Strength Of Pipelines Research Articles

Considerations on the Evaluation and Management of Volumetric Surface Defects on Pipelines Using 3D Scanning and Finite Element Analysis

The paper proposes an original approach in the evaluation of the Volumetric Surface Defects (VSD) appearing in pipelines. The methodology we propose consists in performing, in the first phase, a superficial polishing (molding) of the VSD, such as the micro-cracks are eliminated. The second step implies 3D scanning of the molded VSD. The third step implies a comparative evaluation, using the Finite Element Analysis, of the pipeline with the polished VSD, and rectangular shaped machined VSDs. The comparative analysis will allow choosing the best scenario, both in terms of pipeline strength and economic efficiency (expressed in volume of the removed material).

Acquiring a low yield ratio well synchronized with enhanced strength of HSLA pipeline steels through adjusting multiple-phase microstructures

Intercritical treatments within the dual-phase (α+γ) region were applied on HSLA pipeline steels, for acquiring a low yield ratio (YR) well balanced with desirable strength. Intercritical cooling treatment (ICT), step cooling treatment (SCT) as well as direct cooling treatment (DCT) after full austenization were designed to obtain an optima multiphase microstructure. Effects of cooling rate in DCT routine and intercritical temperatures in ICT and SCT routines on microstructural evolution and corresponding mechanical properties were also investigated. Especially, the SCT treatment applied with an intercritical temperature of 750 °C produces a microstructure composited of “soft” coarse polygonal ferrite, and “hard” acicular bainite and lath martensite containing large amounts of dislocation tangles or networks generated by deformation. Such multiple phase constituents guarantee the high strength and remarkable ductility on deformation, meanwhile cleavages propagation is hindered by the high-angle boundaries of bainite and martensite sheaves, which leads to the lowest YR ~0.61 combined with highest tensile strength among all. In addition, by using the Swift equation to elucidate the relationship between the phase component and yield ratio, it is found that simply increasing the fraction of low-temperature transformed phases, like high-strength acicular bainite and lathed martensite, or the percentage of soft polygonal ferrite for good ductility, can hardly solve the problem how to achieve ultralow-YR pipeline steels balanced with enhanced strength. The present result proves that, through utilizing the proposed SCT heat treatment on pipeline steels, an ultralow yield ratio ~0.61 achieved is synchronized with a desirable strength, which efficiently overcomes the trade-off limit between the strength and yield ratio when applying conventional heat-treatment routines. The fact indicates that, rationally adjusting the content of multi-phase microstructure through optimizing the intercritical treatment conditions, can enable us of realizing the synchronous improvement of the YR and strength in HSLA pipeline steels for real engineering.

Strength Analysis of Buried Polyethylene Pipeline Under Ground Subsidence Considering Multivariate Influence

Abstract Due to the combined effects of natural and human factors, the ground subsidence is aggravated, which brings potential hazards to the normal operation of buried polyethylene (PE) pipelines. A variety of variables influences the safety of buried pipelines, while the existing research lacks detailed analysis on the issue. A finite element model of buried PE pipeline was developed to analyze how various factors affected the strength of PE pipeline under ground subsidence. Furthermore, the orthogonal test combined with the gray correlation degree was used to analyze the significance of each influencing factor. The results show that (1) the strain rate of the pipe is different at different ground subsidence rates, and the maximum equivalent stress of the pipe increases with the increase of the strain rate; (2) the maximum equivalent stress diminishes with the increasing wall thickness of the pipeline and the length of the transition section; and (3) the factor that has the most significant influence on the maximum equivalent stress of the pipeline is the settlement, followed by the strain rate and the length of the transition section. The internal pressure has the least influence on the maximum equivalent stress in the context of ground subsidence induced stresses.

