Fatigue Life Of Pipeline Research Articles

Investigating the Effects of Crack Orientation and Defects on Pipeline Fatigue Life Through Finite Element Analysis

Abstract In response to the steady rise in global demand for energy resources such as gas and oil, there is a pressing need to enhance the efficiency and safety of pipeline transportation systems. These systems, integral for transferring vast amounts of energy, must operate under increasingly higher pressures and larger diameters without compromising reliability. This study focuses on utilizing finite element analysis (FEA) to investigate the influence of crack orientation and the presence of defects on the fatigue life of pipelines. By simulating internal pressure scenarios and examining various defect characteristics with the AFGROW software, this research applies damage tolerance principles to offer insights into the fatigue behavior of pipelines. The findings can be applied to extend the operational life and ensure the integrity of these critical infrastructures, thereby supporting the sustainable and safe transport of energy resources.

Optimal Transport Meshless Method Based Fatigue Life Calculation Method for Hydraulic Pipelines under Combined Excitation

The issue of fatigue in modern hydraulic pipelines is increasingly severe, and there remains a lack of effective prediction methods for pipeline fatigue life. In practical engineering, hydraulic pipelines are primarily subjected to random excitation and fluid excitation, representing a typical composite excitation. Most current research relies on solutions considering only single excitations, which leads to inaccuracies. To accurately calculate the fatigue life under composite excitation, this study incorporates resonance excitation and pulsation excitation into the optimal transport meshless method (OTM) within a strong fluid–structure coupling computational framework. Subsequently, by utilizing the hazard point method based on obtained stress data, an estimation of the service life for engine hydraulic lines can be determined. This work provides both practical guidance and theoretical insights for designing hydraulic lines in modern aircraft.

A novel correlation models for predicting stress intensity factor of semi-elliptical crack in welded pipelines under cyclic internal pressure based on Bézier base XIGA

Pipelines are strategic infrastructures that are used for energy transfer in the world. Cracks in the residual stress field are the common defects in welded pipelines. These defects with cyclic internal pressure cause crack growth and decrease the fatigue life of pipelines. In this study, a novel correlation model is proposed to predict the stress intensity factor (SIF) of the semi-elliptical crack front in welded steel pipeline subjected to cyclic internal pressure. For this purpose, the Bézier extraction base extended isogeometric method is applied for numerical analysis and preparing a database of results based on the thermo elastic-plastic equation. Taguchi standard L25 orthogonal array was used as the analysis design to create the simulations. New correlations were proposed for SIF prediction using the multivariate linear regression method. These correlations were obtained based on a parametric study that included three parameters. These parameters are dimensionless crack geometry (a/c), pipe geometry (D/t), and loading (P/Pb) or (σres/E). The R-Square (R2) values of the presented model for the welding residual stress and cyclic internal pressure were obtained as 0.989 and 0.992, respectively. The results of FEM analysis with similar conditions were compared to the results of XIGA and correlation models to validate the presented method. The maximum difference between them is approximately 3.71% for the cyclic internal pressure, and 2.94% for the welding residual stress. RMSD for the cyclic internal pressure model is 0.49, and for the welding residual stress model is 0.51. Therefore, the proposed correlation models have acceptable accuracy in predicting the SIF and fatigue crack propagation rate of the semi-elliptical crack in the steel pipes.

Fatigue condition assessment of subsea pipelines under vortex induced vibration and cyclical lateral displacement

ABSTRACT Subsea pipeline may suffer from vortex-induced vibration (VIV) and cyclical lateral displacement (CLD), which can result in fatigue failure of subsea pipeline. This paper presents a fatigue damage assessment of subsea pipelines under VIV and CLD. A finite element model of pipeline considering the pipe–soil coupling action is developed, and dynamic response of subsea pipeline under VIV and CLD is implemented to obtain time history of equivalent stress. The integrated fatigue damage of subsea pipeline under VIV and CLD is estimated using Palmgren–Miner linearly cumulative fatigue damage theory. The effect of pipe diameter, span length, pipe length and tidal period on fatigue damage of subsea pipelines under CLD is analyzed. A case study of a subsea pipeline in the strong tide area is performed. The results show the fatigue life of pipeline under VIV and CLD is 14.1 years, which is 2.3 years lower than the pipeline under VIV alone. The study can support more accurate estimation of fatigue life of subsea pipelines.

Fatigue Crack Propagation of Welded Steel Pipeline under Cyclic Internal Pressure by Bézier Extraction Based XIGA

Residual stress and cracks after welding are widespread mechanical defects in gas and oil pipelines. Internal pressures cause crack propagation and reduce the fatigue life of pipelines. This study developed a new procedure, based on an extended isogeometric analysis (XIGA) to investigate the effect of welding residual stress and cyclic internal pressure on the crack propagation rate and fatigue life. A new approach based on a thermo elastic-plastic equation is introduced for residual stress analysis. The fundamental aspect of this approach is determining the redistribution of residual stress while the crack is growing, and computing the stress intensity factor (SIF) in the residual stress field. Grid points around the crack surface and crack front are identified by the level set method. Then, discontinuous enrichment functions are added to the XIGA approximation. Thus, remeshing is not required in this method. The residual stress results calculated by the presented numerical method are in good agreement with the hole-drilling strain-gage method results. The interaction integral method was used to extract SIF. The superposition method was employed to consider the effect of welding residual stress and cyclic internal pressure on the SIF. Also, the modified Walker equation was used to calculate the fatigue life caused by cyclic internal pressure and welding residual stress. To validate the results, the same analysis was performed using the finite element method. The results of the presented method are in good agreement with finite element method (FEM) results.

