Discussion on Manufacturing Difficulties Associated with Cold-rolled Finned Stainless Steel Tube for Heat Exchanger(PartⅢ)—Re-discussion on Deterioration of Performance of Stainless Steel Tube by Cold-working Process and Relative Control Measures

Described in the essay are th e physiochemical properties,the manufacturing process flow and experience in material selection of the propylene,and analyzed are the manufacturing process for the finned tube,and the standardized status thereof.Discussed are the difficulties in cold-rolling process for the finned tube,and proposed accordingly are the countermeasures.Based on relevant analysis,it is identified that the propylene leakage via cracking is mainly caused by the over plastic deformation embrittlement of the finned section of the tube as made in the 304 steel,and directly put in service in the as-cold worked status,and lack of effective NDT inspection.Accordingly possible countermeasures are worth taking,including shortening the height of the fin,reducing the cold-work deformation amount,specifying expressive requirements for the anneal softening status of the mother tube,properly determining the pre-heating(ambient)temperature of the roll,and the strain rate so as to control the distribu- tion morphology of the deformation-induced martensite(and/or the twin crystal),and adopting the heat treatment process for rapid recovery of the austenitic phase transition as well as conducting strict ET or NDT inspection.