Piping Loads Research Articles

Plastic limit load of Grade 91 steel pipe containing local wall thinning defect at high temperature

This paper aims to predict the plastic limit load of Grade 91 pipe at high temperature by experimental and numerical analysis methods. The elastic–plastic constitutive relation of P91 considering creep damage at high temperature is proposed and the effectiveness is verified by high-temperature instantaneous tensile test after creep of P91 sample. Then, using the elastic–plastic constitutive relation considering creep damage, the plastic limit loads of P91 pipe containing local wall thinning (LWT) defect at high temperature have been calculated by finite element (FE) method and the accuracy is checked by high-temperature burst experiment after creep of T91 pipe containing LWT. Finally, the fracture analysis and metallographic analysis of Grade 91 sample and pipe containing LWT defect are performed. The results show that the elastic–plastic constitutive relation of P91 considering creep damage proposed by this paper can well describe the elastic–plastic behavior of P91 under creep condition and is useful to calculate the plastic limit load of P91 pipe containing LWT. The failures of P91 tensile samples and T91 pipes containing LWT defect are both plastic fracture. This research would provide an optional method for structure integrity analysis of the pipe containing LWT defect at high temperature.

압축하중을 받는 압입강관말뚝의 지지거동 특성

The pressure penetrating steel pipe pile method which can be constructed in a narrow space using the hydraulic jack is used on the foundation reinforcement, extension of the structure and basement, restoration of the differential settlement etc.. This method is possible to construct in narrow areas and low story height, the non-noise and non-vibration works, and it is possible for the construction site to be clean without slime. And it is possible to confirm the bearing capacity of pile due to penetrating the pile with the compression load of hydraulic jack. In this study, the static load test with the load-transfer test was carried out to investigate the bearing behavior characteristics of the pressure penetrating steel pipe pile. Four series of static load test were executed to investigate the variation of bearing behavior of the pressure penetrating steel pipe pile. As a result of these tests, the allowable load of the pressure penetrating steel pipe was evaluated more than 637 kN, and the shaft resistance corresponding to 81~86% of each applied load was mobilized with only a small portion of the base resistance acting. And it was also evaluated that the unit skin friction was mobilized to maximum value after two months.

고정도 챔퍼링 공구 셋트의 개발

There has been a string of negligent accidents at the seaside, and there is presently a shortage of professional equipment to deal with such accidents. The purpose of this paper is to assess the development of a rescue lift. The critical load of a support pipe, and the stability of the rescue lift, were investigated using structural analysis. Critical-load analysis was used to study the effects of variations in the pipe length and the ratio of the moment of inertia. The total weight of the developed rescue lift is approximately 20.7 kg, and the lift passed the load tests.

구조해석을 통한 구조용 인양기 개발

There has been a string of negligent accidents at the seaside. In addition, there is a shortage of professional equipment to deal with these negligent accidents at present. The purpose of this paper is to assess the development of a rescue lift using a structural analysis. The critical load of a support pipe on the rescue lift is investigated in this paper. The stability of the rescue lift is also determined in a structural analysis. In the critical load analysis, the effects of variations in the pipe length and the ratio of the moment of inertia are investigated. The total weight of the developed rescue lift is approximately 20.7kg, and the lift passed the load tests.

Ultimate creep load and safety assessment of P91 steel pipe with local wall thinning at high temperature

Safety assessment of pipe with local wall thinning (LWT) at high temperature is highly important in power and nuclear engineering. Based on strain criterion and isochronous stress–strain curves at high temperature, this paper studied the ultimate creep load of pipe with LWT under creep condition by orthogonal experimental design and finite element numerical simulation. Firstly, the influence of LWT geometries was analyzed, which indicated that relative defect depth was the most significant factor to ultimate creep load. Secondly, the ultimate creep load formulas were regressed based on the ultimate creep loads of pipe with LWT at different creep times. And safety assessment curves for the pipe with LWT at high temperature by different strain criteria were proposed. Finally, the engineering method of allowable load of pipe with LWT by different strain criteria was constructed. The research results try to improve the safety assessment and structure integrity analysis of pipe with LWT at high temperature.

Pipe Failure Analysis and Impact of Dynamic Hydraulic Conditions in Water Supply Networks

Abstract Water pipe failures are associated with pipe characteristics, material properties, environmental and loading conditions. Understanding the impact of individual factors, their dynamics and interactions is extremely complex. The steady and unsteady state hydraulic conditions may impose excessive loading on assets. The resulting cyclic loadings when acting upon degraded (e.g. corroded) pipes could contribute to the development and acceleration of failures. This paper investigates the impact of the dynamic hydraulic conditions on pipe failures by analysing historical burst records, designing and implementing an extensive experimental programme and investigating case studies by correlating dynamic pressure and pipe failures.

