Pipeline Integrity Assessment Research Articles

Failure pressure prediction of high-strength steel pipe bend considering pipe and corrosion geometry

This study examines the influence of pipe bend geometry and corrosion geometry on the failure pressure of high-strength steel pipe bends subjected to internal pressure and axial compressive stress. Finite element analysis determines the impact of bend angle, bending radius, defect depth, defect length, defect spacing, and axial compressive stress on failure pressures. The findings reveal that increasing the bend angle reduces failure pressures significantly, with corrosion defects exacerbating this effect. Increased bending radius increases normalized failure pressure from 0.88 to 0.91 for intrados defects and decreases it from 0.98 to 0.93 for extrados defects. Additionally, single defects cause a slight 2.5–3.0% reduction in normalized failure pressure, while longitudinally and circumferentially aligned defects result in a 13–15% decrease in normalized failure pressure. Defect depth and length also significantly influence the failure pressure, particularly for deeper and longer defects (up to 48.2%). Furthermore, an empirical equation for predicting failure pressures in corroded pipe bends with high accuracy (R2 = 0.99) is developed based on Artificial Neural Network. This enhances pipeline integrity assessment and design practices.

A classification and quantitative assessment method for internal and external surface defects in pipelines based on ASTC-Net

Classification and size quantification of defects on both the internal and external surfaces of pipelines are critical to pipeline integrity assessment. However, defect classification is challenging because of the similarities of defect signals on the internal and external surfaces. In addition, most existing size quantification methods are not sufficiently accurate. To solve these problems, this paper proposes a classification and quantitative evaluation method based on an asymmetric student–teacher with a classifier network (ASTC-Net). First, a novel approach for expanding defect magnetic flux leakage (MFL) data is validated through experiments and simulations. Second, ASTC-Net is built to address the problem of defect classification and quantification. Finally, the superiority of the method is verified by experiments. The results show that this approach pioneers the accurate classification of defects on both internal and external surfaces by achieving an accuracy of 99.41%. Furthermore, a high-precision quantitative assessment of defect size is realized, with length, width, and depth errors of only 0.35 mm, 0.34 mm, and 0.41% of the wall thickness, respectively. These experimental results clearly demonstrate that this method has exceptionally high accuracy in defect classification and quantification, offering vast prospects for its application in pipeline MFL evaluation.

Integrity Assessment of an In-Service Gas Pipeline Featuring Dent Defect at a Highway Crossing

Underground pipelines are susceptible to different types of damage/flaws such as metal loss, buckling, dents, gouges, cracks, etc. during installation and operation. The structural integrity of the pipelines featuring such defects needs to be ensured for safe operation and to avoid serious hazards (fire/explosion/fatality/injury etc.). This paper discusses the integrity assessment of an actual case of an in-service gas pipeline featuring dent damage located at a highway crossing. A routine in-line inspection (ILI) of the considered pipeline showed the presence of a dent type of damage with a maximum depth of 5% spread over an area of 325 mm x 275 mm. Since the pipeline is located approximately 7.5 m below a 10-lane expressway with heavy traffic, dig verification of the dent was found to be not feasible. Level-3 integrity assessment based on API 579-1/ASME-FFS-1 2021 Fitness-For-Service standard has been performed using commercial finite element (FE) software ABAQUS/CAE. The considered pipeline is subjected to overburden pressure of soil embankment and cyclic loads such as vehicular loads (as per IRC: 6-2017) and internal pressure. The dented pipeline segment was assessed for potential failure modes i.e., protection against plastic collapse, local failure, collapse from buckling, and fatigue damage. FE analysis of the pipeline-soil system has been carried out considering the material and geometric nonlinearity, and contact interactions. The study suggests the pipeline is safe for further operation with existing dented defects. The methodology presented in this paper can act as a guide for the integrity assessment of pipelines with dent damage located at highway crossings.

