ABSTRACT Types S31600 and S31254 stainless steel heat exchanger plates have suffered crevice corrosion and stress corrosion cracking under gaskets in rich amine service in a sour gas plant. The gasket material, ethylene-propylene-diene monomer (EPD M), has been used successfully for man y years z other sour gas plants. Laboratory testing has duplicated the corrosion observed and shown that the mechanism is synergistic sulfide-halide attack. The use of a bromine plus chlorine-activated curing system for the EPDM rubber gaskets provided the necessary halides. Laboratory testing identified some nickel-based super alloys which were resistant to this corrosion and also demonstrated that essentially halogen-free, peroxide-cured EPDM gaskets do not cause attackofS31600orS31254. The heat exchanger packs were replaced with S31600 plates and peroxide-cured EPDM gaskets having specified total halogen concentration of 200 ppm maximum. Field operating experience has bee excellent.
INTROD1JCTION
The Caroline sour gas field is situated approximately 120 km northwest of Calgary, Alberta Canada. Production started in March 1993. The field averages about 35 mole% hydrogen sulfide (H2S) and 7 mole% carbon dioxide (CO2). These acid gases are removed at the gas plant in a two-train, two-stage process. Approximately 50% of the sour gas is treated in two independent methyldiethanolamine (MDEA, ?amine A?) systems (trains 1 and 2) to remove most of the acid gases. The resultant sweetened gas is then combined with the rest of the sour gas flow for final treatment in two independent Sulfinol (?amine B?) systems (trains 1 and 2). All systems employ plate and frame rich/lean heat exchangers (HX). Plate material was, Unified Numbering System (UNS) alloy S31600, i.e., American Iron and Steel Institute (AISI) type 316 stainless steel (SS). Some plates were UNS S31603, AISI type 316L SS. The HX plates were sealed together in the pack using ethylenepropylene- diene monomer (EPDM) rubber gaskets