夹套式热力管网的聚乙烯外套管的失效分析

Failure analysis of polyethylene-cannula enwrapping thermal pipeline

对夹套式热力管网发生早期腐蚀泄漏的原因进行分析,发现因聚乙烯夹套接头普遍开裂,地下水渗入导致钢管发生严重电化学腐蚀.对聚乙烯夹套的开裂进行了失效研究,结果发现,在环境应力影响下聚乙烯分子链片晶的扭连集结被打开,相邻片晶之间的结合被切断,材料的变形抗力与断裂抗力发生明显降低,在宏观上表现为脆性断裂.管线焊结方式使聚乙烯外套接头处的裂缝无需形核,只需长大,开裂所需能量很低.漏泄处温度过高导致聚乙烯套管焊缝强度进一步降低,加速其老化过程.

It was analyzed that the jacket-type underground thermal pipeline was of early failure by corrosion comparing to its service life. The electrochemical corrosion was found to be the main reason because the polyethylene-cannula preventing the pipeline from environment corrosion was cracked mostly and the underground water entered into the jacket. The results showed that, under the effect of environment stress, the intertexture form of the polyethylene molecular chain crystalline lamellae was damaged and the bonds among crystalline lamellae were cut off. The deformation resistance and fracture resistance of polyethylene were decreased remarkably, and then the brittle fracture of polyethylene-cannula took place. At the polyethylene-cannula welding seams there presented the crack nuclei to grow up under stress effect, so the fracture energy was very low. The strength of polyethylene-cannula welding seams was decreased deeply and the aging process was accelerated by high environmental temperature.