末级再热器出口集箱管座发生裂纹，是长期困扰燃煤电厂的重大设备隐患。通过分析末级再热器出口集箱管座上部角焊缝热影响区产生裂纹的原因及焊接装配形式的分析，认为不合理的焊接接头型式、较大的拘束应力和长期高温运行后导致金属热强性降低，是集箱管座产生裂纹的主要原因。为此，按照DL/T 869—2012标准要求，将承插式焊接接头改为全焊透焊接接头，用加强型管座提高焊接接头强度，控制焊接工艺参数等措施，提高了焊接接头的强度和高温力学性能，消除了超标焊接隐患。12号锅炉从2011年12月大修后运行至今，末级再热器出口集箱焊口经过多次磁粉探伤，均未发现裂纹等超标缺陷，证实了改进集箱管座焊接接头型式是正确的。

Fillet welds on outlet header joint of final reheater, is a major equipment hidden danger which has troubled coal-fired power plants for a long time. Through analysis of fillet welds on outlet header joint of final reheater and welding assembly type, found main reasons are unreasonable welded joint type, excessive restraint stress and decreasing of metal heat resisting strength while boiler operated under high temperature for a long time. Therefore, in accordance with the DL/T 869—2012 standard requirements, change socket-welded joints to full penetration welding joint, use reinforced header to increase the strength of welded joint, and control of welding process parameters can improve the strength of welded joint and high temperature mechanical properties, that eliminates the hidden trouble of excessive welding. After No. 12 boiler overhauled in December 2011 and operated to now, we have not found excessive defects such as fillet welds on header joint of final reheater after many magnetic particle testing, it’s confirmed that improved the welded joint type is correct.