Failure pressure prediction by defect assessment and finite element modelling on natural gas pipelines under cyclic loading

https://doi.org/10.1016/j.jngse.2020.103445Get rights and content

Highlights

  • Develop a finite element model for pipeline defect assessment under cyclic loading.

  • The cyclic loading reduces the threshold internal pressure causing pipeline failure.

  • The decrease of the cyclic loading frequency increases the local stress at defect.

  • The increased R-ratio of cyclic loading enhances the local stress at defect.

Abstract

In this work, a 3-dimensional finite element (FE) model was developed to investigate the effect of cyclic loading, which is induced by vibration during operation of in-line inspection (ILI) tools, on local stress and strain distributions and failure pressure of an X80 steel natural gas pipeline containing a corrosion defect. Modelling was also conducted on a low-grade X60 steel pipe for comparison. Parametric effects, including internal pressure, R-ratio, cyclic frequency and dimension of the corrosion defect (primarily the defect depth), were determined. The cyclic loading greatly increases the von Mises stress and strain at the corrosion defect and reduces the threshold internal pressure to cause plastic deformation at the defect. As the internal pressure increases, both the von Mises stress and the strain increase and the high stress/strain zones expand along the defect length direction. The local stress and strain at the corrosion defect increase with decreased R-ratio and cyclic frequency, resulting in a reduction of failure pressure of the pipeline. An increased defect depth enhances local stress and strain concentrations, reducing failure pressure of the pipeline. A novel method is developed to assess corrosion defect during ILI tool operation and predict the failure pressure of pipelines under cyclic loading for the first time of its kind.

Introduction

In-line inspection provides an accurate technique (e.g., magnetic flux leaking or ultrasonic tool) to detect and size various types of defects on pipelines (Vanaei et al., 2017). Defect assessment based on ILI data analysis is an essential component of pipeline integrity management program (API, 2016; Pluvinage, 2008). In the past decade, the authors’ group has conducted extensive research on pipeline defect assessment. FE based models were developed to evaluate failure pressure of corroded pipelines and predict the defect growth rate (Xu and Cheng, 2012, 2013, 2017; Sun and Cheng, 2018, 2019a, 2019b). The modelling scope is extensive, including the defect geometry (depth, length and width), steel grade, internal pressure, soil strain, interaction of multiple corrosion defects, stress-corrosion interaction, etc.

During ILI operation, the tool moving inside a pipeline may cause vibration, especially when the tool encounters obstacles such as rough inner wall surface, dents, girth weld between pipe segments, corrosion pits, etc. (Zhang et al., 2015, 2020). Vibration will also happen on pipelines that are suspended on erosive soil supports. The vibration can apply a cyclic loading on the inner wall of the pipeline (Zhang et al., 2015), affecting the local stress and strain distributions at the defect and the failure pressure of the pipeline.

The presence of corrosion defects on pipelines can reduce pipe wall thickness and introduce an additional stress concentration, causing reduction of load-bearing capability of the pipelines (Gong and Zhou, 2018; Abdalla et al., 2014). To date, a wide variety of numerical models and computational codes have been developed for pipeline defect assessment (Xu and Cheng, 2012, 2013, 2017; Sun and Cheng, 2018, 2019a, 2019b; Choi et al., 2003; Ma et al., 2013; Chegeni et al., 2019; Wu and Li, 2019; Mondal and Dhar, 2019; Gong and Zhou, 2017). However, to the authors’ best knowledge, none of them has considered the mechanical response due to the ILI-induced vibration and its effect on ocal stress and strain concentrations and the pipeline failure. This work developed a novel method to assess corrosion defect during the ILI tool operation and predict the failure pressure of pipelines under cyclic loading for the first time of its kind.

In this work, a FE model was developed to simulate the stress and strain distributions at a corrosion defect on an X80 steel natural gas pipeline under cyclic loading. A stress-based failure criterion was used to predict the failure pressure of the corroded pipeline. Parametric effects, including internal pressure, defect depth and loading parameters (i.e., cyclic frequency and R-ratio), were modelled. For comparison, modelling was conducted on a pipeline made of a low-grade X60 steel.

Section snippets

Pipeline steels and geometry of corrosion defect

Both X60 and X80 steel pipes were modelled in this work. They represent the typical low- and high-grades of pipeline steel, respectively. The mechanical properties of the two steels are shown in Table 1. To model a corrosion defect, some simplifications were made so that the results could be applicable for a wide range of geometric shapes. In modified ASME B31G standard, the maximum depth and length along the axial direction of pipeline are used to depict a corrosion defect, which is usually

Comparison of the modelling results with testing data as published and the DNV results

A comparative analysis was performed to verify the reliability of the FE model developed in this work. It is noted that selections of the pipe steel, dimensions of corrosion defect and operating conditions ensure a sound base for comparison of the modelling results with experimental data. Fig. 4 shows the modelling failure pressures compared with the published experimental data (Benjamin and Cunha, 2007) and the DNV modelling results. The relative error (RE) between the experimental testing

Conclusions and implication

A FE model is developed to simulate the local stress and strain distributions at corrosion defect on pressured gas pipelines which are under cyclic loading induced by vibration of ILI tool operation. The presence of cyclic loading greatly increases the local von Mises stress and strain at the corrosion defect, reducing the threshold internal pressure to cause local plastic deformation at the defect. As the internal pressure increases, both the von Mises stress and strain increase. The high

Author statement

The first author, Guojin Qin, is a graduate student. He conducted all numerical modelling work, and performed the result analysis. He also drafted the manuscript.

The corresponding author, Dr. Frank Cheng, is the principal investigator of the project. He planned the scope of work and designed the research plan. He worked with the first author to analyze the results, and revised the manuscript for submission.

Declaration of competing interest

None.

Acknowledgement

This work was supported by China Scholarship Council (CSC no. 201908510201) and the University of Calgary.

References (26)

Cited by (32)

  • Roadmap to urban energy internet: Techno-enviro-economic analysis of renewable electricity and natural gas integrated energy system

    2022, Journal of Cleaner Production
    Citation Excerpt :

    Nowadays, natural gas pipelines between cities are interconnected, and the reduction of natural gas demand will also lead to changes in node pressure, resulting in network pressure fluctuations. Excessive pressure fluctuations will affect the safety of the whole system (Qin and Cheng, 2020). Consequently, it is necessary to consider the pressure fluctuation of the pipeline network caused by the reduction of natural gas use when designing the urban energy internet.

  • A new method for assessment of burst pressure capacity of corroded X80 steel pipelines containing a dent

    2022, International Journal of Pressure Vessels and Piping
    Citation Excerpt :

    Moreover, an X65 steel was also selected for modeling to provide additional confirmation in terms of the modeling reliability. Generally, models used for FE analysis for steels include the bilinear stress-strain relationship [22], isotropic hardening model [47], true stress-strain data [48], and Ramberg-Osgood (R–O) relationship [1]. As suggested by API 579-1/ASME FFS-1 2016 [49], the R–O model was used for both X65 and X80 steels in this work.

View all citing articles on Scopus
View full text