Effect of Room Temperature Creep on Hydrostatic Leak Test

Because of the stochastic nature of line pipe characteristics a small percentage of the pipe joints in a given pipeline may possess actual yield strengths below the specified minimum yield strength. During a hydrostatic test these segments may experience some plastic deformation as the hoop stress approaches the yield point. It is well known that the effect of room temperature creep near the yield becomes notable and therefore can affect pressure trending during the hold period (leak test). In this work a numerical model is developed for the analysis of creep deformation. A conceptual study is carried out to demonstrate potential effects of creep on hydrostatic test pressure trending during a leak test. This analysis can help operators understand the potential effects of creep and distinguish it from other factors such as temperature changes or leakage and can help identify, or rule out, the occurrence of pipe yielding during hydrostatic tests.