Reliability and failure pressure prediction of various grades of pipeline steel in the presence of corrosion defects and pre-strain L.Y. Xu, Y.F. Cheng * Department of Mechanical and Manufacturing Engineering, University of Calgary, Calgary, Alberta T2N 1N4, Canada article info Article history: Received 24 March 2011 Received in revised form 1 September 2011 Accepted 26 September 2011 Keywords: Reliability assessment Pipelines Corrosion defects Failure pressure Pre-strain abstract The reliability assessment of various grades of pipeline steel with corrosion defects was conducted through a finite element analysis (FEA) model. The failure pressure of pipelines was also evaluated by three industry models for comparison. Results demonstrate that the failure pressure of pipelines is reduced by the increasing corrosion depth and the decrease of the steel grade. Predictions by ASME B31G and the modified B31G models tend to be higher than FEA results for low grade steels, while the DNV model shows the close result to FEA. The predictive reliability by ASME B31G and the modified B31G decreases with the increases in corrosion depth and the steel grade. The geometry of corrosion defects affects remarkably the local stress and strain distributions, and plays a critical role in the failure pressure prediction. The applied strain in the longitudinal direction simulating the soil strain, regardless of tensile or compressive, would reduce the failure pressure of pipelines. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction With the rapidly increasing demand for oil and gas supplies, pipeline industry is driven to develop large diameter, thin wall thickness, high operating pressure and high grade steel pipeline systems. Moreover, there have been increasing pipeline activities in the harsh geographic environments, such as the Arctic and sub- Arctic regions, where significant soil movements are encountered. Strain-based design methods have been developed to consider the longitudinal strain capacity of the line pipe steel during pipeline design to resist the soil-induced strain in these regions [1e4]. During service, the remaining strength of pipelines depends on a number of factors, including the operational conditions, and defects introduced by construction, third-party damage, corrosion and ground movement, etc. In particular, corrosion and ground movement constitute two important causes resulting in pipeline failure [5e8]. Corrosion is of concern because any loss of the pipe wall thickness means a reduction of pipeline structural intensity and hence an increase in the risk of failure, while the ground movement produces a longitudinal load on the pipe, creating a stress/strain to threaten the pipeline safety. Thus, a synergistic effect of corrosion and the soil-induced strain on the pipeline integrity should be considered in strain-based design of pipelines. Corrosion can cause several kinds of defect on pipelines. The reduction of the wall thickness of pipe in a large area is general corrosion, which usually results in a low risk of failure. However, defects due to localized corrosion have a high failure risk to the pressurized pipelines. Generally, a defected pipeline due to corrosion is allowed to operate after the reliability assessment to recalculate its maximum allowable operating pressure. Models have been developed to estimate the remaining strength of pipelines by calculating the failure pressure in the presence of local corrosion defects [9e12]. Particularly, American Society of Mechanical Engineers (ASME) B31G standard [13], which was originally developed and published in 1984, has been used widely to determine the remaining strength of the corroded pipeline. Moreover, a computer code named “modified B31G” is also used [14e16]. The DNV-RP-F101 describes another method to evaluate the corroded pipelines under complex conditions, e.g., corrosion- induced defects, internal pressure, and the longitudinal compressive and bending loads due to soil movement [17]. These three models are named “industry models” in the following text for simplification. With the development of new, high-strength steel pipelines in remote geographic terrains, these industry models need to be modified to consider factors, such as the increased grade of pipe steel and the longitudinal pre-strain applied, etc. Furthermore, these models usually provide prediction of the failure pressure for the corroded pipelines at a relatively high tolerance. In this work, a finite element analysis (FEA) model was developed to * Corresponding author. Tel.: þ1 403 220 3693; fax: þ1 403 282 8406. E-mail address: fcheng@ucalgary.ca (Y.F. Cheng). Contents lists available at SciVerse ScienceDirect International Journal of Pressure Vessels and Piping journal homepage: www.elsevier.com/locate/ijpvp 0308-0161/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijpvp.2011.09.008 International Journal of Pressure Vessels and Piping 89 (2012) 75e84