Pipe Specimens Research Articles

Experimental and numerical investigation of ratcheting behavior of SS316L seamless straight pipe under cyclic internal pressure and in-plane cyclic bending

In this paper, the ratcheting behavior of SS316L seamless straight pipes under cyclic internal pressure and in-plane cyclic bending is investigated experimentally and numerically. In order to applying the simultaneous cyclic bending and cyclic internal pressure, a special fixture was designed that can be mounted on the gripers of fatigue machine and so ability to apply cyclic pressure to inside pipe specimen and apply in-plane cyclic bending on pipe specimen simultaneously. According to experimental fatigue data, increasing the cyclic bending load and cyclic pressure, increases the accumulation of ratcheting strain in hoop and axial directions. So axial ratcheting strain creates due to cyclic bending and hoop ratcheting strain creates due to cyclic pressure inside pipe specimen. Finally, the finite element analysis was performed by ABAQUS software base on the nonlinear kinematic/isotropic hardening model and the experimental fatigue data were compared with the numerical results and it was found that the numerical results are in good agreement with experimental data.

Validation of applicability of induction bending process to P91 piping of prototype Gen-IV sodium-cooled fast reactor (PGSFR)

The application of the induction bending process to pipe systems in various industrial fields is increasing. Recently, efforts have also been made to apply this bending process to nuclear power plants because it can innovatively reduce welded parts of the curved pipes, such as elbows. However, there have been no cases of the application of induction bending to the piping of nuclear power plants.In this study, the applicability of the P91 induction bending piping for the sodium-cooled fast reactor PGSFR was validated through high temperature low cycle fatigue tests and creep tests using P91 induction bending pipe specimens. The tests confirmed that the materials sufficiently satisfied the fatigue life and the creep rupture life requirements for P91 steel at 550 °C in the ASME B&PV Code, Sec. III, Div. 5. The results show that the effects of heating and bending by the induction bending process on the material properties were not significant and the induction bending process could be applicable to piping system of PGSFR well.

Ratcheting assessment of pressurized elbow pipes using the visco-plastic Chen-Jiao-Kim hardening rule frameworks

In this study, the ratcheting responses of pressurized long and short radius 90° elbow pipes made of 304L austenitic stainless steel under displacement-controlled cyclic loading is evaluated mainly using the Chen-Jiao-Kim (CJK) kinematic hardening rule at room temperature. Visco-plastic flow rule and isotropic hardening are introduced into the CJK model to better reflect the time-dependent behavior and cyclic hardening characteristics of the 304L stainless steel material. The model is implemented employing the user material subroutine (UMAT) in the ABAQUS finite element software. The predictions show that the maximum ratcheting strain occurs at the flank of the long and short radius 90° elbow pipes. The influence of internal pressure, cyclic loading, and bending radius on the ratcheting responses of the elbow pipes is respectively investigated. It is found that the predictions of the CJK model are very nearly the same as the test data. In addition, the ratcheting responses of two long radius elbow pipe specimens under force-controlled cyclic bending are evaluated. Further, the C-TDF (The Committee of Three Dimensional Finite Element Stress Evaluation) combined with CJK model and Linear Matching Method (LMM) is respectively used to determine the shakedown and ratcheting boundaries of the pressurized long and short radius 90° elbow pipes under displacement-controlled and force-controlled bending. The comparison with the test data in this study shows that the shakedown and ratcheting boundaries determined by LMM, divides the shakedown and ratcheting zone well.

Behavior of FRP grid-reinforced ultra-high performance concrete (UHPC) pipes under lateral compression

In this paper, ultra-high performance concrete (UHPC) pipes internally reinforced with fiber-reinforced polymer (FRP) grid (abbreviated as “FRP grid-UHPC pipe”) are proposed. The lateral load carrying performance of FRP grid-UHPC pipes was explored by testing 15 pipe specimens. The test variables included the presence and amount of FRP grid reinforcements, pipe thickness, as well as the presence of carbon FRP (CFRP) jacketing. Results showed that separation failure and flexural fracture were the primary failure modes for the pipes with and without FRP grid reinforcements, respectively. The typical load-vertical displacement curve of a FRP grid-UHPC pipe exhibited a two-stage ascending behavior. Without CFRP jacketing, the two ascending segments were linked by a load reduction, while the transition was smooth with CFRP jacketing. For the variables, it is found that the presence of FRP grid reinforcements could enhance the pipe initial cracking load by approximately 30%, while increasing the FRP grid layers could lead to a much steeper rising in the second ascending segment. Increasing pipe thickness and applying CFRP jacketing could increase the slopes of both initial and second ascending segments. Therefore, increasing pipe thickness (from 30 mm to 45 mm) and applying 1-ply CFRP jacketing could enhance the pipe ring stiffness by 422% and 115% respectively, which was more efficient that increasing the FRP grid layers.

