Failure analysis of pressure vessel with sight ports using finite element analysis

Liquid level in a pressure vessel can be monitored through the sight ports. Since a sight port is the assembly of various components (e.g., body frame, gasket, sight glass, cover frame, bolt, and nut); each component is critical to the performance of pressure vessel. Under high stress condition, the poor design and/or installation of sight port may cause the failure of pressure vessel. In the present work, a pressure vessel was tested under simulated service pressure via the hydrostatic test. Failures from the plastic deformation of cover frame and the leakage of water were observed during the hydrostatic test. Finite element analysis (FEA) was applied to analyze the root cause of these failures. It was found that the stresses on cover frame were higher than the limitations of materials (i.e., SUS316 stainless steel) due to the improper geometries and locations of openings, reinforced pad, and sight ports. Therefore, the new pressure vessel with obround openings, shorter and thicker sight ports, and larger reinforced pad was designed and evaluated using FEA. After the hydrostatic test, no water leakage and failure were found at any components of the new pressure vessel.