废热锅炉的焊缝热处理及泄漏原因分析与修复

Heat Treatment of Welded Seam and Analysis and Repair of Leakage about Waste Heat Boiler

E-406废热锅炉,是安庆石化炼油厂硫磺回收设备之一,三类压力容器。锅炉主体的壳体材料为20 gδ26 mm钢板,换热管为φ45 mm×5 mm的20钢管加表面扩散型渗铝。经过整体焊后热处理。最后管子和壳体的气密性及水压试验完全合格。开车几天后,炉管产生严重泄漏。打开箱体,发现管口焊缝多处有微裂纹。经打磨焊缝发现:管子和管板间角焊缝的根部有未焊透和少量气孔与金属夹杂物,造成局部缝隙高温高压汽体膨胀隔热与泡沫腐蚀。而未去除干净的少量渗铝层,在氩弧焊接时有形成焊接气孔、金属夹杂物和结晶裂纹的倾向,以及出口尾气中H2S、SO2等气体腐蚀而加速管子和管板间焊缝的开裂。经现场打磨并重新采用电弧焊接修复后,使用至今一年多,一切工况正常完好。

E-406 waste heat boilers is one of sulfur recovery equipment,the third type of pressure vessel,in Anqing Petrochemical Refinery.The heat exchange pipe is 20 steel pipe（φ45 mm× 5 mm）,and the material of boiler body（shell） is 20g δ 26 mm steel plate which is aluminizied with diffusion type in surface,and is heat treated after whole welding.Finally,air tightness testing and hydraulic pressure testing are fully qualified.Running a few days later the furnace tube causes serious leakage.Opening the cabinet,there are many micro-cracks at the nozzle of weld seam.Polished weld seam,there are part of not welding fully and small amount of metal inclusions and air holes at angular weld seam between tube and plate,bring about insulation expansion and foam corrosion of high pressure and high temperature vapor in the local aperture.There are the tendency of forming welding air holes,metal inclusions and crystal cracks in not cleaned small amount of aluminizing layer when TIG welding,as well as the weld seams are corroded by H2S,SO2 etc in tail gas of export,to accelerate cracking of weld seam between tube and sheet.The boiler have been all condition normal intact after repaired by on-site burnishing and arc welding again for more than one year.