Practical numerical analysis of a crack near a weld subjected to primary loading and hydrogen embrittlement

Structural failures by fracture in oil and petroleum industries can have severe consequences both in terms of loss of life and of economics. Material fabrication processes, such as welding and rolling, and plant environment, such as corrosive surroundings, lead to brittle fractures of oil and petroleum industry structures. Structures, such as pressure vessels, are constantly exposed to hydrogen in the presence of high pressure and moderate temperature. This leads to hydrogen embrittlement. Also, exposure to high pressure and temperature over time by itself ages the material, and leads to temper embrittlement. Hydrogen and temper embrittlements are the primary causes for brittle fracture. In this paper, the most common type of this complex interaction, namely that of the residual stresses in a welded thick wall pressure vessel subject to primary loading and exposed to an atmosphere that contains hydrogen at elevated temperature, is discussed and analyzed. A real case of a crack in a welded pressure vessel under high hydrogen partial pressure and moderate temperature is selected as a reference structure. A strategy that involves both modeling and use of data from previous experiments is established that can help in assessing the service life of such a structure that contains residual stress from processing, is cracked, and is exposed to a corrosive atmosphere.