Cracked Pipes Research Articles

Study on fracture transferability from compact type specimen to pipe for 316LN stainless steel

The transferability of continuum damage parameters for ductile fracture from CT specimen to pipe has been investigated for 316LN stainless steel. The authors have earlier established crack initiation stress and crack evolution energy as damage parameters for 316LN SS, based on coupled experimental and numerical analysis. Using these fracture parameters, XFEM crack growth simulations were carried out for through-wall circumferentially cracked straight pipes of 80NB diameter. To verify the applicability of damage parameters for various crack geometries, the stress triaxiality ahead of a growing crack in CT specimen and through wall crack in pipes has been assessed. The average triaxiality for CT specimen is 1.25 and for the pipes, it varies from 0.4 to 0.62 depending on initial through wall crack size. The predicted maximum load, load-displacement response, crack growth and pipe ovality are compared with the experimental results.

Mode II stress intensity factors for circumferential through-wall-cracked pipes under torsional loading

In this study, a systematic three-dimensional finite element analyses (3D FEA) are performed to evaluate the Mode II stress intensity factor (SIF) for circumferential through-wall cracked pipe under torsion moment. A wide range of crack lengths and pipe radius over thickness ratios are considered. Empirical solution of the mid-thickness Mode II SIF is developed as functions of crack lengths and pipe sizes. The deviating angle and the effective SIF regarding a through-wall crack (TWC) under combined bending and torsion moments are further discussed. The research outcome can provide more computational efficiency in structural integrity assessment of pressurized pipes and tubular structures.

Stress intensity factors for external corrosions and cracking of buried cast iron pipes

The municipal water distribution systems across the world include a significant amount of cast-iron pipes. Many of the buried cast-iron pipes are over fifty years old and require rehabilitation. Municipalities decide on a rehabilitation solution between the replacement and re-use of the existing pipes based on the remaining strengths of the pipes. Fracture mechanics has appeared as the most viable tool for remaining strength assessment of the deteriorating pipes. However, a method of assessing the stress intensity factor (SIF) is often not available to municipal engineers to apply fracture mechanics. This paper presents a method for calculating the SIFs of buried cast iron pipes subjected to corrosion and crack on the exterior surface. Different semi-elliptical-shaped defects were characterized using various aspect ratios (crack-depth to crack-length ratio) and relative depths (crack-depth to pipe thickness ratio). The SIFs were assessed for invert/crown and springline position cracks under internal pressure and vertical surface loads. A simplified method is proposed for evaluating the SIFs of buried pipes subjected to the exterior surface defects.

Anisotropic effects on crack propagation in pressurized line pipes under running ductile fracture scenarios

The current analyses present results of running ductile fracture propagation in high strength X100 line pipe steels under the influence of anisotropy. Mechanical anisotropy is commonly available in pipe products as a result of the manufacturing process, especially, those subjected to hot/cold-worked deformation. The outcomes of the present analyses show that its effect on the behavior of running ductile fracture in cracked pipes undergoing depressurization is meaningful. For instance, the Crack-Tip Opening Angle (CTOA) not only exhibits a strong dependence to the pipe’s diameter size, but also to the material’s anisotropy nature when compared to a hypothetical isotropic material. Moreover, laboratory scale tests such as those performed on Battelle Drop Weight Tear (BDWT) samples provide useful information about initiation of ductile crack propagation when the anisotropy features are taken into account in the material description.

Multiple Crack Detection in Thick-walled Pipes Using Artificial Bee Colony Algorithm

An analytical method for diagnosis of cracks in thick-walled pipes with a circular hollow section is investigated in this study. In the proposed method, the defect is assumed to be a non-leaking crack, which is modeled by a massless linear spring with infinitesimal length at the crack location. In order to find the cracks in the pipe, the vibration-based method related to the modal properties of the pipe is utilized. In the modal analysis, the mass and stiffness matrices influence the dynamic properties of the pipe. It is assumed that the mass matrix remains unchanged after the crack initiation, while the corresponding stiffness matrix changes. The stiffness matrix of a cracked element can be formulated by the finite element method with two unknown parameters: location and depth of the crack. Using the eigensolution for an undamped dynamic system to formulate the objective function yields to a complicated optimization problem, which can be solved by an iterative numerical optimization method. Among the optimization approaches, the Artificial Bee Colony (ABC) algorithm is a simple and flexible technique for minimizing the objective function. In this paper, the analytical model is utilized to find the size and position of cracks in a pipe using the ABC algorithm and subsequently some numerical examples are examined in order to assess the accuracy of the method. The results show that the proposed method is able to acceptably estimate the location and depth of multiple cracks in the straight pipes as well as curved ones.

