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The present study proposes a new semi-empirical burst capacity model for corroded oil and gas pipelines under combined internal pressure and longitudinal compression. The proposed model evaluates the burst capacity of a corroded pipeline under combined loads as the burst capacity of the pipeline under internal pressure only, which is developed in a recently completed study, multiplied by a correction factor to account for the effect of the longitudinal compression. Extensive parametric elastoplastic finite element analyses (FEA) are carried out, the results of which are used as the basis to develop the correction factor as a function of the corrosion defect sizes and magnitude of the longitudinal compressive stress. The proposed model is validated by a large set of parametric FEA and full-scale burst tests reported in the literature and is shown to provide marked improvements over two existing models, the DNV and RPA-PLLC models, for corroded pipelines under combined loads.

In this paper, the stress compensation method (SCM) adopting an elastic-perfectly plastic (EPP) material is further extended to account for limited kinematic hardening (KH) material model based on the extended Melan's static shakedown theorem using a two-surface model defined by two hardening parameters, namely, the initial yield strength and the ultimate yield strength. Numerical analysis of a cylindrical pipe is performed to validate the outcomes of the extended SCM. The results agree well with ones from literature. Then the extended SCM is applied to the shakedown and limit analysis of KH piping elbows subjected to internal pressure and cyclic bending moments. Various loading combinations are investigated to generate the shakedown limit and the plastic limit load interaction curves. The effects of material hardening, elbow angle, and loading conditions on the shakedown limit and the plastic limit load interaction curves are presented and analyzed. The present method is incorporated in a commercial finite element simulation software and can be considered as a general computational tool for shakedown analysis of KH engineering structures. The obtained results provide a useful information for the structural design and integrity assessment of piping elbows.

This study presents a detailed assessment for the response of elbow elements in ABAQUS under internal pressure. Two main cases are considered: (1) a standalone 90 deg pipe bend, which was analyzed using both elastic and elasto-plastic material characterizations using shell and elbow elements; and (2) a geometrically nonlinear analysis with a materially elastic characterization of a piping system was conducting using shell, elbow, and pipe elements. Although the results show the capabilities of elbow elements to simulate the response of pipe bends in the elastic regime, the elements do not provide reliable predictions beyond the elastic range. Additionally, an assessment of the ASME B16.49 2017 elbow thickness equation and previously published stress estimate equations was carried out by comparisons with elbow and shell elements predictions.

This paper investigates ratcheting behavior of SS316 L thin-walled steel pipes subjected to cyclic internal pressure experimentally and numerically. Numerical simulations were performed using abaqus software, and nonlinear isotropic/kinematic hardening model. According to experimentations, it was found that the ratcheting strain is only significant in the hoop direction of a pipe subjected to cyclic internal pressure. The effects of pressure amplitude and mean pressure on ratcheting behavior of thin walled pipe in hoop direction were studied experimentally and numerically, and it was observed that increasing the pressure amplitude and mean pressure increased the percentage of ratcheting strain. Another important point about the results was the dominance of pressure amplitude on mean pressure. The results showed that at higher mean pressures the effect of pressure amplitude on increasing the percentage of ratcheting strain was greater. Finally, the experimental and numerical results were in good agreement.

Engineering solutions for crack-tip opening displacement (CTOD) and J-integral estimations for pipelines with a surface crack are proposed based on parametric finite element (FE) analyses for various geometries, material properties, and internal pressure conditions. Two kinds of CTOD definitions are considered in relation to strain-based estimation solutions for dealing with confusion regarding the definition of CTOD and to extend the applicability of tensile strain capacity (TSC) assessment. Moreover, influence functions of internal pressure are also suggested to take account of the effect of internal pressure on TSC. Using the proposed solutions, TSCs for cracked X65 and X70 pipes were assessed based on initiation and ductile instability. Curved wide plate tests were performed to obtain experimental TSCs, which were compared with those from the proposed solutions. Moreover, TSCs from the proposed solutions were also compared with those from other TSC-predicted models in order to assess their validity.

This paper carries out the limit and shakedown analysis of 45 deg piping elbows made up of elastic–perfectly plastic materials by means of the recently proposed stress compensation method (SCM). The elbows are subjected to steady internal pressure and cyclic in-plane closing, opening, and reversed bending moments. Different geometries of the piping elbows and various combinations of these applied loads are investigated to generate various plastic limit and shakedown limit load interaction curves. The plastic limit bending moment and plastic limit internal pressure calculated with the SCM are compared to those determined by the twice-elastic-slope approach. Full step-by-step (SBS) elastic–plastic incremental finite element analysis (FEA) is utilized to verify the structural cyclic responses on both sides of the curves obtained and further to confirm the correct shakedown limit loads and boundaries. It is shown that the SCM calculates the shakedown limit load accurately and possesses about 40 times the computation efficiency of the SBS elastic–plastic incremental method. The effects of the ratios of mean radius to wall thickness and bending radius to mean radius of the piping elbow as well as the loading conditions on the plastic limit and shakedown limit load interaction curves are presented. The results presented in this work give a comprehensive understanding of long-term response behaviors of the piping elbow subjected to cyclic loadings and provide some guidance for the design and integrity assessment of piping systems.

