某大型造纸厂制浆用蒸煮锅,系1965年出厂的压力容器,锅体尺寸φ3250mm×30mm×12000mm,材质为20K,工作压力位0.8MPa,工作温度为175℃,介质为10%NaOH溶液加木片,每次的蒸煮时间为3.5h。8年前,在容器定期检验中发现:中循环鼻子下部的内环缝有多处裂纹:长50~600mm,深8~16mm,断续分布在整条焊缝上,如图1所示。图1蒸煮锅经对上述裂纹进行焊接修复,容器安全等级定为四级,监督使用一年。在此后的每年容器复检中,该焊缝均有裂纹出现,最严重的裂纹长达800mm,深约 A large paper mill pulp cooking pot, the Department of 1965 factory pressure vessel, the pot size φ3250mm × 30mm × 12000mm, made of 20K, the working pressure of 0.8MPa, the working temperature is 175 ℃, the medium is 10% NaOH solution plus Wood chips, each cooking time 3.5h. Eight years ago, periodic inspection of the container revealed that there were multiple cracks in the inner ring of the lower part of the circulating nose: 50 to 600 mm long and 8 to 16 mm deep, intermittently distributed over the entire weld, as shown in Figure 1. Figure 1 cooking pot by the cracks on the welding repair, container safety rating of four, one year of supervision. In the subsequent annual container review, the weld cracks have appeared, the most serious crack up to 800mm, deep about