某燃气站场弯头泄漏原因分析

在某燃气站场投产前的试压过程中,发现一处弯头外弧侧管体出现纵向裂纹,导致试压泄漏。通过力学性能检验、组织分析、扫描电镜分析及能谱分析,讨论了该弯头失效原因。分析结果表明,弯头中的疏松缺陷是造成弯头开裂的主要原因。其中,弯头中的疏松缺陷起源于原材料在冶炼过程中存在的夹渣,因后续工艺未能及时发现和清除,在弯头成型过程中裂纹缺陷恶化,因此在很小水压强度试验压力下裂纹起源于弯头内表面,主裂纹沿晶界间疏松缺陷向心部开裂扩展,主裂纹两侧及尖端周围有沿晶开裂二次裂纹,最终部分裂纹贯穿整个壁厚,发生了泄漏事故。

Analysis of Leakage Cause of Elbow of a Gas Station

A longitudinal crack was found in the pipe body on the external arc side of the elbow,which led to leakage during the pressure test before a gas station was put into production.The specific failure causes of the elbow were discussed by mechanical property test,microstructure analysis,SEM analysis and energy spectrum analysis.The results show that shrinkage defect in the elbow was the main cause of cracking.Specifically speaking,the shrinkage defect in the elbow originates from slag inclusion in the smelting process of raw materials.Due to the failure to find and remove it in time in the subsequent process,the crack defect deteriorates in the bending process.Therefore,the crack originates from the inner surface of the elbow under the test pressure of low water pressure strength.The main crack extends to the center of the shrinkage crack along grain boundaries.There are secondary intergranular cracks on both sides of the main crack and around the tip.Finally,some cracks penetrate through the whole wall thickness,resulting leakage accident.