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Each material has its own effect and behavior on external impacts like heat, force, tension, compression, torsion etc. It is important to study and analyze these behaviors before selecting a material for an engineering application in the design aspects itself. If predicted values analyzed by both mathematical and software are available it is easy to get the reliable details in the pre design itself. By this one can ensure the safety of the component and the system also. In this investigation, the effects of torsional loads on mild steel round shafts with various diameters and lengths have been analyzed. The additional effects like angle of rotation, rpm and duration also considered to find the optimum predicted value. The data observed by various experiments are analyzed by design of experiments especially by response surface methodology. Minitab software is used for canalization. The data are tabulated and kept for future reference. Noise effect due to the gradual torsional load performed in the gear box and other rotating components is also studied for healthy working environment. The nature and characteristics of material also be explained by this noise analysis.

Lined pipes are Carbon Manganese pipes (backing steel) with a thin liner of corrosion resistant alloy, mechanically bonded to the backing steel. Lined pipes are cheap to produce compared to clad pipes, where the liner is metallurgically bonded to the backing steel, but they are also more complex to design for. One particularly challenging aspect is to determine load/displacement levels for potential disbondment between the liner and the backing steel. In that context, the strength of the metallurgical bond between the backing steel and the liner in a lined pipe may have an important influence. The metallurgical bond may be characterized by residual stresses in the liner and the friction coefficient between the inner surface of the backing steel and the outer surface of the liner. Current industry testing practice to determine the magnitude of residual stresses is defined in API 5LD, but these tests fail to consider boundary effects and Poisson’s ratio effects which have a substantial impact on the measured stress levels. An analytical formulation for stress levels in the liner close to free boundaries, and interaction between axial and hoop stresses are presented in this paper and validated by detailed finite element analyses. This formulation provides excellent transparency in terms of understanding which physical parameters are important in the surface interaction between the liner and the backing steel, and, among several applications, they are a highly useful tool to reinterpret the test regimes suggested in API 5LD.

Based on the importance and complex working environment of X70 pipelines, stress measurement and analysis were done on an in-service process pipe, an anamorphic pipe in tunnel and three new welded pipes. Stresses in both the inner and outer walls of pipes were measured by X-ray diffraction, and thus the components of complex stress, internal pressure working stress, welding residual stress (WRS) and bending stress, were obtained by comparative analysis on stresses of various pipes. The results show that the maximum WRS occurs in the heat affected zone on inner wall, and its orientation is parallel to the weld seam. These maximum WRSs in various measured spots are mostly more than 0.80 σ 0.2 and up to 1.05 σ 0.2 . However, on outer wall the stresses are less than 0.40 σ 0.2 , and WRS appear in the weld area of 40 mm wide. For the tunnel pipeline, its maximum axial and circumference stresses were up to 0.93 σ 0.2 and 0.80 σ 0.2 , respectively.

This study examines the applicability of a micromechanics approach based upon the computational cell methodology incorporating the Gurson–Tvergaard (GT) model and the CTOA criterion to describe ductile crack extension of longitudinal crack-like defects in high pressure pipeline steels. A central focus is to gain additional insight into the effectiveness and limitations of both approaches to describe crack growth response and to predict the burst pressure for the tested cracked pipes. A verification study conducted on burst testing of large-diameter, precracked pipe specimens with varying crack depth to thickness ratio ( a / t ) shows the potential predictive capability of the cell approach even though both the GT model and the CTOA criterion appear to depend on defect geometry. Overall, the results presented here lend additional support for further developments in the cell methodology as a valid engineering tool for integrity assessments of pipelines with axial defects.

Sandwich Pipes (SPs) have been developed to overcome the required flow assurance and pressure capacity issues in deep and ultra-deep waters. This research aims at studying the influence of certain structural parameters on the pressure capacity (also referred to as the plastic buckling pressure) of Sandwich pipelines. The use of high grade steel pipes, as the internal or external pipes, has also been considered as one of the design parameters in this study. Moreover, a comprehensive parametric study, considering a practical range of the parameters that influence the response of SPs (and considering 3840 SP configurations) was conducted. The results from this large array of pipes were used to formulate a practical equation, capable of estimating the plastic buckling pressure of SPs. The accuracy of the proposed equation was evaluated by comparing the results with the experimental and numerical results available in the literature. The comparative results demonstrated that the proposed equation could predict the buckling capacity of such pipes with a reasonable accuracy. Furthermore, the proposed equation was used, along with a general optimization procedure, to establish the most optimum and cost-effective combination of structural parameters for SPs suitable for use in various water depths.

Surface-breaking cracks affect the material and structural properties of concrete pipes. Therefore, the nondestructive evaluation of the crack depth is important to assess the serviceability of these pipes, which are commonly used in underground infrastructure and trenchless installations (micro-tunneling). This paper presents theoretical, numerical and experimental results for the depth evaluation of surface-breaking cracks. The wall of a concrete pipe is represented as a plate in the numerical and the analytical studies. In the experiments, an ultrasonic piezoelectric transmitter is used as a source. The propagation of the ultrasonic pulse is analyzed using the wavelet transform. A newly proposed wavelet transmission coefficient (WTC) is measured using an equal spacing configuration for the crack depth evaluation in concrete pipes and concrete plates. The results from laboratory and in situ tests show good potential for the practical application of the WTC for the depth evaluation of surface-breaking cracks.