An Electrocrystallization Approach for Modeling Protective Scale Formation in CO2 Corrosion of Carbon Steel

The CO2 corrosion of carbon steel has been extensively studied and many models have been developed to estimate the corrosion rate in various industrially relevant conditions [1]. These models agree moderately well in non-scaling environments but can produce significantly different results under higher temperature and higher pH conditions where protective scales of iron carbonate may be formed [2,3]. The scaling effect is typically incorporated in empirical models using a ‘scaling factor’ [2,3]. Nesic and co-workers developed a model that attempts to calculate the corrosion rate in scaled conditions from first principles [4,5,6], later including a numerical model to describe the formation kinetics and growth morphology of the surface layer [7]. In this and other models, the driving force for scaling is the degree of supersaturation (S) of FeCO3 at the steel surface, and it is generally assumed that protective films are formed by precipitation from solution, at a rate dependent on S [7,8,9].To investigate the formation and structure of these surface scales, Williams and colleagues [10-14] completed a series of experiments using in-situ synchrotron x-ray techniques. The majority of this work accelerated the corrosion process through the application of a small anodic potential step, and focused on solutions of moderate chloride content, saturated with CO2 at ~ 1 bar, pH adjusted to ~ 6 and at temperatures of ~ 80 °C. Small Angle X-Ray Scattering (SAXS) showed that the first stage in scaling was the formation of a precipitated layer of Amorphous Ferrous Carbonate (AFC) [13], while X-Ray Diffraction (XRD) revealed that the reduction of corrosion rate was associated with the slower formation of crystalline siderite (FeCO3) and sometimes chukanovite (Fe2(OH)2CO3) (see Figure 1). Hassan et al [14] then developed a model for this process in which the protective scale forms directly on the steel surface by an electrocrystallization mechanism, using an Avrami model to describe the crystal nucleation and growth. The relative volume of siderite as a function of time was fitted with an Avrami-like equation. The anodic current transients formed during potentiostatic experiments (see Figure 1) were then fitted with separate components due to iron dissolution and electrocrystallization, allowing various kinetic parameters to be extracted from the experimental data.In this paper, we extend these previous ideas on the importance of considering electrocrystallization as a fundamental step in the scale formation process. There exist several models of the potentiostatic current time transient in the electrocrystallization literature [15,16]. Taking the potentiostatic data from Hassan et al [14], we fit the current time transient to some models from literature [15,16]. This fitting provides rich information about the kinetics of nucleation. We speculate on some differences from the models in Luo et al [15] by current transient fitting. We also provide expressions for surface coverage of siderite under different applied potentials with the Avrami equation to account for the scale protection factor more rigorously. Improved estimates of the protection factor by our methods can lead to reduced overestimation of corrosion rates thereby improving pipeline integrity assessments in existing software packages. References Kermani, A. Morshed, Corrosion 59 (2003) 659–683.Nyborg, NACE 02233, Corrosion 2002, OnePetro 2002.Nyborg, NACE 10371, Corrosion 2010, OnePetro 2010.Nešić, M. Nordsveen, R. Nyborg, A. Stangeland, Corrosion 59 (2003) 489–497.Nordsveen, S. Nešić, R. Nyborg, A. Stangeland, Corrosion 59 (2003) 443–456.Nesic, K.-L.J. Lee, V. Ruzic, NACE 02237, Corrosion (2002).Sun, S. Nešić, Corrosion 64 (2008) 334-346.L. Johnson, M.B. Tomson, Paper No. 268, CORROSION/91, NACE International, 1991.Van Hunnik, Pots,Hendriksen NACE 96006, Corrosion(1996).Ingham, M. Ko, G. Kear, P. Kappen, N. Laycock, J. A. Kimpton, D. E. Williams, Corrosion Science, 52, 3052-3061 (2010).Ingham, M. Ko, N. Laycock, J. Burnell, P. Kappen, J. A. Kimpton,D. E. Williams, Corrosion Science, 56, 96-104 (2012).Ko, B. Ingham, N. Laycock,D.E. Williams, Corrosion Science, 90, 192-201 (2015).Ingham, M. Ko, N. Laycock, N. Kirby and D.E. Williams, Faraday Discussions, 180, 171-190 (2015).Hassan Sk, A.M. Abdullah, M. Ko, B. Ingham, N. Laycock, D.E. Williams, Corrosion Sci., 126, 26–36 (2017).Gong Luo, Yuan Yuan, De-Yu Li, Ning Li, Guo-Hui Yuan, Coatings 2022, 12(8), 1195.Bewick, H.R. Thirsk, M. Fleischmann, Trans. Faraday Soc. 58 (1962) (2200- &). Figure 1

A dynamic fracture model of the pipeline with girth weld considering welding residual stresses

