Analysis of Cracking Reasons for the Welded Joints of Horizontal Pipes in the Low-Temperature Superheater of Ultra-Supercritical Units
Taking the inlet leaky horizontal pipe of the low-temperature superheater in a 1 000 MW ultra-supercritical unit as the research subject,chemical composition analysis,low-magnification metallographic examination of cracks,microscopic metallographic examination,scanning electron microscopy observation,and mechanical property testing were conducted to analyze the causes of leakage failure in the horizontal pipe of the low-temperature superheater.The results indicate that the cracks initiate from the coarse grain area on the outer wall of the pipe in the welding heat-affected zone,propagate intergranularly in the coarse grain area,and are covered with a large amount of oxides inside.Wedge-shaped holes exist at the junction of three grains.Additionally,numerous holes are present near the crack tips,and some of them are chain-like distributed.Based on these characteristics,the nature of the leaky cracks in the horizontal pipe of the low-temperature superheater is creep cracks.Suggestions for optimizing the welding process are proposed to prevent creep cracking in the low-temperature superheater.
万方数据
维普