Напряженно-деформированное состояние трубопровода под воздействием комбинированной нагрузки

Theoretical and experimental study of the stress-strain state of a pipeline under the influence of two types of loads was carried out: 1) bending force in vertical plane; 2) combined action of bending force in vertical plane and internal pressure. The experiments were performed on a pipe sample: steel grade Ст3, outside diameter 114 mm, wall thickness 4.5 mm, length 0.94 m. Hoop and longitudinal strains were measured in different areas of the pipe sample wall under the bending force in the vertical plane. To determine other parameters of the pipe stress-strain state the theories of thick-walled and thin-walled cylindrical shell, the Hooke’s law, the Zhuravsky–Vlasov formula for calculating the greatest shear stress in a circular tube, the principle of superposition were used. The distributions of the stress-strain state parameters (hoop, longitudinal, radial strains; hoop, longitudinal, shear stresses; von Mises stress) of the pipe sample wall around the perimeter of different pipe cross sections are found. It is revealed that hoop and shear stresses have a significant effect in the considered cases of loading. The values of hoop and shear stresses should be taken into account when calculating von Mises stress and assessing strength of the main pipeline according to the maximum-distortion-energy theory.

The Research of the Stress-Strain State of the Pipeline System, Taking into Account the Change in Spatial Location

In the work, the influence of changes in the geometry of the technological pipeline on the stress-strain state is studied, taking into account the complexity of the strapping of technological equipment and the parameters affecting the deformation. The authors analysed the stress-strain state of technological pipeline systems with a change in their spatial location, simulated 3 options for the spatial location of the pipeline system. The best option was selected to ensure its reliable operation, depending on the design parameters. In conclusion, the effect of hydraulic load on the VAT of the pipeline was investigated. The calculations were carried out according to the standard method in the PC program “Start” and using the finite element method in the PC SolidWorks. It is established that a change in the geometry of the pipeline system significantly affects its stress-strain state. On the example of changing the geometric arrangement of equipment piping shown the possibility of reducing VAT in the pipe bends by 19%. It is shown that when assessing the strength of technological pipelines with complex geometry and a significant number of elements, it is necessary to take into account hydraulic loads, which can increase the VAT in pipeline elements up to 21.7%.

The influence of grooving corrosion on the strength of pipelines

The aim of the present work is to develop a model of grooving corrosion of the pipeline using APM WinMachine program. Corrosion is caused by chemical reaction of the metal with the environment (outside) and the transported product (inside) undergoing on the boundary of the metal and the media. This issue is widely investigated in multiple national and foreign studies; however, it is still relevant nowadays. This paper presents results of calculation of the stress-strain state of two segments of the pipeline with the given parameters. Engineering calculations were carried out using the finite element method. The stress maps were built based on the calculated models of pipelines.

Методические особенности конечно-элементного исследования прочности трубопроводов водо-водяных энергетических реакторов с учётом локальных утонений от воздействия эрозионно-коррозионных процессов

The methodological features pertinent to strength analysis of the pipelines used in the secondary coolant circuit of nuclear power plants (NPPs) with taking into account local thinning caused by flow accelerated corrosion processes are addressed. The geometric features of pipelines are essential not only for assessing the flow accelerated corrosion intensity in metal, but also for the final strength assessment, in particular, in analyzing the strength of pipelines with walls containing local thinning spots. The pipeline structure lifetime prediction accuracy depends directly on the strength analysis of pipeline elements in which local thinning spots have occurred, especially if these elements themselves have a complex shape. Elbows, sockets, adapters (transitions), and shell rings can be referred to such elements. All of them are thin-walled structures having a complex shape. Software systems like ERCO and PELBOW are best suited for numerically studying them. These computer programs are based on the shell finite element method, using which the thickness at each finite element node can be specified either in the form of certain dependencies or (in some cases) manually. In accordance with the 3D finite element theory of thick-walled shells, a pipeline section can be approximated by a mesh of finite isoparametric 3D elements of a thick shell. The flow accelerated corrosion wear (FACW) depends essentially on the chemical composition of steels. Domestically produced Grade 10Kh9MFB steel is compared with foreign Grade P91 steel (that is close to the former in chemical composition and in performance characteristics), which has positively proven itself and widely applied for making NPP pipelines, with a view to recommend Grade 10Kh9MFB steel for use.

