Failure of AISI 304H stainless steel elbows in a heat exchanger. (August 2018) - Bahrami, A.
Abstract: This work investigates the effects of grain boundary oxidation on the failure of AISI 304H stainless steel elbows in a heat exchanger in a power plant after 8 years of service at 400 °C. Optical and electron microscopes, elemental mapping, electron dispersive spectroscopy (EDS), inductively-coupled plasma atomic energy spectroscopy (ICP-AES) and hardness tester were used to understand the failure mechanism. Elemental mapping of the samples operating for 8 years showed high concentrations of oxygen and carbon at the grain boundaries. Results showed that cracks were propagated along the grain boundaries due to the brittleness of the oxide layer at the boundaries. Results confirmed the intergranular and brittle nature of the fracture. Microhardness profilometry showed that oxidized/carburized grain boundaries are significantly harder than matrix inside grains. Highlights: Failure analysis of AISIS 304H stainless steel elbows in a heat exchanger tubes is performed. Grain boundary oxidation/carburization is found to be the major cause of failure. Grain boundary oxidation/carburization is associated with embrittlement of grain boundary. The correlations between the microstructure and observed failure are discussed.