Problems with heat treatment of shell and tube heat exchanger tube boxes
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There is an existing shell-and-tube heat exchanger, whose tube sheet is made of carbon steel with partition plates, but the pipe connections are made of stainless steel (as required by the client). What should be the heat treatment procedure in this case?
Overall heat treatment after completion of fabrication.
Let’s do it together; what else can we do? After all, box heat treatment is meant to eliminate welding stresses. You can’t possibly perform heat treatment first and then weld the stainless steel fittings. .
Overall stress-relief heat treatment. It is mainly used to eliminate welding stress.
Post-weld heat treatment mainly tends to cause sensitization in austenitic stainless steels, resulting in a reduced resistance to intergranular corrosion. If no such conditions exist in the surrounding environment, the only option is to opt for overall heat treatment.
Obviously, using stainless steel pipes as connectors is not for corrosion prevention purposes; therefore, overall heat treatment is carried out after welding.
Overall heat treatment, the rate of temperature rise and fall during heat treatment; care should be taken to quickly avoid the sensitization zone of stainless steel
It can be heat-treated as a whole, or the pipe can be welded after heat treatment. If it is a pressure vessel, consult the inspection officer, as only carbon steel tank containers with partition diaphragms are subject to heat treatment; heat treatment is applied only when the diameter of the lateral connections is greater than 1/3 of the cylinder diameter