AbstractThe fracture analysis of girth‐welded pipes is a vital link in the integrity assessment of oil and gas pipelines. However, the effect of welding residual stresses (WRS) on the load‐carrying capacity of the girth‐welded pipe with the crack remains unclear. In this study, based on the WRS simulation results verified by the full‐scale pipe welding experiment, a dynamic fracture finite element model could describe the fracture process of the pipe with the crack in the inner surface of the girth weld considering WRS was developed by the Gurson–Tvergaard–Needleman (GTN) damage model. Based on this fracture model, the fracture behavior of the pipe under tensile load in the presence of WRS was clarified, and the effect of WRS on the load‐carrying capacity was studied. The results indicated that the critical displacement and strain capacity of the pipeline decreased by 12.42% and 13.04% due to the negative action of the WRS.

Burst pressure of thin-walled pipes with arbitrarily orientated isolated surface corrosion defect

Accurate prediction of the burst pressure is essential for structural integrity assessment of pipelines. Current design codes and models for residual burst pressure assessment of pipelines with surface corrosion defects are only applicable to axially orientated defects. Theoretical and empirical models for the prediction of burst pressure of thin-walled pipes with pre-existing localised and arbitrarily oriented surface corrosion defect are proposed. The theoretical model is based on power-law hardening and J2 flow theory while the empirical model is derived from nonlinear finite element analysis results of the burst pressure. Burst pressure experiments are used to validate the model predictions. The theoretical and empirical models are found to be reliable in predicting the effect of defect width, length, and orientation on the burst pressure.

Data Modeling Techniques for Pipeline Integrity Assessment: A State-of-the-Art Survey

Pipelines are economical and efficient modes of transporting oil and gas. Pipelines will inevitably confront various risk factors through their lifespan, which could lead to defects. Defects in pipelines can compromise the integrity of the pipeline systems and may result in catastrophic accidents. Thus, it is vital to conduct the integrity assessment of pipelines so that the safe operation of the pipelines can be ensured. Up to the present, widely used approaches for pipeline integrity assessment include defect characterization, growth rate prediction, and failure pressure evaluation. Although the theoretical developments of pipeline integrity assessment methods have yielded fruitful achievements and significantly benefit the industry practices, there is still a lack of a systematic review covering the whole process from data collection to model establishment of the pipeline integrity assessment. Therefore, a comprehensive review is conducted in this paper on the pipeline defect integrity assessment from the data modeling perspective. Firstly, the description of data required to construct pipeline defect integrity assessment models is presented, where the required data for modeling can be obtained from pipeline inspection measurements, monitoring sensors, testing experiments, etc. Then, different modeling techniques applied to pipeline integrity assessment are reviewed, which are classified into physics-based models, data-driven models, and multi-model fusion. Also, the advantages and limitations of these techniques are discussed. Finally, the possibility of applying the existing models to a digital twin of pipeline defect is explored. This paper aims to provide a guideline for researchers to select optimal models according to data availability and research requirements, which can benefit the research community, as well as, the industry.

Integrity assessment of supercritical CO2 transport pipelines

With global warming, carbon capture and storage (CCS) technology is attracting increasing interest as a major technology for carbon peaking and carbon neutrality. Pipeline transportation, as one of the most cost-effective modes of transportation, has become the major transport method for large-scale long-distance supercritical carbon dioxide (CO2) transportation. Because corrosion is a major factor affecting pipeline operation, this paper aims to assess the integrity of supercritical CO2 pipelines. A finite element model of the pipeline with corrosion defects is created based on the corrosion morphology of the supercritical CO2 pipeline, and sensitivity analysis of the parameters affecting the burst pressure of the supercritical CO2 pipeline is carried out. Based on finite element analysis and burst pressure model of the intact pipeline, a nonlinear fitting method is used to establish the burst pressure equation of supercritical CO2 pipelines with corrosion defects. Compared to experimental data, the predictive equation has a high accuracy for the burst pressure of X60-X80 steel pipelines. It can serve as a reference for the design and integrity assessment of supercritical CO2 pipelines.

