Metallurgical Failure Investigation of Minor Leakage in a Fuel Oil Return Line of a Combined Cycle Gas Turbine EngineMetallurgische Fehleruntersuchung einer kleinen Leckage an einer Heizölrückleitung einer Kombizyklus-Gasturbine

Abstract

A small fuel oil return line of a stationary gas turbine engine failed by high cycle fatigue cracking. In the metallurgical root cause investigation, performed by the original equipment manufacturer’s laboratory, it was determined that insufficient support of the fuel line and the ensuing vibration led to dynamic alternating bending stresses, that had their maximum immediately adjacent to the connector weld of the flange. The piping system was made of metastable austenitic stainless steels. Constraint in the system at the flange, geometric notches in the weld caused by root reinforcement and excess weld metal at the weld toe, were all determined to have been contributing factors. What is more, the unavoidable metallurgical notch represented by the heat affected zone (HAZ) of the weld joint with its coarsegrained microstructure, may also have con