Failure Mode Of Pipe Research Articles

Startup and Multiphysics Analysis of a Compact kW-Class Thermal Spectrum Microreactor

Self-regulating compact nuclear microreactor concepts are being developed for use in space and at terrestrial remote sites. The current emphasis is on the development of high-assay low-enriched uranium–fueled reactors that rely on metal hydrides to achieve size, specific weight, and power parity with the legacy highly enriched uranium systems. In the case of terrestrial applications, metal hydride–moderated systems can also improve economic feasibility. The neutronic design of metal hydride–moderated high-temperature reactor cores is complicated by the need to optimize and synchronize delayed spatial and temporal reactivity feedback from outer reflectors. Zebra is a thermal spectrum proof-of-principle core designed for demonstrating the reactor dynamics of hydride-moderated spectrum reactors, which is studied in this work. The reactor, including the fuel, yttrium hydride moderator, heat pipes, central control rod, structural supports, and the beryllium reflector, weighs ~425 kg. The design shares several features common with nuclear criticality test geometries routinely used in National Criticality Experiments Research Center (NCERC) experiments such that a prototype of the reactor can be readily assembled and tested. Additional features, such as heat pipes and hydrogen barrier clads, were added to minimize the potential for large thermal gradients that in turn could induce hydrogen loss or structural deformation during extended periods of operation at ~1000 K. In this work, normal and off-normal state performance of the Zebra rector core was analyzed using MCNP and Abaqus-based Reactor Multiphysics (MARM) software. Up-to-date nuclear, thermal, and mechanical performance data were used to characterize the performance of the yttrium hydride moderator. Steady-state analyses established that at a postulated power between 20 and 50 kW(thermal), the reactor core is nearly isothermal irrespective of quality of conduction coupling between heat pipes and fuel plates. Additionally, heat pipe failure modes, including simultaneous failure of all heat pipes in a quadrant of a reactor, were examined to bound the maximum credible temperature spike in the reactor core for extreme off-normal operating conditions. Finally, we detail the startup design challenges for the hydride-moderated thermal core, and analyze load-following cases to achieve “self-regulation” using the Dynamic Analysis of Reactor Transients module of MARM. The reactor is self-regulating with a reactivity temperature coefficient of ~−1 pcm/K at the operating point based solely on nuclear cross-section feedback. It can be further strengthened using additional spectral shift neutron absorbers and incorporating design features that enhance core expansion. This work captures that hydride-moderated systems are feasible for various self-regulating applications once systematic checks are verified in order to achieve a well-engineered core design.

Investigating the Impact of Cumulative Pressure-Induced Stress on Machine Learning Models for Pipe Breaks

Significant financial resources are needed for the maintenance and rehabilitation of water supply networks (WSNs) to prevent pipe breaks. The causes and mechanisms for pipe breaks vary between different WSNs. However, it is commonly acknowledged that the operational management and water pressure influence significantly the frequency of pipe breaks. Pipe breaks occur when the water pressure exceeds the tensile strength of a pipe, or due to repetitive pressure cycles that result in fatigue-related failures. Considering these pipe failure modes, a new metric known as cumulative pressure-induced stress has been introduced. This metric takes into account both static and dynamic pressure components that contribute to pipe breaks, including mean pressure and the magnitude and frequency of pressure fluctuations, respectively. The impact of CPIS on pipe breaks has not been extensively investigated. Consequently, this study investigates and evaluates the impact of this metric when incorporated as an explanatory variable in Random Forest (RF) models that analyse the key causes of pipe breaks in two WSNs. Different RF models were developed both with and without incorporating pressure components. Subsequently, the performance of these models and the significance of each input variable were assessed. The results of this study suggest that CPIS is an important variable, especially in cases where pressure-related factors play a significant role in pipe breaks. Consequently, incorporating CPIS has shown a notable improvement in the accuracy of pipe break models.

