Causes of economizer tube explosion in 600 MW unit

A 600 MW unit economizer tube burst accident occurred. The causes of tube burst were analyzed by means of macroscopic observation and wall thickness measurement, magnetic particle detection, chemical composition analysis, mechanical property test, metallographic examination, scanning electron microscope and energy spectrum analysis. The results show that the outer wall of the bent pipe was seriously worn and the wall thickness reduction caused by corrosion was too large, and the roundness of the burst bent pipe exceeded the standard.Under the action of internal pressure film stress,the outer bending and rerounding process of the bent pipe would cause large bending stress and tensile stress, which further increased the stress on the wall of the outer bending part of the bent pipe, so that the remaining wall thickness could not withstand the internal medium pressure, resulting in a burst accident.