裂解炉稀释蒸汽管道三通开裂原因分析

Analysis of cracking cause of the tee in diluted steam tube of cracking furnace

针对某乙烯裂解装置稀释蒸汽管道304H耐热不锈钢三通使用1年后发生开裂的情况,从材料成分、力学性能、金相组织、残余应力和断口特性等方面进行了分析。结果表明,裂纹分别启裂于三通的内壁和外壁,多数裂纹开裂处伴有晶间腐蚀特征,裂纹扩展特性以沿晶型为主;断口附近腐蚀产物存在O,S,Cl等酸性腐蚀介质。三通主管表面最大轴向应力达到147 MPa,三通相贯线附近距裂纹20 mm处的最大环向应力达到114 MPa,说明运行中的三通表面应力达到了材料屈服强度的1/2。分析认为,裂纹的产生是由于材料发生敏化后,在应力和腐蚀介质共同作用下形成的以沿晶为主的应力腐蚀开裂,更换三通材料或通过适当的固溶处理降低三通中的残余应力是避免三通开裂的重要途径。

In view of the cracking occurred in 304H heat-resistant stainless steel tee for dilute steam tube in an ethylene cracking device after one year of operation,the material composition,mechanical properties,metallographic structure,residual stress and fracture characteristics were tested and analyzed.The results show that the cracks are originated in the inner wall and the outer wall of the tee respectively,most of the cracks are accompanied by intercrystalline corrosion characteristics,and the crack propagation characteristics are mainly intercrystalline.Acid corrosion media such as O,S and Cl exist in the corrosion products near the fracture site.The maximum axial stress on the main surface of the tee reaches 147 MPa,and the highest hoop stress at 20 mm away from the crack reaches 114 MPa,which means the surface stress in the operating tee reached 1/2 times the yield strength of the material.It is considered that the generation of cracks is attributed to the intergranular stress corrosion cracking under the combined action of stress and corrosion medium after the material sensitization.Replacing the tee material or reducing the residual stress in the tee through the appropriate solid solution treatment is an important way to avoid the tee cracking.