Underground pipeline stresses caused by damage near anchor mounting

The article considers the issues of underground pipeline strength, which are operated in geological or technogenic complication conditions (movements of indigenous soil in the tectonic fault zone, mutual displacements and rotations of rock blocks, etc.). The work aims at studying of a mobility limitation effect of a pipeline anchorage imposed on the stress state in the pipe wall in the site of a local damage foundation. The pipeline static was investigated in a geometrically linear formulation, modeling it with a tubular cross-section, and with a momentless cylindrical shell for straight issues. The interaction of the pipe with a dense base through soil backfill was described by the hypothesis of Winkler's elastic layer. The deformation of the anchored pipe caused by base local continuity disturbances was studied, which was modeled by the given jumps of longitudinal displacement and the block angle of rotation. This approach makes it possible to evaluate the strength of long underground communications not on the external load from the ground, which is usually unknown, but according to the observed parameters of riverside movements. The limiting state of the pipeline under the internal pressure of the transported product and under additional loading from kinematic perturbation was investigated by the energy theory of strength. The authors formulated boundary value problems for differential tensile-compression equations and torsion of a straight bar with discontinuous right-hand sides. On the basis of analytical solutions to the problems, the effect of normal separation crack damage, foundation blocks convergence and their turn around the axis of the pipe on the stress-strain state of the pipeline was studied. Plots of displacement distribution, angles of rotation and equivalent stresses of von Mises are constructed depending on the magnitude and direction of the mutual displacement and reversal of the riverside at different distances from the anchor to the base defect. It has been found that overlapping anchors in the form of anchorage leads to a significant increase in the equivalent stresses in the pipe. It has also been found that for pipes under internal pressure, the approximation of the base blocks is more dangerous than their divergence.

Burst strength analysis of pressurized steel pipelines with corrosion and gouge defects

The development of a defect on pressurized pipeline could easily threaten its structural integrity and if not managed on time could lead to burst failure. One of the safest ways to mitigate against this type of failures is to determine the residual strength of the damaged pipe section by estimating the safe operating pressure. Gouge and pit corrosion are two examples of regular defects found in steel pipeline walls that result in lower burst strength. Studying how defects impact the performance of steel pipelines could offer useful information on how to consider, treat and in a way prioritise their level of threat whenever presented with the decision. To achieve this, burst pressure analysis using 3D finite element analysis were carried out to simulate both cases of defect damage on pipe structure considering their different geometries. A parametric study carried out suggests both defect configurations reduce burst strength of pipelines, but the severity of damage depends on most importantly the length and depth of the defect as well as the mechanical and configuration of the pipeline. The simulated results suggests, the geometric representation presented by idealised pit corrosion profile in the pipeline longitudinal direction proves to have the greater influence on lowering burst strength. Thus, pit corrosion appears to be more damaging to the pipelines.

Integrated Mechanical Strength Tests of the Main Pipeline for Transporting Crude Oil and Refined Products

The state, problems, and prospects of conventional, unified and special laboratory, bench and full-scale tests to substantiate the systematic assessment of strength, durability, survivability, cold resistance, reliability, and safety of the key elements of pipeline transport of crude oil and refined products are considered. These tests correlate with the stages of the pipeline life cycles and basic and reference computational-experimental methods of determining the criterial characteristics of pipe steels, pipes and main pipelines with regard to domestic and foreign practices. The experimental basic mechanical characteristics obtained in standard static tensile tests (yield and strength limits, elastic moduli) are part of the basic static strength calculations of newly designed and operating pipelines. Standard hardness and impact elasticity tests are used to control the pipe steel quality. The results of standard tensile tests provide additional design information for the assessment of static strength with respect to the ductility and degree of steel hardening during elastoplastic deformation. Unified laboratory tests are meant for refining the pipeline strength with allowance for the stress state 3D effects, absolute sizes of the pipeline cross section, strain rate, anisotropy, cold resistance, corrosion, and the presence of welded joints. The assessment of pipe steel crack resistance and pipes according to the criteria of linear and nonlinear fracture mechanics with allowance for technological and operational defects holds a specific place in laboratory and bench testing. The experience in conducting these tests, accumulated in the Russian oil pipeline system is considered.