Pipelines are used to provide variety of services in modern community and have grown rapidly in past few decades due to growing socio-economic requirements. Most of the water mains are buried in shallow depths where the soil is partially saturated with significant spatial and temporal variations. Even though the behavior of buried pipes in such unsaturated soil condition is substantially different when compared to dry or fully saturated soil, the effect of soil saturations is overlooked in the current pipe stress prediction methods, leading to unrealistic predictions of the pipe stresses. In this study, three-dimensional (3D) finite element (FE) method was employed with advanced constitutive soil models to analyze the behavior of pipes buried in unsaturated soil condition. Having validated the FE model using reported field test data, an analytical model was proposed to predict the maximum stress in buried pipes considering soil saturation effect using a series of 3D FE analyses. Results from the FE analyses reveal that the maximum pipe stress can be significantly different when soil is in unsaturated condition when compared to dry condition. The proposed formula shows a good agreement with the field data and FE results, so that the expression can be used in the prediction of maximum pipe stress when they are buried under realistic (i.e., nondry) soil conditions.

The syringe in a subcutaneous auto-injector may be subjected to internal pressure transients due to the normal operation of the injection mechanism. These transients are similar to transients in fluid-filled pipelines observed during water hammer events. In this paper, the effect of an air gap in the syringe and a converging section is studied experimentally and numerically in a model system which consists of a fluid-filled metal tube that is impulsively loaded with a projectile to simulate the action of the auto-injector mechanism operation. The air between the buffer and the water results in a complex interaction between the projectile and the buffer. Also, there are tension waves inside the tube due to the presence of a free surface and the motion of the buffer, and this causes distributed cavitation which, in turn, gives rise to steepening of the pressure waves. The converging section can amplify the pressure waves if the wave front is sharp, and it can enhance the collapse of bubbles. Pressures as high as 50 MPa have been measured at the apex of the cone with impact velocities of 5.5 m/s.

Based on the detailed three-dimensional (3D) finite element (FE) limit analyses, the present study investigates the plastic limit loads of complex-cracked pipes with two-layered materials for determining maximum load-carrying capacity or critical crack length of pipes with two-layered materials. The complex cracks in pipes with two-layered materials consist of a partial through-wall crack and 360-deg circumferential surface crack in the inner side of pipe in the same plane in pipe, which could be developed in the preemptive weld overlay region on the dissimilar metal weld (DMW) of nuclear pipe. In terms of FE limit analyses for complex-cracked pipes with two-layered materials, total thickness of pipe, depth of 360-deg internal surface crack, length of partial through-wall crack and the effect of strength mismatch between two materials are systematically considered in the present study. As for loading conditions, axial tension, global bending moment, and internal pressure are employed in the present FE analyses, and then, the confidence of the present FE procedure is confirmed by comparing the FE results with the existing solutions for complex cracks in single material. The results of the present FE plastic limit loads are compared with the existing solutions for complex-cracked pipes with two-layered materials. Also, a simple approach using equivalent single material based on the weighted average concept instead of using the properties of two materials is suggested for predicting plastic limit loads of two-layered materials. The present results can be applied to leak-before-break (LBB) analyses of nuclear piping with weld overlay.

In recent years, the gas wells with high pressure, high temperature, and high H2S are increasing gradually, but the burst of casing and tubing in these wells will cause the gas channeling and overflow, and the gas with H2S flows up to surface, which causes huge damage. Although the API 5C3 and ISO 10400 standards have presented the prediction model of minimum internal pressure yield strength (IPYS) and burst strength for the casing and tubing in the process of strength design, the effect of temperature on the internal pressure strength is not considered completely. It is well known that it is extremely important to understand the failure mechanism of casing and tubing under the synergy of temperature and internal pressure. Hence, the full-scale internal pressure test is performed for N80 casing under temperature and internal pressure by adopting self-developed experimental equipment, by which the important mechanical parameters (such as minimum IPYS, burst strength, stress-hardening rate, and so on) of casing before and after hardening have been obtained. The impacts of temperature on the internal pressure strength are analyzed based on the comparison of test values with theoretical values given by API 5C3 and ISO 10400 standards. Finally, the failure mechanism and hardening characteristic of N80 casing have been clarified under the synergy of temperature and internal pressure. Research results can provide important references for internal pressure strength design of casing in deep well with high temperature.

