静水压试验后直缝埋弧焊管鼓胀原因分析

Analysis on Causes for Bulging of SAWL Pipe after Hydrostatic Test

静水压试验后部分X80Mφ1219mm×27.5mm规格直缝埋弧焊管的外周长超出相关标准上限。为查找不合格原因,调查了钢板板厚,研究了鼓胀焊管的化学成分、拉伸性能、硬度及显微组织。结果显示:鼓胀焊管母材的显微组织中块状铁素体比例高于其余焊管,显微组织差异导致钢板拉伸曲线出现较明显的屈服平台,形变强化能力变差,从而造成焊管在静水压试验后出现鼓胀。

During the production process of the φ1219 mm×27.5 mm X80M steel pipe,the outside perimeter of some pipes exceed the standard upper limit after the hydrostatic test.The reasons for the said nonconformance of the pipe are analyzed by means of checking the thickness of the steel plate,studying the chemical composition,tensile property,hardness and microstructure,etc.of the bulging pipe.As a result,it is identified that the blocky ferrite proportion in the microstructure of the base metal of the bulging pipe is higher than that of the other pipes.This microstructure difference leads to an obvious yield platform of the tensile curve of the steel plate,and poor deformation enhancement ability as well,which in turn causes bulging of the pipe as undergone the hydrostatic test.