This paper examines a cast-in-place composite polymer liner used in retrofitting cracked cast iron pressure water pipes. The installation of the liner can result in the formation of geometric imperfections (wrinkles) of different patterns and sizes if the external circumference of the liner exceeds the internal circumference of the host pipe. A series of split-disk tests were conducted on 25-mm wide ring samples of the polymer liner to examine the effects of the presence of three different wrinkle configurations, the loading rate, and cyclic loading on the circumferential strength of the liner. In all the test samples, cracking of the resin occurred at the wrinkle, but ultimate capacity was always greater than the cracking load. A reduction in the ultimate hoop strength of up to 23% occurred, depending on the wrinkle pattern. Cyclic loading corresponding to 50-year service life was applied, leading the resin in some samples to crack at the wrinkle. At a very slow loading rate of 0.1 mm/min, the ultimate s...

Analytical and numerical methods have been developed for the solution of stress-strain and limit state problems of piping systems (in the case of the presence of flaws in them as well). The fracture strength of pipe steels during long-term service has been studied. A methodology and a software have been developed for the assessment of stress-strain state to extend the life of active pipelines. The developments made are used to increase the reliability of Ukrainian piping systems.

Fitness-for-service (FFS) assessment is a quantitative engineering evaluation of operational components. In the context of pressure vessels and piping systems FFS assessment is performed periodically to ensure the operational safety and structural integrity. In this paper, a simplified method is developed for Level 2 FFS assessment (as described in API 579) of pressure vessels and piping systems containing thermal hot spots or corrosion damage. The method is based upon variational principles in plasticity, the mα-tangent method (an extension of the mα method), the concept of decay length and reference volume. The use of the mα-tangent method extends the range of applicability to components and structures experiencing significant stress gradients in and around the damaged spot. The method is shown to provide a reasonably accurate estimate of the remaining strength of ageing pressure components. The method is demonstrated through an example, and the results are compared with Level 3 inelastic finite element analyses.

Summary The objective of this paper is the investigation and evaluation of the performance and life expectancy of NPT threaded connections as applied to a particular type of reciprocating compressor unit. The study focused on the assessment of the levels of excitation forces acting on the threaded connections and the resulting stress. These forces and stresses were determined from field vibration measurement results applied to a mechanical model of the system. As an extensive literature search did not yield satisfactory data for specific fatigue properties of NPT connections, we applied a first-principles approach to the problem and calculated the stress concentration factors from a detailed finite element study of the thread engagement under axial and circumferential loads. The results and details are reported here. Stress levels determined by this methodology were compared to the allowable fatigue limits for the piping and valves materials and a life expectancy was calculated. The same methodology can be applied to other situations involving threaded connections.

The certification of glass-fibre reinforced plastic (GFRP) piping systems is regulated by normative standards in which test series of 10,000 h are required to estimate the residual properties at the end of the expected life (normally, 50 years). In this paper, the possibility to reduce the test duration, whilst maintaining an equivalent prediction of long-term properties, is discussed. Experimental results from standard test procedures conducted on GFRP pipes of four different types and respective data analysis support this possibility. The estimation error when using only data from shorter tests is consistently less than 10% if compared to the standard methods.

A reliable methodology is required for fatigue design of steel cylinders for Compressed Natural Gas (CNG) carriers in order to meet target safety level at an acceptable cost. This includes description of physical models that represents actual long term fatigue capacity of the Cargo Containment cylinders. The design methodology includes length of welds, fabrication tolerances, fabrication methodology and non destructive testing. It also involves definition of characteristic values for loading and capacity in addition to recommended Design Fatigue Factors. Three alternative fatigue design procedures requiring different Design Fatigue Factors to achieve a system target safety level of annual probability of failure less or equal to 10 −5 are presented.

The estimation of leak and break frequencies in piping systems is part of the probabilistic safety assessment of technical plants. In this paper, a statistical method based on the evaluation of German operational experience for piping systems with different diameters is described because an earlier estimation has been updated and extended introducing new methodical aspects and data. A major point is the inclusion of structural reliability models based on fracture mechanics calculation procedures. As an example of application the statistical estimation method for leak and break frequencies of piping systems with a nominal diameter of 50 mm (the volume control system of a German pressurized water reactor) was updated. Moreover, the evaluation of the operational experience was extended to 341 years with respect to cracks, leaks and breaks in the volume control system of German pressurized water reactors (PWR). Using the actual database, new calculations of leak and break frequencies have been performed and the results have been compared with previous values.

Pipes consisting of layers of different materials (multilayer pipes) are considered. The fracture toughness value of the main pipe is taken into account as a parameter relevant to fracture assessment connected with the resistance of pipe material against slow crack growth. With the aim of simplifying estimation of main pipe material fracture toughness, non-homogeneous test specimens cut directly from multi-layer pipes are suggested and numerically analysed. The values of the corresponding stress intensity factor K I and biaxiality factors B are calculated for the case of two and three layer test specimens. Based on the results obtained, the transferability of fracture toughness values measured on laboratory specimens to pipe systems is discussed. It is shown that in most cases of multi-layer commercial pipes and routine fracture toughness measurements the values of the stress intensity factor calculated on the basis of homogeneous specimens can be used.