Effects of corrosion defect growth on submarine pipeline under operating pressure and axial displacement

Corrosion defect growth with time seriously threatens the safe operation of submarine pipelines and the study about its effects on strength degradation is essential for pipeline integrity assessment. In this work, a three-dimensional finite element model was developed to simulate the defect growth on pipeline exposed to sea mud environment based on multiphysical field coupling and deformed geometry. The deeper defect and larger operating pressure (OP) enhance local stress concentration and corrosion rate. The corrosion rate decreases first and then increases with the axial displacement (AD) of pipeline. The OP causes pipelines to corrode preferentially on the defect bottom while AD trends to form uniform corrosion on the total defect surface. There is an anti-synergistic effect between OP and AD on pipe thinning. A residual service life estimation method based on the unsteady multi physical field simulation was proposed for the submarine pipeline.

An effective computational tool with different levels of corroded pipeline integrity assessment

An effective computational tool with different levels of corroded pipeline integrity assessment

Study Details Management of Mercury for Production Facilities

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 31465, “Management of Mercury Offshore for Onshore Production Facilities,” by Mohamed Sopiee Saaibon, Zainab Kayat, and Fatimah A. Karim, Petronas. The paper has not been peer reviewed. Copyright 2022 Offshore Technology Conference. Reproduced by permission. The objective of the complete paper is to provide an approach to mitigating the adverse effects of mercury found in production fields. It includes an evaluation of treatment-facility requirements and suitable technologies for production fields and facilities. The evaluation covers assessment of pipeline integrity and managing unexpected increases in mercury content to ensure that mercury removal units (MRU) can treat gas within design specifications. Introduction Mercury is present as a contaminant in many oil and gas reservoirs; southeast Asia is a well-known for high concentrations of mercury. The presence of mercury poses a threat to the operator’s integrated upstream value chain. The primary concern is exposure of mercury to downstream aluminum heat exchangers for liquefied natural gas (LNG) production. The production lines and risers, although made of carbon steel, are exposed to integrity threats and, consequently, risk deferment of production. Initial Problem Concerns regarding mercury’s presence in hydrocarbon processing systems arose when substantial liquid mercury was detected at the operator’s downstream onshore LNG plant at levels three times beyond the design of its existing onshore MRU within the plant. Such high mercury concentration in feed gas was not expected because the wells had been operational for only 1 year. Immediate measures taken to handle these high quantities of mercury to protect the plant and its aluminum equipment included the following: - Reduction of feed-gas intake and production slowdown - Closing of wells with high mercury content - Mixing of that gas with low-mercury gas - Preparation for MRU adsorbent changeout No method exists to predict mercury production, and thus mitigation and equipment design—particularly that of an MRU across an integrated oil and gas production system—cannot be based on subsurface production data alone. A holistic approach to determine reservoir mercury concentrations from geology by on onsite sampling and mapping, from the wellhead to the production facility along the pipeline to the plant, was initiated.

A comparative study on constraint parameters for characterizing fracture toughness of X60 and X100 pipe steels

The fracture toughness resistance curve (e.g., J-R curve and crack tip opening displacement (CTOD) or δ-R curve) is important in facilitating strain-based design and integrity assessment of oil and gas pipelines, where influence of ground movement and presence of planar weld flaws must be accounted for. In the present study, duplicate single edge notched bend (SE(B)) and clamped single edge notched tension (SE(T)) specimens with two different initial crack lengths were tested at room temperature for longitudinally-oriented specimens machined from X60 and X100 pipe steels where the notch is along the through-thickness direction. The results showed the expected trends of higher fracture toughness resistance curves for shallow-cracked over deep-cracked specimen types and tension over bending loading modes. Eleven constraint parameters (i.e., QHRR, QSSY, QLM, QBM, A2, A2BM, h, Tz, Cp, Ap, Vp) were calculated based on 3-D finite element analysis for all tested SE(B) and SE(T) specimens. The results indicated that the shallow-cracked SE(B) specimens exhibit a constraint condition similar to the intrinsically low-constraint deep-cracked SE(T) specimens made of the X60 pipe steel. Among all of the constraint parameters, the Ap parameter based on the equivalent plastic strain isoline was found to correlate the best to the material fracture toughness for currently tested specimens. Furthermore, a linear master curve between various critical fracture toughness values and Ap parameter was obtained for all the tested specimens with different crack lengths, loading modes and pipe steels.

