三层PE防腐管道补口质量缺陷及其解决办法

我国的天然气长输管线大多采用较为成熟的三层PE防腐,补口材料选用聚乙烯热收缩套(带),但因其施工要求高、补口质量制约因素多,使补口处成为管线安全的薄弱环节,对投产2~6 a的防腐补口应用进行调查,发现管道环焊缝补口处的热收缩带存在翘边、剥离、破损等缺陷。其原因在于火焰加热存在相关缺陷,湿膜法施工的化学交联不能形成,热收缩带(套)与三层PE间搭接部位的回火控制不到位。为了严格控制补口质量,避免管道腐蚀发生,针对性地提出了相应的解决办法:①应先分析补口材料的性质,制订施工工艺技术规定;②针对湿膜法施工,要求环氧底漆表面干燥前,必须完成热收缩带(套)补口操作;③钢管的预热温度要低,甚至不需要预热;④干膜法施工时,钢管表面预热温度、固化的环氧树脂温度一定要达到80℃;⑤热收缩带(套)加热时,不允许采取火焰加热器直接加热,宜使用中频加热,且应注意回火的温度与时间。

Solution to the defects in 3LPE field coating for welded joints of pipelines

The majority of long-distance oil and gas pipelines in China have well-developed 3LPE coatings for corrosion prevention, with polyethylene heat shrinkable sleeves (tapes) as coating materials. Due to higher requirements for operations and multiple restrictions, field coatings have become a vulnerable element in pipeline safety. Survey results for coatings with a service life of 2-6 years show that edge warp, stripping, worn and other defects are common in heat shrinkable sleeves (tapes) around the coating of circumferential welds. Major contributors for such defects include defects in flame heating, failures in the generation of chemical cross-linking during the execution of wet membrane techniques and improper control over tempering between heat shrinkable sleeves (tape) and the 3LPE coatings. To obtain high coating quality and protect pipelines against corrosion, corresponding solutions were proposed: ① specific technical procedures should be stipulated in accordance with the properties of materials deployed for coating; ② as for the implementation of the wet membrane techniques, heat shrinkable sleeve (tape) coating should be completed prior to drying of epoxy primer surface; ③ preheating temperatures of the steel pipe should be low; in some circumstances, no preheating is required; ④ during the implementation of dry membrane techniques, preheating temperatures of the steel pipe surface and temperatures of solidified epoxy resin should reach 80℃; ⑤ no direct heating by using fired heater for the heating of the heat shrinkable sleeves (tape) should be allowed. Instead, medium-frequency heating can be used. Cares should be taken to control tempering temperatures and time.