A Special Thermal Fatigue Failure Mode of Pipe in Nuclear Power Plant and Its Countermeasures

Thermal fatigue phenomenon is well known and feedbacked in the nuclear power industry. Targeted screening principles has been developed and applied. However, a thermal fatigue failure, “Swirl Penetration” of small-diameter pipeline, was identified through a Reactor Coolant System (RCS) leakage in a nuclear power plant. Unexpectedly, this failure is not within the scope of previous screening principles of thermal fatigue. It is characterized in that the high-temperature main piping is connected downward with a certain length of vertical small-diameter piping, and then the vertical piping turns horizontally through an elbow. The reactor coolant in the lower pipeline does not flow under normal operation conditions. Subject to long-term cyclic thermal fatigue, cracks initiate and propagate in the elbow. Through researches, corrective measures are put forward to prevent, mitigate or discover it.

The Effect of Internal Pressure on Radial Strain of Steel Pipe Subjected to Monotonic and Cyclic Loading.

Steel pipes in different engineering applications may fail, leading to numerous environmental disasters. During loading, certain mechanical and chemical phenomena develop inside the pipes and cause them to burst. In this study, the influence of internal pressure on the elastic and plastic behaviour of E355 steel pipes was investigated on small specimens with different wall thicknesses. First, the failure modes of pipes subjected to monotonic loading were assessed, and then the behaviour of specimens subjected to cyclic internal pressure was analysed in terms of variation of radial strain. The strain and stress states of pipes were analysed using the finite element method. The results revealed that the hardening of materials inside the pipes increases the risk of cracking and bursting because of elasticity limits being exceeded, causing entry into the plastic domain. The transition of mechanical behaviour can be observed in the microstructure of steel in cracked areas from the inside to the outside of the pipe.

Failure modes of piping under seismic loads which have both load and displacement controlled characteristics

Evaluation for BDBE requires best estimation based on realistic failure phenomena. However failure modes of piping under seismic loads are not clear, because seismic load is alternate one and has both load- and displacement-controlled characteristics. For design and seismic PRA (probabilistic risk assessment), the failure mode is assumed to be collapse under PGA (peak ground acceleration). However, this conservative assumption is not appropriate for risk assessment with best estimation and uncertainty. The objective of this study is the clarification of realistic failure modes of piping under seismic loads.Previous experimental studies showed ratcheting deformation and fatigue as the most probable piping failure modes. Collapse cases were seldom. Authors pay attention to the analogy of failure modes between thermal alternate loads and seismic alternate loads. Ratcheting and collapse under thermal loads can be evaluated by the famous Bree diagram, where main parameters are constant pressure and alternate thermal loads. The Bree diagram was extensively applied to piping ratchet and collapse with such parameters as constant gravity force and alternate seismic loads. The frequency of seismic loads was also introduced as an additional parameter.As the results of experimental and analytical studies, ratcheting and collapse under seismic loads can be evaluated by the Bree-like diagram, where main parameters are constant gravity force, dynamic loads and their frequencies. Furthermore, frequency dependent characteristics of seismic loads were understood. They act like load controlled when frequency is lower than natural frequency. In the case of higher frequency than natural frequency, they become closer to displacement controlled. When higher than twice of natural frequency, they are less damageable than displacement-controlled.

Dam Breach Analysis Using HEC-RAS and HEC-GeoRAS: The Case of Kesem Kebena Dam

Ethiopia has been booming with active construction of dams within the past few decades for different infrastructural needs, but has never experienced demolition or failure of dams in its history; hence little attention is being given to possible breach scenarios of dams and the resulting floodings. This paper makes analysis of the possible breach of kesem dam and the resulting flood inundation. In this study, the dam has been checked for both overtopping and piping failure modes using one dimensional river analysis model called HEC-RAS. Empirical equations were used to predict dam breach parameters of the two failure modes for use in this model. PMF inflow with a peak 9237.77 m3/s is used as an input to the reservoir to check if overtopping failure was possible. The spill way has proven to have adequate capacity for the flood due to the PMF. Therefore, breaching of the embankment was not possible. Piping failure was also simulated in HEC-RAS and the resulting breach due to piping failure, was analyzed and flood hydrograph was obtained at different cross sections along the river. These are flood hydrographs at 20 km, 40 km and 60 km at the downstream. The resulting flood plain was also mapped using HEC-GeoRas to show the extent of flooding.