Experiments and numerical simulations were conducted to investigate the dynamic response in a pipe-on-pipe impact event, in which a missile (swinging) pipe with one end hinged and the other end free impinges on an orthogonal simply-supported/clamped target pipe at its centre. This study focuses on the effects of the impact location on the missile pipe and the wall thickness of the pipes. The experiments were carried out by using a spring-powered catapult impact setup, the specimens used were made of seamless steel pipes of two different thicknesses, 1 mm and 3 mm respectively, and the target pipes were clamped. Seven tests were carried out using the catapult. Numerical simulations using the explicit finite element code LS-DYNA were performed on an HPC360 workstation for each of the seven test cases. The results of the experiments and numerical simulations were compared, showing good agreement. Having confirmed the validity of the numerical model, numerical simulations were applied to the cases of a simply-supported target pipe, and the partitioning of the energy dissipation was calculated. As the response mode depends significantly on the initial impact position, the evolution of the response mode was examined numerically as the point of impact on the missile pipe was moved from the hinged end to the free end. It was found that there is a particular impact location for which the target pipe was most seriously damaged using the same impact speed.

Creep is the significant factor that caused failure of steam pipelines with high temperature and high pressure in the period of long-term service. In this paper, the creep tests were performed at serviced temperature of 520 °C for 1.25Cr–0.5Mo pipe material, and the creep and fracture constants were obtained by fitting the creep test data. Based on the modified Karchanov–Rabotnov constitutive equation, compiled the user subroutine computing the damage of the pipe element or 3D solid element, the creep damage prediction was carried out by finite element methods using ABAQUS codes for the steam pipelines with high temperature and high pressure, which serviced in a petro-chemical plant, the damage distribution and maximum damage location of the pipelines were obtained, which is testified by metallographic examination result. Furthermore, the local creep damage analysis of a tapered pipe serviced for 100,000 h was also carried out because tapered pipes used in the main steam pipeline is one of weakness in the piping system. Damage distribution and evolution in the analyzed tapered pipe were obtained. The location with the maximum damage value was determined, which is coincident with cracking position of the actual tapered pipe.

This paper firstly presents net-section limit moments for circumferential through-wall and part-through surface cracks at the interface between elbows and attached straight pipes under in-plane bending. Closed-form solutions are proposed based on fitting results from small strain FE limit analyses using elastic–perfectly plastic materials. Net-section limit moments for circumferential cracks at the interface between elbows and attached straight pipes are found to be close to those for cracks in the centre of elbows, implying that the location of the circumferential crack within an elbow has a minimal effect on the net-section limit moment. Accordingly it is also found that the assumption that the crack locates in a straight pipe could significantly overestimate the net-section limit load (and thus maximum load-carrying capacity) of the cracked component. Based on the proposed net-section limit moment, a method to estimate elastic–plastic J based on the reference stress approach is proposed for circumferential cracks at the interface between elbows and attached straight pipes under in-plane bending.

A newly developed hydraulic joint for pipe jacking is described and compared with conventional compression rings. It is shown that with the hydraulic joint, thrust eccentricities are largely reduced, resulting in a much more uniform stress profile at the pipe ends and hence a considerably reduced pipe damage potential. Higher jacking forces can be applied (fewer or no intermediate jacking stations are necessary), longer pipes can be used (fewer joints are necessary), smaller radii of curvature are feasible (fewer or no intermediate jacking pits are necessary) and frictional forces are reduced. The measurement of joint displacements and joint liquid pressures permits an effective real-time monitoring of the jacking process. 30 of the 40 pipelines with a total length of 8.2 km completed so far had curved alignments. The smallest radius of curvature was 86 m using 3 m long pipes with an internal diameter of 1.2 m. Practical experiences gained with the hydraulic joint are summarized.

Local wall thinning of pipes, resulting from corrosion, is the major cause of accidents in nuclear power plants. In order to assure the integrity of pipes, a variety of NDE techniques have been proposed. It is well recognized that the utilization of guided waves to detect flaws in pipes has been a very effective tool for long-range inspection in NDE. Since most conventional research on guided waves has focused on long-range inspection, it is difficult to evaluate a defect in a local area. An objective of this study is to develop a non-contact inspection technique for the quantitative evaluation of defects on a local area in a cylindrical tube. Therefore, the purpose of this study is to introduce an advanced inspection system and a new signal processing method for the evaluation of defects such as corrosion in a pipe. In this study, an advanced non-contact method for pipe inspection is proposed, which generates the ultrasonic guided wave by laser and receives it by a dual air-coupled transducer. Information on each directional defect location and length is obtained by using a line scan along a circumferential and longitudinal direction. Received signals are analyzed by using the peak-to-peak amplitude of waveform and the maximum center frequency magnitude of the frequency spectrum. The optimal mode selection of guided waves based on a dispersion curve is also discussed. The experimental results using the proposed method show that the location and the size of the defect could be evaluated successfully in the 2-dimensional scanning images.

