Pipe Strain Research Articles

Field performance of large section concrete pipes cracking during jacking in Chongqing – A case study

Long-distance large-section pipe jacking inevitably encounters a variety of complex engineering problems in the construction process, one of which is the pipe concrete cracking during jacking. A large-area rupture and leakage occurred at pipe No. 61 during the large-section concrete pipe jacking adopted in the project studied in this paper. After a detailed field investigation and on-site pipe strain monitoring, the possible causes of pipe cracking were analysed. First, a direct compression failure of the pipes was ruled out. Additionally, a large number of pores were found inside the concrete fragments falling from pipe No. 61’s site. Thus, we suspected that the pipe cracking was attributed to the conversion of the pipe’s compressive stress into the concentrated tensile stress by the substantial pores inside the pipes, which resulted in a concrete tension fracture. The core sampling results of the pipes after monitoring confirmed that there were indeed plenty of small pores in multiple pipe concretes, while the strain monitoring results indicated that the compressive stress of the pipes during normal jacking had the potential to produce the tensile stress that could crack the concrete. Combining this with the jacking deviation monitoring curves, it could be deduced that the upper right side of the pipes was most prone to failing initially. This coincided with the rupture area of pipe section No. 61 but was also consistent with the prediction of pipe No. 60 cracking, thus proving the rationality of the pipe rupture cause hypothesis. Finally, no cracking occurred after improving the production quality of the pipes. This not only shows that the pipe quality is indeed the root cause of cracking but also effectively solves the engineering problems and provides an excellent reference for similar projects.

Experimental study of burial depth effect on embedded pipe deformations in sandy slopes under dynamic landsliding

This paper studies the influence of burial depth on slope response and pipe performance under earthquake induced landslide. Three physical models are constructed and tested using 1 g shaking table device. The slope is divided into four sections as toe, lower and upper sections of the slope face and crest. The pips which perpendicularly cross the slope are embedded at these positions in three burial depths to demonstrate burial depth effect in each section.According to the experiments, dynamic slope response which moderately develops at deeper depths at toe and lower section, displays a clear downtrend at upper section and crest. Also, the pipe response depends on pipe route and slope displacement pattern. The pipe deformations have positive correlation with depth at upper section and crest, but show opposite behavior at toe and lower section. Moreover, the horizontal strains impact on total strains in buried pipes reduces at greater depths.

Modeling and Simulation of Deepwater Pipeline S-Lay With Coupled Dynamic Positioning

Dynamic position (DP) control and pipeline dynamics are the two main parts of the deepwater S-lay simulation model. In this study, a fully coupled analysis tool for deepwater S-lay deployment by dynamically positioned vessels is developed. The method integrates the major aspects related to numerical simulation, including coupled pipeline motion and roller contact forces. The roller–pipe interaction is incorporated in the S-lay pipeline model using a contact search method based on a lumped-mass (LM) formulation in global coordinates. A proportional-integration-differentiation (PID) controller and a Kalman filter are applied in the vessel motion equation to calculate the thrust allocation of the DP system in time domain. Numerical simulation results showed that the dynamic effects add a significant contribution to the tension, but have little influence on the maximum pipe stress and strain. The dynamic response of the coupled S-lay and DP pipeline deployment system increases the demand on the tensioner load carrying capability as well as the maximum DP thruster power.

Three-Dimensional Strain-Based Model for the Severity Characterization of Dented Pipelines

Oil and gas pipelines traverse long distances and are often subjected to mechanical forces that result in permanent distortion of its geometric cross section in the form of dents. In order to prioritize the repair of dents in pipelines, dents need to be ranked in order of severity. Numerical modeling via finite element analysis (FEA) to rank the dents based on the accumulated localized strain is one approach that is considered to be computationally demanding. In order to reduce the computation time with minimal effect to the completeness of the strain analysis, an approach to the analytical evaluation of strains in dented pipes based on the geometry of the deformed pipe is presented in this study. This procedure employs the use of B-spline functions, which are equipped with second-order continuity to generate displacement functions, which define the surface of the dent. The strains associated with the deformation can be determined by evaluating the derivatives of the displacement functions. The proposed technique will allow pipeline operators to rapidly determine the severity of a dent with flexibility in the choice of strain measure. The strain distribution predicted using the mathematical model proposed is benchmarked against the strains predicted by nonlinear FEA. A good correlation is observed in the strain contours predicted by the analytical and numerical models in terms of magnitude and location. A direct implication of the observed agreement is the possibility of performing concise strain analysis on dented pipes with algorithms relatively easy to implement and not as computationally demanding as FEA.

