Stress relief for bended stainless steel heat exchangers

[zibaeng]

Hi.
We use U-type Stainless steel heat exchangers for boilers. These heat exchangers are subject to stress because of bending. My question is how can we relieve stress? I know we can't use PWHT for stainless steels because of knife attack.

 

[metengr]

You locally re-solution heat treat the u-bends.

 

[zibaeng]

Would u explain more please?

 

[metengr]

Please review the material specification for the austenitic stainless steel material. Within the specification is the minimum solution annealing temperature for the material. After u-bending, the bent end of the tube is placed with in an induction heating clamp or small furnace. The bend portion of the tube is then heated to the minimum solution treatment temperature for x minutes and water quenched. You will need to qualify the above and establish a procedure.