Effects of Axial Stress on Burst Strength of Corroded Pipes

Abstract Pipes in service are often subjected to in-situ axial stresses in addition to the pressure loading. These additional axial stresses are known to affect the burst strength of uncorroded pipes. Therefore, it is expected that the burst strength of corroded pipes also has a dependency on axial stresses. However, incorporating the axial stress effect in burst strength assessment models for corroded pipes is much more challenging than for uncorroded pipes, due to the significantly increased difficulty in analytical characterization of the complex stress and strain distributions within a corroded pipe. Although methods for treatment of axial stresses in remaining burst strength models are available in a few industry codes, it appears that investigation of the applicability and accuracy of these methods is limited. Adopting a recently proposed and validated plastic instability-based failure criterion, Finite Element Analysis (FEA) was performed on previously tested pipe samples to investigate the effects of axial stress on burst pressure of corroded pipes. In general, the axial stress was found to have an insignificant impact on the burst pressure of pipe samples with localized corrosion in this study. An in-depth investigation of the stress and strain response within the corrosion region revealed that the constraint effect of the surrounding uncorroded pipe body greatly reduces the axial stress effect on the burst pressure of pipes with localized corrosion. This finding poses a question to the assumption of the proportional relationship between the stresses within the corrosion region and uncorroded pipe body adopted in the burst strength assessment models in some industry codes. The outcome of this study proves the need for future research to improve the methods to account for the axial stress effect in burst pressure prediction for corroded pipes.