Simplified evaluation of pipe strains crossing a normal fault through the dissipated energy method

A dissipated energy method is proposed in this paper to calculate the maximum and minimum pipe strains crossing a normal fault perpendicularly. Two plastic hinges are assumed to form on either side of the fault plane. The curved pipe segment between plastic hinges has different lengths on the footwall and hanging wall sides due to the difference in bearing and uplift soil resistances. A curved pipe length ratio is determined for use in deriving simplified geometric relations. Four energy components are then computed considering rotations at plastic hinges, plastic elongations of the curved pipe segment, and yielding of axial, uplift and bearing soil springs. Minimization of dissipated energy is carried out to find the optimal position of the curved pipe segment for different fault offset. The pipe strains evaluated from the proposed technique are compared with calculations using the existing three-beam analytical method and centrifuge experiments. Upon the successful calibration of the calculation model, a sensitivity analysis is performed to assess the influence of backfill material, dip angle, burial depth and pipe strength. In the end, an illustrative example is presented to employ the developed analysis framework to run fragility analysis for three pipelines with different diameter to thickness ratios.

Measurement of Pipe Strain Using an Ultrasonic System

Ultrasonic sensors can be used to measure strain occurring on an object. In this investigation, an ultrasonic signal utilized the reflected signal as a means of monitoring the condition of a pipe. This is an alternative to the strain gage which is commonly used but has a limited life span. The ultrasonic signal was transmitted to a specific location on the pipe, and then reflected by the pipe surface which experienced strain towards the ultrasonic receiver. Collimation of the transmitted and received signals is performed by aluminum probe cones attached to both ultrasonic transducers. Changes in the strain due to the pipe bending will result in changes in the electric signal due to the changes in the sound intensity. The received electric signal was processed by a signal conditioning circuit consisting of preamplifier, amplifier, band-pass filter and rectifier before being displayed. Two experiments were conducted to establish the relationship between strain on the pipe and the ultrasonic intensity. In order to verify the results, an experiment was conducted using a strain gage and the results were identical. The results show that the system is able to measure strain when the pipe bends.

Fragility analysis of gray iron pipelines subjected to tunneling induced ground settlement

Tunnel excavations can cause ground surface settlement which in turn affects the structural integrity of adjacent pipelines. This paper explores the probabilistic risk assessment of gray iron pipes subjected to tunneling. In the beam-on-spring analysis, a modified Gaussian distribution profile was incorporated as displacement-controlled boundary conditions on spring elements. The modeling strategy was evaluated by comparing calculated pipe strains with field and centrifuge experimental measurements, as well as empirical solutions. The calibrated numerical model was then used to perform parametric fragility analyses using a machine learning technique called Lasso Regression to demonstrate the relative importance of various parameters. It has been found that existing pipelines with a smaller pipe diameter and a larger pipe wall thickness buried at a shallower depth in loosely compacted soils with a smaller soil friction angle are less prone to failure due to tunneling induced ground settlement.

Mutual effect of Coriolis acceleration and temperature gradient on the stress and strain field of a glass/epoxy composite-pipe

• Three-dimensional thermoelastic solution for a composite pipe using the heat transfer equation along thickness. • Effect of body forces created by rotation and the Coriolis acceleration. • Approximation of Bessel equation as an Euler type differential equation while assuming a thin wall composite pipe. • Evaluation of angular velocity and the composite pipe wall thickness as two important parameters in making the Coriolis effect. Rotating composite pipes due to their light-weight, high specific strength and stiffness and excellent fatigue resistance are a good substitute for most common metallic alloys. This paper presents the exact three-dimensional thermoelastic solution for a composite pipe using the heat transfer equation along thickness, by taking into account the body forces created by rotation and the Coriolis effect. A Bessel nonhomogeneous differential equation is derived for displacement along the radial direction, which can be approximated by a Euler equation using the pipe wall thinness restriction. The composite pipe rotational speed and wall thickness are two key parameters which are used to illustrate the Coriolis effect on the pipe stress and strain filed. Results indicated that for the wall thickness to inner radius ratios less than 0.1, all stresses, strains, and displacements were experienced 4% increase, except for radial stress, upon which Coriolis acceleration had no effect . In the case of thermomechanical loading, increasing the pipe wall thickness resulted in variation of the thermal stress and the centrifugal force values. Numerical verifications showed that for thickness to radius ratios less than 0.05 the amount of deviation between Bessel (numerical) and Euler (analytical) formulation is less than 5%.