Bellows structure is used to absorb the thermal expansion maintaining the boundary of the inside to outside, and it is applied to constitute the containment vessel (CV) boundary of the nuclear power plant. In this study, in order to develop the evaluation method of the ultimate strength of the bellows structure subject to internal pressure beyond the specified limit, the failure test and finite element analysis (FEA) of the bellows structure were performed. Several types of the bellows structure made of SUS304 were tested using pressurized water. The failure modes were demonstrated through the test of five and six specimens with six and five convolutions, respectively. Water leakage was caused by contact of the expanded convolution and the neighbor structure in the specimens with the shipping rod mounts. On the other hand, local failure as leakage in the deformation concentrated location and ductile failure as burst in the expanded convolution were observed in the specimen without shipping rod mounts. The maximum pressures in the test observed local and ductile failure were over ten times larger than the estimated values of the limited design pressure for in-plane instability by the EJMA standard. To simulate the buckling and deformation behavior during the test, the implicit and explicit FEA were performed. Because the inversion of the convolution accompanied by convolution contact observed in the test was too difficult a problem for implicit analysis, the maximum pressures in the step of solution converged were compared to the maximum pressures in the tests. On the other hand, explicit analysis enabled to simulate the complex deformation during the test, and the results were evaluated considering ductile failure to compare the test results.

Bolted connections inserting gaskets such as box-shape flange connections have been widely used in mechanical structures, nuclear and chemical industry, and so on. They are usually used under internal pressure. In designing the box-shape flange connections with gaskets under internal pressure, it is important to clarify the gasket stress distribution for evaluating the sealing performance of these connections. However, no research in which the sealing performance of these connections is examined under internal pressure has been carried out. Thus, the design for box-shape connection such as thickness of flange cover, number of bolts, gasket width, and so on is not clarified. In this paper, the contact gasket stresses of these connections under internal pressure are analyzed using the finite element method (FEM), taking into account a hysteresis in the stress–displacement curve of the gasket. And then, using the contact gasket stress distributions obtained from FE analysis and the relationship between gasket stress and leak rate obtained from a gasket sealing test (JIS B2490), a method for estimating an amount of leakage is examined. Leakage tests were also conducted to measure an amount of gas leakage using an actual box-shape flange connection with a gasket. The estimated results are in reasonable agreement with the experimental results. In addition, the effect of gasket width, flange cover thickness, and flange cover material is examined on the sealing performances of box-shape flange connections under internal pressure. The effects of the above factors are discussed on the sealing performance in designing box-shape flange connections.

The so-called “in-vessel retention (IVR)” is a severe accident management strategy, which is widely adopted in most advanced nuclear power plants. The IVR mitigation is assumed to be able to arrest the degraded melting core and maintain the structural integrity of reactor pressure vessel (RPV) within a prescribed hour. Essentially, the most dangerous thermal–mechanical loads can be specified as the combination of critical heat flux (CHF) and internal pressure. The CHF is the coolability limits of RPV submerged in water (∼150 °C) and heated internally (∼1327 °C), it results in a sudden transition of boiling crisis from nucleate to film boiling. Accordingly, from a structural integrity perspective, the RPV failure mechanisms span a wide range of structural behaviors, such as melt-through, creep damage, plastic deformation as well as thermal expansion. Furthermore, the geometric discontinuity of RPV created by the local material melting on the inside aggravates the stress concentration. In addition, the internal pressure effect that usually neglected in the traditional concept of IVR is found to be having a significant impact on the total damage evolution, as indicated in the Fukushima accident that a certain pressure (up to 8.0 MPa) still existed inside the RPV. This paper investigates structural behaviors of RPV with the effects of CHF and internal pressure. In achieving this goal, a continuum damage mechanics (CDM) based on the “ductility exhaustion” is adopted for the in-depth analysis.

Pipelines can be subjected to bending loads due to a variety of factors such as seismic activity, slope instability, or discontinuous permafrost. Experimental studies of Sen et al. [1–3] showed that pipelines can fail under bending loads due to pipe body tension side fracture which is a mostly overlooked failure mode in pipelines. Recent numerical studies on the structural behavior of cold bent pipes [4–6] also confirmed the likelihood of the pipe body tension side fracture. Furthermore, it was shown that both the material properties and the level of internal pressure can have a considerable effect on the failure mode of the pipe. In this current work, the parametric studies of internal pressure and material properties are extended to straight pipes using finite-element analysis. The differences in the structural behavior due to using stress–strain curves from test specimens in longitudinal and circumferential direction of the pipe are demonstrated. Using failure criteria based on the equivalent plastic strain, different failure modes corresponding to different levels of internal pressure and yield strength are shown on straight pipes.

Wide plate testing has been traditionally applied to evaluate the tensile strain capacity (TSC) of pipelines with girth weld flaws. These wide plate tests cannot incorporate the effect of internal pressure, however, numerical analysis in recent studies showed that the TSC is affected by the level of internal pressure inside the pipeline (Wang et al. 2007, "Strain Based Design of High Strength Pipelines," 17th International Offshore and Polar Engineering Conference (ISOPE), Lisbon, Portugal, Vol. 4, pp. 3186–3193). Moreover, most of the past studies focused on the effect of circumferential flaws on the TSC for pipelines of steel grade X65 or higher. The current Oil and Gas Pipeline System Code CSA Z662-11 provides equations to predict the TSC as a function of geometry and material properties of the pipelines. These equations were based on extensive studies on pipes having grades X65 or higher without considering the effect of internal pressure. This paper investigates the TSC for pipelines obtained using an experimental technique considering the effect of internal pressure and flaw size. Eight full-scale tests of X52 NPS 12 in. pipes with 6.91 mm wall thickness were conducted in order to investigate the effect of circumferential flaws close to a girth weld on the TSC for vintage pipelines subjected to eccentric tensile forces and internal pressure. The tensile strains along the pipe length and on the outer circumference of the pipe were measured using biaxial strain gauges and a digital image correlation (DIC) system. Postfailure macrofractography analysis was used to confirm the original size of the machined flaw and to identify areas of plastic deformation and brittle/ductile fracture surfaces. From the experimental and numerical results, the effect of internal pressure and flaw size on the TSC and the crack mouth opening displacement (CMOD) at failure were investigated and presented.

