某热电厂换热管弯头失效原因分析

Failure analysis of heat exchange pipe elbow in a thermal power plant

某电站项目换热器用小口径蛇型换热管,材质为20G,规格∅25×3mm,弯曲角度180°,弯轴半径27.2 mm,通过数控顶鐓弯管机完成弯制。但在弯制某一批次钢管时,发现起弯点侧有明显褶皱现象产生,在运行过程中严重影响弯头处工质流动特性。废品率近30%,导致弯管工作全面停止。基于对弯制顶鐓力、材料屈强比进行分析和调试,并结合宏观形貌进行分析,最终确定该失效形貌产生原因。由于小口径管弯头处为管组薄弱区域,时常发生失效现象。进而对小口径换热管弯头常存在的失效现象进行梳理,选取弯头泄漏和裂纹存在样管,并分析其原因,以期后续生产制造过程中避免该问题出现。

The small size serpentuator used for heat exchanger of a power plant were made of 20G,with the diameter of 25mm and thickness of 3mm,meanwhile with the bending angle of 180°,bending shaft radius 27.2mm,and the bending was completed by CNC upsetting pipe bender.However,when some batch of steel pipes were under bending,it was found that there were obvious wrinkles at the turn initiation point,which seriously affected the flow characteristics during operation.The scrap rate was nearly 30%,led to the emergency shutdown of the bending work.Based on the analysis and test of the bending upsetting force,combining the material yield ratio,and the analysis of the macro morphology,the cause of the failure was finally confirmed.As the elbow of the pipe is the weak area of the pipe group,failure often occurs.The failure phenomenon of small caliber heat exchange pipe elbow were selected,the sample pipe with elbow leakage and cracks were selected,and the causes were analyzed,so as to avoid this trouble in the subsequent production and manufacturing process.