Collapse Experiments and Reliability Analyses of Corroded Pipes for Offshore Applications

Abstract

The collapse pressure of subsea pipelines containing corrosion defects is usually predicted by deterministic methods, either numerically or through empirical formulations. A simple deterministic procedure for estimating the collapse pressure of pipes with narrow and long defects has been recently proposed by Netto, T. A. (2009, “On the Effect of Narrow and Long Corrosion Defects on the Collapse Pressure of Pipelines,” Appl. Ocean Res., 31(2), pp. 75–81) and Netto, T. A. (2010, “A Simple Procedure for the Prediction of the Collapse Pressure of Pipelines With Narrow and Long Corrosion Defects—Correlation With New Experimental Data,” Appl. Ocean Res., 32(1), pp. 132–134). The formulation was based on a combined small-scale experimental program and nonlinear numerical analyses accounting for different materials and defect geometries. This paper presents additional experimental tests on corroded pipes under external pressure. The collapse pressure calculated using the equation proposed by Netto is compared with this new set of experiments and also with test results available in open literature. These results are used to estimate the equation uncertainty. A sensitivity analysis is also performed to identify how geometric parameters of the defects influence the reduction of collapse pressure. However, loads and resistance parameters have uncertainties. These uncertainties are related to the geometric and material parameters of the pipe and the operational conditions. To account for these uncertainties, a method to predict the probability of collapse of a corroded pipeline along its operational life is proposed. The methodology is illustrated through a case study in which concepts of structural reliability are used to evaluate the detrimental effect of corrosion damages in a pipeline, providing the basis to develop a risk-based maintenance strategy.