pipe Lack of fusion Pipe material grade not meeting specification MAN MATERIALS Page 7 of 10

8 S No CAUSES SIGNIFICANT / IN- SIGNIFICANT 1 Improper surface cleaning (scale/oily surface) Insignificant 2 Preheat & Post heat meant cycle not done as per approved procedure Insignificant 3 Ammeter & voltmeter used in welding machine not calibrated Insignificant 4 Visual inspection of weld joints not done Insignificant 5 Inspection NDE method not performed Insignificant 6 Interpass temperature not maintained properly Insignificant 7 Unqualified welder Insignificant 8 Lack of Awareness on WPS/PQR InSignificant 9 Lack of fusion Significant 10 Unapproved welding consumables used Insignificant 11 Pipe material grade not meeting specification Insignificant Page 8 of 10

9 S No CAUSES Verification status 1 Improper surface cleaning (scale/oily surface) 2 Preheat & Post heat ment cycle not done as per approved procedure 3 Ammeter & voltmeter used in welding machine not calibrated 4 Visual inspection of weld joints not done 5 Inspection NDE method not performed 6 Interpass temperature not maintained properly Base materials are cleaned properly before start of welding process & scales/oil if any are removed. Heat treatment process carried out as per approved WPS Ammeter & voltmeter used in welding machine are calibrated at periodic intervals as per calibration plan Visual inspection performed after PRV welding by qualified inspectors. Again inspected before clearing to painting in valve & in PDI (Pre Despatch Inspection) NDE-PT performed & cleared Temperature measured using Themal chalk & infrared temperature measurement gauge & welding performed. By this interpass temperature maintained as per approved WPS 7 Unqualified welder Welders are qualified as per the WPS & PQR & approval given for welding. Approved welders are only utilized to perform welding 8 Lack of Awareness on WPS/PQR Training given to all welders & briefed on WPS & PQR requirements. WPS & PQR display made in weld shop for better communication 9 Lack of fusion Found having lack of bonding between Weld metal & base metal 10 Unapproved welding consumables used 11 Pipe material grade not meeting specification Welding consumables procured from approved sources only Chemical & mechanical properties verified by supplier & Material Test certificate given. At L&T valves, material confirmation done using PMI & ensured Page 9 of 10

10 WHY WHY ANALYSIS Significant Cause / : lack of fusion in the weld Nonconformance Why? Lack of bonding due to welding work Why?? Non control on welding parameter Why? Lack of awareness of Welding operator Root Cause: Lack of awareness of Welding operator 4.0 Corrective action: Based on the above, the following corrective actions are suggested: a) Retraining to be given to welders to communicate on the process control measures to be followed to avoid weld defects. b) Shell test to be done for extended duration (60 minutes) during internal testing at L&T valves for critical valves. Prepared by Reviewed & Approved by Raja Chacko M. Gunasekaran Date: Page 10 of 10