Improvement of burst capacity model for pipelines containing surface cracks and its implication for reliability analysis

This paper presents the improvement of a widely used burst capacity model for steel oil and gas pipelines that contain longitudinal external surface cracks, namely the CorLAS model, through the addition of a correction factor that is quantified by the Gaussian process regression (GPR). The correction factor is assumed to depend on four non-dimensional input features that characterize both the crack geometry and pipe material properties. A database consisting of 212 full-scale burst tests of pipe specimens that contain longitudinal surface cracks is established based on the open literature, which is employed to train the GPR model and evaluate its performance. It is shown that GPR is highly effective in improving the accuracy of the CorLAS model predictions. The improvement is further shown to have a marked effect on the time-dependent probability of burst of pipelines containing growing surface cracks through two hypothetical pipeline examples: when employing the CorLAS model, the probabilities of burst are significantly higher, exceeding those obtained using the improved CorLAS model by more than one order of magnitude.

Service-lines as major contributor to water quality deterioration at customer ends

Biofilm detachment contributes to water quality deterioration. However, the contributions of biofilm detachment from different pipes have not been quantified or compared. Following the introduction of partial reverse osmosis (RO) in drinking water production, this study analyzed particles at customers’ ends and tracked their origins to water distribution mains and service lines. For doing so, filter bags were installed in front of water meters to capture upstream detached particles, while biofilm from water main and service line were sampled by cutting pipe specimens. The results showed that elemental concentrations of the biofilm in mains were higher than those of service lines (54.3–268.5 vs. 27.1–44.4 μg/cm2), both dominated by Ca. Differently, filter bags were dominated by Fe/Mn (77.5–98.1%). After introducing RO, Ca significantly decreased in biofilms of mains but not service lines, but the released Fe/Mn rather than Ca arrived at customers’ ends. The ATP concentrations of service lines were higher than mains, which decreased on mains but increased in service lines after introducing RO. For the core ASVs, 13/24 were shared by service lines (17), mains (21), and filter bags (17), which were assigned mainly to Nitrospira spp., Methylomagnum spp., Methylocytis spp., and IheB2–23 spp. According to source tracking results, service lines contributed more than mains to the particulate material collected by filter bags (57.6 ± 13.2% vs. 13.0 ± 11.6%). To the best of our knowledge, the present study provides the first evidence of service lines’ direct and quantitative contributions to potential water quality deterioration at customers’ ends. This highlights the need for the appropriate management of long-neglected service line pipes, e.g., regarding material selection, length optimization, and proper regulation.

Experimental and numerical investigation of ratcheting behavior in seamless carbon steel 90° elbow pipe with small dimensions under constant internal pressure and in-plane cyclic bending

The purpose of this study is to identify the effects of mean fatigue load, amplitude fatigue load, internal pressure and loading history on ratcheting behavior of seamless A234 WPB steel elbow pipe. So, in this paper the ratcheting behavior of seamless 90° elbow pipe of A234 WPB steel under constant internal pressure and in-plane cyclic bending is investigated experimentally and numerically. At first, in order to the confirm of elbow pipe material, a series of experimental tests were performed on elbow specimen, including: chemical composition analysis, metallography testing, hardness testing and uniaxial tensile testing. In the next step, the fatigue tests were performed on elbow pipe specimens at ambient temperature (25 °C) under asymmetric cyclic loading with load-control conditions. According to the experimental fatigue data, concluded that the increasing of mean load, amplitude load and internal pressure, increases the accumulation of ratcheting strain in axial direction at intrados and extrados locations, and also in hoop direction at crown location. So that the increasing of mean load or amplitude load has the greatest effect on the ratcheting strain at intrados and extrados locations. Also, it was found that the loading history affected to ratcheting behavior and premature failure of pressurized elbow pipes. Finally, the finite element simulation was carried out by ANSYS software based on the nonlinear kinematic/isotropic hardening model, and the FE simulation results were compared with experimental fatigue data and it was found that the numerical results are in good agreement with experimental fatigue data.

Inner surface peening for long and narrow helical pipe using acoustic cavitation

The inner surface peening of helical pipes is highly challenging due to the inaccessibility of the inner surface. To the end, we propose to peen the inner surface by introducing acoustic cavitation inside the pipe. We also provide a theory to account for how the inner surface peening can be achieved by the acoustic cavitation for a long helical pipe. We evaluate the validity of theory with experiments conducted on helical pipe specimens. The experimental results well agree with the theorical predictions. Also, it was found that a significant amount of compressive residual stress was achieved by the acoustic cavitation on the inner surface. The experimental results imply that the acoustic-cavitation-generation of compressive residual stress is effective regardless of pipe length, which promises that the present peening method will be applicable for a wide range of helical pipe length.