Influence of internal stresses in steel as a factor of corrosion cracking and destruction of drill pipes during their operation

Drill pipes in the oil-gas industry play a major role in the extraction of petroleum products. These pipes are the main link in the drilling rig, these pipes create the necessary rotation and transfer the load to the cutting element (chisels), and they also serve to lift working tools from the bottom of the well to the surface. The main goal of the drill pipe is to supply the drilling fluid, which performs the function of cooling the bit. The destruction of such pipes leads to large economic losses, therefore, these pipes must have high quality primarily in terms of mechanical properties. Based on the foregoing, this work is aimed at studying the causes of accidental destruction of steel drill pipes during their operation in the presence of an increased level of internal stresses in them. As the main method for assessing the level of residual internal stresses, a method is proposed for measuring the groove width during the longitudinal opening of ring samples cut from the body wall of drill pipes. This method is distinguished by its clarity and high speed of obtaining the result. The increased level of internal residual stresses, combined with external working loads during operation, leads to a significant reduction in the service life of drill pipes under the influence of corrosion cracking mechanism.

Evaluation of the conditions of drill pipes failure during tripping operations

The experimental evaluation of the power criterion for the metal fracture of the reserve and the long operated drill pipes was carried out. The conditions under which, during tripping operations, the failure of explored drill pipes, containing external or internal transverse annular cracks are possible. An interrelation between the depth of critical external or internal transverse annular cracks in drill pipes with the weight of the drilling string is considered, taking into account the influence of dynamic loads during tripping operations. It is shown that internal transverse annular cracks in lowering operating drilling strings at depths of more than 1400 m are more dangerous than external ones, while at depths up to 1400 m, external cross-sectional circular cracks are more dangerous.

Modeling and Simulation of Subcooled Coolant Loss Through Circumferential Pipe Leakage

Abstract This work demonstrates the leak flow behavior of subcooled water at high pressure and high temperature through a narrow slit analogous to a pipe crack. The modeling and simulations are based on the loss of coolant accident in the primary loop piping of pressurized heavy water reactors where a subcooled liquid is subjected to a rapid depressurization. Prediction of critical leak flow pattern is crucial in the design methodology of costly high energy pipelines in the perspective of leak before break consideration. For a variety of entry and exit conditions, the interphase mass transfer has been studied using computational techniques. Presence of thermodynamic nonequilibrium was detected on several occasions due to high transit velocities. A comparison with experimental findings indicates the validity of a flashing model for safety analysis of similar high energy thermal systems.

Quantitative Research on Cracks in Pipe Based on Magnetic Field Response Method of Eddy Current Testing

The quantitative evaluation of defects in eddy current testing is of great significance. Impedance analysis, as a traditional method, is adopted to determine defects in the conductor, however, it is not able to depict the shape, size and location of defects quantitatively. In order to obtain more obvious characteristic quantities and improve the ability of eddy current testing to detect defects, the study of cracks in metal pipes is carried out by utilizing the analysis method of three-dimensional magnetic field in present paper. The magnetic field components in the space near the crack are calculated numerically by using finite element analysis. The simulation results confirm that the monitoring of the crack change can be achieved by measuring the magnetic field at the arrangement positions. Besides, the quantitative relationships between the shape, length of the crack and the magnetic field components around the metal pipe are obtained. The results show that the axial and radial magnetic induction intensities are affected more significantly by the cross-section area of the crack. Bz demonstrates obvious advantages in analyzing quantitatively crack circumference length. Therefore, the response signal in the three-dimensional direction of the magnetic field gets to intuitively reflect the change of the defect parameter, which proves the effectiveness and practicability of this method.

Modeling the Repair of a Crack in an HDPE Pipe

A pipe is a buried or aerial pipeline carrying goods, whether in liquid or gaseous form. Pipes are most often made from polymer tubes. These pipes prove to be subject to damage caused by a lack of material or crack thus calling for methods of repair or reinforcement.The objective of this study is to analyze by finite element analysis the presence of a horizontal crack in a high-density polyethylene pipe subjected to patch-corrected internal loading.Part of this study is devoted to analyzing the Von Misses stress distribution along a horizontal line, the applied loading type effect, the orientation of the fibers and the nature of the patch have been highlighted.The second part of our study is based on the calculation of the J-Integral where the same parameters of the first part were considered.The results clearly show that the mechanical characteristics of the composite must be optimized to provide an effective repair safely and allow relief of stress concentrations at the crack front.

