Suitable CRA for Bolting Material 2

[Golflinks]

Piping for high pressure sour gas injection facility made from type 316L. Due to low blow down conditions the design temperature is -175 deg F. Bolts will be exposed to high humidity marine offshore environment. DSS 2205 not suitable nor will PTFE coated SS (B8M SS) due to variable quality of PTFE coating. Is there any other cost effective suitable alternative to UNS S31254 or Incoloy 925?
Also please clarify if cost of 6%Mo SS and Incoloy 925 would be the same (Vendor statement)

 

[TVP]

I am not very knowledgeable about the costs associated with various corrosion resistant alloys, but multiphase alloys (nickel-cobalt-chromium-molybdenum) may be a possibility. I recommend you read the following article on multiphase fastener alloys from SPS:

http://www.spstech.com/aero/news/090602.html

They also have an excellent booklet on these alloys called Superalloys Developed by SPS Technologies for Aerospace Fasteners which you can obtain by clicking on the following link:

http://www.spstech.com/aero/prod_lit/index.html

I am not entirely sure about the low temperature performance of these alloys, but since they have essentially an FCC crystal structure, there should not be a pronounced change in properties.

 

[TVP]

I just came across a technical article on the AvestaPolarit website on bolt performance in seawater that may be useful:

http://www.avestapolarit.com/upload/documents/technical/acom/acom93_1.pdf