加氢精制换热器Ω环与管板焊缝开裂的讨论

Discussion on the Weld Cracking Between the Ω Sealing Ring and the Tubesheet in the Hydrofining Unit U-tube Exchanger

Ω环焊接密封是高温高压苛刻工况U形管式换热器中管箱与壳体法兰接头的一种常用特殊结构,但在使用中Ω环泄漏却时有发生。对一台加氢U形管式换热器Ω环与管板焊缝上部两次开裂,从材料的耐蚀性、工况的腐蚀性以及焊接的可靠性等方面进行了分析讨论,发现由于换热器设计时没有考虑铵盐结晶及注水溶解,引起了使用中诸如管箱隔板焊缝开裂、U形管束换热管铵盐垢下腐蚀泄漏、直至Ω环与管板焊缝开裂。建议在完善工艺与检修过程防腐控制的同时,管束选用321,完善Ω环与管板的焊接条件,并增加管箱底部支撑。

The Ω welding sealing ring, a special flange connection structure between the channel and the shell in the U-tube exchanger, is commonly used in high temperature and high pressure working condition. The Ω welding sealing ring leakage occurs frequently during the exchanger usage. Crack in upper weld between the Ω ring and the tubesheet of a U-tube exchanger of hydrogenation unit has been found twice. The causes of cracking are analyzed in the aspects of corrosion resistance of materials, corrosion of working conditions and reliability of welding structure and so on. The crystallization of ammonium salt and the water injection dissolution, which is not considered in the exchanger design, led to the weld cracking between the pass partition and the shell, the deposit corrosion of the U-tube due to the ammonium salt crystallization, and the weld cracking between the Ω ring and tubesheet. It is recommended to improve anti-corrosion in the operation process and the maintenance process. Meanwhile,the 321 austenitic stainless steel should be used in the exchanger bundle. The welding conditions should be perfected when the Ω ring welded to the tubesheet. The bottom support should be added to the channel.