INFLUENCE OF METAL SHRINKAGE IN LONGITUDINAL WELDS OF SLEEVES ON CONTACT PRESSURE IN MAIN GAS PIPELINE REPAIR

摘要

Effectiveness of main pipeline repair in service is largely determined by contact pressure, created at sleeve mounting on pipe defective section. At correct selection of contact pressure value, long-term performance of the repaired section is ensured through partial unloading of the pipe wall. Such a result is achieved due to lowering of pressure in the main line before repair, and tight pressing of the sleeve around the pipe with a special device. Arc welding of sleeve reinforcing elements also is of considerable importance, resulting in formation of contact pressure, caused by shrinkage of multilayer longitudinal butt welds. In the work computational method was used to study the influence of sleeve wall thickness and pipeline diameter on the magnitude of contact pressure caused by deposited metal shrinkage. It is shown that contact pressure caused by metal shrinkage during welding performance has the strongest influence on unloading of a defective pipe wall in pipelines of 1020 mm and smaller outer diameter. Further increase of contact pressure magnitude caused by metal shrinkage can be achieved by increasing sleeve wall thickness. Such a technique is not effective for pipes of 1220 mm and greater diameter.