Novel XFEM variable strain damage model for predicting fracture in small-scale SENT and full-scale pipe tests

The tensile strain capacity (TSC) of a welded pipeline under bending and/or axial loads is critical to pipeline integrity assessment, and the fracture toughness expressed as a J-R curve plays a key role in predicting the TSC. The single edge notched tension (SENT) tests have been recommended for fracture toughness measurement of pipelines due to the similar low constraint geometries with the full-scale pipelines. The extended finite element method (XFEM) has been increasingly implemented in predicting the fracture of pipelines from small-scale to full-scale tests. However, current damage criteria based on a fixed critical stress or strain value have not been well calibrated, and limitations have been found. This paper develops a novel XFEM variable strain-based damage model by adopting a critical varying strain profile that accounts for the crack-tip constraint derived from a modified Mohr-Coulomb (MMC) fracture criterion. The novel damage criterion is calibrated by reproducing results like those measured from small-scale SENT tests of X100 pipe steel and full-scale pressurized tests of X52 circumferentially surface-cracked pipeline. Two sets of optimal damage parameters are calibrated specifically for X100 and X52. The initial crack in each model is simulated by cutting a notch in the XFEM domain resembling the original crack pre-machined on the specimen. Previously, researchers inserted a XFEM planar crack into the finite element mesh. The comparisons between results from notched models and planar cracked models reveal a distinct difference in the crack tip constraint and fracture resistance. Predictions from the novel variable damage criterion demonstrate advantages over those from the simple fixed damage criterion.

IMPROVING PREDICTION QUALITY WITH XGBOOST MODEL FOR BENDING CAPACITY OF X65 DEFECTED PIPE

There is a desire of a quality model predicting bending capacity of the defected pipe for pipeline integrity assessment. While the analytical model faces with the difficulty in modeling the local defect and corresponding local stress, the Finite Element method is a valuable alternative. A common approach for predicting interested variable is to scrape the result data and develop a data-driven model such as the classical linear regression, CART or XGBoost. Along with generating numerical database with FEM, this study illustrates the advance of XGBoost model compared with its counterparts in predicting the moment capacity of the defected X65 pipe.

Structural integrity assessment of hydrogen-mixed natural gas pipelines based on a new multi-parameter failure criterion

Due to non-pollution and high combustion efficiency, hydrogen energy is promising as a clean and renewable energy source to gradually replace fossil fuels and reduce carbon emissions. However, the low-cost, large-scale and long-distance transportation of hydrogen has always been a problem perplexing the development of hydrogen energy. Mixing hydrogen with natural gas and transporting it in natural gas pipeline is an effective solution to this problem. In this paper, the structural integrity of hydrogen-mixed natural gas pipelines under extreme loads are studied. Firstly, a mechanical model of hydrogen-mixed natural gas pipeline was established. Secondly, a new multi-parameter failure criterion containing the ratio of yield and tensile strength (Y/T) is provided. Thirdly, based on the multi-parameter failure criterion, a novel burst pressure equation of the hydrogen-mixed natural gas pipelines is presented. Fourthly, the accuracy of the burst pressure equation is verified by experiment and finite element method. The results show that the new multi-parameter failure criterion can be used to accurately predict the burst pressure of hydrogen-mixed natural gas pipelines with high accuracy. Our research has important theoretical significance and application value for the development of classical strength theory and the integrity assessment of mixed hydrogen natural gas pipeline.

Constraint effect on fracture toughness resistance curves of an X60 pipe steel

The fracture toughness resistance curve (e.g. J-R curve and crack tip opening displacement (CTOD) or δ-R curve) is important in facilitating strain-based design and integrity assessment of oil and gas pipelines, where influence of ground movements and presence of planar weld flaws must be accounted for. In this paper, duplicate single edge bend (SE(B)) and clamped single edge tension (SE(T)) specimens with two different initial crack sizes were prepared from an X60 pipe steel. The longitudinally-oriented specimens were notched in the through-thickness direction and experimentally tested at room temperature. In general, the results showed the expected trends of higher resistance curves for both shallow-cracked versus deeply-cracked specimen types and tension versus bending loading modes. Eleven constraint parameters (i.e. QHRR, QSSY, QLM, QBM, A2, A2BM, h, Tz, Cp, Ap, Vp) were calculated based on three-dimensional (3-D) finite element analyses (FEA) for various tested SE(B) and SE(T) specimens.The results and analysis indicated that the shallow-cracked SE(B) specimens exhibited a constraint condition similar to the intrinsically low-constraint deeply-cracked SE(T) specimens. Among all of the constraint parameters, the Ap parameter based on the normalized equivalent plastic strain contour was found to have the most promising trend in terms of correlating the material’s toughness to constraint level for currently tested specimens. Further on-going investigations are underway to extend the evaluation to resistance curves for specimens made from X100, X80 and X70 pipe steels to allow for the characterization of strain hardening effect, as well as the evaluation of their associated weld metals and heat affected zones (HAZs).