The stress intensity factor plays an important role in the calculation of the local flexibility due to the crack in a cracked structure. Many researches on the stress intensity factors in a cracked beam or rotor have been made, but there are some difficulties in calculating the stress intensity factors in a cracked pipe. Maiti et al. obtained the local flexibility due to the crack in a pipe experimentally by deflection and natural frequency methods without calculating the stress intensity factor. In this paper, the stress intensity factor in a cracked pipe can be calculated by dividing a cracked pipe into a series of thin annuli, and a method to calculate the local flexibility due to the crack in a pipe is presented. The experiment results are given to verify the effectiveness of such a method.

We study the decrease in the strength of a pipe containing an artificial defect. On the basis of the analytic and numerical models, we consider the influence of the structural features of a split sleeve on its load-carrying ability. We also analyze the joint operation of a sleeve and a pipe containing an artificially made axial surface defect. The results of the numerical analysis are compared with the experimental data.

Fracture mechanics based structural integrity assessments of pressure vessels and piping are widely used to support the economic and safe management of operating engineering plant. Assessments of defects at weldments can be highly sensitive to the through-thickness distribution of residual stress assumed in the fracture calculations. Increasingly, finite element modelling approaches are applied to predict residual stress in engineering structures arising from the welding process. However, such methods are complex and require analysts to make many assumptions and approximations. Guidelines covering the calculation of residual stresses in weldments are being prepared for inclusion in the R6 defect assessment procedure and will be accompanied by a series of validation benchmarks. The benchmarks will allow analysts to evaluate and improve the accuracy of weld modelling approaches and assess their suitability for use in fracture assessments. The first part of this paper presents an austenitic stainless steel bead-on-plate weldment validation benchmark based on the extensive round robin measurements performed by members of the European NeT project. The benchmark defines thermal and residual stress performance targets against which a weld simulation approach can be evaluated. Guidance is also provided on how to validate predicted residual stress profiles for use in a high integrity fracture assessment. The second part of this paper provides a commentary on how the weld simulation accuracy and performance targets have been established.

Poor performance of pipe joints can contribute significantly to reduction of the overall performance of pipe systems. The most common problems attributed to joint defects are infiltration, exfiltration, and erosion of the soil surrounding the pipe, which can ultimately produce pipe failure. Thus, modeling of joints in pipelines is a critical issue influencing both the short- and long-term performance of these systems. Although joints may often be the weakest points along the pipe and can have a significant influence on pipe performance, little research has been conducted with regard to joint design. Even joint response to simple loading conditions is largely unknown because of the complexity of interactions between the pipes and the gasket. A three-dimensional, finite element analysis of a Rieber-type rubber-gasketed polyvinyl chloride (PVC) water pipe joint was carried out to investigate the influence of gasket modulus, rubber–PVC friction, insertion length, and joint rotation on the overall performance of the pipe joint system. The numerical analyses were performed with ABAQUS.

Closed form analytical relations are developed for wave propagation effects on buried pipelines which interconnect tanks and/or buildings. The relations cover the axial strain induced in a pipe with various end conditions, the induced axial force at the pipe/tank interface, and the relative displacement at the tank for a pipe with a free end condition. The relations utilize the concept of a pipe development length, defined as the distance over which soil friction forces must act to induce a pipe strain equal to a given level of ground strain. If the available length is less than this development length, the pipe strain is less than the ground strain. Finally an example illustrates the application of the relations and presents simplified upper bound values for pipe strain, axial force, and relative displacement.

This paper presents an evaluation model for the restraint effect of pressure-induced bending (PIB) on the opening of a circumferential through-wall crack (TWC) and a result of its application to the calculation of crack-opening displacement (COD) of postulated cracks for a practical leak-before-break (LBB) analysis. Three-dimensional finite element analyses with different crack lengths, restraint conditions, pipe geometries, magnitudes of internal pressure, and material tensile properties were used to investigate the influence of each parameter on the PIB restraint for the plastic COD. From these investigations, we proposed an evaluation model based on elastic–perfectly plastic behavior. Comparison with finite element analysis results demonstrated that the proposed model reliably estimated the PIB restraint effect on the plastic crack opening of a circumferential TWC and properly reflected the effect of each parameter within the range over which the analytical expression was derived. The model was then used to calculate restrained CODs of postulated cracks for a practical LBB analysis. When plastic crack behavior was considered, the PIB restraint effect was considerable for some LBB analysis cases of the primary piping systems in a typical nuclear power plant. This effect was estimated to be negligible by existing linear elastic-based models.

This paper presents some results of an extensive investigation on the failure of the pressurized double-piping system (pipe-in-pipe system) being one of the main structural elements of the thermo-conditioning installation in the sewage treatment plant. The investigation included the survey of the failed piping, checking of the design and manufacturing against the standards of various types, theoretical analysis employing the results of works carried out on buckling propagation. As an useful and highly informative element of the investigation three tests have been designed to expose the phenomena, which lead to an explanation of the cause of the failure under consideration. They also verified the results of the theoretical analysis performed.

