Combined Internal Pressure Research Articles

Numerical and Experimental Study on Balanced Performance and Axial Stiffness of Fiber-Reinforced Rubber Pipe.

Balanced fiber-reinforced rubber (FRR) pipes not only provide displacement compensation when transporting pressurized media but also prevent additional forces and displacements from being exerted on the connected pipeline system. Investigating the balanced performance of FRR pipes and the axial stiffness of balanced pipes is crucial for optimizing pipeline design and improving the reliability of pipeline systems. This paper develops a numerical model of FRR pipes that considers the nonlinearity of the rubber material and the interaction between the rubber matrix and fiber-reinforced layers. Using this model, the balanced performance of the pipe is calculated, and its axial stiffness under combined internal pressure and axial load is analyzed. Numerical results are compared with experimental data for validation. The results indicate that the pipe's balance is achieved through the combined effects of the elongation and rotation of the reinforcing fibers and the deformation of the rubber matrix, highlighting the significant impact of the rubber matrix on the mechanical performance of the FRR pipe. Furthermore, the pipe's balanced performance and axial stiffness are highly sensitive to the winding angle of reinforcing fibers. The proposed numerical model fills the gap in using numerical methods to evaluate the balanced performance of FRR pipes and provides valuable insights for their design and optimization.

Assessment of Buckling Failure in Oil Storage Tanks: Finite Element Simulation of Combined Internal and External Pressure Scenarios

Investigating the structural behaviour and buckling susceptibility of cylindrical oil storage tanks is crucial for ensuring their safe and reliable operation. In this study, the structural behaviour and buckling susceptibility of closed roof-top cylindrical oil storage tanks under combined internal and external pressure scenarios were investigated using the finite element analysis (FEA) technique. By utilizing the FEA technique, the combined effect of wind-induced pressure of 250 Pa, applied on the outer surface of the tank and internal pressure of 0.5 MPa, applied on the outer surface of the storage was analysed. The result reveals significant stress concentrations and deformation patterns, particularly on the windward side of the tank, thus, emphasizing the susceptibility of the storage tank to buckling under the specified operating conditions for both the filled and half-filled tank; with internal pressure emerging as the primary contributor to mechanical strain and deformation experienced in the tank, while the wind load plays a secondary but significant role in the deformation of the tank. The fe-safe predicted useful life shows that under the specified operating conditions, the filled storage tank will survive 1 429 hours (2 months) while the half-filled tank will survive 3 551 hours (5 months) before failure due to buckling. Thus, the useful life estimation results show the importance of varying oil levels and operating conditions in the structural assessments of storage tanks.

Condition assessment of underground corroded pipelines subject to hydrogen damage and combined internal pressure and axial compression

In this work, a 3D finite element (FE) based model was developed to assess the condition of an underground hydrogen transmission pipeline containing a corrosion defect under combined internal pressure and soil movement-induced axial compression. The use of mechanical properties of X100 pipeline steel under different hydrogen charging time models the degree of hydrogen damage in pipelines. Parameter effects, i.e., axial compressive stress, hydrogen damage, defect geometries, and pipeline diameter-to-thickness ratio, were determined. The results demonstrated that the synergistic effect of axial compression, internal pressure, corrosion, and hydrogen damage can lead to a significant decrease in the failure pressure of pipelines. The failure pressure decreased with the wall thickness reduction and increased hydrogen damage, axial compressive stress, defect length, defect depth, and pipe diameter. The competitive effect was observed between the degree of metal loss and hydrogen damage in determining the burst capacity of pipelines. In situations where the pipeline integrity was severely compromised, the failure pressure exhibited minimal reduction despite the increasing severity of hydrogen damage. The stress distribution at the defect zone was influenced by axial compressive stress but remained unaffected by hydrogen damage under normal operating conditions (i.e., an internal pressure of 10 MPa). This work is expected to help operators understand the applicability of elder and in-service pipelines for hydrogen transmission.