Mechanical performance of spun-cast full-scale precast pipes incorporating hybrid conventional rebar cage and steel fibers

Precast reinforced concrete (RC) pipes are an important component of urban infrastructure for conveyance of stormwater and sewage disposal. This study investigates the mechanical performance of spun-cast precast full-scale pipes under three-edge bearing test (TEBT) and patch or point load tests for replicating the field loading scenarios. Six types of precast pipes incorporating various amount of conventional rebar reinforcement and local steel fibers were tested. Straight steel fibers of 25 mm length were cut from locally manufactured long steel wires. Two steel fiber dosages (i.e., 20 kg/m3 and 40 kg/m3) in concrete mixture were examined for mechanical behavior of pipes along with conventional rebar cage. It was observed that full-scale precast pipes without steel fibers and conventional rebar cage failed in an abrupt manner into various pieces. However, pipe made with concrete mixture incorporating steel fibers only without conventional rebar cage also failed into pieces but showed post-peak behavior and fiber crack bridging phenomena. Pipes having double conventional steel reinforcement ratio showed 60% higher ultimate load. Pipes incorporating 20 kg/m3 and 40 kg/m3 along with conventional rebar cage showed 10% and 30% higher ultimate load compared to that of identical pipe without steel fibers. Improved deflection softening and hardening behaviour were observed for pipes with fibers. Furthermore, multiple secondary cracks were observed during TEBT for pipe specimens incorporating fibers. Similarly, higher ultimate load and improved cracking behavior was observed under patch load for pipe specimens incorporating steel fibers. All the tested pipes incorporating steel fibers and conventional rebar cage satisfied the Class III and Class IV requirements of ASTM C76. It can be envisioned that the implementation of hybrid spun-cast pipes incorporating conventional rebar cage and local steel fibers lead towards the development of economical pipes for controlling the premature cracking and improved structural behaviour.

A modified cyclic cohesive zone model for low-cycle fatigue crack initiation prediction for subsea pipelines under mode I loading

A modified cyclic cohesive zone model (CCZM) is developed for low-cycle fatigue crack initiation prediction for subsea pipelines. The traction and separation law in the model is modified by employing a piecewise function and linear softening for improving the computational convergence but maintaining the material nonlinearity. The validity of the modified model is evaluated with experimental results of two full-scale pipe specimens and also the results estimated by six published models. An engineering application is further presented to demonstrate the capability of the model and a parametric study is performed for investigating the impact of model parameters on model prediction.

Classification of failure modes of pipelines containing longitudinal surface cracks using mechanics-based and machine learning models

This paper applies the mechanics-based approach and five machine learning algorithms to classify the failure mode (leak or rupture) of steel oil and gas pipelines containing longitudinally oriented surface cracks. The mechanics-based approach compares the nominal hoop stress remote from the surface crack at failure and the remote nominal hoop stress to cause unstable longitudinal propagation of the through-wall crack to predict the failure mode. The employed machine learning algorithms consist of three single learning algorithms, namely naïve Bayes, support vector machine and decision tree; and two ensemble learning algorithms, namely random forest and gradient boosting. The classification accuracy of the mechanics-based approach and machine learning algorithms is evaluated based on 250 full-scale burst tests of pipe specimens collected from the open literature. The analysis results reveal that the mechanics-based approach leads to highly biased classifications: many leaks erroneously classified as ruptures. The machine learning algorithms lead to markedly improved accuracy. The random forest and gradient boosting models result in the classification accuracy of over 95% for ruptures and leaks, with the accuracy of the decision tree and support vector machine models somewhat lower. This study demonstrates the value of employing machine learning models to improve the integrity management practice of oil and gas pipelines.

Influence of Acetone and Primer on Strength and Ductility of Chlorinated Poly(vinyl chloride).

Primer is widely used to prepare bonding of chlorinated poly(vinyl chloride) (CPVC) pipe. The study examined the influences of primer and its major component, acetone, on CPVC's mechanical properties. Two types of CPVC product, sheet and pipe, were used in the mechanical testing. Sheet specimens were immersed in acetone or primer for 40 and 10 min, respectively, i.e., the maximum allowable time without mass loss, and then dried in air before the mechanical testing. Pipe (ring) specimens were treated either through immersion in acetone or primer for 30 min or in contact with these solvents locally on the inner surface for 2.5 h, and then air dried for 10.5 days before the mechanical testing. Results showed that CPVC's strength decreased after the absorption of these solvents, and air dry could remove acetone but not completely primer. The study also showed that pipe specimens by local contact with primer could generate brittle fracture. In view that sheet specimens always fractured in a ductile manner, brittle fracture of the pipe specimens could not be caused by CPVC degradation. Rather, strength decrease in the local region could provide a plausible explanation for the brittle fracture behavior, though further investigation is needed.

