Annealing of an old ASME coded pressure vessel

Does anyone have experience in heat treating of carbon steel pressure vessels? I've run into a situation where we've found high hardness on an old vessel (266 BHN) going into an H2S application (up to 10,000 ppm). Our standards specify an upper limit of 235 BHN on process piping and vessels. I haven't run into this situation before, so was wondering what the process was to soften an older vessel that has been used in sweet natural gas service in the past. Is it possible to anneal this type of vessel? Also, the high hardness reading was found on one nozzle weld. The others were below 235 BHN. Any insight is appreciated.

How old is the vessel?  Wondering if maybe a stress relieve treatment would suffice instead of full on annealing/normalizing.  Any records on the heat treatment history?  One thing I've found in multi-step heat treatments is that a lot of scale can build up.

Vessel is 12 yrs old. The records I can find on the vessel do not indicate any type of heat treating performed at time of fabrication. I also found that it was previously in H2S gas service prior to now (we rent compressor packages that service different applications). Is there an industry standard or guideline  that you know of that calls out what hardness is considered "too high"?

Thanks for the reply!

Mech_Engineer said:

Vessel is 12 yrs old. The records I can find on the vessel do not indicate any type of heat treating performed at time of fabrication. I also found that it was previously in H2S gas service prior to now (we rent compressor packages that service different applications). Is there an industry standard or guideline  that you know of that calls out what hardness is considered "too high"?

Thanks for the reply!

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NACE will limit hardness to 22 HRC pretty much across the board, which lines up with your company standards of ~235 HBW.  I typically deal with NACE MR0175 & NACE MR0103.