A constraint correction method based on use of a single test specimen

Commonly, fracture toughness tests on deeply cracked specimens are used to assess defects in large-scale components. The paper presents a method for selection of test specimen type, size and crack length in order to obtain fracture toughness estimates relevant to defects in cracked pipes. The method uses available closed-form T-stress, stress intensity factor and limit load solutions to determine the required specimen dimensions. The paper reports elastic–plastic finite element analyses for single edge notched bend (SENB) and single edge notched tension (SENT) specimens and cracked pipes which demonstrate good agreement of the matching approach, although care is needed in selecting the appropriate limit load solution for SENT geometries.

Failure behavior of SA508 Gr.1a LAS and SA312 TP316 SS pipes with a circumferential through-wall crack under large amplitude cyclic loads

This paper presents cyclic fracture test results using small-scale through-wall cracked pipe specimens to investigate the effects of large-amplitude cyclic loads on failure behaviour for different pipe materials. SA508 Gr.1a low-alloy steel (LAS) and SA312 TP316 stainless steel (SS) pipes were used in the experiment. The tests were conducted under quasi-static monotonic, displacement-controlled, and load-controlled cyclic loadings at room temperature (RT). Regardless of the pipe material, displacement-controlled reversed cyclic loading significantly reduced deformation-ability and fracture resistance, promoting crack growth. These effects were more pronounced in the SA312 TP316 SS than in the SA508 Gr.1a LAS specimen. The material-dependence on fracture behaviour was considerable under monotonic load, but was near-negligible under displacement-controlled reversed cyclic loading. Under load-controlled cyclic loading, the number of cycles to failure, the maximum allowable crack extension, and deformation-ability of pipe specimens decreased as the amplitude and compressive level increased. For all load-controlled cyclic loads, the SA312 TP316 SS specimen was less resistant to failure than the SA508 Gr.1a LAS specimen. Regardless of the loading type, a circumferential through-wall crack grew out of the initial crack plane for the SA508 Gr.1a LAS specimen, but propagated in a straight line from the initial crack plane for the SA312 TP316 SS specimen.

Integrating Structural Resilience in the Design of Urban Drainage Networks in Flat Areas Using a Simplified Multi-Objective Optimization Framework

Structural resilience describes urban drainage systems’ (UDSs) ability to minimize the frequency and magnitude of failure due to common structural issues such as pipe clogging and cracking or pump failure. Structural resilience is often neglected in the design of UDSs. The current literature supports structural decentralization as a way to introduce structural resilience into UDSs. Although there are promising methods in the literature for generating and optimizing decentralized separate stormwater collection systems, incorporating hydraulic simulations in unsteady flow, these approaches sometimes require high computational effort, especially for flat areas. This may hamper their integration into ordinary commercially designed UDS software due to their predominantly scientific purposes. As a response, this paper introduces simplified cost and structural resilience indices that can be used as heuristic parameters for optimizing the UDS layout. These indices only use graph connectivity information, which is computationally much less expensive than hydraulic simulation. The use of simplified objective functions significantly simplifies the feasible search space and reduces blind searches by optimization. To demonstrate the application and advantages of the proposed model, a real case study in the southwest city of Ahvaz, Iran was explored. The proposed framework was proven to be promising for reducing the computational effort and for delivering realistic cost-wise and resilient UDSs.

Predicting ductile fracture of cracked pipes using small punch test data

This paper proposes a numerical method to simulate ductile fracture of a cracked pipe using small punch test data. The method is using FE damage analysis method based on the multi-axial fracture strain energy density model. The parameters in the damage model can be extracted solely from small punch test data, using which compact tension and circumferential through-wall cracked pipe tests are simulated. To validate the proposed method, simulation results are compared with TP316L experimental data. For the compact tension test, faster crack growth is predicted but for the pipe test, good agreement is obtained. The effect of the stress triaxiality on the prediction accuracy is discussed.

Analysis of Leakage Cause of L415M Spiral Submerged Arc Welding Pipe

The causes of longitudinal crack in gas pipeline during pressure were analyzed by means of mechanical property test, microstructure analysis, sem analysis and energy spectrum analysis. The results show that the leakage of L415M spiral submerged arc welded pipe is caused by the contact between the base material of steel pipe and low-melting copper alloy in the process of high temperature, resulting in the brittleness of liquid metal. Specifically, when the leakage site of the steel pipe is heated at an abnormal high temperature, copper penetration along the grain boundary causes embrittlement, strength reduction and crack along the grain boundary, finally leading to the crack and leak of the steel pipe.

