重催油浆蒸气发生器管板开裂原因及防治

锦州石化公司催化裂化装置油浆蒸气发生器,为浮头式蒸气发生器,投入使用一年多就发生失效,其失效形式表现为蒸气发生器管板大面积开裂,裂纹大多从管束开始呈环状及径向管板延伸。利用对比法、金相显微分析方法以及开裂机理分析方法,对重催油浆蒸气发生器管板开裂原因进行了管板化学成份、管板机械性能、宏观、微观断口形貌及管板开裂过程分析。实验结果表明,管板的化学成份和机械性能均符合国标GB6654-96,说明管板开裂不是由于材质本身造成的;裂纹符合应力腐蚀特征;壳程内蒸气的发生和流动诱发振动,使管束发生振动,特别在汽液两相流作用下使振动加剧,使管板焊接接头部位产生循环载荷造成疲劳破坏。得出疲劳和应力腐蚀共同作用引起重催油浆蒸气发生器管板的开裂,其中疲劳是管板开裂的最重要的原因。提出了简单易行的改进措施。

Reason and Prevention of Cracking on Tube Sheet of Oil Slurry Stream Generator

The steam generator of Jinzhou refinery is head - floating steam generator whose tube sheet was cracked after it was put into use in more then a year. The wide - area cracks in the tube sheet of oil slurry steam generator were found, and the cracks started from the tube bundles, and went along with the direction of radius. With the correlation method, the metalloseopy method and the crack mechanics analytic method, the reason of the cracking on the CCU tube-plate was analyzed. The chemical components, mechanical properties, the appearance of cracks in macro and micro of the samples were analyzed. Experimental result indicates that both the chemical components and mechanical properties of the tube sheet meet GB6654 - 96, that is to say, material do not result in cracking on the CCU tube - plate. Cracks meet the feature of stress corrcsion. The generating and flowing of the stream induces pipe bundle vibration that becomes especially stronger under the action of gas - fluid two phase flow, which produces cyclic load on the welded joint of tube-plate and brings fatigue broken. The conclusion is that an interaction between fatigue and stress corrosion is the reason of the cracking on the CCU tube - plate. Fatigue is the more important reason of the cracking on the CCU tube - plate. The improvements of preventing cracks are put forward.