Analysis of premature cracking causes of ASTM A213-T12 superheater tube

The failure behavior of the superheater tube made of ASTM A213-T12 steel was studied. The microstructure and hardness at different positions of the tube, the element distribution at the crack location, and the morphology and phase composition of the corrosion layer were analyzed by optical microscopy (OM), microhardness tester, scanning electron microscopy (SEM), and X-ray diffractometer (XRD). The results show that the pearlite undergoes spheroidization at the fracture site and the hardness is significantly reduced compared to the normal position. The failure is closely linked to corrosion and creep. On the one hand, sulfur corrosion and oxidation corrosion occur on the outer layer of the superheater tube, which greatly reduces the thickness of the tube. On the other hand, the creep resistance of the tube is significantly reduced by the thinning. There are numerous creep voids in the microstructure at the failure site. Meanwhile, oxygen can diffuse into the voids to promote oxidation corrosion.