中碳钢管敷设野外输油管道的实践

The Practice of Laying Medium-Carbon Steel Pipes in Field.

根据中碳钢管敷设野外输油管道的实践，提出了用中碳钢管替代低碳钢管必须解决的问题，论述了解决方法。中碳钢管材（Ｊ－５５）的化学成分，含碳量介于４０＾＃与４５＾＃钢之间，含硫量明显低于低碳钢，含锰量变化区间较大，计算出的碳当量大于０．６％，表明管材的呆焊性较差；其机械性能，抗拉强度和屈服极限比低碳钢高，冲击韧性相对较上，延伸率变化区间大；其机械性能，抗拉强度和屈服极限比低碳钢高，冲击韧性相对较小。

According to the experience of laying medium-carbon steel pipeline in field,the problems encountered during substituting low-carbon steel pipe by medium-carbon steel pipe are introduced and the solutions to these problems discussed. The medium-carbon steel pipe (J-55) has a poor weldability due to its chemical compositions: carbon content in between that of 40# and 45# steel,sulphur content much less than that in low-carbon steel, manganese content changing within a large range, and a calculated carbon equivalent of over 0.6%. Comparing with low-carbon steel, it has a higher tensile strength and yield strength, lower impact flexibility,and larger rate of elongation,and has the characteristics of more than enough strength but not plasticity and flexibility, and a high risk of brittle fracture. In order to achieve enough mechanical strength without cracking in the welded pipeline, unequivocal regulations are made for the processing, installation and testing of pipeline and related facilities ,and detailed requirements specified for pipe welding procedures. It is necessary to carry out safety evaluation for the pipeline system,so as to achieve reasonable process design and qualified construction and to remove timely any hidden danger occured during pipeline operation. It is proved feasable to lay medium-carbon steel pipe in field for oil transportation provided that reasonable welding procedures be ad opted, and strict qualification and safety evaluation followed.