Research on pipe crack detection based on image processing algorithm

Pipe cracks detection based on machine vision is a new and effective technology. However, it requires high quality of the image. Moreover, images with adequate lighting, evident cracks, clean backg...

Research on pipe crack detection based on image processing algorithm

Research on pipe crack detection based on image processing algorithm

On elastic-plastic and creep fracture mechanics parameters estimates of non-idealized axial through-wall crack in pressurized pipe

The present paper provides engineering estimates for plastic J-integral and crack opening displacement (COD) of a non-idealized axial through-wall crack (TWC) in pipes based on detailed 3-dimensional finite element (FE) analyses. The behaviors of plastic J-integral and COD of a non-idealized axial TWC in typical pressurized pipes in nuclear power plants were systematically investigated. The FE model and analysis procedure employed in this study were verified by comparing the present FE results with the limited existing solutions for pipes with an idealized axial TWC. Based on the FE results, the new plastic influence functions, h1 and h2, which include the effect of a non-idealized TWC on plastic J-integral and COD, are provided as tabular solutions. By employing the plastic influence functions, plastic J-integral and COD of a non-idealized axial TWC along crack front can be directly predicted based on GE/EPRI method. In the present paper, plastic J-integral and COD estimates based on the reference stress concept have also been suggested. Finally, the estimated results were compared with elastic-plastic FE results by using actual stress-strain data and Ramberg-Osgood constants for TP 316 stainless steel. In addition, the engineering estimates proposed in this study were extended to estimating the creep fracture mechanics parameters at elevated temperature. Based on Norton and RCC-MRx creep models, C*-integral and creep COD rate values predicted from the present engineering solutions were validated by comparing with creep FE results. The results provided in this paper demonstrate that the present estimates can be applied to calculating plastic J-integral and COD, C*-integral, and creep COD rate of a non-idealized axial TWC.

The application of a reflected non-axisymmetric torsional guided wave model for imaging crack-like defects in small-diameter pipes

Crack imaging of a pipe can provide detailed information about defects within the pipe such as the circumferential and axial position of the defect and its circumferential coverage. Due to the complicated propagation characteristics of a non-axisymmetric guided wave within a small pipe and the limited surface area available to install the transducer, crack imaging within a small-diameter pipe is difficult. This paper reports a reflected non-axisymmetric torsional guided wave model for imaging a crack in a small pipe. First, the reflected non-axisymmetric torsional guided wave model was proposed based on the theory of the normal mode expansion method. Then, the crack imaging algorithm was determined based on the theoretical reflected non-axisymmetric torsional guided wave model. Subsequently, the relationships between the angular profiles of the reflected T(M,1) and the axial distance of the cracks, the relationships between the angular profiles of the reflected T(M,1) and the circumferential length of the cracks predicted by the theoretical model were supported by the simulation results and the experimental data. Next, the crack imaging based on the proposed reflected non-axisymmetric torsional guided wave model was carried out for four pipes to verify its practicability. The axial position and circumferential range of the cracks within the four pipes were different. The experimental and numerical results demonstrated that the reflected non-axisymmetric torsional guided wave model has the potential to image cracks within a small pipe.

Calibrating Johnson’s formula for applying DCPD method to an axial through-wall crack in a pipe

Direct current potential drop (DCPD) method is widely employed in the determination of crack length in conductive materials. It is based on the change of structure potential drop caused by the variation of the electrical resistance under a steady direct current. The accuracy of DCPD method depends on the calibration curve which describes the relationship between crack length and potential drop. Generally, the calibration curve for the crack in a plate sample is given by Johnson’s formula analytically. However, the traditional Johnson’s formula is only applicable to a center-cracked plate but not to a cracked pipe. In this paper, Johnson’s formula has to be calibrated to estimate the length of a through-the-thickness crack in a pipe. Considering the geometrical difference between a pipe sample and a plate sample, the calibrated Johnson’s formula is established based on the existence of parallel circuit in a pipe and the proposed unique reference sample. The calibration curve between axial through-wall crack length and potential drop is carried out by the calibrated Johnson’s formula. The calibrated formula has been verified for the axial through-wall crack in a pipe sample by numerical and experimental approaches. Compared with the traditional Johnson’s formula, the results illustrate that the present calibrated formula is successful to estimate the crack length in a pipe. This paper extends the applicability of the original formulation of Johnson’s formula to cracked pipes.