Evaluation On Embrittlement Phenomena For Welded Pressure Vessel Steel Exposed To Hydrogen

Seri Izzatie , Abd. Azizs (2009) Evaluation On Embrittlement Phenomena For Welded Pressure Vessel Steel Exposed To Hydrogen. Project Report. UTeM, Melaka, Malaysia. (Submitted)

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Abstract

Pressure vessel especially welded pressure vessel steel often failed catastrophically due to hydrogen embrittlement. Some examples of pressure vessels case histories of failure cases are due to hydrogen embrittlement phenomena. In accordance to that reason, evaluation on embrittlement phenomena of welded pressure vessel exposed to hydrogen must be carried out. ASTM A516 Gr 70 carbon steel which is commonly used for pressure vessel is selected for the study. The specimens are submerged arc welded in Xgroove type. Electrolysis is carried out to expose the specimen towards hydrogen at three different exposure times which are 5 hours, 7 hours and 17 hours. As comparison, nonhydrogenated specimens are tested. In weldment, there are three main zones; base metal (BM) zone, heat affected zone (HAZ) and weld metal (WM) zone. However, microstructure and mechanical tests are only done on BM and HAZ as they have greater tendency to cause failures due to hydrogen embrittlement. Optical microscope and Scanning Electron Microscope (SEM) analysis are used to study the microstructure of the specimens. From the experiment, the difference between BM and HAZ overall microstructure, grain size and shape are clearly observed. Dislocations are more severely occur in the HAZ region and the hardness of the specimens is increased by the increasing of cathodic charging time. The complexity of HAZ microstructures in a slim region is expected to cause the dislocation in the specimens’ structure and initiate the cracks. Long hydrogen exposure times could cause the decrement in some important properties of the specimens which lead to hydrogen damages.

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