In circumferential welding of a pipe component, it is often considered that axisymmetric model can provide a reasonable prediction of the residual stress distributions. However, in general, the axisymmetric model cannot reproduce the traveling arc along circumferential welds and rapid change of residual stresses that can be observed in the overlapping region. Moreover, it tends to overestimate the hoop residual stresses in circumferential welds. Therefore, three-dimensional finite element (FE) model is essential for the accurate simulation of circumferential welding which can incorporate the three-dimensional effects. This paper presents the three-dimensional FE simulation of circumferential butt welding of a steel pipe. The thermo-mechanical model used as well as the simulation methodology is detailed, and the results are discussed. In addition, parametric studies with inside radius to wall thickness ratio ranging from 10.0 to 100.0 have been presented to investigate the effects of pipe diameter on residual stresses. Axial and hoop residual stresses are plotted for the considered range of pipe diameters, and the differences are discussed.

The authors have previously proposed plastic limit load solutions for thin-walled branch junctions under internal pressure and in-plane bending, based on finite element (FE) limit loads resulting from three-dimensional (3-D) FE limit analyses using elastic–perfectly plastic materials [Kim YJ, Lee KH, Park CY. Limit loads for thin-walled piping branch junctions under internal pressure and in-plane bending. Int J Press Vessels Piping 2006;83:645–53]. The solutions are valid for ratios of the branch-to-run pipe radius and thickness from 0.4 to 1.0, and for the mean radius-to-thickness ratio of the run pipe from 10.0 to 20.0. Moreover, the solutions considered the case of in-plane bending only on the branch pipe. This paper extends the previous solutions in two aspects. Firstly, plastic limit load solutions are given also for in-plane bending on the run pipe. Secondly, the validity of the proposed solutions is extended to ratios of the branch-to-run pipe radius and thickness from 0.0 to 1.0, and the mean radius-to-thickness ratio of the run pipe from 5.0 to 20.0. Comparisons with FE results show good agreement.

An important rotor fault, which can lead to catastrophic failure if undetected, is fatigue crack in the shaft. The cracked rotor problem received the first attention in 1970, since when the interest among the researchers started. Vibration behavior of cracked structures, in particular cracked rotors, has received considerable attention in the last two decades. The problem of damage and crack detection in structural components has acquired important role in recent years. However, the studies are mainly dealt with single crack. If the structure is cracked in at least two positions, the problem of crack sizing and location becomes decidedly more complex. Relatively few authors have addressed the multi-crack assessment for structures. The objective of this present study is to summarize the different studies on double/multi-cracks and to note the influences, identification methods in vibration structures such as beams, rotors, pipes, etc. And thus this paper brings out the state of the research on multiple cracks effects and their identification.

One of the most popular pre-reinforcement methods of tunnel heading in granular soils would be the grouting with pipes, which is so-called the umbrella arch method. This technique allows safe excavation even in poor ground conditions by creating longitudinal arching parallel to the tunnel axis. The complexity of boundary conditions of the methods, however, imposes difficulties in representing the tunnelling procedure in laboratory and analytical models. Full-scale study to identify the reinforcement mechanism of the tunnel heading, therefore, has rarely been carried out. In this study, a large scale model testing for the pipe-reinforced tunnel heading in a granular soil was performed to understand reinforcing mechanism and improve design practice. Reinforcing patterns considered are non-reinforced, crown-only-reinforced, face-only-reinforced and crown and face-reinforced cases. The behaviour of ground and pipes was instrumented during tunnelling. The effects of reinforcing pattern and pipe length were investigated, particularly in terms of ground displacement and stress changes. Supplemental numerical analyses were carried out to investigate the effect of pipe length which cannot be covered by the model tests. It is revealed that the pipe reinforcement of heading increases longitudinal arching along the tunnel axis, decreases settlements significantly, and consequently improves the face stability.

Vibration has severely increased at the branch pipe of the main steam header since the beginning of commercial operation of nuclear power plants. Intense broadband disturbance flow at a discontinuous region such as elbows, valves or headers generates an acoustical pulsation which is propagated through the piping system. The pulsation becomes the source of low frequency vibration at the piping system. If it coincides with the natural frequency of the pipe system, excessive vibration results. High-level vibration due to the pressure pulsation related to high dynamic stress, and ultimately, to failure probability fatally affects the reliability and confidence of the plant piping system. This paper discusses steady-state high vibrations appearing in the branch piping system due to the effect of acoustical pulsations transmitted from the large main steam header by broadband turbulence in a 700 MW power plant. The excitation sources and response of the piping system are investigated by using on-site measurements and analytical approaches. Energy absorbing restraints with additional stiffness and damping factor were designed and installed to reduce vibration damage.

Stress corrosion cracking (SCC) is an important degradation mechanism to be considered for safety assessment of nuclear piping components made of austenitic steels, especially in the heat-affected zones. Damage due to SCC occurs in a susceptible material, in a corrosive environment, in the presence of high temperature and high applied/residual stresses. The operating conditions and the environmental conditions show variations during the lifetime of the power plant. Also, there will be variations in micro-structural properties of the material of piping components. These variations should be taken into account while assessing the safety of the piping component against SCC. This can be accomplished by treating the relevant variables as random or fuzzy depending upon the source and type of uncertainty. In this paper, an attempt has been made to compute the fuzzy failure probabilities of a piping component against SCC with time, using an approach combining the vertex method with the Monte Carlo simulation technique. The initiation and propagation stages of stress corrosion cracks are modelled using a modified PRAISE approach. The degree of sensitisation, material fracture toughness, yield strength, ultimate strength and applied stress are considered as random variables, while operating temperature and oxygen concentration are considered as fuzzy variables. The R6 procedure is used in the computation of the fuzzy failure probabilities. The usefulness of the approach is demonstrated through an example problem.

