Back in November and December, in our “Some Equipment Cannot Be Saved” thread, we discussed ongoing work on a stainless steel pressure vessel that suffered from significant Stress Corrosion Cracking (SCC). Ward had mobilized to do some planned work on the reactor and discovered advanced SCC in the bottom head that could not be simply excavated and weld repaired.
Phased array ultrasonic testing showed that the knuckle section of the head (which was not under the original half pipe jacket) was not subject to noticeable/significant SCC, so the customer had to decide whether to move forward with a repair or purchase a new reactor.
Primarily due to schedule requirements, the customer decided to move forward with Ward’s repair plan to remove and replace the dished section of the lower head. The new section included a new half pipe jacket which would help the customer with their process as a bonus, based on the blockages found in the original half pipe.
The repair was challenging and involved designing and building a custom rigging cart to get the 1200 pound head into position, between the legs of the original vessel. We carefully laid out and removed the original center section of head and the fit-up of the new dish was literally perfect with a consistent weld joint all around. We welded for several shifts, only to find a small amount of remaining SCC in one area, which required us to call an audible and manufacture a small formed section that allowed us to remove the affected area and continue.
100% RT was required due to the original design requirements of the vessel, so on-site radiography was mobilized to sign off on the final weld.
In the end, the customer was able to put their reactor back into service in a fraction of the time and at significantly less cost than if we had built a new vessel.
It’s not possible to save all equipment. However, having all possible options can go a long way towards getting your process operating profitably sooner rather than later and repair is an important tool in your kit.