Vibration Analysis of Curved Panel Subjected to Internal Pressure and Axial Compression

This paper discusses the change of the natural frequencies and the corresponding mode shapes of an isotropic metallic curved panel subjected to combined internal pressure and axial compression. Tensor calculus is employed to devise the differential operator matrices of the geometrical relation in an orthogonal curvilinear reference system. In the framework of the Carrera unified formulation and by applying the finite element method, the principle of virtual work is used to describe the free vibration of a cylindrical shell subjected to progressive external loading conditions as a virtual procedure of the experimental test vibration correlation technique. Finally, numerical examples are provided, and the effects of the material and geometric characteristics are evaluated. The results show that crossing and veering phenomena between natural frequencies appear when varying the curvature of the panel and the value of the inner pressure, and those effects have to be taken into account for a proper design of this type of structure.

Implementation of multiscale mechanisms in finite element analysis of active composite structures

Interrogation of composite structures for inherent damage is investigated implementing three-tier analysis scheme. The analysis starts at the structure level where a general-purpose Finite Element code ABAQUS is employed to obtain the stress field in the second level of analysis that is the composite laminate. A special material routine is prepared to propagate the local fields to the individual plies and hence to the third level of analysis which is the microstructure modelling of the composite. Through the third level of analysis, interface damage between fiber and matrix is checked implementing a certain failure criteria. The interaction between the different length scales; that are, structure, macro, and micro scales, is implemented using the non-mechanical strains caused by damage. Embedment of electrically active fibers in the laminate serves as a tool to interrogate the structure for inherent damage through the electric displacement generated due to the electro-mechanical coupling. To verify the developed multi-scale model, a comparison with the experimental results of a tube problem under combined internal pressure and axial load is presented. The results show good agreement in both the undamaged and damaged state. As an application, a plate with a hole under biaxial load is solved. The output includes not only the structure global behavior during damage but also detailed information about the location of damage within the structure, the plies that exhibit damage, type of damage and the fiber/matrix debonded length. Comparison between the electric displacement of the active fibers in the undamaged and damaged states is presented as well.

Limit Load Solution for Thin-Walled Cylinder with Circumferential Crack under Combined Internal Pressure, Axial Force, Bending Moment and Torsion Moment

T his research aims to establish the limit load solution for thin-walled cylinder with circumferential crack under combined internal pressure, axial force, bending moment and torsion moment. The solution is derived based on the net-section collapse principle and the von Mises yield criterion. The material considered in this work is assumed to be elastic-perfectly plastic. The solutions obtained from this work are compared with the results from the finite element models. The comparison shows that the equations established from NSC analysis provide acceptable results for the case of cracked cylinder under combined axial force and bending moment. For the case of cylinder subjected to internal pressure or torsional moment, however, these equations can be used to predict the limit load only if np ≤ 0.40 and nT ≤ 0.6 . This is because when the effects of internal pressure or torsional moment are included, the distribution of stresses on the crack plane at the yielding does not correspond to the NSC principal.

Directional dependence of critical axial strain in X65 pipeline steel subject to combined internal pressure and bending loading

In this exploratory study, a X65 seam weld pipeline steel is investigated by considering the effect of anisotropy on plasticity and fracture responses of biaxially (combined bending and internal hydrostatic pressure) loaded pipes having different crack lengths, diameter sizes and internal pressure levels. The results indicate that directional dependency is strong for pipes with relatively large diameters, deep cracks and loaded at high internal pressure. However, critical strain seems to be slightly influenced by anisotropy when the pipe diameter-to-thickness ratio decreases. That is, smaller pipes are quite insensitive to its effect irrespective of crack depth, crack length and internal pressure level.

Interaction Assessment of Diagonally Spaced Identical Corrosion Defects and Fully Aligned Unequal-Sized Corrosion Defects Under Combined Loads

Abstract In this study, the interaction effects of closely spaced corrosion defects on the burst capacity of oil and gas pipelines under combined internal pressure and longitudinal compression are investigated by using parametric three-dimensional elasto-plastic finite element analyses. Full-scale burst tests reported in the literature are used to validate the finite element model. It is observed that the interaction effects of diagonally spaced defects on the burst capacity are strongly related to the overlapping portion of the defect width or circumferential spacing between the two defects. The analysis results indicate that the strongest interaction between diagonally spaced defects under combined loads occurs if the defects have zero circumferential separation. The interaction weakens as the defects are more and more overlapped or separated circumferentially. It is also observed that the interaction effect associated with longitudinally or circumferentially aligned, unequal-sized corrosion defects is negligible under the internal pressure only or combined loads.

