Report on

Root cause Analysis& Corrective action for

LEAKAGE IN WELD JOINT

Team Members:

D. Muralidharan – DGM, Production

M.K. Baranidharan – DGM, Quality control

Raja Chacko –Manager, Quality Assurance

S.Pradeep – Welding Engineer

L. Rajagopal – Manager, Quality Control

Date: 24-Jan-2014

Ref:Communication from Rajpura Boiler on 23/01/2014

CONTENTS

1.0 Problem description

2.0Background

3.0 Preliminary Analysis

4.0 Correction

5.0 Root cause Analysis

6.0 Verification

7.0 Corrective action

1.0 Problem description:

Weld leak noticed inbetween “Tee” and pipe joint(refer image) in 18” CL 3000 C12A PRV Actuator with GUGate valve @ 250 to 300 bar (around 6 months after installation) during commissioning .

2.0 Background:

4 valves of 18” CL 3000 C12A Gate supplied to Rajpura boiler

2nos each to Unit 1 & unit 2. Complaint received in valve supplied to Unit 1.

Project / Rajpura Boiler
Valve Type / Gate
Valve size / 18”
Class / 3000SP
Material / C12A
Quantity / 1 No
Main valve serial no / C903077
Tag number / 01LBA01AA010
Customer P.O / LMB/RJP/PCV-CL4500/LOI-132(U1) 129
L&T Valves Sale Order / 6001993/10200
Bypass valve / DN80 CL 3100 SPL F91 Globe valve (by pass)
Pipe detail / 1” F91 SCH XXS Pipe & 3” F91 SCH XXS Pipe

3.0 Preliminary Analysis

1)Valve serial no : C903077. Body Heat no : H6941. Foundry : PK Steel castings.

2)100% area coverage done in the Body casting & found accepted (RT No: PKV4234)

3)“Tee” Forging received & found meeting the material specification (Supplier Hitech forging TCNO : 343 dt 27/09/2012)

4)NDE-UT done in the Tee forging & found accepted(TCNO : 343 dt 27/09/2012)

5)1” pipe received & found meeting the material specification(Supplier: Sumitomo metal, Japan)

6)Test certificate, Valve test report made

7)Welding done as per approved WPS. Preheating , PWHT done as per approved procedures

8)Pressure test done as per approved GAD & witnessed by LMB QA

9)SCN (Stores Credit Note) done after inspection at per L&Tprocedures & valves were cleared to painting. Before dispatch (PDI) inspection carried out & cleared.

4.0 Correction:

Suggested to carry out weld on leaked joint.Before doing weld repair, gauging to be done to remove the defects & on acceptance of NDE-PT, repair weld to be done. PWHT to be done after repair at site by qualified welder.On completion of repair weld, NDE-PT to be done to ensure that there is no defects.

5.0Root Cause Analysis:

RCA - ROOT CAUSE ANALYSIS SHEET – GLAND LEAKAGE

PROBLEM DESCRIPTION

description area

/

description data

WHAT
Leakage thro weld joint / Welding Leak noticed during pressure testing at site
WHERE / Weld joint / Leakage noticed in-between “Tee”” & 1” pipe weld joint

WHEN

/ During pressure testing / During pressure testing @250 to 300 bar, leakage noticed

HOW BIG

/ Continuous flow / Leakage noticed at site

Similar Parts

/ Balance 3 valves / Site feedback to be received
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 in Tee joint / 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 / Tee joint material grade not meeting specification / Insignificant
12 / Pipe material grade not meeting specification / Insignificant

6.0 Verification:

S No / CAUSES / Verification status
1 / Improper surface cleaning (scale/oily surface) / Base materials are cleaned properly before start of welding process & scales/oil if any are removed.
2 / Preheat & Post heat ment cycle not done as per approved procedure / Heat treatment process carried out as per approved WPS NO : WPS/LT/14.
3 / Ammeter & voltmeter used in welding machine not calibrated / Ammeter & voltmeter used in welding machine are calibrated at periodic intervals as per calibration plan
4 / Visual inspection of weld joints not done / Visual inspection performed after PRV welding by qualified inspectors. Again inspected before clearing to painting in valve & in PDI (Pre Despatch Inspection)
5 / Inspection – NDE method not performed in Tee joint / NDE-UT performed in Tee joint & cleared
6 / Interpass temperature not maintained properly / 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 / Due to lack of bonding between Weld metal & base metal & defect propagated at high pressure (@250 bar) & high temperature(@500°C)
10 / Unapproved welding consumables used / Welding consumables procured from approved sources only
11 / Tee joint material grade not meeting specification / Chemical & mechanical properties verified by supplier & Material Test certificate given. At L&T valves, material confirmation done using PMI & ensured
12 / Pipe material grade not meeting specification / Chemical & mechanical properties verified by supplier & Material Test certificate given. At L&T valves, material confirmation done using PMI & ensured

*SCN- Stores Credit Note- During clearing of valves to painting

7.0 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

Enclosure:

1)Test certificate

2)Valve test report

3)Body- RT report

4)PRV weld- PT report

5)Welding work instruction report for PRV weld

6)Heat treatment work instruction for PRV weld

7)Tee joint – Material test & NDE-UT report

8)1” Pipe – Material test certificate

9)Consumable test certificate

10)Approved WPS No: WPS/LT/14

Prepared byApproved by

S.Pradeep L.Rajagopal

Date: 24.01.2014

== End of report ==

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