Ali Kheradmehr - Faculty of Science and Research Branch of Islamic Azad University Bushehr Branch, Iran
Taher Armaghani - Department of Mechanical Engineering, MahdiShahr Branch, Islamic Azad University, Mahdishahr, Semnan, Iran
Mohsen Izadi - Faculty of Science and Research Branch of Islamic Azad University Bushehr Branch, Iran
Hamed Mohammaddoost - Department, of Chemical Engineering,Shiraz Branch, Islamic Azad University, Shiraz, Iran

Coating is one of the important aspects to consider in construction of gas transmission pipelines and the most common protection coating which applied is 3-layer polyethylene. The main goal of this study is the analysis of the effect of hydrostatic test on interlayer bonding of 3-layer polyethylene coating. Finite element method (F.E.M) by ANSYS software employed for modeling and calculations. Integrated octagonal elements with 8 node and 24 degrees of freedom has been used and grid independency evaluated. Soil weight and internal hydropressure has been considered and plannar strain assumed in problem solution. Von mises strain and stress show that pipe material maintains in safe margin below yield strength, but plastic deformation occurs in epoxy resin, binder and polyethylene. This deformation reduce interlayer bonding of polyethylene and also pipe to coating. Therefore in the cases with high corrosion risk, due to soil corrosive conditions application of other protection coatings like polyurethane or polyuria is proposed.

Gas transmission, 3-layer polyethylene coating, finite element method, hydrostatic test, stress