Monitoring Shear Strain in Shallow Subsurface Using Mini Pipe Strain Meter for Detecting Potential Threat of Slope Failure

Abstract The following study examines a new soil measurement method to achieve simple and reliable slope monitoring to ensure labor safety. The method measures the increase in shear strain in the shallow subsurface of the slope. The target that is measured in the soil using this method is different from that of the conventional methods, which use extensometers and inclinometers. Although the increase in shear strain in the shallow subsurface is considered negligible, this study discusses the potential application of the measurement for detecting the potential threat of slope failure. A mini pipe strain (MPS) meter was developed to measure shear strain in the shallow subsurface of slopes. A full-scale test model of slope failure was constructed via excavation to examine the detectability of the threat of slope failure using an MPS meter. Corresponding to the development of slip surfaces in deep positions, less than 0.5 % of shear strain in the shallow subsurface is clearly observable. Although the inverse of the shear strain rate (1/ν) showed a drastic decrease prior to failure, the slope did not fail immediately; in addition, creep phenomena was observed. An unstable slope may be considered a stable one because of the lag time prior to failure. Identifying the second or third creep could provide a few minutes for workers to escape. Accordingly, the threat of workers being injured by collapsing soil can be reduced by using the proposed method and sensor.

Study on the contact behavior of pipe and rollers in deep S-lay

S-lay is a widely used method for offshore pipe installation. In recent years, S-lay has gradually applied to the deepwater condition. Because of the increasing pipe weight in deep S-lay, there exist severe and complex contact problems between the overbend pipe and roller supports of the stinger. In deep S-lay design, it is difficult to solve this nonlinear mechanics problem, and there remain confusion and difficulties to predict the roller contact forces and the pipe strain level in S-lay design.The present paper develops a refined finite element model with the framework of ABAQUS, which considers the complex surface contact behaviors in the overbend section. The features of the contact state of different rollers within one roller box are discussed, and the resultant support forces from each roller box are calculated and compared with the commercial design code. The overbend strain level of five S-lay cases is investigated and the pipelaying safety is checked by DNV rules. The simulation results show that the proposed model can provide more accurate and reasonable predictions on roller forces and pipe strain distribution for deepwater S-lay design.

Study on Dynamic Strain Regularity and Influencing Factors of Shallow Buried Metal Pipe under Collapse Impact Load

With the combination of model experiment and numerical simulation, we explore the effect of collapse height, weight, and pipe‐soil stiffness ratio on dynamic strain of shallow buried metal pipe under the collapse impact load. By analyzing the strain at different measuring points of the buried pipeline, the strain law of the buried pipeline under the collapse impact load is obtained. Based on the range analysis and variance significance analysis, it was found that the pipe‐soil stiffness ratio has a more significant impact on the dynamic strain of the buried pipeline under impact compared to the collapse height and the weight. Then, the numerical simulation method was used to further analyze the effect of pipe‐soil stiffness ratio on the dynamic response of buried pipelines; the following conclusions are drawn: As the stiffness ratio of pipe‐soil increases, the plastic stress and strain of the buried pipeline will decrease, and influence of the pipeline by the collapse impact is slighter.