Application of the combined probabilisticstatistical methods of quantitative assessment of strength and durability of main pipelines with single and combined defects

Main gas and oil pipelines are the most important objects of the fuel and energy complex of the state. They are subjected to strict requirements for reliable and safe operation. Therefore, it is necessary to assess their strength (current strength) and durability (prediction strength) when operating main pipelines. The wall of the pipes of the existing main pipelines is subjected to various loads and influences. To prevent pipeline failure, strength and durability calculations are performed. The parameters of the load and mechanical resistance of the pipes are taken into account when calculating. Therefore, the "load — resistance" model is used to quantify the reliability of the main pipeline. This paper presents the main theoretical provisions of the methodology for assessing the strength and durability of trunk pipelines with single and combined defects in the framework of a combined probabilistic-statistical approach, and also an example of the use of the technique for a section of a trunk pipeline examined by an inline flaw detector.

Numerical Study of Seismic Vibrations of Closely Located Buried Large Structures

The paper presents an efficient numerical technique for 3D-modeling of seismic stability of large buried structures. This technique allows considering the subsoil-structure contact interaction, gravity field effects, the inhomogeneous structure of soil and the varieties location of the earthquake hypocenter. As part of this technique is substantiated sizing of the soil-structure computational domain and continuum model for hard and soft soil foundations describing. The numerical technique for determining the kinematic conditions at the lower boundary of the computational domain from the experimental accelerations at the soil surface is given, offered special non-reflecting waves boundary conditions. The methods described above and algorithms for seismic resistance solving have been implemented in certified software package “Dynamica-3”, parallelization of the algorithm has been held according to the spatial domain decomposition principle. The developed numerical technique allows correctly posing the problem of seismic vibrations of buried structure, reducing computing costs and increasing the efficiency of numerical studies of Earthquake Engineering. Through this, the multiple recalculation of the task with different action scenarios generated from experimental seismograms by probabilistic methods became technically possible. The results of these calculations allow reflecting the experience of many earthquakes, which increases reliability of the estimates. The paper presents the model calculations results of seismic stability of large-sized buried structure—the mutual vertical and horizontal displacement of soil and building walls—which can then be used to assess strength of adjacent underground pipelines. A number of numerical experiments on seismic vibrations of nearby large-sized structures have been carried out to assess the mutual influence of structures on their behavior in an earthquake. It is established that the influence of nearby large-sized objects on seismic vibrations of structures differs for different buildings.

Problems of simulating subsea pipeline condition on the arctic shelf under seismic impact

Introduction. The paper represents an approach to studying a model of interaction of a system ‘pipeline – soil’ under conditions of frost penetration and seismic impact. The given problem is connected with the reclamation of the shelf of the Russian sector of the Arctic. There is a feature of induced earthquakes connected with hydrocarbon production. These earthquakes occur in a few years after the beginning of field development and lead to the worst condition of the pipelines. The research aims to the development of a method for subsea pipeline strength assessment allowing for nonlinear properties of an elastic foundation under the seismic impact. Materials and methods. The research is based on mathematical models of structural strength assessment under seismic conditions in the Arctic. The results are empirically obtained from the safety assessment method for a subsea pipeline under the seismic impact. The work was performed by the procedure of the analysis of existing arctic offshore projects. Results. The paper develops suggestions on the analysis of subsea pipelines on a nonlinear elastic foundation under conditions of a seismic impact. The suggestions were submitted for consideration to the Russian Maritime Register of Shipping. Buried below the seabed, the subsea pipelines provide an efficient and safe mode of transporting energy resources. Issues of relations of the subsea pipelines with surrounding and frozen ground are considered, pipeline thermal operation modes and seismic risks resulting in damages to the pipelines are taken into account. Conclusions. Solving the problem of the subsea pipeline condition assessment under arctic conditions is of practical interest in developing energy resource transportation ways. Simulation of a subsea “hot” pipeline is considered allowing for the nonlinearity of elastic foundation properties and seismic impact.

