Fatigue-induced fracture assessment for duplex stainless steel protruding tube-to-tubesheet welded joints in multiple-tube test specimen

A novel fatigue testing result and its numerical discussions are presented for protruding tube-to-tubesheet welded joints. The welded joint specimen is made up of an innovative stainless steel grade for pressure vessels of urea production plant, i.e., duplex stainless steel (DSS). Multiple-tube test specimen in which a bundle of tubes fabricated to the tubesheet by welding, is employed. During the fatigue test, several initial cracking positions were observed from the central tube and surrounding tubes. The crack propagation (CP) phenomena, i.e., CP from the central tube to surrounding tube and from the surrounding tube to central tube, were characterized for the multiple-tube problem. Two types of fracture pattern were occurred. These distinctive cracking behaviors are studied using numerical analyses, i.e., FEM stress analysis and X-FEM CP simulation. The possible crack initiating positions as well as the fracture patterns are identified based on the stress distributions. The CP behaviors between the tubes are carefully examined using stress intensity factor (SIF). Additionally, fatigue life cycles and fatigue resistance of the specimen are discussed. The fatigue-induced fracture of the DSS specimen is rigorously investigated and presented using the experimental and numerical methods.