Last month, we talked about how some equipment just can’t be revived. Recently, Ward was asked to help a good customer with a leaking half pipe on a pressure vessel head. The initial attempt was just to perform a local weld excavation and re-weld, however dye penetrant testing after welding showed some cracking issues with the half pipe base metal. We determined that we should try to remove a section of half pipe and graft in a new section. We rolled and split a section of piping, removed the old section, cleaned up the base metal and, just to be on the safe side, we performed another LPT – this time on the head base metal under the original half pipe. Unfortunately, stress corrosion cracking had set in and a whole new issue presented itself. We tried grinding out the cracks and re-welding, however the cracking was simply too deep, so we had to abandon the half pipe repair. Also unfortunate was the fact that compromised base metal didn’t just condemn the half pipe jacket, but the vessel itself, due to head minimum thickness requirements. We attempted to grind the base metal cracks out while monitoring thickness via ultrasonic testing, but the cracking was just too deep.
Although not yet a foregone conclusion, there still may be a path forward for this vessel – the head will be checked via phased array UT and, if the areas outside of the central section that had half pipe is in good condition, we may be able to cut out and replace the center/dished section of the head with new half pipe. Tune in next month for a brief update if there has been progress and wish us (and our customer) luck!
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