Reliability evaluation method for pipes buried in fault areas based on the probabilistic fault displacement hazard analysis

doi:10.1016/j.jngse.2020.103698

Journal of Natural Gas Science and Engineering

Volume 85, January 2021, 103698

https://doi.org/10.1016/j.jngse.2020.103698 Get rights and content

Highlights

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An investigation of reliability analysis on pipes subject to fault movements.
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A new strain demand prediction method is proposed based on artificial neural network.
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The probability of fault displacement is evaluated based on PFDHA.
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Uncertainties arise from fault displacements and pipe structures are both considered in reliability assessment.

Abstract

The tectonic fault poses a great threat to buried pipe segments. Buckling or rupture of pipes will ensue due to large strain induced by continuously increasing fault movements. In this study, a reliability-based methodology is conceptually proposed for designing new buried pipes or assessing existing pipes installed in fault areas. Uncertainties associated with the influencing factors of pipe structure and seismic loading (fault displacement) generated by earthquakes are considered. For pipe structural reliability, a developed back-propagation neural network (BPNN)-based surrogate model is utilized for the strain demand term in the limit state function for reliability calculations. Given statistical data for the basic variables including diameter, wall thickness, internal pressure, intersection angle or dip angle, and soil spring resistances, the conditional probability of failure can be obtained at a particular fault displacement by Monte Carlo simulation. Uncertainty of the fault displacement is estimated based on probabilistic fault displacement hazard analysis (PFDHA) having results given as probability of exceeding a certain fault displacement level for a specific site, then the occurrence probability of a specific fault displacement at a specific time can be indirectly obtained. The actual probability of failure (PoF) is calculated as an integral of fault displacement based on the total probability which is the product of the conditional PoF of pipe structure and occurrence probability of the specific fault displacement. This developed methodology is applied to a case study about a pipe project from China. Results show that the probability of failure increases with the elapsed time but stay within the safety margin for the next 30 years. Generally, the result of PFDHA is an essential input parameter in reliability analysis for pipes buried in fault regions. The multidisciplinary combination of structural reliability analysis and fault displacement hazard analysis is of practical significance for the reliability-based study of pipes in fault regions.

Introduction

Active faults are one of the most dangerous threats to long-distance transmission pipelines. The induced offset on the ground in the fault plane between the hanging wall and the foot wall, namely the ground permanent displacement (GPD) or fault displacement, induces large longitudinal strains in the buried pipes. Excessive strain could lead to the failure in pipes, such as rupture and buckling, which may cause significant risks arising from concomitant environmental and societal risks. It is therefore imperative to study the pipe response to fault displacements for the sake of integrity management.

Stress-based design is chiefly used for the design of new pipes, in which a certain design factor is used by the designer to control the stresses under the yield or plasticity limit of the material (a guaranteed safety margin). However, due to the high ductility of steel materials where large strains can be attained with a marginal increase in the stresses, stress-based design can be highly conservative for pipe segments withstanding displacement-controlled loads brought upon the pipe in geological hazard areas, e.g., the longitudinal ground sliding in areas of moving slopes, the transverse ground subsidence and bulge due to thaw settlement and frost heave, and fault displacements in seismic areas. In these cases, it is more appropriate to employ the strain-based design method. Furthermore, deterministic design cannot account for uncertainties in basic variables representing pipe geometry, pipe mechanical properties, and loads. These uncertainties, however, can be considered in a reliability-based approach.

Reliability-based analysis has recently received considerable attention from the pipeline industry. Its application on pipes under seismic or ground displacements is gradually popularized. Zhou (2012) developed limit state functions for the tensile rupture and compressive local buckling for pressurized pipes withstanding longitudinal displacement loading exerted by unstable slopes, the probability of failure was calculated at a given sliding magnitude. Fan et al. (2015) conducted the sensitivity analysis on pipes under seismic intensities and fault displacements based on the probabilistic design module built in ANSYS. In probabilistic seismic hazard analysis, uncertainty is regarded as an intrinsic nature of earthquakes, which is an important branch of engineering seismology (Bozorgnia and Bertero, 2004). The probability density function of seismic intensity in seismic excitation or GPD triggered by fault motion in earthquakes is used in pipe integrity analysis. Faraji and Kiyono (2011) evaluated the influence of seismic load uncertainties and damage state reliability definition in the water pipeline network in Padang (Indonesia). Yin Cheng et al. 0 applied uncertainties arising from earthquakes in pipe risk analysis and gave the annual rate of pipe failure with respect to fault-pipe intersection angles, soil types, and buried depths.

For pipes constructed in seismic areas, most studies concern pipe responses to seismic excitations, which can be classified into the dynamics analysis domain (Ariman and Muleski (1981); Chen and Li (2007); Ebenuwa and Tee (2019); Mashaly and Datta (1989)). But intense earthquakes are more likely to induce ground movements which result in the local deformation in pipelines. Existing relative researches are conditionally performed either based on structural engineering or earthquake engineering. In particular, for pipes subjected to fault displacements, the design uncertainty can be categorized into two types: pipe structure-related uncertainties, such as pipe dimension, material mechanics, and pipe-soil interaction properties; the other one is seismic and fault displacement-related uncertainty, that is, the probabilistic occurrence of earthquake and magnitude of induced ground displacement. As for the uncertainties from the two aspects, most studies attend to one of them, but the combination of the two is barely considered together. Kiremidjian (1984) presented a pioneering method for determining the probabilities of fault displacement at specific locations on a fault of finite length, and it was extended to enable the estimation of the risk to engineered structures. Kiremdijian method is applicable to every structure installed in fault zones. However, when using Kiremdijian method, Kennedy et al. (1977) calculated the pipes’ strain demand deterministically missing out on the incorporation of the associated strain demand uncertainties.