Centrifugal model tests are conducted in order to clarify the effects of pipe roof supports and the excavation method on the displacements above a tunnel face. The excavation process must be taken into account when estimating the displacements. Therefore, an excavation robot is newly developed which is three-dimensionally controlled by computer programs and is able to excavate the tunnel face in arbitrary shapes. The robot can accurately simulate such excavation methods as the full-face excavation method and the ring-cut excavation method. The difference in displacements between the two excavation methods is discussed in terms of the existence or the nonexistence of pipe roof supports. The results of the model tests show the quantitative effects of the ring-cut excavation method and clarify that the method decreases the ground displacements remarkably. The model tests also indicate that the maximum settlement of a ground excavated by the full-face excavation method with pipe roof supports is one fourth of that without them.

The development and the use of finite element analyses in the 1970s and 1980s changed the nature of culvert assessment because they permitted consideration of the geometrical and material details of the burial condition, as well as the construction process, culvert geometry, and earth and vehicle loads. While these procedures have been used to study a wide range of new culvert and pipe structures, there has been little consideration of the structural deterioration that is precipitating most current infrastructure investments. This study therefore examines the influence of corrosion on the stability of corrugated steel culverts. Corrosion in the lower half of the structure is considered, including a range of losses in wall thickness and lateral extents. Changes in the factor of safety against yield are assessed as corrosion develops, as are changes in culvert resistance to buckling failure. For the five specific design cases considered, the governing design criterion was stability against yield, and the factor of safety against yield was found to decrease almost in proportion to wall thickness (when maximum wall thrust within the corroded zone was considered). This decrease occurred because the corroded metal culverts experienced little change in the distributions of thrust or moment as a result of local losses in wall thickness. While the results presented are purely theoretical, they provide a starting point for an appreciation of the influence of metal culvert deterioration and can guide future research, including physical test programs.

This paper reviews recent data that have come available on flaws in nuclear components. It examines whether the conclusions in a previous paper [Bullough R, et al. The probability of “large” defects in thick section butt welds in nuclear components. Int J Pressure Vessels Piping 2001; 78: 553–65] still hold in the light of this new information. A new model for estimating the distribution of flaws greater than 15 mm in through-wall extent for submerged arc welds is also reviewed. In this model, four potential flaw formation mechanisms are considered: (i) lack of fusion, (ii) weld metal solidification cracking, (iii) hydrogen-induced cracking in the heat-affected zone, and (iv) hydrogen-induced cracking in the weld metal. The distribution of large flaws remaining after pre-service inspection is calculated for each mechanism as the product of the probability of forming the flaw and the probability of the flaw being undetected during pre-service radiography. The assumptions and general applicability of the model are discussed.

An in-pipe robot with active pipe-diameter adaptability and automatic tractive force adjusting is developed for long-distance inspection of main gas pipelines with different diameter series. Its physical design employs the scheme that three sets of parallelogram wheeled leg mechanism are circumferentially spaced out 120° apart symmetrically. This structural design makes it possible to realize the adaptation to pipe diameter and tractive force adjusting together. On the basis of analyzing the mechanical actions of the adaptation to pipe diameter and tractive force adjusting, the related mechanical models are established, and their control system structure and control strategy are discussed. To verify the pipe-diameter adaptability and tractive force adjusting of the robot, related field experiments are implemented in actual underground gas pipeline. The experimental results show that the theoretical analysis in this paper is valid and the prototype of this robot can work well in actual underground gas pipelines. Compared with other similar robots, this robot, which employs active mode for its adaptability to pipe diameter, can be adaptable to the wide range of gas pipeline diameters from ∅400 mm to ∅650 mm and automatically provide a stable and reliable tractive force with strong capacity of tractive force adjusting. As a mobile carrier for visual inspection and nondestructive testing to monitor block, corrosion, crack, defect, and wall thickness of main gas pipelines, its inspection range of one-time job in pipelines is extended beyond 1000 m.

To calculate stress intensity factors in elastic pipes with long flaws, the known Cheng-Finnie method is used. A universal description of the mode of behavior of beam is proposed, for which equations of the method of initial parameters with allowance for geometric nonlinearity (effect of axial force on lateral deformation) have been derived and are employed. This allowed us to determine, apparently for the first time, the values of stress intensity factors in thin-walled pipe in a geometrically nonlinear formulation, when increase in pressure leads to their somewhat “ retarded” increase. The results have been generalized for a more complex flaw-crack starting from the dent tip.

CoJack is a new method to calculate and monitor pipe jacking online using non-linear constitutive equations to additionally take the load history of the pressure transfer rings and the resulting consequences of the load-distribution effects into account. Therefore, CoJack removes the risk factor of an overload of the pipes during the jacking and thus it decisively improves the safety and economic efficiency of jacking measures. It improves and provides for the supervision of jacking projects from the very first planning stage via the construction process to the final acceptance.

