Analysis of Gas Boiler Failure and Successful Modification of Its Design

This study addresses recurring failures of a gas boiler with a steam capacity of 65,000 kg/h, which is operating in a Polish industrial plant. To determine the cause, material examinations were carried out, including chemical composition and microstructural analysis of SA178A steel, as well as strength tests. The results revealed no significant material degradation outside the cracking zones, suggesting that the failures were primarily caused by thermo-mechanical interactions. A finite element model in Ansys Workbench software was developed, incorporating thermal and mechanical boundary conditions, to reproduce the behavior of the critical section. The analysis demonstrated stress concentrations at the junction between the box and the membrane wall, resulting from large thermal displacement differences. The plastic strains under static loading do not exceed 5%, which implies that, without considering the cyclic nature of boiler operation, the wall should not experience failure. Analysis taking into account only 3 full operating cycles indicates a continuous increase in plastic deformation, which leads to the occurrence of ratcheting. To mitigate these effects, a modification of the sealing box design was proposed. Simulations indicated a reduction in plasticized zones by approximately 65%, and the effectiveness of the solution was confirmed by two years of failure-free operation. The findings highlight the importance of an integrated diagnostic, numerical, and design approach to improving boiler durability.