Pipe Fracture Research Articles

Dynamic analysis of whipping behavior induced by the circumferential fracture of high energy pipes considering fluid-structure interaction effect

To analyze the dynamic characteristics of whipping behavior induced by the circumferential fracture of high energy pipes, a numerical model of the piping system was presented based on the bidirectional fluid-structure interaction method. The reliability of this model was validated against experimental results. Furthermore, the dynamic characteristics of whipping behavior were studied, as well as the effects of some main parameters. The numerical results suggest that the entire whipping behavior can be divided into four stages: free-whipping stage Ⅰ, free-whipping stage Ⅱ, collision stage and periodic stage. The dynamic response of whipping behavior is different in the four stages and is dominated by a single mode with a frequency of 29.35 Hz under the combined action of the thrust force and U-bolt restraints. The increase of inlet flow rate causes the enhancement of thrust force and thus makes its dynamic response more complicated. The parameter analysis shows that the whipping behavior can be suppressed by choosing the small initial clearance, setting the suitable gap and increasing the straight segment length of U-bolt restraints. The above results are helpful to understand the dynamic characteristics of whipping behavior and provide valuable suggestions for the optimization of the protection measures.

Study on multi-cluster fracture propagation and quantitative evaluation method considering perforation erosion

This article pinpoints the problem of multiple clusters of crack extensions with perforation erosion, proposes a modified calculation formula for the variation of perforation diameter. Established a proposed three-dimensional numerical model to analyze the effect of different construction and completion parameters on fracture extension. The results show that: (1) With the pumping of sand-carrying fluid, the perforation erosion will lead to the increase of the flow coefficient and diameter of each cluster of perforation, which shows that the perforation erosion exacerbates the imbalance in flow distribution at the fracture inlet of each cluster as well as the non-uniform expansion of multi-cluster cracks. (2) The effect of perforation erosion increases with the enhancement of limited entry, and although the negative effect of perforation erosion is overall smaller than the positive effect of limited entry, it somewhat weakens the flow restriction ability of the perforation. (3) When the effect of limited entry is strengthened, considering the effect of perforation erosion the flow difference coefficient and the fracture length variation coefficient are significantly increased, and show a tendency to decrease (4) Use low proppant concentration to minimize damage to fractured pipe columns while meeting fracture inflow capacity.

Changes in magnetic characteristics of pipes during hydraulic and pneumatic tests of trunk pipelines

To identify the zones with the highest tensile stresses and deformations, a two-parameter magnetic method based on the measurement of coercive force and residual magnetic induction was applied. For realization of the method a mobile hardware and software complex DIUS-1.21M with an electromagnetic U-transducer was used, which was located along the pipe axis and along the pipe ring. Measurements were carried out on three pipes: in the first one magnetic characteristics were measured in the absence and under the influence of internal pressure; in the second and third ones — before the test and after the pipe fracture. It was revealed that internal pressure leads to the growth of residual magnetic induction in all zones both along the axis and along the ring, which indicates the occurrence of axial and circular tensile stresses in these zones, and the change of coercivity occurred ambiguously. It was found that fracture significantly increases the scatter of magnetic characteristics, which is explained by the complex nature of the stress-strain state of the fractured object.

Multiple contamination sources, pathways and conceptual model of complex buried karst water system:constrained by hydrogeochemistry and δ2H, δ18O, δ34S, δ13C and 87Sr/86Sr isotopes

Karst groundwater contamination has emerged as a worldwide environmental and health hazard. Karst aquifers, even for the buried karst systems, have strong contamination sensitivity and great pollution risk due to the good pipe fracture connectivity. The large burial depth and invisible hydrologic connectivity pose a challenge for the diagnosis of the contamination sources and identification of the contamination pathways of buried karst aquifers. To address it, a comprehensive application of hydrogeological and hydrogeochemical investigation combined with multiple isotopes (δ2H, δ18O, δ34S, δ13C and 87Sr/86Sr) were performed to elucidate the multiple contamination sources and migration pathways of contaminants in Jinci Spring, a complex buried karst water system. The results obtained highlight that the hydrological connectivity and source availability determine the specific contamination process in buried karst aquifer. Karst aquifer under the river channel is observed to be influenced by the vertical infiltration of polluted river water as indicated by elevated chloride levels (mean 79.4 mg/L) and higher δ2H (mean −8.8 ‰) and δ18O (mean −64.5 ‰) values. Evidenced by the excess of sulfate (mean: 1454 mg/L) and depleted δ34S (mean: −1.6 ‰), the lower karst aquifer may receive the leaking recharge of the mining waste water in the overlying coal seams. The occurrence of nitrate in karst water may be induced by reverse recharge from neighboring confined quaternary aquifers, indicated by the elevated nitrate concentration (15.0–50.8 mg/L) with high 87Sr/86Sr ratios (mean 0.7124). Our findings suggest that over-pumping of deep karst waters may produce additional pollution sources by altering the natural recharge relationship between montanic karst waters and the neighboring pore waters within the basin. Research in this paper improves our understanding of groundwater pollution and hydrological connectivity in buried carbonate aquifers and the protection of karst water resources.

