Review of Engineering Fracture Mechanics Model for Pipeline Applications

Abstract

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.

Classification of failure modes of pipelines containing longitudinal surface cracks using mechanics-based and machine learning models

“…The CorLAS-S model was originally proposed by Jaske and Beavers [33] to predict burst capacities of pipelines containing longitudinal crack-like surface breaking flaws based on elastic-plastic fracture mechanics principles. The model has been continuously updated since then and is now in Version 3 [34,55] with main formulations given by, where A is the area of the longitudinal profile of the surface crack with a length 2c and a maximum depth a, as illustrated in Fig. 1; A 0 is the reference area that equals 2cw t with w t denoting the pipe wall thickness; M is the Folias factor that accounts for the defect bulging induced stresses due to pipe internal pressure [26], and D is the pipe outside diameter.…”

“…Polasik et al [55] modified the CorLAS model to apply it to through-wall cracks. This is referred to as the Cor-LAS-T model in the present study.…”

“…Many models have been developed to evaluate the failure stress of pipelines containing surface and throughwall cracks, for example, the well-known Battelle (i.e. Ln-Sec) model [40] and modified Battelle model [38,39], CorLAS model [34,55], PAFFC [45], PRCI MAT-8 [4,5], and failure assessment diagram-based approaches recommended in API 579 [3], BS 7910 [10] and R6 [24]. However, the employment of these models in Shannon's approach to separate failure modes has, to our best knowledge, not been reported in the literature.…”

“…A database of full-scale burst tests involving pipe specimens containing surface cracks is collected from the open literature as the basis for training the ML models and also comparing the predictive accuracy of the mechanics-based approach and ML models. For the mechanics-based approach, the well-known CorLAS model ( [55,64,66]) is selected to evaluate σ hb , whereas the Battelle model and an extension of the CorLAS model for through-wall cracks [55] are used to evaluate σ hr . Five ML models are considered for comparison with the mechanics-based approach, namely the naïve Bayes (NB) model, SVM, decision tree (DT), random forest (RF) and gradient boosting (GB).…”