Post-Buckling Failure Modes of X65 Steel Pipe: An Experimental and Numerical Study

In service pipelines exhibit bending loads in a variety of in-field situation. These bending loads can induce large longitudinal strains, which may trigger local buckling on the pipe's compressive side and/or lead to rupture of the pipe's tensile side. In this article, the post-buckling failure modes of pressurized X65 steel pipelines under monotonic bending loading conditions are studied via both experimental and numerical investigations. Through the performed full-scale bending test, it is shown that the post-buckling rupture is only plausible to occur in the pipe wall on the tensile side of the wrinkled cross section under the increased bending. Based on the experimental results, a finite element (FE)-based numerical model with a calibrated cumulative fracture criterion was proposed to conduct a parametric analysis on the effects of the internal pressure on the pipe's failure modes. The results show that the internal pressure is the most crucial variable that controls the ultimate failure mode of a wrinkled pipeline under monotonic bending load. And the post-buckling rupture of the tensile wall can only be reached in highly pressurized pipes (hoop stress no less than 70% SMYS for the investigated X65 pipe). That is, no postwrinkling rupture is likely to happen below a certain critical internal pressure even after an abrupt distortion of the wrinkled wall on the compressive side of the cross section.

Evaluation of the Response of Buried Steel Pipelines Subjected to the Strike-slip Fault Displacement

In this paper, the response of buried steel pipeline subjected to the strike–slip fault displacement is studied. This study aimed to identify the seismic fault under the pipe at the intersection of large displacement (up to 3 meter fault displacement) and identify failure modes in the pipe. Innovation studies the effect of thickness ratio of the diameter of the pipe failure modes of the fault displacement. The nonlinear finite element method analysis was conducted. By using ABAQUS software, nonlinear finite element analysis was carried out on the pipeline under fault displacement. Numerical modelling aimed at obtaining the amount of displacement corresponding to the nonlinear behaviour in the pipeline, as well as identifying failure modes pipes in displacement from 0.2 to 3 meter in diameter to thickness ratio, taking into account the impact of the pipeline. The results showed the nonlinear behaviour of the displacement 57.5 cm pipeline damage starts and the displacement of 1 meter buckling occurs in pipes. The displacement of 1 meter fault, failure mode is local buckling pipe, and displacement and deformation of the pipe is 1 meter looks like the letter S. The displacement of 1.5 meter high (3 meter) failure mode tube is wrinkling. And deformation of the pipe in the fault displacement of 1.5 meter, like the letter Z. With the increase in displacement from 1.5 meter to high wrinkling occurs in pipes and up to 3 meter displacement continues. Plastic strain in the fault displacement of 80 cm in diameter to thickness ratio of 112 and 96 occurs, Plastic strain ratio of diameter to thickness of 86 does not occur. Reduction in the diameter of the thickness has a positive impact on reducing plastic strain in the pipe.

Nonlinear finite element analysis of failure modes and ultimate strength of flexible pipes

Designs of flexible pipe utilized in offshore dynamic riser applications need to be subjected to strength assessment over the entire length in relation to the dynamic motion of the connected floater. Such assessment includes many uncertain factors including soil properties, internal pressure, ocean metadata and others. Failure of flexible pipe, moreover, leads to serious financial loss and environmental degradation. Thus, flexible pipe failure modes and safety need to be evaluated in terms of ultimate strength under various loads.Ultimate strength assessment of flexible pipe is quite complicated and time-consuming compared with that of a steel catenary riser, due to the composite materials, geometric complexity and the contact mechanism between layers The material nonlinearity and large deformation, moreover, render stable convergence of nonlinear analysis to a solution problematic. This paper proposes practical and stable methods of ultimate-strength assessment using 8-layered and 5-layered 3D FE models subjected to axial tensile and compressive loads, respectively. In the 5-layered model, four inner layers (carcass, pressure sheath, pressure armour, and anti-friction tape) are replaced by one equivalent pressure layer which plays a role of withstanding pressure applied together with the axial compression. It aims to improve the convergence of nonlinear analysis by simplifying the interactions between layers. For each analysis, the failure mechanisms and the interactions between layers are investigated in detail with incremental loading. The effect of initial imperfection, i.e. ovalizations are also examined. In the compressive strength analysis, the influence of various external pressure are additionally studied.