Root cause analysis of the brittle fracture of pipes of boiler heating surfaces after long-term operation

Root cause analysis of the brittle fracture of pipes of boiler heating surfaces after long-term operation

Study on the mechanical properties and acoustic emission signal characteristics of freezing pipe

The increase in freezing depth requires thicker, stronger, and colder freezing walls, and various complex factors in deep strata greatly increase the risk of freezing pipe fracture. To address the phenomenon of freezing pipe fracture, this paper designs freezing pipe and joint mechanical performance experiments based on acoustic emission (AE) technology, mainly testing the deformation of freezing steel pipes and composite joints at normal and low temperatures, changes in load bearing capacity, and corresponding AE characteristics of the process. Additionally, the associated AE characteristics throughout the process will be analyzed. The ultimate goal is to establish a discriminative pattern for identifying the critical fracture of freezing pipes based on the analysis of AE signal characteristics in conjunction with mechanical properties. The sensitivity of the AE system under low-temperature conditions and the reliability of the test were tested through pencil lead break experiments, and saltwater noise detection experiments were conducted to prevent noise interference from low-temperature saltwater flow and pipe wall friction in the identification of crucial signals for freezing pipe fracture. This study provides a basis for identifying the deformation mechanics and fracture warning of freezing pipes through dynamic analysis of AE monitoring information.

Influence of brine leakage on frozen wall development in offshore sand layer when active freezing: A numerical study

Brine leakage after freezing pipe fracture when active freezing will cause local structural defects or even failure of frozen wall. A water-heat-solute coupled model that includes a modified Michalowski model considering both temperature and salt concentration was proposed to simulate the freezing construction in offshore sand layer. It was verified by the artificial freezing model tests of saturated saline sand under seepage. The structural defects of frozen wall were observed at the boundary between straight and arch walls on the upstream. The range of the structural defect and the closing time of frozen wall both rise with larger pressure head. The brine leakage was then simulated to evaluate the effects of both pressure head and fracture range of freezing pipe on the structural defect of frozen wall. As indicated by the normalized unfrozen water content contour, there are obvious flaws in determining whether the frozen wall is closed only by the average temperature when brine leakage. A characteristic index, the area ratio of structural defect of frozen wall, was derived from the normalized unfrozen water content contour. The structural defect results from brine leakage when the pressure head is below 2.0 m, otherwise from both brine leakage and groundwater seepage. It is recommended that in addition to monitoring temperature during active freezing, additional moisture monitoring devices should be installed to prevent brine leakage hazards.

Time-Dependent Reliability Analysis of Fracture Failure of Corroded Cast Iron Water Pipes and Bayesian Updating for Lifetime Prediction

Affected by the underground soil environment, buried cast iron pipelines are subject to corrosion during their long-term service, resulting in damage accumulation to the pipe wall and the eventual fracture failure of pipes. This paper aims to propose a probabilistic method to quantitively assess the time-dependent reliability of fracture failure of corroded cast iron pipes. A Gamma-based corrosion process of the pipe wall is derived according to the reported corrosion models. The first-order reliability method and the Monte Carlo simulation are used to cross-validate and conduct the time-dependent reliability analysis based on the fracture failure criterion. Furthermore, uncertain physical parameters of the pipes are updated by the Bayesian Markov Chain Monte Carlo (MCMC) algorithm based on the regional historical data of failed pipes, and lifetime predictions of buried cast iron pipelines are then obtained. A worked example is provided to illustrate the application of the proposed method. It is found that the Gamma process can well simulate the corrosion process hence can be employed to calculate the probability of pipe fracture failure. Sensitivity analysis reveals that the pipe internal water pressure, the fracture toughness, and the geometry of corrosion pits are the most influential parameters to the probability of fracture failure. It is also found that the predicted lifetime of corroded cast iron pipes in the worked example decreases from 110 to 85 years after the Bayesian updating.

