Mild Steels at -80¦C

[JMOwen]

I am currently evaluating the design of some large but lightly stressed welded storage frames. We have many years of experience of similar designs fabricated in mild steel (S275/43A) operating in a -20°C environment.

My concern is that that the new generation of frames will be in service at -80°C and must have a 25 year design life.

Brittle fracture is obviously the main concern. There is no stress cycling to speak of of fatigue is unlikely to be an issue. Specifiying 304 stainless steel would solve the problem but adds significant cost. Aluminium is prohibitively expensive because of the welding costs.

 

[TVP]

Ferritic steels are all brittle at -80 C. I would investigate a lower cost stainless steel. There is a Group here at Eng-Tips called "stainless steel for engineers" which you need to "join" in order to post in there. Go to the login page and see how you can join this Group, as there have been some very good discussions on lower cost stainless steel grades.

 

[GRoberts]

3 1/2 Nickel steels can retain toughness down to -150F. They are weldable with a little care. Since you mention structural steel, I don't know if anyone makes it in roled shapes, but it can be had in plate and pipe, since it is usually used for handling and storage of cold liquids.