The paper presents a model for calculating installation loads imposed on pipes during the pulling operation in horizontal directional drilling. The model is implemented into a numerical program PipeForce 2005. The analysis includes pulling load contributions from directional changes, fluidic drag, solid friction and pipe’s weight. The emphasis in this paper is on details related to directional changes during the HDD installation. The formulation approximates the borepath as series of linear segments between the measured points (field-measured locations of the drilling head) and predicts the shape of the pipe in the borepath. Based on this shape, the layout of the borepath and the pipe stiffness, the contact forces between the pipe and the borepath are evaluated using the theory of deflections of flexible bars. The pulling force for the pipe is calculated to equilibrate the weight of the pipe and friction between the pipe and the soil and between the pipe and the drilling fluid. A comparison of theoretical predictions and field data is presented.

This article presents an approach for the internal inspection of tubular structures immersed in water through the use of sonar techniques, generating enhanced 3D graphs which represent the inner surface of these structures. These graphs not only show the inner contour of the pipe but also integrate the intensity of the echoes employed to create the profile. The enhanced profile is generated by superimposing the peak intensity from the returning echoes at the calculated x, y, and z coordinates where it reflected from the pipe wall. The proposed method is capable of showing anomalous conditions, inside pipes filled with liquid, with dimensions smaller than the theoretical lateral and axial resolution of the transducer, in contrast to traditional methods where these kinds of defects are not disclosed. The proposed inspection method and its capabilities were validated through the realization of simulations and experiments. The presented approach was particularly developed with the aim of scanning internal sections of pipes filled with liquid using rotary ultrasonic sonars, but it is expected that this research could be expanded to the inspection of other submerged structures, such as water tanks, or pressurized vessels.

This contribution deals with the short term and the long term behaviour of multilayer pipes subjected to internal hydrostatic pressure. A new methodology for prediction of long term behaviour of multilayer pipes under internal hydrostatic pressure taking into account the material differences and the composite pipe construction is presented, which considers the possibility of the composite polymeric pipe having a metallic interlayer. The three dimensional theory of thick walled multilayer pipes together with a combined quadratic/linear regression analysis is used, and the contribution of each component to the long term strength of the composite pipe is quantitatively assessed. This procedure is incorporated in the pipe software ADAP developed by the author that deals with automated design and analysis of pipelines. Short term stress analysis of multilayer pipe consisting of two polymeric facings and a metallic interlayer is carried out with three methods; namely the analytical method of multilayer thick walled tubes, the finite element method, and the computational software ADAP. In addition, an analytical stability analysis was carried out. It has been shown that all three methods produce similar quantitative and qualitative stress results. According to these computations, for multilayer polymers/metal/polymer pipes, higher stress values are predicted for the metallic interlayers. Using the new long term extrapolation procedure, the layer at which the failure under internal pressure would be initiated is identified and the state of stress of each layer is quantitatively assessed. Using this extrapolation methodology for multilayer polymer pipes at elevated temperatures, the theoretical sharp knee predicted by the existing standards is replaced by a transition zone between the ductile and the brittle behaviour of thermoplastic layers. An example of this procedure for a multilayer pipe consisting of two polymeric facings and a metallic interlayer is presented. The proposed methodology can be used as an extrapolative procedure for prediction of the long term resistance of composite and multilayer pipes as well as for optimisation of multilayer plastics and hybrid pipes.

The indenter force vs. deflection characteristics of pressurised pipes with long offset indentations under plane strain conditions have been investigated using finite element (FE) and analytical methods with four experimental tests performed on aluminium rings. Two different materials and five different geometries were used to investigate their effects on the elastic–plastic behaviour. A comparison of the experimental, FE and the analytical results indicates that the analytical formulation developed in this paper, for predicting the force–deflection curves for pressurised pipes with offset indenters, is reasonably accurate. Also, all of the analyses presented in this paper indicate that by using a representative flow stress, which is defined as the average of the yield and ultimate tensile stresses, the analytical method can accurately predict the force–deflection curves.

Using advanced numerical tools, which account for the cold-expansion manufacturing process, the axial capacity of welded slip pipeline joints under compressive loading is investigated. The numerical results are in good agreement with available experimental data, and show the effects of several geometric parameters. Internal pressure effects are also examined, and an assessment of previously reported simplified design equations is conducted.

One consequence of the evolution of long and deep wells is that the design margins become increasingly smaller. Casing and tubing are pushed towards their yield strengths to meet the requirements of hot and highly stressed conditions. Also, the pipe used during drilling and intervention is subjected to elevated pressures and axial loads. These factors motivated the present study to develop an exact well design model for burst and collapse under axial load. In critical wells, the tubing designs are commonly based on triaxial software packages. It will be shown here that results from the conventional approach are accurate only under certain conditions. This paper presents an exact solution to the three-dimensional well tubular design problem. The term well tubular design, used in this paper, refers to the calculation of burst, collapse and axial loading limitations of drill pipe, snubbing pipe, tubing and casing. The new model calculates design factors that are exact, thereby offering a tool for improved well tubular design. The presented theory is based on the von Mises yield criterion and the Lame thick-walled solution for the pipe. The new model is dimensionless, so the same graph can be used for all pipe materials and pipe dimensions. The model is also valid for cases with applied torque, bending or buckling. The general model is based on incipient yielding at the inside pipe wall, and the collapse predictions from the model for diameter-to-thickness ratios less than 14 are in agreement with experimental evidence. For large casing strings, the model should be used with caution for collapse predictions. The model is valid for burst calculations for all pipe sizes. Bending and torque effects are modeled by considering both the inside and outside pipe walls.