Numerical simulation on the erosion characteristics of dense particles in the annular channel of downhole fracture pipe

ABSTRACT An extra-dense volume concentration (more than 30% vol.) of two-phase flow between liquid and solid is always encountered in the narrow annular channel in the hydraulic sand fracturing technology of the oil-gas exploitation industry. Here we investigated the characteristics of erosion in the annular channel during fracturing based on the DDPM (Dense Discrete Phase Model) and a predictive model for the erosion rate of the annular channel is developed by considering flow velocity, mass flow rate, and particle size. Its indicate that as flow velocity increases, the maximum rate of erosion rises exponentially. A larger mass flow rate may lead to a decrease in the erosion rate, with a critical mass flow rate of 5.23 kg/s identified. Additionally, the erosion rate initially decreases and then increases with an increase in particle size, with a critical particle size of 0.7 mm also observed. Finally, a predicting model for the maximum erosion is proposed, the results of agrees well with available numerical simulation values. It is expected that all findings in this study can provide some guidance for predicting the erosion and operating parameters of the pipeline in the process of fracturing technology.

Experimental Study on the Seismic Performance of a Steel Slag CFDST T-Joint

In this paper, a kind of steel slag, concrete-filled double-skin steel tube (CFDST) T-joint is proposed to promote sustainable structural development. In order to examine the seismic performance of the steel slag CFDST T-joint, a series of hysteresis experiments were carried out on 4 CFDST T-joints with the main pipe under axial compression load and the brace pipe subjected to cyclic axial loading. The seismic performance of the CFDST T-joint was experimentally investigated in terms of the failure mode, load–displacement hysteresis relationship, stiffness degradation, energy dissipation and ductility. The effects of the hollow ratio and the steel slag concrete of the CFDST main pipe on the seismic performance of CFDST T-joint specimens were compared and analyzed. The experimental results show that the failure modes of the CFDST T-joint mainly included two kinds of failure, with those being main pipe fracture and joint area compression-bending failure. The seismic performance of the joints could be improved with a 12% ultimate bearing capacity and 54% ultimate deformation capacity with the hollow ratio of the CFDST main pipe increasing from 0 to 0.5. The seismic performance of the joints could be improved with a 54% ultimate deformation capacity by filling the steel slag concrete with a 0.5 hollow ratio.

Centrifuge and numerical modeling of brittle damage of buried pipelines subjected to tunneling induced ground settlements

Tunnel excavations can seriously threaten the structural integrity of nearby pipelines. In the present study, centrifuge tests and numerical simulations are conducted to systematically investigate the brittle damage of buried pipelines subjected to tunneling induced ground settlements. In the numerical model, the pipeline is characterized as peridynamic (PD) shell structures, and the surrounding soil is modeled as discrete independent Winkler springs, and the modified Gaussian distribution profile is incorporated as displacement-controlled boundary conditions on springs. The effectiveness of the proposed numerical model is demonstrated by comparing against the centrifuge test results. A pipeline is subjected to bending due to tunneling until the initiation of cracks, after which the cracks propagate inwardly quickly and penetrate through the cross-section. Eventually, a ring crack occurs at the cross-section above the tunnel centerline. From parametric analyses, the following factors delay the pipeline damage, i.e., thicker pipe wall, shallower burial depth, loosely soils, smaller soil friction angle, and smaller tunnel-pipeline crossing angle. A pipeline with a thicker wall and a higher critical energy release rate can have a greater initial pipe fracture angle. In any case, the fracture angle always increases steadily if the amount of ground settlement continues to grow.

Similarity Model Test on Stress and Deformation of Freezing Pipe in Composite Strata during Active Freezing

In order to prevent the problem of freezing pipe fracture in the process of artificial freezing construction, taking the main shaft freezing project of Shandong Yuncheng Mine as the background and based on the similarity theory, the similarity model test of freezing pipe in the composite stratum of the active freezing section is carried out. The test results show that the distribution of freezing temperature field in sand layer and clay layer is “W”-shape, and the temperature at the interface of outer ring pipe is slightly higher than that of the inner ring pipe. The change rate of freezing temperature can be divided into three stages: rapid decreasing section, slow decreasing section, and stable section. Compared with the clay layer, the sand layer has the shorter freezing closure time and the lower freezing average temperature. The frozen pipe is always in the state of vertical compression in the clay layer, while in the state of vertical compression first and then vertical tension in the sand layer. The maximum compressive strain in the clay layer is −305 με, which is equal to the vertical compressive stress of 64.1 MPa. The maximum tensile strain in the sand layer is 406 με, which is equivalent to the tensile stress of 85.2 MPa. The bending direction of different freezing pipes is different in the different soil layers. The maximum bending strain of the frozen pipe in the clay layer is 779 με, which is 2.6 times the vertical strain at the same location, corresponding to the bending stress of 163.4 MPa and reaching 0.69 times of the yield limit of frozen pipe, while the bending strain in the sand layer is very small. The vertical strain and bending strain of freezing pipes at the interface of soil layers are very small, but the bending strain is still dominant.