Experiment and statistical assessment on piping failures in soils with different gradations

ABSTRACTA series of upward seepage tests on sand specimens with three grain size distributions (i.e., two uniform soils and one gap-graded soil) were conducted to better understand the seepage failure of sea defense systems and coastal hydraulic structures. The objectives were to provide a detailed description of the piping progress and failure mechanism of soils subject to seepage and to investigate the influence of soil gradations on the piping failure modes. In addition, a data set consisting of a wide range of grain size distributions was compiled to assess statistically the accuracy and applicability of critical hydraulic gradient, icr, prediction methods. Experimental results indicated that the piping failure modes of sand specimens depended on soil internal stability, which was related to the grain size distribution. Piping failure of uniform sand, classified as internally stable soil, was associated with an effective stress equal to zero, whereas piping failure of gap-graded sand, classified as internally unstable soil, was caused by the internal erosion of fines. The average icr values of uniform sand are in good agreement with Terzaghi’s theoretical value. However, the average icr value of gap-graded sand is far lower than Terzaghi’s icr value. The statistical results indicated that Terzaghi’s method with Kezdi’s internal stability criterion shows the most accurate results with the smallest variance (model bias mean μ = 1.04 and coefficient of variation (COV) = 8.08%) for predicting the icr of internally stable soils. For internally unstable soils, methods based on the force equilibrium on a soil particle generally produce reasonable μ values (μ = 1.20–1.75), but the COV values are considerably high. The discrepancy between the predicted and measured icr values is discussed. The Results and Discussion in this study provide insightful information for the design, strengthening, and maintenance of coastal waterfront structures against soil piping and erosion.

Signature Failure Modes of Pipelines Constructed of Different Materials When Subjected to Earthquakes

AbstractThe 2010/2011 Canterbury (New Zealand) earthquakes caused significant damage to buried pipeline infrastructure. Observations of damaged pipes that were made during either repair or replacement were used to define representative examples of the damage to each of the commonly used pipe materials. The different pipe materials that were considered included steel reinforced concrete, polyvinyl chloride, high-density polyethylene, cast iron, asbestos cement, and vitrified clay. Photographs of damaged pipes at the time of repair were collected and analyzed to identify pipe failure modes. It was determined that different pipeline materials exhibited different failure mechanisms during the earthquakes and that each pipe material was found to have a distinct failure signature. In particular, polyvinyl chloride pipes behaved in an unexpected brittle way. The failure mechanisms of each type of pipe are described using engineering nomenclature, and the signature failure modes are categorized and tabulated to f...

Effect of length of thinning area on the failure behavior of carbon steel pipe containing a defect of wall thinning

The present study performed pipe failure tests using 102 mm-Sch. 80 carbon steel pipe with various simulated wall thinning defects, to investigate the effect of axial length of wall thinning and internal pressure on the failure behavior of pipe thinned by flow accelerated corrosion (FAC). The tests were conducted under loading conditions of four-point bending with and without internal pressure. The results showed that a failure mode of pipe with a defect depended on the magnitude of internal pressure and axial thinning length as well as stress type and thinning depth and circumferential angle. Both load carrying capability (LCC) and deformation capability (DC) were depended on stress type in the thinning area and dimensions of thinning defect. For applying tensile stress to the thinned area, the dependence of LCC on the axial length of wall thinning was determined by circumferential thinning angle, and the DC was proportionally increased with increase in axial length of wall thinning regardless of the circumferential angle. For applying compressive stress to thinned area, however, the LCC was decreased with increase in axial length of the thinned area. Also, the effect of internal pressure on failure behavior was characterized by failure mode of thinned pipe, and it promoted crack occurrence and mitigated a local buckling of the thinned area.

Piping Stress-Strain Correlation for Seismic Loading

This paper establishes limits on piping material strains for ASME Boiler and Pressure Vessel Code Level D loadings that ensure a limitation of deformation and provide suitable safety margins. In establishing the strain limits, potential piping failure modes due to compressive wrinkling and low-cycle fatigue are considered. A stress-strain correlation methodology to convert linear, elastically calculated Code Class 2 and 3 equation (9)-Level D stresses to strains is established. This correlation is based on the fatigue evaluation procedure of the Code and is verified by comparison with test results. A detailed discussion of test results compared with the stress-strain correlation methodology is also presented.