Performance Quality Testing under Combined Loading of Polyethylene Pipes Reinforced with Aramid Fiber

Performance Quality Testing under Combined Loading of Polyethylene Pipes Reinforced with Aramid Fiber

Determination of collapse loads in pipe bends with ovality and variable wall thickness under internal pressure and in-plane opening moment

The combined effect of ovality and variable wall thickness on collapse load of pipe bends under in-plane opening bending moment with internal pressure was investigated using finite element limit analysis considering large geometric change effect. The material was assumed to be elastic–perfectly plastic. The collapse moments were obtained from moment-rotation curves drawn for each bend using twice-elastic-slope method. Thickening/thinning effect on collapse load is very minimal and can be neglected. The effect of ovality is significant with the reduction of collapse load by a maximum of 39.1% for the maximum internal pressure and ovality considered. Based on the finite element results, a mathematical expression is proposed to determine collapse load of the pipe bends with ovality and this equation has been verified with experimental collapse loads.

Fluid-dynamic loading of pipes conveying fluid with a laminar mean-flow velocity profile

The fluid-conveying pipe is a fundamental dynamical problem in the field of fluid–structure interactions. The possibility of modelling such a system analytically is mainly dependent on the availability of suitable analytical models for the fluid-dynamic loading acting on a vibrating pipe. The aim of this paper is an analytical study of the velocity profile effects for a straight pipe. The main contribution is the derived asymptotic model for the fluid-dynamic loading of the laminar and uniform mean flows that is applicable for any circumferential wavenumber of the mode shape of the pipe. The velocity profile effects are expressed in terms of the correction factors for the fluid-dynamic loading, which consists of three components being related to the translational, Coriolis and centrifugal accelerations of the fluid. This model also takes into account the effects of the fluid compressibility and the finite pipe length. The asymptotic model is derived from the solutions of the Pridmore-Brown equation for the Fourier transform of the vibrational fluid pressure. The solution procedure is based on the Frobenius power series method. The results about the velocity profile effects are compared with the previous, accessible studies in this field. As an application case, the discussed model is used to predict the flow effects on the first-mode natural frequency of a beam-type pipe with both ends clamped.

Analysis of Expansion Joints Movement Test in FCC Unit

The turboexpander is an equipment that works under very critical conditions requiring very low allowable nozzle forces and moments. A solution to minimize the piping loads transmitted to the equipment is the use of expansion joints (EJ). A usual piping stress analysis normally is not enough to guarantee the turboexpander reliability. This paper shows the results obtained in a movement test realized on metallic bellows EJ used in a turboexpander piping system. The EJ were designed according to the expansion joints manufacturer association code (EJMA), the diameters range from 0.457 to 2,898 m, the material of the bellows is Inconel 625 LCF and the shell materials are “killed” carbon steel, for refractory lined EJ or stainless steel 304H. A special test device was developed to apply the design movements on the EJ at the factory. A digital dynamometer was used for data acquisition and the tests were performed on 16 EJ of two distinct types: hinged and gimbal. The EJ were pressurized with water during the test. The reactions and corresponding displacements for each step of the test were recorded during loading and unloading.

Aanalysis of springback phenomenon in pipe bending

The term springback is defined as the change in geometry of a component after forming, when the forces are removed from forming tools. As springback affects the final shape of the part, it can lead to significant difficulties in the assembly of component when springback is not proper. This problem leads to fabrication of inconsistent sheet metal parts; the elastic strain recovery in the material after the tooling is removed. Bendingis the plastic deformation of metals about a linear axis called the bending axis with little or no change in the surface area. Bending types of forming operations have been used widely in sheet metal forming industries to produce structural stamping parts such as braces, brackets, supports, hinges, angles, frames, channel and other nonsymmetrical sheet metal parts. Among them, quite a few efforts have been made to obtain a deep understanding of the springback phenomenon. The beam theory has been applied to formulate the curvature before and after loading of pipe. This research work has focused on study effect of springback effect with a new approach. The ANSYS software is used to analyze spring back effect. The detail study of this springback effect is presented in this paper.

Limit Load Determination and Material Characterization of Cracked Polyethylene Miter Pipe Bends1