The article of record as published may be found at http://dx.doi.org/10.1115/1.4033772 A new mechanical device was developed to apply internal pressure loading to a cylindrical structure in order to determine its failure strength and failure mode under pressure loading. The device can be used for a uniaxial testing machine to apply internal pressure to a cylindrical structure. As a result, the developed device does not require any fluid to generate internal pressure loading. The device consists of two truncated conical shape of rams and eight pieces of the identical shape of wedges. The effectiveness of the device was assessed using both detailed finite element analyses of metallic cylinders as well as the analytical analysis. Then, a set of experimental tests were undertaken for aluminum alloy cylinders in order to evaluate experimental failure strength against the numerical and analytical results. Finally, composite cylinders made of glass-fiber or carbon-fiber woven fabrics were tested using the device, and the experimental results were compared to the predicted results using a multiscale analysis model. Those results agreed well with each other. Defense Threat Reduction Agency (DTRA)

This study presents an experimental testing regime conducted on filament wound composite pressure vessels (CPVs) made up of an asymmetric and unbalanced layup (chopped strand mat (CSM)/−82.7 deg/±54.3 deg) and subject to an internal pressure. Polyester reinforced with e-glass CSM and direct roving was used. The mechanical properties of the different lamina used in the test specimens were identified through a series of standardized tests. The evolution of strain and volume changes with respect to the applied pressure loading were recorded. The results also present a characterization of identifiable first-ply failure (FPF) loads based on strain evolution and volume changes, and monitors when ultimate failure occurs.

The main aim of the paper is to investigate and validate the behavior of a pipeline in the conditions of excavator elements external interference. A number of experimental tests were conducted. Four different cases were taken into account: two geometries of indenter with and without internal pressure. Discrete model of a tested pipe was developed and validated with the actual one. Simulations were performed using ls-dyna implicit code. The results obtained from the analyses were compared with the experimental tests and showed good accuracy in terms of force characteristics obtained in all simulated cases. Moreover, stress distribution in every case was also compared and discussed.

This article presents an approach to the minimum weight design for toroidal shells with strengthening component subject to internal pressure. The optimal shape is obtained by adjusting the geometry and wall thickness of the cross section associated with the thickness and position of the strengthening component. Constraints include first yield pressure, plastic pressures, plastic instability pressure, and internal volume of toroid. The weight saving can reach over 70% in some toroid configurations. The comparison of two optimization methods shows that differential evolution (DE) slightly outperforms particle swarm optimization (PSO) in the majority of investigated cases.

In the present paper, the closed-form expressions for the stress intensity factors (SIFs) and the elastic crack opening displacements (CODs) of complex-cracked pipes are derived based on the systematic three-dimensional (3D) elastic finite-element (FE) analyses. The loading conditions that are evaluated include global bending moment, axial tension, and internal pressure. In terms of geometries, the geometric variables affecting the SIFs and the elastic CODs of complex-cracked pipes, i.e., the crack angle of through-wall cracks (TWCs), the crack depth of fully circumferential, internal surface cracks in the inner surface of pipe, and the ratio of pipe mean radius to thickness, are systematically considered in the present FE analyses. The FE analysis procedure employed in the present study has been validated against the existing solutions for the circumferential TWC pipes. Using the present FE results, the shape factors of SIF and elastic COD for complex-cracked pipes are tabulated as a function of geometric variables. The results are applied for closed-form expressions of SIF and elastic COD when the pipe is subjected to simple loading conditions of bending, axial tension, or internal pressure. The proposed closed-form expressions can estimate SIF and elastic COD of complex-cracked pipes within maximum differences of 2.4% and 5.9% with FE results, respectively.

The elastic–brittle–plastic unified solutions of limit internal pressure are presented for double-layered combined thick-walled cylinder by the triple-shear unified strength criterion. The unified solutions obtained in this paper are especially versatile that can take into account of material brittle softening and intermediate principal stress quantitatively. The conventional existing elastic-perfectly plastic solutions, based on the Tresca yield criterion, Mises yield criterion, or twin-shear strength theory, can be categorized as special cases of the present unified solutions which can overcome their shortages. Parametric studies were carried out to evaluate the influences of various factors such as brittle softening parameter, strength theory parameter, cohesion, internal friction angle, and intermediate principal stress coefficient on the unified solutions. It is shown that proper choices of failure criterion, material behavior model, and brittle softening are significant in combined cylinder design. The new solutions can be naturally degraded to the existing formula and agree well with the results of the prevailing failure criteria. It is concluded that the unified solutions have an important practical value for the optimum design and engineering application of combined thick-walled cylinder.

