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1. Haward Technology Middle East 1Section 10
Machinery Root Cause Failure Analysis
(RCFA), Prevention & Troubleshooting
Appendix 3
Fatigue circumferential weld

2. Haward Technology Middle East 2Section 10
Machinery Root Cause Failure Analysis
(RCFA), Prevention & Troubleshooting

3. Haward Technology Middle East 3Section 10
Machinery Root Cause Failure Analysis
(RCFA), Prevention & Troubleshooting
 Challenge. Chuck Lenzie Generating Station had
experienced repeated weld failures on the attachments
to the hot-reheat drip leg. Historically the plant would
identify a leak and perform NDE and a weld repair. But
because of prior failures, Lenzie personnel conducted a
pre-outage inspection of all drip legs and discovered
yet another leak in the hot-reheat system. Insulation
was removed after unit shut down and a
circumferential crack was discovered in the SA335
Grade P91 base material (Fig 1).

4. Haward Technology Middle East 4Section 10
Machinery Root Cause Failure Analysis
(RCFA), Prevention & Troubleshooting

5. Haward Technology Middle East 5Section 10
Machinery Root Cause Failure Analysis
(RCFA), Prevention & Troubleshooting

6. Haward Technology Middle East 6Section 10
Machinery Root Cause Failure Analysis
(RCFA), Prevention & Troubleshooting
 The crack was located approximately 3 in. below the
hot-reheat bypass valve drain line feeding into the drip
leg (Fig 2). To determine the failure mechanism, NV
Energy sent the affected section of the drip leg out for
metallurgical analysis. The lab’s conclusion: The
failure was caused by thermal fatigue initiated from
the internal surface between the hot-reheat bypass
valve drain line and the drip leg’s end-cap girth weld.

7. Haward Technology Middle East 7Section 10
Machinery Root Cause Failure Analysis
(RCFA), Prevention & Troubleshooting
 A root-cause analysis was performed and experts
attributed the failure to a leaking manual drain valve,
which emptied the hot-reheat drip leg. The drip leg
normally maintains a condensate level at or above the
drip-leg drain line to minimize thermal transients.
Condensate level is controlled by a thermocouple,
which opens the DCS-controlled drain valve when
temperature reaches Tsat + 45 deg F

8. Haward Technology Middle East 8Section 10
Machinery Root Cause Failure Analysis
(RCFA), Prevention & Troubleshooting
 The drain line for the hot-reheat bypass valve drains to
the drip leg which normally contains a minimum
condensate level. Since the drip leg was empty
because of a leaking bottom drain valve, it
experienced thermal transients leading to thermal
fatigue and finally base-metal failure.

9. Haward Technology Middle East 9Section 10
Machinery Root Cause Failure Analysis
(RCFA), Prevention & Troubleshooting
 Project participants:
 David Hall, plant engineering and technical services
manager
 Dan Schiller, lead production technician
 Jimmy Daghlian, staff engineer

10. Haward Technology Middle East 10Section 10
Machinery Root Cause Failure Analysis
(RCFA), Prevention & Troubleshooting

11. Haward Technology Middle East 11Section 10
Machinery Root Cause Failure Analysis
(RCFA), Prevention & Troubleshooting

12. Haward Technology Middle East 12Section 10
Machinery Root Cause Failure Analysis
(RCFA), Prevention & Troubleshooting

13. Haward Technology Middle East 13Section 10
Machinery Root Cause Failure Analysis
(RCFA), Prevention & Troubleshooting

14. Haward Technology Middle East 14Section 10
Machinery Root Cause Failure Analysis
(RCFA), Prevention & Troubleshooting