Failure Analysis of Low-Pressure Evaporator in Heat Recovery Steam Generator with 200 ton/h of Capacity

A steam-gas power plant (SGPP) combines a gas power plant (GPP) and a steam power plant by using the exhaust gas from the GPP to produce steam in the heat steam recovery generator (HRSG). The SGPP, which has a 200 ton/h HRSG capacity, experienced cracks, ruptures, and fatigue at the connection of the low-pressure evaporator pipe. Fatigue is a common failure mechanism in mechanical components due to thermal stress. However, the exact cause of the failure was unknown; therefore, a root cause analysis was conducted. Analysis included the thickness, metallography, chemical composition, tensile testing, thermography, defect testing, and hardness testing. The research showed thermal stresses were the cause of the low-pressure evaporator HRSG pipe failure. In addition, inspection results revealed a decrease in tensile strength, material hardness, and thermal expansion that exceeded the allowed limit.