2001 Volume 50 Issue 12 Pages 564-569
Two types of steel, i.e., CrMoV steel and 3.5 NiCrMoV steel, are commonly used for the rotor materials in condensing turbines. Test specimens for SCC test made of these two types of steel were inserted into capsule and the capsule was installed in a branching pipe from the extraction pipe of an actual turbine in the wet zone. The results were as follows:
(1) The intergranular crack was observed and the crack propagation rate was about 3.4×10-4mmh-1 for CrMoV steel and 1.4×10-4mmh-1 for 3.5NiCrMoV steel at 363K of this test temperature, respectively.
(2) A comparison of the crack propagation rate determined using a published prediction formula with the value determined through tests in an actual turbine showed that the actual measured value was high. When determining the stress corrosion cracking inspection interval in the locations of small condensing turbines at which the temperature is comparatively low, the prediction formula shall be set to considerably conservative evaluation side.
(3) The three-point bend test pieces used to examine SCC initiation were exposed for up to 27, 000 hours, however, no SCC initiation was observed in either of the test specimens.