The quality of Natural Gas Piping Systems (NGPS), must be ensured against manufacturing defects. The main purpose of the present paper is to investigate the effect of loading mode and load angle (30 deg, 45 deg, and 60 deg) on the limit load of miter pipe bends (MPB), under different crack depths a/W = 0–0.4 at a crosshead speed 500 mm/min. The geometry of cracked and uncracked multi-miter pipe bends are pipe bend angle, α = 90 deg, pipe bend factor, h = 0.844, standard dimension ratio, SDR = 11, and three junctions, m = 3. The material of the investigated pipe is a high-density polyethylene (HDPE), which is commonly used in NGPS. The welds at the miter pipe junction are produced by butt-fusion welding. For all loading modes the limit load is obtained by the tangent intersection (TI) method from the load–deflection curves produced by the specially designed and constructed testing machine at the laboratory5. Tensile tests are conducted on specimens longitudinally extruded from the pipe with thickness, T = 10, 30 mm, at different crosshead speeds (5–500 mm/min), and different gauge lengths (G = 20, 25, and 50 mm) to determine the mechanical properties of welded and unwelded specimens. The fracture toughness is determined on the basis of elastic plastic fracture mechanics (EPFM). Curved three-point bend specimens (CTPB), are used. All specimens are provided with artificial precrack at the crack tip, a/W = 0.5. The effect of specimen thickness variation (B = 10, 15, 22.5, 30, 37.5, and 45 mm) for welded and unwelded specimens is studied at room temperature (Ta = 23 °C) and at different crosshead speeds, VC.H, ranging from 5 to 500 mm/min. The study reveals that increasing the crack depth leads to a decrease in the stiffness and limit load of MPB for both in-plane, and out-of-plane bending moment. In case of combined load (out-of-plane and in-plane opening; mode), higher load angles lead to an increase in the limit load. The highest limit load value occurs at a loading angle, ϕ = 60 deg. In case of combined load (out-of-plane and in-plane closing; mode), the limit load decreases with increasing load angles. At a load angle ϕ = 30 deg, the higher limit load value occurred in both cases. For combined load opening case, higher values of limit load are obtained. The crosshead speed has a significant effect on the mechanical behavior of both welded and unwelded specimens. The fracture toughness, JIC, is greater for unwelded than welded specimen.

Effect of Load Angle on Limit Load of Polyethylene Miter Pipe Bends1

The aim of this paper is to investigate the effect of crack depth a/W = 0–0.4 and load angle (30 deg, 45 deg, and 60 deg) on the limit load of miter pipe bends (MPB) under out-of-plane bending moment with a crosshead speed 500 mm/min. The geometry of cracked and un-cracked multi miter pipe bends are: bend angle, α = 90 deg, pipe bend factor, h = 0.844, standard dimension ratio, SDR = 11, and three junctions, m = 3. The material of the investigated pipe is a high-density polyethylene (HDPE), which is applied in natural gas piping systems. Butt-fusion welding is used to produce the welds in the miter pipe bends. An artificial crack is produced by a special cracking device. The crack is located at the crown side of the miter pipe bend, such that the crack is collinear with the direction of the applied load. The crack depth ratio, a/W = 0, 0.1, 0.2, 0.3, and 0.4 for out-of-plane bending moment “i.e., loading angle ϕ = 0 deg”. For each out-of-plane bending moment and all closing and opening load angles the limit load is obtained by the tangent intersection method (TI) from the load deflection curves produced by the specially designed and constructed testing machine at the laboratory (Mechanical Design Department, Faculty of Engineering, Mataria, Helwan University, Cairo/Egypt). For each out-of-plane bending moment case, the experimental results reveals that increasing crack depth leads to a decrease in the stiffness and limit load of MPB. In case of combined load (out-of-plane and in-plane opening; mode) higher load angles lead to an increase in the limit load. The highest limit load value appears at a loading angle equal, ϕ = 60 deg. In case of combined load (out-of-plane and in-plane closing; mode) the limit load decreases upon increasing the load angle. On the other hand, higher limit load values appear at a specific loading angle equal ϕ = 30 deg. For combined load opening case; higher values of limit load are obtained. Contrarily, lower values are obtained in the closing case.

Plastic Load of Precracked Polyethylene Miter Pipe Bends Subjected to In-Plane Bending Moment1

The main purpose of the present paper is to investigate the effect of crack depth on the plastic load (collapse load) of miter pipe bends (MPB) under in-plane bending moment. The experimental work is conducted to investigate multimiter pipe bends, with a bend angle 90 deg, pipe bend factor h = 0.844, standard dimension ratio (SDR) = 11, and number of welding junctions m = 3 under a crosshead speed 500 mm/min. The material of the investigated pipe is a high-density polyethylene (HDPE), which is used in natural gas (NG) piping systems. The welds in the miter pipe bends are produced by butt-fusion method. The crack depth varies from intrados to extrados location according to the in-plane opening/closing bending moment, respectively. For each in-plane bending moment, the plastic load is obtained by the tangent intersection (TI) method from the load–deflection curves produced by the testing machine specially designed and constructed in the laboratory.5 The study reveals that increasing the crack depth leads to a decrease in the stiffness and plastic load of MPB for both in-plane closing and opening bending moment. Higher values of the plastic load are reached in case of opening bending moment. This behavior is true for all investigated crack depths. A circumferential external crack has an obvious effect on the behavior of load–deflection curve. The linear elastic region in both mode of loading decreases with increasing crack depth.

