No abstract

Many of the targeted applications for powder-metallurgy materials, particularly in the automotive industry, undergo cyclic loading. It is, therefore, essential to examine the fatigue mechanisms in these materials. The mechanisms of fatigue-crack initiation and propagation in ferrous powder-metallurgy components have been investigated. The fatigue mechanisms are controlled primarily by the inherent porosity present in these materials. Since most, if not all, fatigue cracks initiate and propagate at the specimen surface, surface replication was used to determine the role of surface porosity in relation to fatigue behavior. Surface replication provides detailed information on both initiation sites and on the propagation path of fatigue cracks. The effect of microstructural features such as pore size and pore shape, as well as the heterogeneous microstructure on crack deflection, was examined and is discussed. Fracture surfaces were examined to elucidate a mechanistic understanding of fatigue processes in these materials.

Operating pipelines may contain crack-like flaws created during fabrication or induced by service. Stress-corrosion cracking (SCC) and fatigue are two common mechanisms that cause cracks to develop in operating pipelines. Engineering fracture mechanics models are typically used to assess the potential for crack-like flaws to result in pipeline failure. To this end, an inelastic fracture mechanics model was developed and incorporated into the CorLAS™ computer program that is used by many pipeline operators. This paper reviews and documents the details of the fracture mechanics model. It provides the equations used to compute the parameters in the model and discusses their engineering basis. Correlations of predictions made using the model with the results of tests and pipeline failures are presented. Typical applications of the model are also reviewed. Finally, areas of possible improvements are discussed.

GE performed an ultrasonic phased-array (USCD DUO) in-line inspection (ILI) survey of a 24-inch and 26-inch products pipeline. The primary purpose of this ILI survey was to detect and characterize stress corrosion cracking (SCC). A dig verification was subsequently performed throughout 2008 in order to establish a higher level of confidence in the detection and depth-sizing capabilities of this technology. Presented herein is an overview of the USCD technology and experience, the method used for validating the ILI survey results, enhancements to the ILI data analysis, and the impact on managing the integrity of the subject line section.

Pipeline operators around the world use in-line inspections and corrosion control systems to manage the integrity of their systems. Determining when to inspect is a critical consideration, which depends in part on whether corrosion growth takes place between inspections. Remaining life estimates based on estimated corrosion growth rates typically form the basis for reassessment intervals. Remaining life assessments often use assumptions about corrosion rates that, while conservative, can lead to unrealistic results. Excess conservatism leads to short reassessment intervals and unnecessary mitigation. This paper discusses how data analyses can be used to identify and verify areas where corrosion is actually taking place. By identifying and addressing these areas, operators can minimize unnecessary mitigation in low growth areas, ensure high growth areas are mitigated in a timely manner, and extend overall reassessment intervals. This paper discusses an integrated approach to identifying corrosion activity using a combination of statistics, inspection signal comparisons, and engineering analyses. The approach relies on a full understanding of the mechanisms that cause corrosion and its growth. Pipeline operators can use this approach to calculate remaining life, prioritize repairs and mitigation, and extend reassessment intervals. This process is collectively known as Statistically Active Corrosion (SAC) 1,2,3.