Failure and Fracture Analysis of K-Type Thermocouple at the Inlet of a Boiler Mixed Desuperheater

Abstract

In order to analyze and study the causes of thermowell fracture and make scientific and reasonable selection of thermowell type，the comprehensive failure analysis of thermowell fracture was carried out by scanning electron microscopy combined with energy spectrometer，Xray diffractometer and other surface analysis methods，and the vibration of the casing was simulated and calculated.Results showed that corrosion product film was formed on the fracture surface of thermowell，and fatigue striation was observed.From the calculation results，it could be found that the vibration frequency of the thermowell under the action of steam exceeded its own natural frequency，and far exceeded the safety coefficient.Furthermore，the comprehensive analysis showed that the corrosion fatigue and other main causes under the comprehensive actions of variable working conditions led to the environment sensitive fracture of thermowell.

Keywords

• thermowell|321 stainless steel|corrosion|fatigue|environment sensitive fracture