Consideration of Fatigue Evaluation of SUS316 and SUS430 Steels under Multiaxial Stresses Combined Internal Pressure and Axial Load using Hollow Cylinder Specimen

This study focuses on discussing fatigue life evaluation method of SUS316 and SUS430 steels under wide ranged proportional multiaxial loading conditions. Fatigue tests under 7 types of loading path which are combined axial stress and inner pressure were carried out using hollow cylinder specimens at room temperature. It has been considered that the proportional loading does not cause additional hardening, however this study shows that the complex loading path causes additional hardening without principal direction change of stress and strain in a cycle. The Itoh-Sakane model which evaluates loading and lives under non-proportional multiaxial fatigue by only considering the maximum and the minimum principal stress or strain and their principal directions. However, this model is also needed to consider middle principal stress because change of the middle principal stress influence fatigue life under current loading paths. Therefore, the Itoh-Sakane model was modified to evaluation fatigue life of SUS316 and SUS430 under combined internal pressure and axial loading conditions.

A Burst Capacity Model for Corroded Pipelines Subjected to Combined Internal Pressure and Longitudinal Compression

Abstract 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.

Assessment of the interaction of corrosion defects on steel pipelines under combined internal pressure and longitudinal compression using finite element analysis

Extensive parametric three-dimensional elasto-plastic finite element analyses are carried out to investigate the interaction effect on the burst capacity of oil and gas pipelines containing closely-spaced corrosion defects under combined internal pressure and load-controlled longitudinal compression. The analysis considers two identical, semi-ellipsoidal-shaped corrosion defects aligned circumferentially or longitudinally on the pipeline. The analysis results reveal that the interaction between circumferentially-aligned defects under combined loads is marked: the burst capacity corresponding to the two-defect case can be lower than that corresponding to the single-defect case by as much as 18% as a result of the enhanced bulging of the defect region due to the presence of the longitudinal compression. This is in direct contrast to the observation that the interaction effect is marginal for circumferentially-aligned defects subjected to internal pressure only. On the other hand, the interaction between longitudinally-aligned defects under combined loads is negligible due to the so-called shielding effect; this is again in direct contrast to the observation that the interaction between longitudinally-aligned defects under internal pressure only is marked. The adequacy of four practical interaction rules, which are developed for the loading condition of internal pressure only, for the combined loading condition is also examined. The findings of this study have important practical implications for the integrity assessment of corroded pipelines under combined loads.

Burst capacity analysis of thin-walled pipe elbows under combined internal pressure and bending moment

Structural integrity analysis of pipe elbows is of critical significance because they not only withstand the internal or external pressure but also absorb the bending moment in a pipeline system. While the burst capacity of pipe elbows under internal pressure only have been extensively investigated in the literature, the study on the burst capacity of pipe elbows under combined internal pressure and bending moment is still limited. In this paper, the effect of bending on the burst capacity of thin-walled defect-free and local wall-thinning (LWT) elbows subjected to combined internal pressure and bending moment is systematically investigated. A correction factor is defined to quantify the bending effect on the burst capacity; extensive parametric finite element analysis (FEA) is carried out to analyze the dependence of the correction factor on the bending mode and magnitude, elbow size and steel grade, and LWT size and location. The results indicate that as the magnitude of the bending increases, the burst capacity of both the defect-free and LWT elbows generally deceases. For the defect-free elbows, the elbow steel grade has a significant influence on the correction factor while the influence of the elbow geometry is marginal. For the LWT elbows, the correction factor depends markedly on the LWT location and bending mode.

Study on steel wire reinforced thermoplastic pipes under combined internal pressure and bending moment at various temperatures

Steel wire reinforced thermoplastic pipe (PSP) is a polymer–matrix composite pipe of excellent quality, and it shows great potential in different industries. In this study, bearing capacity of PSP under combined internal pressure and bending moment at various temperatures was investigated. Tests were conducted through a specifically designed mechanical testing system, and the temperatures varied from 20 °C to 60 °C. With a pre-set internal pressure of 2.8 MPa, bending moment was applied until failure. It was found that the fracture of steel wires leads to the failure of pipe, and higher temperature has a negative effect on the pipes’ bending capacity. A finite element (FE) model was subsequently established to analyze the failure process and influence factors of PSP under combined loads.