Experimental Study on the Dynamic Strain of a Thin-Walled Pipe in the Gas Cloud Explosion with Ignition Energy

Experimental Study on the Dynamic Strain of a Thin-Walled Pipe in the Gas Cloud Explosion with Ignition Energy

UOE pipe strains measurement during manufacturing process using digital image correlation

UOE pipe manufacturing processes influence directly on pipeline resilience and operation capacity. At present, most spread pipe manufacturing method is UOE. This kind of manufacturing process is based on cold forming principle. To avoid appearance of unwanted effects, the need to know the level of strains resulted after every technological step appeared. For this case a manufacturing process by using special designed equipment is simulated. The experimental simulation presented in this paper is performed for L 415MB (X60) steel plate with 7.9 mm thickness and a width of 1250 mm. As a result a DN 400 (16 inch) pipe is obtained. Manufacturing process is monitored by Digital 3D Image Correlation System Q-400 and the principle of operation is based on Digital Image Correlation.

The stiffness of axial pipe–soil springs and axial joint springs tested by artificial earthquakes

This study proposes an experimental method to obtain the stiffness of axial pipe–soil and axial joint springs in time and frequency domains. The proposed method can determine axial pipe–soil spring stiffness by using the pipe strains and slippages between pipes and soil. It can also determine axial joint spring stiffness by utilizing pipe strains and joint deformations. The pipe–soil spring stiffness values of ductile cast iron (DCI) and welded steel (WS) pipes are obtained and analyzed through artificial earthquake tests on a 24m × 24m buried pipe network. Artificial earthquakes are produced with trinitrotoluene explosives. Three theoretical models are discussed, and their results are compared with the test results. The comparisons indicate that the proposed experimental method is valid to obtain the stiffness of axial pipe–soil and axial joint springs. The stiffness values can be a benchmark to study the pipe–soil interaction and flexible joints. The effects of axial pipe–soil spring stiffness on the joint deformations of DCI pipes and pipe strains of WS pipes are also discussed.

Laboratory Investigation of Buried Pipes Using Geogrid and EPS Geofoam Block

This paper describes the results of laboratory tests conducted on flexible PVC pipes with diameter of 160 mm, buried in unreinforced and reinforced trench with geogrid layer and expanded polystyrene (EPS) geofoam block. The repeated load with amplitude of 450 kPa and frequency of 0.33 Hz was applied on the trench surface, using plate loading at a diameter of 150 mm to simulate the vehicle loads. Vertical diameter strain (VDS), strain at pipe’s crown and transferred pressure on the pipe’s crown were recorded throughout the test for up to 500 cycles of loading. The variables examined in the testing program include thickness of EPS block (30, 60 and 100 mm) and its density (10, 20 and 30 kg/cm3). The pipes were embedded at depths 1.5 times their diameter and the width of EPS block was kept constant at 2.0 times the pipe diameter in all tests. The results show that the values of VDS and pipe strain increased rapidly during the initial loading cycles, thereafter the rate of deformation and strain reduced significantly as the number of load cycles increased. According to the results, the minimum VDS and pipe’s crown strain were provided by 100 mm thickness and 30 kg/cm3 of EPS block placed over the pipe with a geogrid layer giving values of, respectively, 0.15 and 0.10 times those obtained in the reinforced trench with a geogrid layer.

Combined Use of Jute Geotextile-EPS Geofoam to Protect Flexible Buried Pipes: Experimental and Numerical Studies

This paper addresses the results of the experimental and numerical studies conducted on 4.2 mm thickness and 110 mm diameter high-density polyethylene (HDPE) pipes buried in fly ash material overlying stone dust beds. The model tests were performed using single and double layers of expanded polystyrene (EPS) geofoam as compressible inclusions. In addition to that, jute geotextile was used as a reinforcement for the infill fly ash along with EPS geofoam inclusion to obtain induced trench condition. The test beds were subjected to loading on the fly ash surface with the help of a rigid steel plate to simulate as a strip footing in different embedment depths of the pipe (1–3 times pipe diameter). The test results revealed that the pressure and strain values in the pipe reduced significantly in the presence of EPS geofoam and jute geotextile related to the location of the pipe. In the case of double layers of EPS geofoam could induce reduction of the pressure up to 87.2% and strain about 63.5% respectively depending on the density and width of EPS geofoam. Whereas, at the same burial depth, in the presence of jute geotextile together with EPS geofoam can be reduced up to 93.8 and 73.4% for pressure and strain respectively depending on EPS geofoam density and number of reinforcement. Moreover, the jute geotextile-EPS geofoam combination of model test results were validated with finite element program. A good agreement was observed on pressure-settlement response and pipe strain between experimental and numerical investigations. The numerical studies show that the jute geotextile distributes stresses in the lateral direction and then the stresses on the pipe significantly reduced.