Low cycle fatigue tests and finite element (FEM) analysis were conducted using 100A pipe bend specimens made of STPT410 carbon steel with and without local wall thinning local wall thinning was machined on the inside of the elbow and was prepared at extrados, crown, and intrados. The parameters of the wall thinning were same (the wall thinning ratio = 0.5, the wall thinning angle = 180 deg, and the wall thinning length = 100 mm) in the all test cases. The pipe bend specimens were subjected to the prescribed cyclic in-plane bending displacement with constant internal pressure of 0–12 MPa. Also, low cycle fatigue tests using sound pipe bend specimens were carried out for comparison. According to the test results, low cycle fatigue strength of wall thinned pipe bend specimens was not so different, regardless of location of wall thinning. Low cycle fatigue strength of the pipe bend specimens was beneath the best fit fatigue curve and its reason can be explained quantitatively by a proposed cumulated damage rule introducing ductility exhaustion considering multi-axial stress state. The validity of the new proposed cumulative damage rule was also confirmed by the another sample analysis using other reference data obtained by pre-overloaded in-plane cyclic bending tests.

Numerical procedures for calculation of reference stresses for pipelines with circumferential defects, based on simulation of global and local ultimate plastic states are proposed. There are some peculiarities of proposed procedures. First, the schematic analysis of the deformation process of pipe with surface defects is suggested, based on which two critical cases have been specified: global (the Net-Section-Collapse (NSC) criterion) and local, which are applicable for a very wide surface defect and for a sharp crack, respectively. The global solution also describes behaviour of through wall defects. Second, within the framework of the available Net-Section-Collapse criterion the unified algorithm for determination of reference stresses (global solution) for irregular-shaped circumferential defects under multifactor loading (internal pressure, axial force, bending moment) is proposed. Third, according to the local modelling, the restricted capability to resist plastic deformations is takes into account by inserting of artificial symmetrical defect. The unified procedure for calculation of reference stresses (local solution) for pipe with irregular-shaped circumferential defects under multifactor loading is developed. Forth, an analysis of proposed procedure by comparing with results of full-scale burst tests.

The present paper provides plastic limit load solutions for axial and circumferential through-wall cracked pipes based on detailed three-dimensional (3D) finite element (FE) limit analysis using elastic-perfectly plastic behavior. As a loading condition, axial tension, global bending moment, internal pressure, combined tension and bending, and combined internal pressure and bending are considered for circumferential through-wall cracked pipes, while only internal pressure is considered for axial through-wall cracked pipes. In particular, more emphasis is given for through-wall cracked pipes subject to combined loading. Comparisons with existing solutions show a large discrepancy in short through-wall crack (both axial and circumferential) for internal pressure. In the case of combined loading, the FE limit analyses results show the thickness effect on limit load solutions. Furthermore, the plastic limit load solution for circumferential through-wall cracked pipes under bending is applied to derive plastic η and γ factor of testing circumferential through-wall cracked pipes to estimate fracture toughness. Being based on detailed 3D FE limit analysis, the present solutions are believed to be meaningful for structural integrity assessment of through-wall cracked pipes.

Accurately predicting the burst strength is very important in the casing design for the oil and gas industry. In this paper, finite element analysis is performed for an infinitely long thick walled casing with geometrical imperfections subjected to internal pressure. A comparison with a series of full-scale experiments was conducted to verify the accuracy and reliability of the finite element analysis. Furthermore, three predictive equations were evaluated using the test data, and the Klever equation was concluded to give the most accurate prediction of burst strength. The finite element analysis was then extended to study the effects of major factors on the casing burst strength. Results showed that the initial eccentricity and material hardening parameter had important effects on the burst strength, while the effect of the initial ovality was small.

The paper examines the denting response of tubular members and pipes subjected to lateral (transverse) quasi-static loading, in the presence of internal pressure. Tubes are modeled with nonlinear shell finite elements, and the numerical results are in good agreement with available experimental data. Using the numerical tools, a parametric study is conducted to examine the effects of pressure level, as well as those of denting device size and pipe end conditions. It is mainly concluded that for a given denting displacement, the presence of internal pressure increases significantly the corresponding denting force. A simplified two-dimensional heuristic model is also adopted, which yields closed-form expressions for the denting force. The model equations are in fairly good agreement with the test results and illustrate pipe denting response in an elegant manner.© 2005 ASME

The temperature field and stress distribution for in-service welding of a flowing media, pressurized pipeline are simulated by use of the finite element method (FEM). In order to investigate the effect of flowing media on the temperature field of in-service welding, the results are compared with those of a no-flow case. It is found that the flowing media took away most of the heat effects from welding. The cooling is accelerated and the peak temperature of the inner surface of the pipe is much lower than that of the no-flow case. An experiment was performed to verify the accuracy of the numerical model. The presence of internal pressure, i.e., flowing media, in the pipeline significantly affects the postcooling axial stress distribution.

