Assessment of the crack growth characteristics at the low corrosion fatigue limit of an A106 Gr b steel pipe weld

In the area of heavy construction, welding processes are vital in the production and maintenance of pipelines and power plants. The fusion welding process generates formidable welding residual stresses and metallurgical change, which increase the crack driving force and reduce the resistance of brittle fracture as well as environmental fracture. This is a serious problem with many alloys as well as A106 Gr B steel pipe. This pipe, used in petrochemical and heavy chemical plants, either degrades due to corrosive environments, e.g., chlorides and sulfides, and/or becomes damaged during service due to the various corrosion damage mechanisms. Thus, in this study, the sulfide corrosion fatigue strength of multi-pass welded A106 Gr B steel pipe was evaluated in a 5.0 wt.% NaCl solution that was saturated with H2S gas at room temperature on the basis of NACE TM 0177-90. The crack growth characteristics of the welded pipe were then assessed at the low limit of sulfide corrosion fatigue strength, which was previously obtained from the sulfide corrosion fatigue (SCF) tests. From the results, in terms of the SCF, all the specimens failed at the heat-affected zone, where a high welding residual stress distributes. It was found that the fatigue crack grew at the low corrosion fatigue limit (σ _{SCFun-notched}), which was 32 % (160MPa) of the ultimate tensile strength (502MPa) of the welded specimens.