Finite element modeling and experimental validation of rectangular pin buckle arrestors for offshore pipelines

Offshore pipelines used for transportation of hydrocarbons in the oil industry are subjected to external pressure, internal pressure to ensure flow, temperature and axial compression which causes buckling. Finite element modeling was performed, and experiments were conducted on pipeline models made of stainless steel of grade SS304. Present research work focuses on the improvement in buckling strength of offshore pipelines stiffened with rectangular pin buckle arrestor along the length of a pipeline using finite element analysis and their experimental validation. The results of finite element analysis showed that an offshore pipeline model without buckle arrestors has a buckling load of 4.69 kN whereas offshore pipeline stiffened with buckle arrestors of length 1000 mm along the length of a pipeline resulted in maximum buckling load of 14.075 kN. Accordingly, pipeline models were fabricated for conducting experiments. Comparison of finite element analysis results and experimental outcomes showed that the efficiency of buckle arrestor increased significantly by incorporating buckle arrestor along the length of a pipeline.

Analysis and design of inclined buckle arrestors for offshore pipeline

Present research work focuses on improving buckling strength of offshore pipelines by strengthening them with inclined stiffeners and inclined stiffeners with connecting rods. Eigenvalue buckling analysis was carried out using Finite Element Methods to find the buckling strength of the considered pipeline models. Seamless stainless steel pipe models of SS304 grade were considered for finite element analysis. The pipeline models were provided with inclined stiffeners whose angle of inclination varies from 100° to 176°. Connecting rods of different lengths is used to improve capacity of inclined stiffeners. In this paper, the effect of inclined stiffener configurations in improving the strength of offshore pipelines against buckling is presented. The finite element analysis results show that a pipeline strengthened with inclined stiffeners and inclined stiffeners with connecting rod showed improved buckling load carrying capacity.

Effective buckle arrestors for offshore pipelines

Offshore pipelines are subjected to various forces, depending on the subsea conditions such as temperature, axial forces, pressure (internal and external), bending, and earthquake forces. The response of offshore pipelines in with-standing these forces involves elastic response as well as inelastic response. Buckle arrestors are installed at regular intervals along the length of the pipeline to prevent buckling occurring due to a combination of forces. Present research work focuses on the improvement in buckling strength of offshore pipelines which are stiffened with 3 different types of buckle arrestors. Buckling experiments were conducted on pipeline models fabricated from seamless stainless steel pipes of grade SS304. The pipeline models stiffened with three different buckle arrestors configurations; longitudinal continuous stiffener, sinusoidal stiffener, and angular stiffener. The purpose of our research is to study the effectiveness of buckle arrestor configuration in improving resistance to buckling and to identify optimum buckle arrestor configurations and their applicability to offshore pipelines. The study was conducted by finite element simulation of buckle arrestors using ANSYS. The stainless steel pipe models of 1 m length, 16 mm outer diameter, 11.8 mm inner diameter, 2.1 mm thickness are considered for finite element analysis and for conducting experiments. The results obtained from finite element analysis and experiment results show that the efficiency of buckle arrestor found to be more in case of pipeline stiffened with longitudinal continuous buckle arrestors.

Probabilistic Aging Pipe Strength Estimation Using Multimodality Information Fusion

Accurate pipe material strength estimation is critical for the integrity and risk assessment of aging pipeline infrastructure systems. To predict the strength without interrupting the serviceability of the pipeline, inference methods are used through the relationship between the bulk yield tensile strength and surface material properties from nondestructive testing, such as chemical composition, microstructure images, and hardness testing. In order to make the best of information provided by multimodality surface measurements, Bayesian model averaging (BMA) method is used in this paper to integrate the information from various types of surface measurements for a more accurate bulk strength estimation. The models being considered are constructed by randomly combining the multimodality surface measurements and each case of linear combinations is included. The models considered are assessed by assigning different weights based on the posterior model probability. Markov Chain Monte Carlo sampling provides an effective way for numerically computing the marginal likelihoods, which are essential for obtaining the posterior model probabilities. To avoid the risk of overfitting, BMA is implemented to account for model uncertainty. The predictive performance of single model and BMA are compared by logarithmic scoring rule. The data collected from industry are used for demonstration and model predictive performance assessment. It is shown that the Bayesian model averaging approach can provide more reliable results in predicting the strength of the aging pipelines.