Fracture Analysis of Butt Welding Area of 5″ Drill Pipe Internal Thread End in an Oilfield

This paper tested fracture morphology analysis, mechanical properties and chemical, metallographic analysis and micro analysis to find out the factors of fracture in the butt welding area of the internal thread of the 5″ drill pipe, which is made of S135 in the casing pulling process of an oilfield. The results show that the chemical element, tensile strength and yield strength, impact performance, metallographic structure, inclusions in microstructure and grain size of the Fracture drill pipe meet the relevant data of the oilfield and industry standards, but the hardness of the fracture does not meet the requirements of the national standard. The important reason of the fracture of the drill pipe is that the oxide skin was not cleaned before the drill pipe joint was welded with the body. During welding, the oxide skin entered the molten weld metal, and large slag inclusions formed in the weld resulted. The secondary cause is improper subsequent heat treatment of drill pipe weld, which leads to increased weld brittleness and accelerated crack growth. This paper puts forward corresponding countermeasures to improve the quality of the drill pipe’s weld and prevent the failure accidents of drill pipe.

Simulation of Branch Pipes Fracture Condition in Low-Pressure Safety Injection System of PWR

In the low-pressure injection system (LHSI) of the PWR unit, two branch pipes of the recirculation pipeline are vulnerable to fracture during minimal-flow operation. Flowmaster was used to create a hydraulic model for the LHSI minimal-flow operation and to simulate the branch double-end shear fracture condition in order to predict the leakage flow volume and the water level drop rate of the refueling water storage tank (RWST) in order to analyze the impact of branch pipe fracture on the water leakage of the RWST. According to the study results, there is very little deviation between the operating condition of the system as it actually is and the Flowmaster model, and the leakage volume following branch pipe fracture is considerably less than that of the RWST. Leakage volume per minute is around 0.025% of the RWST’s overall volume, which has negligible influence on the unit’s safety. Based on the results of the simulation, this study suggests LHSI system operation recommendations.

Correction: Failure Analysis on Premature Fracture of Polyethylene Pipe for Floor Heating System

Correction: Failure Analysis on Premature Fracture of Polyethylene Pipe for Floor Heating System

Failure Analysis on Premature Fracture of Polyethylene Pipe for Floor Heating System

Failure Analysis on Premature Fracture of Polyethylene Pipe for Floor Heating System

Effects of drill pipe length and weight on bit on lateral and longitudinal vibrations

The vibration of a drill string is the topic under study in drilling and mining engineering. Drill string vibrations cause early failure of bits due to fatigue, drill pipe fracture and bearings damage. A modal and harmonic vibrational analysis of a drill string up to 60-65m long was done in a vertical water well by carrying out parametric studies. This paper investigates vibration of a drill string under longitudinal and mainly lateral which is the most dominant under the action of parameters such as drill pipe lengths and weight on bit. Finite element modelling of a drill string was made in Ansys workbench 2020, mechanical. Modal and harmonic frequencies were determined to obtain optimal drill pipe length and possible weight on bits. The drilling environment was assumed by using different weights on bit.

Failure Analysis of Oil Pipe Fracture in Steam Turbine Oil Supply System of Power Plant

Oil pipe fracture of the steam turbine oil supply system of a thermal power plant is carried out by macro inspection, spectral analysis, metallographic analysis, hardness analysis, and scanning electron microscope analysis. The results show that the fractured tubing is a fatigue fracture, and the source of the crack is the fatigue crack formed by the stress concentration of the weld, which eventually leads to the fracture and leakage at the place.

Explicit Incorporation of Discrete Fractures Into Pore Network Models

AbstractFractured porous media exist widely in reservoir rocks and fractures play a critical role in fluid flow processes. High resolution direct numerical simulations of fluid flow can provide important insight into pore‐scale processes and flow mechanisms in fractured permeable media, however, the tremendous computational costs prevent these methods from being applied into larger scale models. Pore network modeling is an alternative solution to this problem, but currently it can only be used in porous media without fractures. This work is concerned with incorporating discrete fractures into pore network modeling to represent fractured porous media. A new fracture matrix pore network model (FM‐PNM) is developed to efficiently simulate the fluid flow properties in fractures associated with the pore matrix. Discrete fractures are transformed into a fracture pipe network and integrated with the pore matrix that is represented by a network of pore bodies and pore throats. These two networks are coupled together to create a single nested network which is topologically equivalent to the fractured porous medium. This method extends the scope of applications of pore network modeling to fractured porous media. The permeability of the coupled network (FM‐PNM) is benchmarked by Lattice Boltzmann simulation for various structures of pore matrix and discrete fracture networks.

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.