Research on Development and Test Analysis of Full-Scale Fatigue Test System of X65 Submarine Pipeline

The fatigue performance of welded joints of submarine pipelines is directly related to the safety and economic benefits of welded structures. Considering the limitations of fatigue calculation, anti-fatigue design and small-scale fatigue test in the evaluation and analysis of pipeline fatigue life, this paper demonstrated the feasibility, scientificity and advancement of submarine pipeline full-scale fatigue test technology in engineering applications. Consequently, a full-scale fatigue test system and its test analysis technology applied for ZY-PFS2000 pipelines have been first developed in China, in which the effects of welding residual stress, stress concentration, initial welding defects, pipeline internal pressure shutdown and internal medium fluctuations on the fatigue life of full-scale pipelines were comprehensively taken into account. Through the full-scale fatigue test (four-point bending + internal pressure) of the X65 submarine pipeline, the fatigue cycles of different specifications of pipelines under different stress amplitudes were obtained. Moreover, the fatigue loading results were evaluated and analyzed in accordance with the international standard of BS 7608 and DNV C203. The research in this paper is conducive to accumulating full-scale fatigue performance data for submarine pipelines in China, not only offering a quantitative basis for the subsequent full-scale fatigue life evaluation and the safety operation cycle, but also providing a reference direction for the future development of submarine pipeline full-scale fatigue test technology.

Strain-based fatigue life analysis of pipelines with external defects under cyclic internal pressure

Gouge and dent are common mechanical defects in oil and gas pipelines. These defects with plastic strain cause stress concentration in the pipelines. Plastic strain is dependent on initial deformation and spring-back behavior of materials. Therefore, they reduce the fatigue life of pipelines. In this paper, the strain-base fatigue life analysis is investigated in pipelines with smooth dent or combination smooth dent and gouge defects under cyclic internal pressure. For this purpose, elastic-plastic multilinear isotropic hardening finite element simulation was used to investigate the effects of various factors, such as residual stress of dent, amplitude internal pressure, pipe geometry, gouge geometry, and smooth dent geometry on stress concentration factor (SCF). Finally, a new method is proposed for predicting the fatigue life of pipelines with uniform dent and uniform dent and gouge combination defects. The model is presented based on the Smith-Watson-Topper (SWT) criterion. A set of fatigue life test specimens with various pipe materials, size and geometry were prepared and tested. The specimens carried a smooth dent, as well as a combination of smooth dent and gouge defects, results of which were collected to validate those obtained based on the proposed model. The results of the predicted tests using the developed formula showed a good correlation to practical experiments.

Analysis of Safe Span Length and Fatigue Life of Submarine Pipelines

Owing to the complex environmental conditions, suspension could induce complicated forces on submarine pipelines and even cause vortex-induced vibration, resulting in fatigue damage of pipelines. Through aiming at the 28-inch submarine pipeline in the East China Sea, the pipeline was segmented according to the similarity, considering the factors of pipe assembly, typhoon, current, wave and seabed topography. The effects of span length on natural frequency in each section of submarine pipeline were analyzed by finite element model. The maximum safe span length allowed by each pipeline section was verified by fatigue cumulative damage theory, and the fatigue life of each pipeline section were predicted. The results showed that each order natural frequency of the pipeline decreased with the increase of span length. The calculated results of empirical formulas were much smaller than those of the FEM analysis. The increase of the gap between the suspended pipeline and the seabed was beneficial to enhance the fatigue life of the suspended pipeline.

Displacement Analysis of Plain Dent on Pipeline Based on FE Calculation

According to the report of the United States transportation department, mechanical damage is one of the most important reasons for the pipeline accident .The most typical form of mechanical damage is indentation. Dent defect is one of the important factors affecting pipeline fatigue life, and it will greatly reduce the fatigue life of the pipeline in service. Meanwhile the dent displacement will be changed with the operation pressure fluctuations of the in-service pipeline, resulting in a circular bending stress, which directly affect the pipeline fatigue life. For typical plain dent on pipeline, the finite element models are established under different circumstances. A large number of the calculation results are sorted and inducted. On this basis, the results are analyzed by univariate. Non-linear regression analysis was utilized to fit the results, some specific expressions of the relationship between the dented pipeline displacements and the wall thickness and diameter of pipeline, the dent depth and longitudinal dent length are obtained after much calculation and analog.