Within the current design codes for boilers, piping, and pressure vessels, there are many different equations for the thickness of a cylindrical section under internal pressure. A reassessment of these various formulations, using the original data, is described together with more recent developments in the state of the art. A single formula, which can be demonstrated to retain the same design margin in both the time-dependent and time-independent regimes, is shown to give the best correlation with the experimental data and is proposed for consideration for inclusion in the design codes.

Pressurized gas pipelines are subject to harmful effects from both the surrounding environments and the materials passing through them. Reliable assessment procedures, including fracture mechanics analyses, are required to maintain their integrity. Currently, integrity assessments are performed using conventional deterministic approaches, even though there are many uncertainties to hinder rational evaluations. Therefore, in this study, a probabilistic approach was considered for gas pipeline evaluations. The objectives are to estimate the failure probability of corroded pipelines in the gas and oil industries and to propose operating limit conditions for different types of loadings. To achieve these objectives, a probabilistic assessment program was developed using reliability index method and simulation techniques, and applied to estimate the failure probabilities of corroded API-5L-X52/X60 gas pipelines subjected to internal pressure, bending moment, and combined loading. The operating limit conditions as well as prototypal evaluation and sensitivity analysis results showed a promising applicability of the probabilistic integrity assessment program.

In this paper a simplified technique is presented to determine the shakedown limit load of a 90-degree pipe bend subjected to constant internal pressure and cyclic in-plane closing bending moment using the finite element method. The simplified technique determines the shakedown limit load without performing time consuming full elastic-plastic cyclic loading simulations or conventional iterative elastic techniques. Instead, the shakedown limit load is determined by performing two finite element analyses namely; an elastic analysis and an elastic-plastic analysis. By extracting the results of the two analyses, the shakedown limit load is determined through the calculation of the residual stresses developed in the pipe bend. In order to gain confidence in the simplified technique, the output shakedown limit moments are used to perform full elastic-plastic cyclic loading simulations to check for shakedown behavior of the pipe bend. The shakedown limit moments output by the simplified technique are used to generate the shakedown diagram of the pipe bend for a range of constant internal pressure magnitudes. The maximum moment carrying capacity (limit moment) the pipe bend can withstand and the elastic limit are also determined and imposed on the shakedown diagram of the pipe bend. In order to get acquainted with the simplified technique, it is applied beforehand to a bench mark shakedown problem namely, the Bree cylinder (Bree, J., 1967, J. Strain Anal., 3, pp. 226–238) problem. The Bree cylinder is subjected to constant internal pressure and cyclic high heat fluxes across its wall. The results of the simplified technique showed very good correlation with the analytically determined Bree diagram of the cylinder.

Fatigue and leak-before-break calculations for a pressure vessel require knowledge of the stress intensity factor at the deepest point of a straight- or curved-fronted (semi-elliptical) surface crack emanating from the bore of an internally pressurized, autofrettaged thick cylinder. A limited number of available solutions is curve fitted. The concept of a tube equivalent plate (TEP), which exhibits crack-constraint characteristics matching those of a thick cylinder, is developed, and the resulting equations are curve fitted. Ratios of the TEP stress intensity factor results are then used to interpolate between certain existing solutions. This provides wide-ranging solutions covering radius ratios from 1.8 to 3.0, autofrettage overstrain from 0 to 100% and crack shapes from straight fronted to semi-circular. The calculation procedure is described using worked examples.

This paper proposes a new failure assessment method for a steel pipe bend subjected to both a bending moment and internal pressure. Consistent with previous studies, it was shown that the maximum bending moment of a pipe bend subjected to a bending moment increases with the addition of internal pressure. However, it was experimentally confirmed that the addition of this internal pressure has the detrimental effect of significantly reducing the critical deformation (maximum bending angle) of the pipe bend. In addition, it was found that, subsequent to the application of a large deflection, cracks initiate at the most deformed part of the pipe bend during the process of unloading the internal pressure and then the applied load. Herein, the authors propose a practical failure assessment method which uses small-scale tests and nonlinear finite element (FE) analyses to predict the critical deformation and crack initiation position for a full-scale pipe bend. The failure criterion, which uses principal stress, mean stress, and equivalent plastic strain, was developed using small-scale tests. A failure assessment was conducted by comparing the predictions of this criterion with stress and strain histories obtained from FE analyses. Also, the authors’ failure criterion was compared with previous failure criteria, and the advantages/disadvantages discussed.

This paper proposes a method for determining endurance limits to leakage for fiberglass pipes under internal pressure using acoustic emission signals and static pressure tests. Results are presented from a series of cyclic internal pressure tests performed on fiberglass pipes fabricated according to ASME RTP-1 (1989) recommendations. The specimens were 8in.(20.32cm) internal diameter and 5ft(1.525m) long. The construction layup consisted of an internal corrosion barrier followed by several layers of continuous filament wound glass. A state of pure hoop stress was imposed via an internal pressure system that allowed free axial movement of the pipe. The purpose of the tests was to evaluate current design procedures and to assess the capabilities of acoustic emission (AE) monitoring to detect damage and to predict the leakage pressure for the pipes. Twenty-four specimens were tested to failure with AE monitoring. The results of these tests are presented, including data on the measured cyclic life of the specimens, comparisons to the static leakage capacity, and the effectiveness of AE in determining damage induced by cyclic loading.