Limit load for cylinders with axial internal surface cracks under combined internal pressure and global bending moment

The global and local limit loads for cylinders with axial internal surface cracks under combined internal pressure and global bending moment are investigated using the elastic-perfectly plastic finite element (FE) method. An ellipse function is recommended to describe the relationship between the normalised global limit pressure and normalised global limit bending moment. The predictions using the ellipse function are conservative compared with the global FE results except for the cases with bending moment dominance, where the predictions may be slightly non-conservative. The investigation shows that the local limit load FE results can be well described by the local limit load model recommended by Lei and the predictions are all reasonably conservative except for cases with very long and deep cracks. Further work is required to validate the recommended global and local limit load solutions for J predictions when they are used in the reference stress J scheme.

Creep analyses for pipe bends under combined internal pressure and bending loads

This work provides detailed analyses of creep behaviors considering the influence of geometry change for pipe bends under combined bending and internal pressure loads based on the finite element method (FE). A modified Karchanov‒Rabotnov (K‒R) equation for creep damage is used in the ABAQUS user defined material subroutine (UMAT) compiled by FORTRAN. Typical results of creep stress, damage, and deformation for pipe bends are presented. Creep relaxation and damage evolution will happen during the creep procedure. The damage evolution procedure seems contrary to that of stress redistribution. There are some differences between the deformation distributions when using geometric non-linearity (GNL) and no GNL, and also the results of stress, damage, and creep failure life for pipe bends show a corresponding distinction. Phenomena of the differences of pipe ovality for pipe bends under different loading types can supply some evidence to explain the failure trait. Pipe bends are stiffened as the GNL choice hinders the deformation, so GNL has a positive effect on creep failure life prediction for pipe bends under combined loadings.

Combined internal and external negative pressure wound therapy: breakthrough treatment for lymphocutaneous intractable fistula.

Lymphocutaneous fistula after lymph node dissection is intractable, yet there is no established treatment strategy. This study demonstrates the wound closure time achieved by a new method of combined internal and external negative pressure wound therapy (CIEN) in patients with lymphocutaneous fistula. The subjects of this study were six consecutive patients with lymphocutaneous fistula after lymphatic surgery, who were treated with CIEN between 2018 and 2020. The CIEN technique can be summarized as follows: first, internal foam is inserted into the fistula from the opening of the fenestration. Next, a slightly larger area of external foam is applied above the fistula flap outside the external margin of the foam-filled fistula. After bridging the internal foam and external foam, negative-pressure wound therapy is carried out on this bridging foam block. CIEN led to rapid and complete wound healing in all six patients. Fistula flap margin ischemia developed in one patient, but adjusting the mode and pressure settings resulted in improvement. Three patients suffered contact dermatitis. There were no signs of tumor or fistula recurrence in any patients after at least 3 months of follow-up. CIEN is an effective and less invasive treatment modality than the conventional method of managing lymphocutaneous fistula.

Numerical investigation of corroded middle‐high strength pipeline subjected to combined internal pressure and axial compressive loading

AbstractBuried oil and gas pipelines may face the threat of geological disasters such as landslides, faults, and floods. However, long‐term buried oil and gas pipelines often have corrosion defects, which bring greater challenges to the safe operation of pipelines. In this study, via the finite element analysis method validated by the testing results, the blasting pressure of a middle‐high strength pipeline with corrosion defects under an axial compressive load, the distribution of the von Mises stress on the pipeline surface, and the local buckling behavior of the pipeline were studied. In the analysis of the influencing factors, the axially compressive load, the size of the corrosion defects, and the characteristics of the pipeline material were studied. Based on 437 sample points, an artificial neural network was adopted to predict the burst pressure of a pipeline with corrosion defects. By comparing the prediction results with the numerical simulation results, the accuracy verification of the prediction model was conducted. When the axially compressive load increases to a certain value, the burst pressure of a pipeline with corrosion defects will begin to decrease rapidly as the axial compressive load increases. The larger the size of the corrosion defect, the smaller the burst pressure of the pipeline. The depth and length of the corrosion defect have a significant influence on the blasting pressure. The lower the steel grade of the pipeline, the smaller the Y/T ratio, and the lower the bursting pressure of the pipeline. Both the axial compressive load and the size of the corrosion defect affect the failure mode of the pipeline. When the corrosion defect's size is small and the axial compressive load is small, the pipeline material fails. When the corrosion defect's size is large enough, and the axial compressive load is large enough, the pipeline is prone to structural instability. An increase in the axial compressive load and the decrease in the corrosion defect's size cause the local stress concentration of the corrosion defects to become more significant. When the axial compressive load on the pipeline is small, the increase in the axial compressive load does not affect the bursting pressure of the pipeline, but it greatly increases the degree of the local buckling of the pipeline. A decrease in the depth and width of the corrosion defects and an increase in their length results in the local buckling of the pipeline becoming more severe.

