Suggestions and solutions to the ice blockage problem in pigging operation

Zhangye-Yongchang Pipeline Section in West-to-East Gas Pipeline II has suffered from abnormal pressure problem due to ice blockage many times in the stage of commissioning and running, caused by the low ground temperature, complex terrain, pipeline trend fluctuation and large drop. Two-straight-four-papilionaceous-cup pig that has high power and performance launch system is selected to carry out pigging operation. The troubleshooting process for blocked pig in two pigging operations is introduced. Ice blockage happened, because of formation of gas hydrate, jet hole and drain hole in pig, changes of throughput and ground temperature. The measures to alleviate ice blockage failure include decreasing water content in gas source, clearing residual water in hydrotest, removing jet hole in pig, alcohol injection, reasonable controlling throughput and pigging at higher ground temperature.