Plastic collapse loads in shape-imperfect pipe bends under in-plane opening bending moment

The combined effect of ovality and thinning/thickening on collapse load of pipe bends under in-plane opening bending moment was investigated using finite element limit analysis considering large geometric change effect. The material is assumed to be elastic-perfectly plastic. Twice-elastic-slope method is used to obtain collapse moment from moment–rotation curves drawn for each bend. Variation of thickness due to thinning in the cross section of pipe bend produces negligible effect on collapse load. The effect of ovality is significant except for pipe ratio 20 with λ = 0.5. A new closed-form solution is proposed to determine collapse moment of pipe bends with ovality and it is validated with existing experimental data.

원형 동관의 2축압축 변형특성 및 조직변화에 관한 연구

The deformation characteristics and microstructure changes in a round copper pipe under biaxial compression was studied using a horizontal compression die. The change of material properties, punch load and deformation behavior were monitored using various compressive deformation rates in the range of 0.5mm/min.~450mm/min. The strains, either tensile or compressive, were estimated from Vickers microhardness test results. The punch load and deformation characteristics of the round copper pipes were found to change greatly at a deformation rate of about 200mm/min. The punch load decreased with increasing compressive deformation rate. The results of numerical simulations agreed well with what was expected from the final microstructure and the hardness profile estimated from the final deformation strains.

Calculation of large-size polyethylene pipes with hollow walls

UDC 539.3 For polyethylene pipes with a hollow (cellular) wall, we have proposed a method for the estimation of the stress-strain state arising under the action of soils. We have considered two modes of the loading of a cellular pipe: with a rigid base and with subsidence into the soil. We have established which of the building standards for pipes with a solid wall should be used in the calculations of pipes with a hollow wall. We have calculated the critical deflections of pipes and determined the criteria that must be used for the assigned geometrical and mechanical parameters of pipes and soils.

Modelling the embedment process during offshore pipe-laying on fine-grained soils

Subsea pipelines are becoming an increasingly significant element of offshore hydrocarbon developments as exploration moves into deep-water environments further from shore. During the lay process, pipelines are subject to small amplitude vertical and horizontal oscillations, driven by the sea state and lay vessel motions. Centrifuge model tests have been used to simulate these small-amplitude lay effects, with varying degrees of idealization relative to the real lay process. In the soft soils found in deep water, pipe embedment can exceed a diameter or more, thus significantly affecting the lateral pipe–soil interaction, axial resistance, and thermal insulation. In this paper, results from centrifuge model tests are used to calibrate a model for calculating the dynamic embedment of a subsea pipeline. The model uses elements of plasticity theory to capture the effects of combined vertical and horizontal loading, and incorporates the softening of the surrounding soil as it is remoulded due to the pipeline motions. Influences from the lay rate, lay geometry, and sea state are included in the calculation process. The model is compared with observed as-laid pipeline embedment data from field surveys at three different offshore sites. Using site-specific soil parameters obtained from in situ testing and idealized pipe loads and motions to represent the load and displacement patterns during offshore pipe-laying, respectively, the model is shown to capture well the final as-laid embedment measured in the field surveys.

A Simplified Strength Checking Approach for a Header–Nozzle Intersection Under Combined Piping Loads

To investigate the strength checking methods for a semi-cylindrical header–nozzle intersection under combined piping loads, the simplified strength checking formulae for two piping load combinations, which are typical in engineering practice, are suggested based on the combined limit piping load interactions of the header. Furthermore, three methods for determining the allowable piping load parameters of the proposed formulae, namely the plastic work curvature (PWC) method of inelastic analysis route for design by analysis (DBA), the twice elastic slope (TES) method of inelastic analysis route for DBA, and the elastic finite element analysis (FEA) method of elastic analysis route for DBA, are presented and compared. Based on the theoretical analyses and the parametric comparison study results of the three methods, it can be concluded that the PWC method, which can take the hardening material effect on the plastic load results into account well and use the engineers' experience independent plastic work as the global indicator of gross collapse, is the most reliable one among the three methods, while the elastic FEA method is of great value for engineers to estimate the allowable piping loads quickly and conveniently.

Experimental Research on Fracture Toughness of High Grade Line Pipe

Crack tip opening displacement (CTOD) tests were carried out on different positions of X70, X80 and X100 pipe by three-point bend testing method. The results show that the crack propagation resistance and the tear modulus of base metal, heat affected zone (HAZ), and weld of X70 and X80 pipe are larger than that of X100 pipe. At the same time,The initial CTOD values and the CTOD values withmaximum load of X70 and X80 pipe are larger than that of X100 pipe.The test results suggest that the fracture toughness, crack initiation and propagation resistance of theX70 and X80 pipe are greater than that of X100 pipe, and the mechanismis analyzed finally.