Failure analysis of Incoloy 800HT pipe at high temperature

In this study, the failure behavior of Incoloy 800HT pipe was investigated. Metallographic analysis and X-ray Diffraction were conducted to find the causes of the failure. It was observed that the microstructure of the failed area was same as that in the undamaged area, which indicated that the failure of the pipe was not caused by the change of microstructure. Then, the finite element method (FEM) was conducted. The results revealed that only axial stress during service was larger than the yield stress at the temperature of 890 °C in the inner wall of the pipe. While for the case of 1032 °C, both the axial and radial stresses were larger than the yield stress. Based on the stress and deformation analysis, the failure mechanism of the pipe was analyzed.

► The welding process, corrosion and creep have insignificant effect on the failure of the pipe.
► The microstructure of the Incoloy 800HT kept constant during the welding and operating process.
► The heat stresses of the pipes at 1032 °C exceeded the yield stress and caused the failure of the pipe.