Comparison of fatigue performance of polyethylene pipe grades in the form of extruded and compression molded specimens

Due to the very long operational lifetimes (up to 100 years) of polyethylene pipes, there is a strong demand for accelerated testing of pipe materials to experimentally prove the ability of a certain material to achieve such lifetime. Among the accelerated tests of performance, the cracked round bar (CRB) test is the most convenient. The CRB test takes advantage of cyclic loading that is applied on cylindrical specimens with a circumferential notch in the middle. The specimens are usually manufactured from plates produced by compression molding from the investigated material. However, for polyethylene pipe producers, the possibility of making the specimens by extrusion would save time and lower the costs. This study is dealing with the comparison of CRB test, and a new test carried out on notched pipe samples produced by extrusion. The goal is to investigate the possibility of measuring the performance directly on extruded pipe specimens. The comparison is illustrated on experimental results of several polyethylene pipe grades of PE80, PE100 and PE100RC often used for pipe manufacture.

Plastic collapse analysis in multiaxially loaded defective pipe specimens at different temperatures

A comprehensive numerical investigation is carried out using a newly developed constitutive model to describe failure at low temperatures in multiaxially loaded cracked pipes made of 316L stainless steel. The kinetic phase transformation and the temperature-dependent fracture criterion are implemented to accurately capture the mechanical response at different temperature levels. Although experimental observations of these simulations were not available, their results were quite consistent with some already published results obtained on similar materials and loading conditions at room temperature. The results indicate that the existing multiaxial plastic collapse failure criterion, including shearing, still provides a fail-safe design margin for low temperature loading conditions, including internal pressure. Moreover, martensite kinetic phase transformation plays an important role, especially during straining at low temperatures.

Assessing the efficacy of non-destructive testing methods to detect pitting corrosion

ABSTRACT Calibration of the non-destructive testing (NDT) methods for pipeline inspections is commonly done via machined defects with simple shapes and known sizes. However, such defects do not represent, e.g. an actual pit morphology observed in the field, which could lead to the unreliable interpretation of the inspection results. This work proposed a systematic approach to create and characterise real pits in stainless steel pipe specimens to assess the sensitivity of selected NDT methods. Pipe samples with three different diameters and thicknesses were used. Pits of different geometries and dimensions were generated by electrochemical methods, and immersion in an acidic ferric chloride solution filled in pre-drilled holes on the external surface of the specimens. NDT methods including radiography, Eddy current and dye penetrant testing were used for detecting and sizing the pits. The results were then compared with true pit depths obtained from cross-section analysis. Radiography and Eddy current methods failed to detect small pits with depths less than 70 µm. The porous metal cover on the pit mouth affected the detectability of radiography, while it had little impact on Eddy current testing. The findings of this investigation could be used to design training and calibration blocks for NDT methods.

Prediction of the peak load and crack initiation energy of dynamic brittle fracture in X70 steel pipes using an improved artificial neural network and extended Finite Element Method

In this paper, a robust technique is presented to predict the peak load and crack initiation energy of dynamic brittle fracture in X70 steel pipes using an improved artificial neural network (IANN). The main objective is to investigate the behaviour of API X70 steel based on two experimental tests, namely Drop Weight Tear Test (DWTT) and the Charpy V-notch impact (CVN), for steel pipe specimens. The mechanical properties in the brittle fracture behaviour of API X70 steel pipes are predicted utilizing numerical approaches with different crack lengths. Next, to simulate the impact of API X70 steel pipes at lower temperatures through a numerical approach, a cohesive approach using the extended Finite Element Method (XFEM) is used. The data obtained are used as input for the proposed IANN using Balancing Composite Motion Optimization (BCMO), Particle Swarm Optimization (PSO) and Jaya optimization algorithms, to predict the peak load values and crack initiation energy of dynamic brittle fractures in API X70 steel with different crack lengths. The results show the effectiveness of ANN-PSO and ANN-BCMO based on the convergence of the results and the accuracy of the prediction of the peak load and crack initiation energy. Note that, the source codes are publicly available at https://github.com/Samir-Khatir/JAYA-ANN.git.

