I am bolting 321 stainless steel ducts (we are discussing changing to grade 91 alloy but this is only a possibility), and want to use locknuts to minimize potential for debris. The application is at 900-1050F at the bolts, so I am not sure what locknuts are available at this temperature.

I was thinking of A193 grade B8M bolts but am open to suggestions if there is a reason to use another bolt spec that is suitable for this temperature.

A: For a high temperature application like this you might want to consider an A286 Lock Nut in the Flexlock style. This is an all metal lock nut and is very oxidation resistant and has great high temperature stability when compared to B8M. A286 is usable to about 1300F which is well within your temperature needs.

Q: I need a shoulder bolt that will not change its shape at elevated temperatures. The bolt is near a mild carbon steel welding process and is under a small load. It is not in the heat affected zone, but it does see an elevated temperature. I am not sure exactly, but if we assume it sees 80% of the A 36 melting temperature, then we should be conservative. Any suggestions appreciated.

A:  For elevated temperatures I would recommend an A-286 shoulder bolt. A-286 fasteners are known for their high strength, creep resistance and oxidation resistance at elevated temperatures. This material would be a significant improvement over carbon steel. A286 bolts will retain their strength to 1300°F .