It is well known that resistance against slow crack growth is important for the lifetime of pressurized polyethylene (PE) pipes. Thus, several methods have been proposed in recent years to evaluate the long-term performance of PE using fracture mechanics. It is generally believed that this leads to results more quickly compared to internal pressure tests. In the presented research work, a method was implemented using fatigue loading of cracked round bar (CRB) specimens to characterize crack growth resistance. The method was applied to five commercially available PE pipe materials and the results were compared with the full notch creep test (FNCT). The same ranking was found with both methods, but it was obvious that fatigue crack growth (FCG) experiments were faster by up to two orders of magnitude, especially when characterizing modern (bimodal) PE types.

Nuclear power plant components suffer pipe shedding, cracking, thermal fatigue, bending and supporting bracket breakage during their life span. Notably, the horizontal inlet nozzle of steam generator is prone to thermal stratification frequently due to its operational characteristics. As a result, PWRs in many countries including the U.S.A. suffered a lot of pipe cracks and leakages around the late 1970s, as the thermal stress inflicted by thermal stratification formed in the horizontal inlet nozzle of steam generator during transition (auxiliary feedwater injection) was not reflected on power plant design.

Most thermoplastic pipes exhibit peaking behavior during the initial backfilling process. It is shown with the actual field data that the peaking deflections can be beneficial for minimizing the long-term deflections of the pipe. An approach similar to the one proposed by Spangler is used to derive a formula for estimating the peaking deflections of thermoplastic pipe due to forces generated during the initial backfilling. The formula is tested in light of a number of field installation cases. The results show that the proposed formula predicts peaking deflections of both polyvinyl chloride and high density polyethylene pipes accurately under a variety of backfilled conditions.

Squeeze-off is used in routine or emergency situations to stop, or nearly stop, flow in polyethylene (PE) pipe by flattening the pipe between parallel bars. Gas and water industries utilizing PE pipe in their systems have designed squeeze-off procedures to suit their pipe material, environmental conditions and constructional needs, where it may be inconvenient and/or expensive to isolate and empty pipelines. The method provides a quick shut-off the lines, saving many hours, and eliminates the need for dangerous, costly and lengthy excavations. Despite its widespread use, it is not known whether squeeze-off of the pipe damages the pipe and, if so, what is the degree of the damage and how it should be minimized. This paper is about the investigation of squeeze-off of pipes of various dimensions made from PE 80 and PE 100 grade high-density PE and crosslinked PE. Experimental investigation on the damage related with the squeeze-off of the pipes was carried out to study the influence of squeeze-off phenomenon on the short and long term performance of the pipes. Hydrostatic pressure tests were performed on the squeezed pipe to examine the degree of damage. The influence of squeezing ratio, pipe diameter and squeeze-off tool geometry on the overall pipe performance was also investigated.

The purpose of this work is to develop a practical method for constitutive modeling of polyethylene, based on a phenomenological approach, which can be applied for structural analysis. Polyethylene is increasingly used as a structural material, for example, in pipes installed by trenchless methods, where the relatively low stiffness of polyethylene reduces the required installation forces, chemical inertness makes it applicable for corrosive environments, and adequate strength allows its use in sewer, gas, and water lines. Polyethylene exhibits time-dependent constitutive behavior which is also dependent on the applied stress level resulting in nonlinear stress–strain relationships. Nonlinear viscoelastic theory has been well established and a variety of modeling approaches have been derived from it. To realistically utilize the nonlinear modeling approaches in design, a simple method is needed for finding a constitutive formulation for a specific polyethylene type. This paper presents such a practical approach to nonlinear viscoelastic modeling utilizing both the multi-Kelvin element theory and the power law functions to model creep compliance. Creep tests are used to determine material parameters and models are generated for four different polyethylene materials. The corroboration of the models is completed by comparisons with results from different tensile creep, step-loading creep, and load-rate tests. POLYM. ENG. SCI., 48:159–167, 2008. © 2007 Society of Plastics Engineers

Weld repairs and alterations of pressure vessels and piping built to ASME codes may require pressure testing to prove the integrity of the weld and/or design. Conventional hydrostatic pressure testing requires filling an entire vessel or piping system with water and pressurizing it to the test pressure. In recent years, several designs were developed to employ bolted devices to perform local pressure testing of flange-to-nozzle, flange-to-pipe, and nozzle-to-shell attachment welds. Due to the cost and equipment downtime associated with performing a full conventional pressure test and the desire to reduce repair costs, several petrochemical companies adopted the use of such devices. The purpose of this paper is to compare the stress values and stress distribution associated with conventional and local pressure testing techniques. The advantages and disadvantages of both approaches are discussed and the conclusions are supported by a practical example.