A stress field parameter for weld hydrogen cracking: Dissertation

Hydrogen-induced cracking in the heat affected zone of steel weldments is studied with special reference to mechanical aspects.The stress field in the vicinity of the root of the root run butt weld and the notch of the Implant specimen is examined.A new parameter £1, analogical to the stress intensity factor, is defined and proposed as a stress controlling factor for weld hydrogen cracking.The effects of various geometric factors on ~ are analysed by defining a specimen severity parameter Fl and determining its values by finite element analysis.An approximate method is established for determining the value of the Fl parameter for real joints of three groove geometries: (i) single bevel, (ii) double Vee and (iii) Oblique y groove.The Fl parameter is applied to correlate various Implant test and Restraint test results.There two further parameters were employed: (i) remaining diffusible hydrogen content of weld metal at l OO° C, HK 100, and (ii) HAZ hardness (HV 1) .These were used to eliminate the difference between the tests in hydrogen level and microstructure, respectively.The results show the high potentiality of the three parameters: ~1, HRIOO and HV 1.Further, the results do strongly imply that the Implant test results can be applied to real structures in assessing the hydrogen cracking risk.The deep notch Implant specimen was found to have many advantages over the shallow and helical notch specimens in this respect.