We've had some corrosion in a 3" Sch. 80 Alloy 800 pipe downstream of a base oil hydrotreater train. Corrosion (cracking) causes pinholes in the high pressure (~1300 psig) line. This line comes off top of the HHPS. Combined Hydrogen/H2S gas stream enters at ~450 F and after quench is ~250-300 F. Problems (leaks) occur downstream of the water injection quill. This has been a recurring problem every year or so. I have obtained API 932-B 'Design, Materials, Fabrication, Operation, and Inspection Guidelines for Corrosion Control in Hydroprocessing Reactor Effluent Air Cooler (REAC) Systems' which seems applicable but am looking for follow-on information & your expert advice.
1.) Are there any other recommended references which would be useful? I'm working in a waste oil re-refinery so my resources are not as vast as for someone at a crude oil refinery.
2.) We currently just use softened municipal water pretreated w/carbon to remove chlorine, calcium, and magnesium. With test strips, I'm seeing < 0.2 ppm chlorine. Hardness < 2 ppm. So that seems okay.
3.) What, if any, deoxygenation should be conducted? Standard calls for 15 ppbw Oxygen in the quench water; I expect I have much more; I don't have a DO meter but I'm not de-oxygenating at all presently. Recommendations? I'm not a microbiologist but I'm guessing the tap water contains 2-6 ppm DO, much higher than the 15 ppbw level called for in this standard. I'm getting a deaerator soon for boiler, should I just take boiler feedwater, cool it & use it for quench or are any other additives problematic? Or is O2 more a concern during lay-up? Currently we don't do soda ash rinse before shutdowns.
4.) Failures in past have been to heat affected zone adjacent to welds, and to welds themselves. Any recommendations on a testing company familiar with this type of corrosion/service to inspect the pipe & make recommendations?
5.) Should post weld heat treating be used? Most references say no, but seems to me it would take the carbide back into solution -- failures have been in heat affected zone near welds or in welds themselves. Line used to be SS. Old SS line (from before when I started) has rust in welds; appears to me whoever made it used a carbon steel brush... I don't think welds themselves failed since switching to Inconel but heat affected area adjacent to them did, presumably due to carbide precipitation?
I'm going to look at quench water flow rate, remove nozzle & inspect spray pattern, and do some other investigation work.
6.) I'm not sure if Inconel 800 is best alloy choice per the standard since standard notes concerns with PTA SCC. Any advice here?
7.) Any advice on injection quill spray angle or pipe size?
8.) Any inspection plan recommendations? We were thinking of doing shear wave UT quarterly & during outages.