With a multi-axial test machine, ratcheting was studied experimentally for pressurized low carbon steel elbows under reversed bending. The maximum ratcheting strain occurred mainly in the hoop direction at flanks. Hoop ratcheting strain was found at intrados for individual specimen. No ratcheting strain was found at the extrados for all tests. Ratcheting strain rate grew with increase of the bending loading level at the same internal pressure or with an increase of internal pressure at the same bending load. Ratcheting simulation was performed by EPFEA with ANSYS in which Ohno-Wang and Chen-Jiao-Kim kinematic hardening rules were applied by user programing. By comparing with the experimental data, it is found that predicted results by the Chen-Jiao-Kim model simulates reasonably. Ratcheting boundary was determined by C-TDF method with the Chen-Jiao-Kim model.

Due to the repeated firing of the gun, large uniform arrays of unequal-depth fatigue cracks develop from the inner surface of the barrel. The combined effect of pressure and autofrettage on the mode I stress intensity factor (SIF) distribution along the fronts of' these three-dimensional, semi-elliptical, surface cracks is herein -Studied. Crack depth inequality is modeled using the two-crack depth level model previously proposed. The analysis is performed via the finite element (FE) method employing singular elements along the crack front. The autofrettage residual stress field is simulated using an equivalent thermal load. The distribution of' the combined stress intensity factor due to pressurization and full autofrettage (K IN =K IP +K IA ), for numerous array configurations is evaluated, for a barrel of outer to inner radii ratio of R o /R i =2. These configurations bear n = n 1 + n 2 =8 to 128 cracks, a wide range of crack depth to wall thickness ratios, a 1 /t =0.01 to 0.40, and various crack depth to half-length ratios (ellipticities) a 1 /c 1 =0.30 to 1.50. The results for K IN distributions clearly indicate that the level of effect of crack depth inequality depends on all three parameters: crack number in the array, crack depth and crack ellipticity. Furthermore, the results indicate that adjacent unequal-depth cracks influence each other only within a limited range of their depths, i.e., the interaction range. The range of influence between adjacent cracks on the maximal SIF (K Nmax ) depends on crack ellipticity and is found to be inversely proportional to the crack density of the array. The results re-empfiasize the favorable effect the residual stress field has on the fracture endurance and the fatigue life of gun barrels bearing uniform arrays of three-dimensional unequal-depth cracks at their inner surface. This favorable effect is governed by the ratio of the gun's material yield stress to its internal pressure-ψ =σ 0 /p. The higher ψ is, the more effective autofrettage becomes.

The paper examines the nonlinear elastic-plastic response of internally pressurized 90 deg pipe elbows under in-plane and out-of-plane bending. Nonlinear shell elements from a general-purpose finite element program are employed to model the inelastic response of steel elbows and the adjacent straight parts. The numerical results are successfully compared with real-scale experimental measurements. The paper also presents a parametric study, aimed at investigating the effects of diameter-to-thickness ratio and moderate pressure levels on the ultimate bending capacity of 90 deg elbows, focusing on the failure mode (local buckling or cross-sectional flattening) and the maximum bending moment. Special attention is given to the response of 90 deg elbows under out-of-plane bending moments.

Two intersecting cylindrical shells subjected to internal pressure and external moment are of common occurrence in pressure vessel and piping industry. The highest stress intensity occurring in the vicinity of junction, which is a complex space curve when the diameter ratio d/D increases. As the new process of theoretical solution and design criteria research developed by the authors, the stress analysis based on the theory of thin shell is carried out for cylindrical shells with normally intersecting nozzles subjected to three kinds of external branch pipe moments. The thin shell theoretical solution for the main shell with cutout, on which a moment is applied, is obtained by superposing a particular solution on the homogeneous solution. The double trigonometric series solution of cylindrical shell subjected to arbitrary distributed normal and tangential forces based on Timoshenko equation is used for the particular solution and the Xue et al.’s solution, for the homogeneous solution based on the modified Morley equation instead of the Donnell shallow shell equation. The displacement function solution for the nozzle with a nonplanar end is obtained on the basis of the Goldenveizer equation instead of Timoshenko’s. The presented results are in good agreement with those obtained by experiments and by three-dimensional finite element method. The present analytical results are in good agreement with WRC Bulletin 297 when d/D is small. The theoretical solution can be applied to d/D ≤ 0.8, λ = d/DT ≤ 8 and d/D ≤ t/T ≤ 2 successfully.Copyright © 2004 by ASME

Tests on two internally pressurized toroidal shells are described in this paper. These were laboratory scale models manufactured by welding 90°, 316L steel elbows. The outside diameter of the toroids was about 310.0 mm, radius of the tube was about 41.0 mm, and the wall thickness was about 3.0 mm. Comparison of experimental and numerical plastic loads, based on pressure versus volume change plots, is given. The magnitude of experimentally derived plastic loads was about 16.0 MPa which was close to the numerical predictions. Both shells failed by developing cracks in welds, at nozzles, at pressure of about 33.0 MPa.

