余热锅炉分汽缸应力腐蚀开裂分析

Stress Corrosion Crack Analysis of Gas-distributing Cylinder of Waste Heat Boiler

某水泥余热发电锅炉分汽缸补焊缝及附近母材出现大量裂纹,部分裂纹出现穿透;宏观观察发现分汽缸表面覆盖有大量黑色粉尘状物质,裂纹沿焊缝呈环向或纵向分布;金相分析及扫描电镜形貌观察结果可见焊缝断口主要为沿晶开裂,同时在断口附近发现大量的沿晶二次裂纹;EDS能谱分析与X射线衍射物相分析结果表明分汽缸窑头侧内壁存在大量碳酸盐和碱浓缩;通过对补焊的未开裂焊缝和附近筒体母材分别进行残余应力测试,结果表明焊缝位置最大应力达251MPa,超出材料屈服强度。综合分析表明:分汽缸内壁存在碳酸盐积聚和碱浓缩,在焊接残余应力和工作应力等因素的共同作用下,分汽缸焊缝及附近区域出现了应力腐蚀开裂。

A large number of cracks appeared in the repair welding and the nearby base metal of cement waste heat boiler gas-distributing cylinder, some cracks penetrated. Macroscopic observation shows that the inner surface of the cylinder is covered with a black dust-like material, and the cracks are distributed in a circular or longitudinal direction along the weld. Metallographic analysis and scanning electron microscopy observation showed that the weld fracture was mainly cracked along the crystal, and massive secondary intergranular cracks were found near the fracture. EDS and XRD results indicate that there are a lot of carbonate and alkali concentrated in the inner wall of the head of cylinder. Residual stress tests were carried out on the uncracked weld and the adjacent base metal respectively, the results showed that the maximum stress at the weld position reached 251 MPa, exceeding the yield strength of the material. The comprehensive analysis shows that there are carbonate accumulation and alkali concentration in the inner surface of the cylinder, and stress corrosion cracking occurs under the joint action of welding residual stress and working stress.