The probabilistic fault displacement hazard analysis (PFDHA), a methodology for conducting a site-specific probabilistic assessment of GPD, is pioneered by Youngs et al. (2003), which can provide probabilistic GPD input for structure analysis. Practically, the combination of structural reliability engineering and PFDHA has an immense potential in reliability-based analysis for the design for pipes buried in seismic areas. To this end, this paper aims to develop a methodology integrating both the above-mentioned uncertainties in reliability analysis on pipes installed in seismic zones, results of which can be referred for decision making at the stage of pipeline design or maintenance planning during the operating period. The document is structured as follows. Section 2 describes the reliability calculation method of pipes subjected to fault displacements, the reliability calculation is based on the work done by Liu et al. (2020) and will be briefly repeated here to provide the necessary background for the work in the current paper. Section 3 illustrates the principles of PFDHA. Section 4 demonstrates the feasibility of the proposed approach through a specific case study. Finally, conclusions are given in section 5.

Section snippets

Limit state function

Reliability-based assessment is a probabilistic evaluation with consideration of the uncertainties of the basic variables; assessment results are given as likelihoods based on a specific limit state. Literally, a limit state is a condition of a structure beyond which it no longer meets the requirement in the relevant design criteria, which can be expressed by a resistance-loading equation as seen in Eq. (1). $g (x) = R - L$ where, $R$ represents the resistance of a structure against a particular failure

Probabilistic fault displacement hazard analysis (PFDHA)

Probabilistic fault displacement hazard analysis (PFDHA) is a methodology for probabilistic analysis of a fault displacement occurrence in a specific site, which is developed from classical probabilistic seismic hazard analysis (PSHA) (Youngs et al. (2003); Zhao et al. (2008); Zhao and Zhou (2009)). In PSHA, the probability of exceeding a ground motion intensity measure (IM) level $x$ can be given as Eq. (4). $P (IM > x) = \sum_{i = 1}^{n_{source}} λ (M_{i} > m_{\min}) \int_{m_{\min}}^{m_{\max}} \int_{0}^{r_{\max}} P (IM > x | m, r) f_{M_{i}} (m) f_{R_{i}} (r) d r d m$ Where, IM can be

Case study

Xinjiang coal gas long-distance transmission pipeline (abbreviated as XinYueZhe pipeline hereafter) operated by Sinopec has a section buried through The Bolokenu-Aqikekuduk fault (abbreviated as Bo-A fault hereafter), the intersection is located in the southeast of Jinghe Country, Xinjiang Uygur Autonomous Region as seen in Fig. 6. The geological survey suggests an oblique fault in the intersection, which can be seen as a combination of the strike-slip fault and reverse fault. The pipe's

Conclusion

A methodology considering uncertainties in both pipe structures and fault displacements is proposed to fill the gap between structural analysis and seismological evaluation in reliability-based design and assessment for new pipelines to be buried and existing pipelines constructed in fault areas. The surrogate BPNN-based model, developed previously (Liu et al. (2020)), is introduced to predict strain demand for reliability computation, then, given a particular fault displacement, conditional

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

This work was supported by the National Science Foundation of China (No. 52004314); Tianshan Youth Program (No. 2019Q088); China National Key Research and Development Project under (No. 2016YFC0802105); Science Foundation of China University of Petroleum, Beijing (No. 2462018YJRC019, No. 2462020YXZZ045); China Petroleum Science & Technology Innovation Fund (No. 2017D-5007-0606); and the China Scholarship Council (No. CSC201906440175).

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View full text

Reliability evaluation method for pipes buried in fault areas based on the probabilistic fault displacement hazard analysis

Highlights

Abstract

Introduction

Section snippets

Limit state function

Probabilistic fault displacement hazard analysis (PFDHA)

Case study

Conclusion

Declaration of competing interest

Acknowledgement

J. Appl. Biomed.

Struct. Saf.

Transp

J. Nat. Gas Sci. Eng.

Eng. Struct.

Biophys. J.

Struct. Saf.

Guidelines for the Design of Buried Steel Pipe

A review of the response of buried pipelines under seismic excitations

Earthq. Eng. Struct. Dynam.

An Introduction to Probabilistic Seismic Hazard Analysis (PSHA)

Probabilistic permanent fault displacement hazard via Monte Carlo simulation and its consideration for the probabilistic risk assessment of buried continuous steel pipelines

Earthq. Eng. Struct. Dynam.

Oil and Gas Pipeline Systems

Critical buckling strain equations for energy pipelines – a parametric study

J. Offshore. Mech. Arct.

A multi-tiered procedure for engineering critical assessment of strain-based pipelines

Continued advancements regarding capacity prediction of strain-based pipelines

Strain design of long pipeline crossing fault under seismic loading

Chn. Petrol. Machin.

Seismic performance analysis of lifeline systems

WIT Trans. Built Environ.

Seismic Technical Code for Oil and Gas Transmission Pipeline Engineering

Applications of artificial neural networks in chemical engineering

Kor. J. Chem. Eng.