Failure Analysis of Deep-Drawn Single Piece Pressure Vessels

Abstract

This study presents a comprehensive failure analysis of fully deep-drawn, thin-walled pressure vessels used in fire extinguisher applications, focusing on the effects of deep drawing and welding processes. Hydrostatic burst pressure testing, tensile and microhardness measurements, microstructural evaluations, and coupled thermomechanical finite element analysis (FEA) were performed to identify the root causes of failure and assess the influence of weld-induced residual stresses.

The experimental results revealed that the weld heat-affected zone (HAZ), particularly at the curved head section of the vessel, exhibited reduced microhardness and structural integrity due to recrystallization and grain refinement. Hydrostatic testing confirmed that failure typically initiated in this thinned, weld-affected region, where residual tensile stresses were also found to be concentrated.

Numerical simulations further substantiated the experimental observations. Thermal-mechanical FEA demonstrated the presence of tensile residual stresses in the HAZ and identified stress concentrations aligned with experimentally observed crack zones. A two-stage FEA approach, incorporating both thermal and structural analyses, was used to simulate weld heat input and internal pressure loading. The resulting stress distributions and crack propagation patterns, evaluated using a semi-elliptical crack model, revealed that Mode I crack opening was dominant, especially at the head section.

Comparative analysis of critical stress intensity factors between the shell and head sections showed that the head region had a significantly lower threshold, explaining its susceptibility to catastrophic fracture. The numerical predictions showed strong correlation with experimental hydrostatic burst test results, validating the use of FEA in predicting failure mechanisms in deep-drawn welded vessels.

Overall, the study highlights the critical role of weld-induced residual stresses and geometric thinning in determining failure zones in pressure vessels. The integration of experimental and numerical techniques offers a robust framework for evaluating structural integrity and improving the safety of welded deep-drawn pressure vessels in industrial applications.