Burst Reasons of Water Wall Tube in Power Plant

A water wall tube of a boiler in a power plant burst. The burst reasons of the water wall tube were analyzed by observing the macroscopic morphology and microstructure of the failed tube, testing the chemical composition and mechanical properties of the tube material, and analyzing the composition of the corrosion products. The results showed that there were obvious corrosion grooves in the burst location, and Na element concentration occurred in local location. The corrosion products were mainly composed of iron oxides (Fe₃O₄and Fe₂O₃) and scale, and a certain amount of NaFeO₂. There was no obvious plastic deformation in the fracture showing brittle failure characteristic on macro morphology and intergranular cracking characteristic on micro morphology. The microstructure of the burst tube was ferrite and pearlite, and there were a large number of intergranular cracks in the microstructure. During the operation of the boiler, the pH of the boiler water was high (10.0-10.2) for a period of time. Based on the above analysis, it was determined that stress corrosion cracking caused by alkali corrosion was the failure reason of the water wall tube.