Item:
- Radiant section headers fabricated from Type 347H and operating at 650°C in a UOP charge heater in the USA
Problem:
- Following a fire in the heater, two through wall cracks and severe bulging were found in the headers. Initial impressions were that the condition was not fully compatible with fire damage
Objective:
- To determine the cause of the cracking and bulging
- To assess whether the headers would be fit for service following repair
Approach:
- Removal of header containing cracks and worst bulges, for detailed examination
- Site inspection of all top headers
- Failure analysis to determine the root cause of the cracking
- Fitness for service assessment of repaired headers
Findings:
- Site inspection revealed damage to be confined to areas around supports
- Metallurgical examination of undamaged header indicated significant remaining life.
- Examination of cracks and bulges reveal surface cracking on both the internal and external surfaces
- Metallographic examination revealed the internal cracks to be due to creep, but the external cracks to be due to thermal fatigue
- Failure demonstrated to be as a result of the ingress of large quantities of rainwater through the insulation boxes onto the hot headers around the support system
- Full UT inspection reveals remaining header to be free of internal and external defects
Benefits:
- Identification of the root cause of the problem
- Assurance that the repaired header could be safely returned to service
- Refurbishment of the insulation boxes eliminated the source of the rainwater ingress