An experimental and numerical analysis of hydrogen assisted cracking and weldability test methodology. Ph.D. Thesis
The preferred method for increasing resistance to hydrogen-assisted cracking (HAC) is the application of an adequate preheating temperature, T(sub ph). The suitability of given welding conditions, including T(sub ph), in avoiding HAC is generally assessed through the use of Tekken and Lehigh weldability restraint tests. The safe welding conditions determined from these tests are then applied in industrial fabrication. It is observed that these safe welding conditions do not always avoid HAC in actual weldments. Therefore, it is necessary to evaluate the weldability testing procedure in its entirety against the more general industrial fabrication practice and understand the inherent differences. The differences arising, at different stages of weldability testing procedure, from weld hydrogen measurement technique, weldability testing procedure, hydrogen diffusion behavior, residual stress development, and dimensional differences in weldability tests and actual weldments were analyzed in detail using an experimental and numerical approach. The weld hydrogen measurement results indicated that the existing hydrogen measurement standards do not measure the weld hydrogen levels in actual weldments, and should, therefore, be modified for use in weldability testing procedure. The Tekken and Lehigh weldability test results suggested that weld induced variation at stress concentration locations strongly influences the HAC tendency and crack propagation behavior. Finite element analysis (FEA) of hydrogen diffusion behavior in weldability tests and actual weld grooves indicated that hydrogen diffusion is a strong function of the groove shape and the weld thermal cycle, and hence, direct applicability of weldability test results to actual weldments can be misleading. Elasto-plastic thermo-mechanical behavior of Tekken and Lehigh weldability tests during welding was carried out using FEA.
- Research Organization:
- Oregon Graduate Inst. of Science and Technology, Beaverton, OR (United States)
- OSTI ID:
- 121793
- Country of Publication:
- United States
- Language:
- English
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