Развитие подходов к решению задач обеспечения прочности, ресурса и безопасности магистрального нефтепроводного транспорта

Ensuring the strength, service life and safety of the trunk pipelines is related to one of the most important areas of the fundamental scientific research and applied developments. Their results are of the undeniable importance for the design, construction and operation of the pipeline systems. In solving these problematic issues, for many decades the provisions were used related to the classical theories of the thin shells and strength theories, which formed the basis of the engineering calculations for determination of the pipeline parameters values. Occurrence of various damages and destructions during the process of operation of the oil pipelines and oil product pipelines, posed new challenges on improving their calibration calculations. Latest directive government decisions on the application of risk-oriented approaches during industrial safety analysis are the basis for the creation and use of the unified methodology for assessment and ensuring functioning of potentially hazardous industrial facilities (including trunk pipelines). Its development is carried out by joint efforts of academic, leading industry institutes and other scientific centers of Russia. Presented analysis of the complex problems of strength, service life and safety is based on the approaches implemented by OOO «Transneft» (head scientific subdivision of PAO «Transneft»).

FLOW CAPACITY OF MAIN OIL PIPELINES WITH PREDEFINED OIL PUMPING STATIONS LOCATION WITH PERIODICAL PARTIAL OIL DUMPING

Transportation of oil via main pipelines often requires the need for a permanent or periodic dumping of some part of the flow for further shipment of crude oil to oil refineries or filling stations. The application of such technology leads to a change in the operating mode of oil pumping stations and the oil transportation system in general. In case of emergency, an analogue of dumping is an oil leak from the pipeline in a case of violation of its integrity. Resetting a part of the flow is accompanied by a change in a liquid flow ahead of and behind the discharge point, which inevitably leads to a redistribution of pressures at the inlet and outlet of transitional petroleum pumping stations. Increasing of pressure at the output of the stations may lead to the violation of the pipeline strength; reducing of input shoring may cause cavitation operating modes of the equipment. Therefore, the study of the impact of discharges on the parameters of the operation of oil transportation systems in order to ensure their reliable, safe and economically efficient functioning is a relevant point of this area. For this purpose, based on the proposed calculated algorithms implemented in the software, the authors conducted the research on the impact of periodic oil discharges on the redistribution of hydraulic flows, energy losses at the bends, pressure at the inlet and outlet of oil pumping stations, as well as the volume of trunk oil pipelines capacity. The approbation of the proposed elaboration is carried out by defining the operational parameters of processing in functioning of oil and transport system «Druzhba» at the Mozyr-Tukholsky pass, which runs throughout the territory of Ukraine. Based on the analysis of the obtained results it was established that, depending on the volume of a discharge, the location of the limiting area, which limits the entry capacity of the trunk pipeline in general, might be changed. At the same time, the bend, ahead of which the part of oil is discharged, is not always limiting. Increasing the volume of a discharge leads to growing capacity of the pipeline at the area ahead of the point of discharge in the case when the limiting pipeline bend is behind the discharge point. If such a bend is located on the pipeline ahead of the discharge point, the increasing discharge does not affect the capacity of the initial area of the pipeline.

An application of the transfer matrix approach for a dynamic analysis of complex spatial pipelines

An effective method for the calculations of stress and residual strength of complex spatial pipelines at static and dynamic loading with taking into account the vibration of internal liquid and Puasson coupling is presented. It based on the well-known transfer matrix approach. The method utilizes the exact mechanical equations for the stress-strained state of straight beam with distributed mass, which connect unknown parameters of forces and displacements at the end of beam calculation element with the parameters at the beginning of the element. At a general level, the solution scheme and calculation models are the same for static and dynamic calculations, the only difference – are the equations. Two different methods are used to find natural vibration frequencies of the distributed mass system: straightforward (“brute force”) and quick, based on Williams-Wittrick frequencies counter. Within such counter a special procedure is developed for taking into account fluid vibration with consideration of volumetric balance condition at T-nozzles. The excellent accuracy of the method is demonstrated by the modeling of thin-walled, water filled pipe behavior after the rod impact. Two seismic analysis procedures are implemented on the base of developed method: standard response spectrum procedure and normal-mode summation procedure (“exact” dynamical), which uses accelerograms. These methods and procedures have been already implemented in calculation software for pipeline strength assessment with the possibility of building of arbitrary complexity models by the user-friendly, visual way. Their effectiveness is demonstrated by the seismic calculation for primary circuit pipings of Zaporizhia NPP.