超超临界机组P91管道裂纹显微组织结构分析

Crack microstructure analysis of P91 alloy pipeline on ultra-supercritical generating set

P91合金管在某电厂超超临界机组中发生U型焊接接口开裂现象。对开裂的U型P91合金管焊口开裂进行宏观和微观分析,结果表明,在焊口内部存在较长的裂纹,由内向外表面以沿晶方式开裂,深度达到82 mm,裂纹尖端出现层状撕裂,表现为热裂纹,内部有较厚的氧化皮。焊缝内部大量片状夹渣缺陷聚集以及结构应力过大导致应力集中,裂纹在焊缝炉前侧贯穿到焊缝根部,而在炉后侧沿深度扩展较浅。

Fracture of U type at welding junction of P91 alloy pipeline occurred on ultra-supercritical generating set. In this study, this phenomenon was observed and the results were analyzed. The results indicated that a long crack appeared inside the welding junction, and spreaded from inside to outside by the means of intergranular cracking,and the depth reached to 82 mm. Crack tip appeared lamellar tearing and showed hot crack. There was some oxide coating inside the pipeline, some impurity in the area of welding and structural stress concentration,which was the important factor to leading to fracture of welding junction. In welding junction ,cracks before the furnace side passed through the weld root and after the furnace side extended shallow along the depth.