This has reference to Mechanical Metallic bellow being proposed to connect, 64 inch exhaust (Design Condition:- Temp. 550 Deg.C and Pressure 0.5 barg) from Gas engine to the exhaust duct.
As per shell DEP Guidelines (DEP 31.38.01.11), Expansion bellow materials shall undergo heat treatment after forming. (As expansion joint forming operation induces strain, heat treatment is essential to relieve the stresses. For high temperature piping systems, creep properties is essential and which can be achieved only by heat treatment)
However , As per EJMA it is not recommended to do heat treatment after forming.
As per Expansion Joint manufacturers association (EJMA) 10th edition, clause no. 4.12.1.9, heat treatment after forming can have a detrimental effect on the bellows pressure capacity. It is not normally considered beneficial for fatigue life to either stress relieve or anneal after forming
However as per Vendor suggestion, heat treatment is not recommended due to small thickness ( i.e. Bellow thickness 1mm with No. of ply 1) of bellow material which leads to distortion or dislocation due to thermal expansion and damages the bellow curvature /convolutions. Pls. note the Bellow Material specifications is ASTM A240 Type 321.
As per vendor the ASTM A240 Type 321 plate /sheet is solution annealed before forming. The forming strain provided by the vendor (5 %) which is less than recommended value of 15% as referred in Table UHA -44 (ASME sec. VIII div.1) and hence it can be concluded that no heat treatment is required after forming as per ASME.
With respect to above identified conflict between DEP guideline, EJMA & Vendor recommendation, can someone please share your experience/ Suggestion/ guidance on heat treatment on the final product ie Mechanical Metallic Expansion bellow.