Applicability of Equivalent Constant Amplitude Loading for Assessing the Fatigue Life of Pipelines and Risers and the Influence of Compressive Stress Cycles

Fatigue life assessment of pipelines and risers is a complex process, involving various uncertainties. The selection of an appropriate fatigue model is important for establishing the inspection intervals and maintenance criteria. In offshore structures, the vortex-induced vibration (VIV) could cause severe fatigue damage in risers and pipelines, resulting in leakage or even catastrophic failure. The industry has customarily used simple fatigue models for fatigue life assessment of pipelines and risers (such as the Paris or Walker models); however, these models were developed based on constant amplitude loading scenarios. In contrast, VIV-induced stress-time history has a variable amplitude nature. The use of the simplified approach (which is inherently non conservative), has necessitated the implementation of large safety factors for fatigue design of pipelines and risers. Moreover, most of the experimental investigations conducted to date with the aim of characterizing the fatigue response of pipelines and risers have been done based on incorporation of constant amplitude loading (CAL) scenarios (which is unrealistic), or converting the variable amplitude loading (VAL) scenarios to an equivalent CAL. This study demonstrates that the use of such approaches would not be lead to accurate assessment of the fatigue response of risers subject to VIV-induced VAL. The experimental investigation performed in this study will also clarify the underlying reasons for the use of large safety factors by the industry when assessing the fatigue life of pipelines and risers. In addition, an experimental investigation was also conducted to highlight the influence of the compressive portion of VIV stress-time history on the fatigue life of such components. It is shown that the compressive stress cycles significantly influence the fatigue crack growth response of risers, and their presence should not be ignored.

FE Calculation and Analysis of Plain Dent Size Influence on Pipeline Displacement

According to the report of the United States transportation department, mechanical damage is one of the most important reasons for the pipeline accident .The most typical form of mechanical damage is indentation. Dent defect is one of the important factors affecting pipeline fatigue life, and it will greatly reduce the fatigue life of the pipeline in service. Meanwhile the dent displacement will be changed with the operation pressure fluctuations of the in-service pipeline, resulting in a circular bending stress, which directly affect the pipeline fatigue life. For typical plain dent on pipeline, the finite element models are established under different circumstances. A large number of the calculation results are sorted, inducted, drawed. On this basis, the results are analyzed by univariate. Non-linear regression analysis was utilized to fit the results by matlab, some specific expressions of the relationship between the dented pipeline displacements and the dent depth, the dent longitudinal length are obtained after much calculation and analog.

Peak Cycle Stress Analysis of the II Type Dent on Pipeline Based on FE Calculation

Dent is one of the important factors affecting pipeline fatigue life, and it will greatly reduce the fatigue life of the pipeline in service. And the peak cycle stress on the dented pipeline is the key parameter to calculate pipeline fatigue life. For typical II type dent in the pipeline, the finite element models are established under different circumstances. A large number of the calculation results are sorted, inducted, drew. On this basis, the results are analysed by univariate and multivariate. Non-linear regression analysis was utilized to fit the results by matlab, some specific expressions of the relationship between the dented pipeline peak cycle stresses and the dent depth, diameter and thickness of pipeline, and the dent longitudinal length are obtained after much calculation and analog.

Fatigue Life Calculation of the in-Service Dented Pipeline

Dent is one of the important factors affecting pipeline fatigue life, and it will greatly reduce the fatigue life of the pipeline in service. Based on a large number of foreign dented pipeline fatigue test results and fatigue life model, for the typical dent defect, using finite element method, various parameters are changed and finite element models are obtained under different conditions. According to many calculation results, a key ratio of peak period stress and pipeline pressure variation are obtained, which are substituted to the fatigue life model and the example are calculated.

Fatigue Crack Growth Behavior in Girth Weld of Natural Gas Transmission Pipelines

A clear understanding of fatigue properties for the pipeline steel and its weld is important to provide information for pipeline design during pipeline construction and predict pipeline fatigue life during pipeline operation. The materials used in this study are API 5L X65 pipeline steel generally used for natural gas transmission. This pipeline was welded by gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW) with V-groove configuration. The fatigue crack growth behaviors of pipeline steel and its girth weld according to crack growth directions and stress ratios were investigated over a wide range of stress intensities in laboratory air.

A Method for Fatigue Analysis of Piping Systems on Topsides of FPSO Structures

Pipelines located on the decks of FPSO systems are exposed to damage due to sea wave induced random loading. In this context, a methodology for estimating the fatigue life of fluid-conveying pipelines is presented. The pipeline is subjected to a random support motion that simulates the effect of the FPSO heaving. The equation of motion of the pipeline is derived by assuming small amplitude displacements, modeling the empty pipeline as a Bernoulli-Euler beam, and adopting the so-called “plug-flow” approximation for the fluid (Fluid-Structure Interactions Slender Structures and Axial Flow, Academic Press, San Diego, Vol. 1). Random vibration analysis is carried out by the Galerkin method selecting as basis functions the natural modes of a beam with the same boundary conditions as the pipeline. The discretized equations of motion are used in conjunction with linear random vibration theory to compute the stress spectrum for a generic section of the pipeline. For this purpose, the power spectrum of the acceleration at the deck level is determined by using the Response Amplitude Operator of the FPSO hull. Finally, the computed stress spectrum is used to estimate the pipeline fatigue life employing an appropriate S-N fatigue curve of the material. An illustrative example concerning a pipeline simply supported at both ends is included in the paper.