制氢装置中变系统管道腐蚀开裂原因分析

介绍了某石化公司制氢装置中变系统不锈钢管道多次发生腐蚀开裂的情况,通过分析确定裂纹形成的主要原因是奥氏体不锈钢应力腐蚀开裂。从机理分析,在温度60~150℃时,二氧化碳腐蚀产物厚而疏松、易破损,所以中变系统管道出现裂纹现象较多。通过对腐蚀部位材质检测,其名义材质为0Cr18Ni10Ti合金,但实际不含钛成分;硬度值在HB 230以上,也高于此类材质要求硬度指标HB 187。这些问题说明供货材料合金组织控制不良,在施工过程中焊接工艺又参差不齐,最终导致焊接部位存在过大的残余应力,这些残余应力先破坏了焊接热影响区的晶间钝化膜,再形成点蚀坑并逐步形成裂纹。通过采取消除应力、水质控制、材质升级、操作优化等措施,取得良好效果,确保了装置的长周期运行。

Cause Analysis of Cracks in Shift Gas System of Hydrogen Generation Plant

Penetrated cracking occurred in austenitic stainless steel pipelines of shift gas system in a hydrogen generation plant. The analysis found that the cracks were mainly caused by stress corrosion of austenitic stainless steel. The mechanism analysis showed that, in the temperature range of 60 to 150 ~C , CO2 corrosion products were thick and loose and could be easily damaged. Therefore, many cracks will appear on the shift gas system. The testing of corrosion parts found that the nominal material 0Cr18Ni10Ti actually had no titanium alloy, and the hardness was above 230HB which was also higher than the required material hardness of 187HB. All these reflected poor control of metallurgical structure of alloy of supplied materials and poor welding in the construction, which eventually resulted in the excessive residual stress. The excessive residual stress destroyed the intergranular passivation film in the welding heat affected area, and then formed CO2 corrosion pits and cracks. The taking of effective measures such as eliminating stress, water quality control, material quality upgrading and optimization of operation conditions, etc has achieved good results, and long - term operation of the unit has been ensured.