The effect of hydrostatic test simulation on the formation of stress in three-layer of polyethylene layers of gas transmission lines

Coating is one of the important aspects to consider in construction of gas transmission pipelines and the mostcommon protection coating which applied is 3-layer polyethylene. The main goal of this study is the analysis of theeffect 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 degreesof freedom has been used and grid independency evaluated. Soil weight and internal hydropressure has beenconsidered and plannar strain assumed in problem solution. Von mises strain and stress show that pipe materialmaintains 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 highcorrosion risk, due to soil corrosive conditions application of other protection coatings like polyurethane or polyuria isproposed.

Keywords:

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