Fatigue Crack Growth Threshold Determination for Welded Joint Constituents of a Steam Turbine LP Rotor

In the present investigation, fatigue crack growth threshold of the base metal, heat affected zone (HAZ), and weld metal of a steam turbine rotor’s welded joint constituents were determined by performing fatigue crack growth rate (FCGR) tests. Two types of test specimens were considered: (1) single-edge notch bend (SENB) and (2) compact tension (CT). Although a CT specimen is more appropriate for an FCGR test according to ASTM E647, in the present investigation the SENB and CT specimens were found to yield an equivalent fatigue crack growth threshold of the welded joint constituent. But, the SENB specimen provided some advantages over the CT specimen in performing the FCGR tests on the welded joints. It was also found that the fatigue crack growth threshold is a function of loading ratio rather than a single material parameter.