Influence of Physical and Chemical Stress on the Properties of CIPP Pipes Based on Vinyl Ester

Cured-in-place pipe (CIPP) is one of the trenchless sewer rehabilitation methods for repairing sewer pipe using different types of resin, curing technology and reinforced polymer fiber. In the research described in this article, the chemical and temperature resistance of CIPP pipes based on vinyl ester resin, cured with hot water, were tested. The specimens of the CIPP pipes were exposed to a chemically aggressive environment and an elevated temperature, namely 20% sulfuric acid (pH = 1) and a temperature of 50°C. The samples were tested every month for short-term flexural properties as well as hardness. Changes of the flexural properties and hardness were compared with reference samples that were stored under laboratory conditions (23±0,5°C, relative humidity 50% ±10%). It was found out that the applied aggressive environment does not have a negative impact on the mechanical properties of the CIPP pipes based on vinyl ester resin even after long-term exposure. Furthermore, the influence of the aggressive environment on the microstructure of CIPP samples was monitored by digital optical microscopy.

Real-time monitoring of stress corrosion cracking in 304 L stainless steel pipe using acoustic emission

A stress corrosion cracking (SCC) monitoring indicator (MI) based on the acoustic emission (AE) technique is proposed for the real-time detection and monitoring of SCC initiation in 304 L stainless steel (SS) pipes used for the primary circuits of nuclear power plants (NPPs). A device is used to accelerate the initiation of SCC to shorten the experiment timeframe. A non-crack AE signal criterion was established, which was conducted by injecting an etchant and distilled water into 304 L SS pipe specimens as experimental and control groups, respectively. Furthermore, to characterize the AE signal responsible for cracking, the characteristics of the AE signal measured in the section between necking and fracture (where cracks occur and propagate) among the stress curves obtained from the 304 L SS tensile test using AE sensors were investigated. Subsequently, the maximum amplitude, energy, frequency characteristics (range and magnitude), and waveform of the remaining AE signals were investigated after removing some AE signals by applying the non-crack AE signal criterion in the experiment where the SCC penetrated the pipe. These were compared with the maximum amplitude, energy, frequency characteristics, and waveform which were investigated in the tensile test to derive common characteristics for the two sets of crack signals to establish an SCC MI. To evaluate the performance of the developed SCC MI, the SCC monitoring experiment was halted when AE signals corresponding to the SCC MI criteria were measured, to fabricate a pipe wherein non-penetrating SCC was formed. In this manner, by applying the SCC MI to detect SCC in real time, we verified that the SCC MI had excellent SCC detection performance. Furthermore, we performed scanning electron microscopy (SEM) image analyses and SEM-energy dispersive X-ray spectrometry analyses to investigate the causes of SCC propagation.

Influence of girth welding material on thermal and residual stress fields in welded lined pipes

An experimental and numerical investigation on the thermal and mechanical response of a lined pipe (compound pipe) under welding is presented. The welding process consists of a single-pass overlay welding (inner lap-weld) and a two-pass girth welding (outer butt-weld). The influence of the filler material of the girth welding has been examined thermally and mechanically as it is a key factor that can affect the quality of lined pipe welding. To this end, a three-dimensional non-linear finite element model based on the ABAQUS code has been developed and successfully validated against small-scale experimental results. This study was conducted on two specimens of lined pipe joined together by a girth welding deposited either by mild steel or by austenitic stainless steel. Furthermore, in this study, a pre-heat treatment required to produce lined pipe specimens has been taken into account. Strains and residual stresses have been measured by means of high temperature strain gauges, residual stress gauges and the X-ray diffraction technique along the inner and outer surfaces of the welded lined pipe whereas the thermal history has been recorded by thermocouples. The findings point out that replacing the girth welding mild steel by austenitic stainless steel has a significant effect on the residual stress results but no influence on the thermal history results.

Generation of synthetic full-scale burst test data for corroded pipelines using the tabular generative adversarial network

This paper employs a deep learning tool, the tabular generative adversarial network (TGAN), to generate synthetic full-scale burst test data for corroded pipe specimens by capturing the joint probability distribution of five dimensionless random variables characterizing a database of 258 real full-scale burst tests collected from the literature. A simple criterion is proposed to identify outliers contained in the synthetic dataset. Two machine learning models, the random forest and extra tree, are trained using the real and synthetic test data to predict the burst capacity of corroded pipelines for the purpose of tuning the hyper-parameters of TGAN and also validating the credibility of the synthetic data. The generated synthetic data are shown to accurately capture the joint probability distribution of the real test data. This study provides a viable option to effectively generate a large number of high-quality synthetic full-scale test data to facilitate the development of engineering critical assessment models employed in the pipeline integrity management practice.