The purpose of this paper is to provide research results for a cylindrical vessel—30 deg lateral intersection with diameter ratio d/D⩾0.5 under increasing internal pressure loading. The results include those from tests as well as from an inelastic stress analysis. The experimentally determined limit load is compared with that from the finite element analysis. The stress concentration factor, the spread of the plastic area, and the behavior of the deformation are provided. Also, a burst test of the model vessel is carried out to provide some data to justify the existing design method and forms a basis for developing an advanced design guideline for cylindrical vessel—lateral intersection under internal pressure loading.

The objective of the study is to determine the effect of diameter/thickness (D/T) ratio on the interaction of axial force, bending moment, torsion and internal pressure in plain pipes. The Tresca and von Mises criteria are used to determine the first yield behavior of pipes when subjected to combined loads. The results show that for certain load combinations, the load interaction behavior is affected by D/T ratio and some load interaction relations change with a load dominance. The general trend is an increase in effective stress as D/T is increased. Most design codes show slightly conservative pipe design.

This paper discusses the stability of underground pipelines with preformed vertical bends buried in sandy soil. More specifically, the minimum cover height required to prevent the pipe from bowing under the action of forces due to temperature change and internal pressure is estimated. The variables considered include the pipe and soil materials, diameter, thickness, overburden height, bend radius, bend angle, internal pressure, fluid specific weight, and temperature variation. A comprehensive three-dimensional finite element analysis is carried out. The results are extracted from the output obtained. These results are put in a database which is used to develop general regression models to determine the relationships among the different variables. Different buckling modes are also considered. All of these results and models are entered into a computer software program for ready access.

This paper presents numerical results obtained using Finite Element Analysis (FEA) in studying large diameter welded neck steel flanges under different loading conditions. Obtained FEA results show the effect of the clamping pressure, internal pressure, axial end load, temperature effect, gasket elasticity modulus on the contact pressure between the gasket and the steel flange. As expected clamping pressure is a determinate factor for the sealing condition. Gasket material is another primary factor in designing flanged joints.

A formulation using the finite element method is presented in this paper to analyze stresses and displacements of underground pipelines with initial imperfections. The formulation includes both thermal expansion of the pipeline and internal pressure. The method is based on large deformation beam theory with the finite element formulation based on Euler-Bernoulli beam elements of constant cross-section. The pipe-soil interaction is modeled as a nonlinear elastic foundation in the problem formulation. The resulting nonlinear finite element model with appropriate boundary conditions is solved using full Newton-Raphson as the iterative procedure. Numerical examples are provided to show the application of the methodology and to demonstrate the effect of the initial imperfections in the stress distribution of a buried pipe. The results show that initial imperfections have a considerable influence on the stress distribution of buried pipelines, leading in some cases to stress levels above the allowable limit established by the design codes. The results also help to identify the critical temperature at which buckling of the buried pipe might occur.

Failure assessment of a pipe with local wall thinning draws increasing attention in the nuclear power plant industry. Although many guidelines have been developed and are used for assessing the integrity of a wall-thinned pipeline, most of these guidelines consider only pressure loading and thus neglect bending loading. As most pipelines in nuclear power plants are subjected to internal pressure and bending moment, an assessment procedure for locally wall-thinned pipeline subjected to combined loading is urgently needed. In this paper, three-dimensional finite element (FE) analyses are carried out to simulate full-scale pipe tests conducted for various shapes of wall-thinned area under internal pressure and bending moment. Maximum moments based on ultimate tensile stress were obtained from FE results to predict the failure of the pipe. These results are compared with test results, showing good agreement. Additional finite element analyses are then performed to investigate the effect of key parameters, such as wall-thinned depth, wall-thinned angle and wall-thinned length, on maximum moment. Moreover, the effect of internal pressure on maximum moment was investigated. Change of internal pressure did not show significant effect on the maximum moment.

A three-dimensional FEM computer program was developed to establish the stress distributions and SCFs in thick walled cylinders with flush and nonprotruding plain cross bores under internal pressure. The displacement formulation and eight-noded brick isoparametric elements were used. The Frontal solution technique was used due to the limited computing facilities. In the far field, the FEM stresses and displacements were in good agreement with the through thickness analytical values. The variation of SCF with d was established for various thickness ratios. For k>1.25, the maximum hoop stress occurred away from the crotch corner when d⩽0.2. For k=1.25, the maximum hoop stress occurred away from the crotch corner when d⩽0.15. For k⩾1.75, d was found to be a geometrical constant equal to 0.2 where the k values have a SCF of 2.734. For k

An investigation of the shakedown behavior of axisymmetric nozzles under internal pressure is presented. The analysis is based on elastic-plastic finite element analysis and Melan’s lower bound shakedown theorem. Calculated shakedown pressures are compared with values from the literature and with the ASME Boiler and Pressure Vessel Code Section VIII Division 2 primary plus secondary stress limits. Results obtained by the lower bound method are also verified by cyclic elastic-plastic finite element analysis.