Analysis of filament-wound sandwich pipe under combined internal pressure and thermal load considering restrained and closed ends

Sandwich pipe consisting of inner and outer filament-wound (FW) skins bonded to a core material is a lightweight alternative to single-wall or pipe-in-pipe systems. In operation the pipe is subjected to thermomechanical loading. In this paper, a 3D finite element model is developed for analysing stresses in FW sandwich pipe under combined internal pressure and thermal load, incorporating temperature-dependent properties. Optimal reinforcement angles are determined for axially restrained ends (as per a long pipeline) and closed ends (pressure vessel condition). The effects of uniform and non-uniform heating on stress-based failure are evaluated. The pipe thermomechanical response is shown to depend on whether the pressure loading is hoop-dominated or biaxial. The core of the axially restrained pipe is highly temperature-sensitive under low pressure. With closed ends the coupled effect of mechanical and thermal loading on the skins is significant. The influences of core thickness and number of skin plies are investigated.

Strain ratcheting failure of dented steel submarine pipes under combined internal pressure and asymmetric inelastic cycling

This paper presents the results of an experimental study in which for the first time the progressive inelastic deformation of high strength steel pressurized pipes with plain and gouged dents was analyzed. The effect of some key loading and geometrical parameters such as initial pre-strain (εmon), dent depth ratio (δ/D) and the presence of the gouge was studied. Local dents with a hemispherical shape and gouges with different dimensions were introduced on the surface of the specimens. Specimens with plain or gouged dents were first internally pressurized, axially compressed to an initial pre-strain then subjected to cyclic nonlinear stressing.The mechanical defects were found to drastically degrade the inelastic cyclic response of the pressurized steel pipes. The presence of a dent, even with small amounts of initial pre-strains, made the pressurized pipes vulnerable to ratcheting failure. Furthermore, the ratcheting responses of the gouged dented specimens significantly differed from those for the corresponding specimens with plain dents. In fact, the combination of a dent and gouge was the severest form of the defect and demonstrated the lowest number of cycles before failure. The degradation effects of gouge were strongly dependent upon the gouge geometry, dent depth and initial pre-strain level.

Response, Localization, and Rupture of Anisotropic Tubes Under Combined Pressure and Tension

Abstract The inelastic response and failure of Al-6061-T6 tubes under combined internal pressure and tension is investigated as part of a broader study of ductile failure of Al-alloys. A custom experimental setup is used to load thin-walled tubes to failure under radial paths in the axial-hoop stress space. All loading paths achieve nominal stress maxima beyond which deformation localizes into a narrow band. 3D digital image correlation (DIC) was used to monitor the deformations in the test section and successfully captured the rapid growth of strain within the localization bands where they burst. The biaxial stress states generated are first used to calibrate the nonquadratic anisotropic Yld04-3D yield function (Barlat et al., 2005, “Linear Transformation-based Anisotropic Yield Functions,” Int. J. Plasticity, 21(5), pp. 1009–1039). The constitutive model is then incorporated through a UMAT into a finite element analysis and used to simulate numerically the experiments. The same calculations were performed using von Mises (VM) and an isotropic nonquadratic yield function. The material hardening responses adopted were extracted for each constitutive model from the necked zone of a tensile test using an inverse method. The use of solid elements captures the evolution of local deformation deep into the localizing part of the response, producing strain levels that are required in the application of failure criteria. The results demonstrate that the adoption of a nonquadratic yield function, together with a correct material hardening response are essential for large deformation predictions in localizing zones in Al-alloys. Including the anisotropy in such a constitutive model produces results that are closest to the experiments.