Influence of additional factors on the integrity of pipelines with small corrosion defects

The ASME and DNV criteria mainly assess large area defects on pressure pipelines. For small corrosion defects, the use of these approaches leads to unduly conservative results for the assessment of pipeline integrity. In the operation of piping systems, the most common cause of accidents is the synergy of multiple effects on the piping. This paper analyse the cases of small corrosion defects when additional bending acts together on a pressure pipeline. Through experimentally validated simulations, diagrams can be produced to assess the safety of pipeline operation: e.g. for nominal stress from internal pressure, corrosion defect size and length of the deflected pipeline, an increase in stress with increasing deflection size from the original pipeline centerline can be seen

Additively manufactured tensile ring-shaped specimens for pipeline material fracture examination - influence of geometry

In order to define a procedure for integrity assessment of pipelines and determining the fracture mechanics parameters, a new type of specimen with a sharp notch, Pipe Ring Notched Tension (PRNT) specimen, is tested. The aim of the study is to determine the influence of the specimen geometry (cylindrical shape, as well as number and length of stress concentrators) on parameters such as force, Crack Mouth Opening Displacement CMOD, Crack Tip Opening Displacement CTOD and J integral. The specimens were fabricated by an additive production method - selective laser sintering (SLS). EOS Formiga P100 machine is used, and the material is polyamide PA12. In addition to Pipe Ring Notched Tension specimens, Single Edge Notched Tension (SENT) specimens with identical cross section were also considered. All specimens were tested on a universal tensile testing machine. A tool specially designed to apply contact pressure to the inner walls in the tension direction was used, simulating the internal pressure. For determining the field of displacement and strain on the surface of the tested samples that occur during the loading, Aramis GOM 2M optical measurement system was used. Aramis is applied for determination of geometry fracture mechanics parameters: CMOD and CTOD (based on δ5 concept). In addition to the examination of fracture properties of additively manufactured PA12, the main topic of this work is the development of the non-standard testing procedure, which will be subsequently applied to the specimens cut from metallic or non-metallic pipes. As an important part of this procedure, the calculation of fracture parameters will be conducted based on the results presented here.

Offshore pipeline integrity assessment considering material and parametric uncertainty

This paper presents a methodology that integrates the semi-empirical corrosion models with probabilistic analysis to study steel structural failure behavior considering material and parametric uncertainties. The semi-empirical models are used to assess the asset’s susceptibility, system degradation rate, and defect growth over time under harsh corrosive environment. The developed model is translated into a limit state function in a probabilistic framework to define the asset’s safe operating envelope. The probabilistic framework is simulated considering the variations in the material properties of steel grades, corrosion response parameters, and types of susceptibility models. The variabilities in the ultimate tensile strength, operating pressure, and wall thickness exhibit the highest contributions to pipeline failure behavior in a harsh offshore environment. It is also observed that the failure probability of the pipeline increases with an increase in the coefficient of variation at the lower bound of failure, while it decreases at the upper bound of failure. The coefficient of variation for the tensile strength shows a 32.2% (the highest) impact on the limit state function performance as the year of exposure progresses. The proposed approach offers a systematic framework for an appropriate material selection and risk-based integrity management strategy for offshore structures, including pipelines.

Buckling analysis of subsea pipeline with idealized corrosion defects using homotopy analysis method

Comprehension on the bucking failure of corroded subsea pipelines is important. Those corrosion defects usually exhibit complex geometries and will complicate the buckling failure behavior of subsea pipeline under external pressure. In this paper, a semi-analytical approach named homotopy analysis method (HAM) is introduced to investigate the buckling failure of subsea pipeline with three idealized corrosion defects. The proposed solutions are proven to be capable of giving accurate and efficient predictions in comparison with finite element result as well as analytical results. Numerical examples indicate that corrosion shapes have pronounced effect on the buckling pressure as well as buckling mode of pipeline with severe corrosion defects and those cases should be carefully concerned in the structural integrity assessment of subsea pipelines.