Geosynthetic Protection for Buried Pipes Subjected to Surface Surcharge Loads

Geosynthetics have been extensively used as reinforcement in several geotechnical engineering applications. Regarding pressurised buried pipes, geosynthetics can protect the pipe against mechanical damages and reduce the consequences of explosions and leakages. This paper presents and discusses the use of geosynthetic reinforcement for the protection of buried pipes against the influence of localized surcharges on the ground surface. Model tests were carried out under plane-strain conditions where increasing surcharge pressures were applied on the surface of a dense sand layer containing a buried pipe. Three polymeric geogrids were used as reinforcements. Reinforcement arrangements consisting of a geogrid horizontal layer, an inverted U arrangement and an arrangement where the geogrid completely enveloped the pipe were tested. The results obtained showed that the presence of the reinforcement was effective in reducing the vertical stresses transferred to the pipe as well as in reducing pipe strains. The arrangement with the geogrid enveloping the pipe was the most efficient and the geogrid that combined satisfactory tensile stiffness and aperture to soil particle diameter ratio was the one which performed best. The testing programme showed the potentials for the use of geosynthetic reinforcement in reducing the effects of surface surcharges on buried pipes.

Local buckling failure analysis of high-strength pipelines

Pipelines in geological disaster regions typically suffer the risk of local buckling failure because of slender structure and complex load. This paper is meant to reveal the local buckling behavior of buried pipelines with a large diameter and high strength, which are under different conditions, including pure bending and bending combined with internal pressure. Finite element analysis was built according to previous data to study local buckling behavior of pressurized and unpressurized pipes under bending conditions and their differences in local buckling failure modes. In parametric analysis, a series of parameters, including pipe geometrical dimension, pipe material properties and internal pressure, were selected to study their influences on the critical bending moment, critical compressive stress and critical compressive strain of pipes. Especially the hardening exponent of pipe material was introduced to the parameter analysis by using the Ramberg–Osgood constitutive model. Results showed that geometrical dimensions, material and internal pressure can exert similar effects on the critical bending moment and critical compressive stress, which have different, even reverse effects on the critical compressive strain. Based on these analyses, more accurate design models of critical bending moment and critical compressive stress have been proposed for high-strength pipelines under bending conditions, which provide theoretical methods for high-strength pipeline engineering.

Methods and Systems for High-temperature Strain Measurement of the Main Steam Pipe of a Boiler of a Power Plant While in Service

It has been a challenge for researchers to accurately measure high temperature creep strain online without damaging the mechanical properties of the pipe surface. To this end, a noncontact method for measuring high temperature strain of a main steam pipe based on digital image correlation was proposed, and a system for monitoring of high temperature strain was designed and developed. Wavelet thresholding was used for denoising measurement data. The sub-pixel displacement search algorithm with curved surface fitting was improved to increase measurement accuracy. A field test was carried out to investigate the designed monitoring system of high temperature strain. The measuring error was less than 0.4 ppm/°C, which meets actual measurement requirements for engineering. Our findings provide a new way to monitor creep damage of the main steam pipe of a boiler of an ultra-supercritical power plant in service.

The Numerical Analysis and Experimental Study of the Stress Intensity Factor and Outer Surface Strain of the Pressure Pipe with Internal Longitudinal-Cracks

The strain characteristics in the outer surface of the pipe and the stress intensity factor in crack front with internal longitudinal-cracks were analyzed by the finite element method. According to the results of analysis, the outer surface strain variation to crack size was got and the relationship of stress intensity factor and crack size was known. Based on resistance strain gauges and fiber optic sensing technology, pressure pipe crack extension monitoring device was designed and the outer surface circumferential strain were tested .The results of finite element analysis and experiment are in good agreement. The outer surface strain variation in this paper can be used to analyze the situation of internal longitudinal-cracks extension.That relationship of stress intensity factor and crack size has an important reference to the safety assessment of pipe with internal longitudinal-crack.