Abstract Fluid transients without friction in pipelines can be solved by a time-domain exact solution, using a simple recursive process without computational grid. But the calculation time cost of this approach is very high because of the recursion algorithm. Its improved method, named as the fast meshless solution (FMS), was developed to speed the computation by introducing the time-line interpolation. However, when the friction is considered, the conventional distributed friction model cannot be employed directly for the FMS is meshless. To address this problem, the fluid friction is lumped at pipe ends, and both steady and unsteady laminar flow are investigated. Three kinds of lumped models are proposed here, and compared with a numerical case of the water hammer. The laminar fluid transients can be calculated fast by the present method, with a little reduced accuracy. This method may be of interest in a quick assessment of the piping fluid transients.

Abstract Fatigue test specimens were prepared and tested with an API 5L X70 spiral welded pipe steel and girth weld. For a few selected specimens, two unloading compliance techniques (elastic compliance and back-face strain compliance) were applied simultaneously to a single specimen for direct comparisons of in-situ crack size estimation. This paper also includes fatigue crack growth rate (FCGR) data of other pipe steels and welds available in the literature. It was observed that most FCGR curves of pipeline steels (X65~X100) remained within the BS 7910 mean and upper bound design curves in the Paris region. On the contrary, the fatigue crack growth rate of the X42 pipeline steel from a reference was high - a very steep slope of the FCGR curve, crossing over the BS 7910 design criteria. It was noted that the FCGR of austenitic stainless pipe steel and girth weld obtained from Arora et al. (2014) showed a very excellent fatigue property.

Abstract Long-distance pipelines are commonly used to transport oil, natural gas, water, etc. However, long-term use without maintenance causes the residue in the pipeline to gradually settle inside the pipeline due to physical or chemical action, and the pipeline becomes an accident. This leads to overpressure and leakages in the pipeline, which in turn affects the safety of the industry and people's lives. The objective of this study is to develop a non-destructive inspection to measure defects in a water pipeline using an ultrasonic technique. The simulated pipe is a SCH80 carbon steel pipe with a standard thickness of about 11mm, and defects such as holes and grooves inside and outside the pipe were designed. A submerged ultrasonic transducer is used to evaluate the simulated pipe defects and acquire the defect data in an imaging system using LabVIEW and Origin software. As a result, the thickness and location of the defects are clearly evaluated. In addition, the ultrasonic detection error was calculated to be less than 6.5%. This helps to use this technique and equipment for the inspection of underground fluid pipelines.

Abstract Fragility function, which defines the conditional probability of exceeding a limit state given an intensity measure (IM) of the earthquake, is an essential ingredient of modern approaches like the performance-based earthquake engineering methodology. However, the generation of such curves generally entails a high computational effort to account for epistemic and aleatory uncertainties associated with structural analysis and seismic load. Moreover, a certain probability function, such as the log-normal distribution, is usually assumed in order to carry out the conditional probability of failure of a structure, without any prior information on the correct probability distribution. In this paper, an artificial neural network (ANN) model is proposed to carry out fragility curves in order to avoid the aforementioned problems. In this respect, this paper investigates the following aspects: (i) implementation of an efficient algorithm to select proper seismic intensity measures as inputs for ANN, (ii) derivation of surrogate models by using the ANN techniques, (iii) computation of fragility curves by means Monte Carlo Simulations and (iv) validation phase.

Abstract This paper is concerned with experimental analyses on the vibration behaviors of a horizontal pipe containing gas-liquid two-phase flow with different flow patterns. The effects of flow patterns and superficial velocities on pressure fluctuations and structural responses are evaluated in detail. Numerical simulations on the fluid-structure interactions within the pipe are carried out using the volume of fluid method and the finite element method. A strongly partitioned coupling method is adopted to ensure the compatibility and equilibrium interface conditions between the fluid and the elastic pipe. The accuracy of the numerical solutions is confirmed by comparing with experimental results. It is found that the fluctuation frequency of the pressure fluctuations of the two-phase flow ranges from 0Hz to 5Hz. The standard deviation value of the pressure fluctuation of the two-phase flow increases with an increase in the superficial liquid velocity, and the maximum magnitude appears in slug flows. The vibration responses of the pipe exhibit strong dependence on the momentum flux of the two-phase flow, which mainly excites the fundamental flexural vibration mode of the pipe. The magnitude of vertical vibration response of the pipe is equal to that of the lateral vibration response, and the vibration response measured at the middle of the pipe does not contain the second-order operating mode. Moreover, the STD value of the structural responses of the pipe increases proportionally with an increase in the gas flow rate, while the predominant vibration frequency of the pipe slightly increases.

Abstract Autofrettage is a widely employed process for strengthening cylindrical or spherical pressure vessels. The process involves applying a uniform load to the inner wall of a vessel to cause a controlled plastic deformation, where the vessel yields starting from the inner wall up to an intermediate radius. When the load is removed, elastic recovery takes place and compressive residual stresses are induced in the vicinity of the inner wall, which strengthen the vessel against high static and pulsating loads during service. Based on the load employed, autofrettage can be of five types—hydraulic, swage, explosive, thermal, and rotational. This work analyzes a rotational autofrettage augmented by a thermal load where the load is applied by rotating the cylinder about its axis while maintaining a temperature gradient across the wall. The combined centrifugal and thermally induced stresses cause plastic deformation in the cylinder. When the cylinder is unloaded by bringing it to rest and cooling down to room temperature, compressive hoop residual stresses are introduced in the vicinity of the inner wall. A finite element method model of the proposed thermally assisted rotational autofrettage is developed for a cylinder made of AH36 mild steel in a commercial package ABAQUS®. The results indicate that the thermal load reduces the rotational speed required for autofrettage, when compared to a conventional pure rotational autofrettage. The thermal load also mitigates the tensile axial residual stresses, which are typical in a purely rotational autofrettage. A conceptual design of the experimental setup is also presented.

Abstract Non metallic composite pipes are one of the most effective ways to transport hydrogen. Basalt fiber materials can be used on hydrogen pipes, simulation models of composite pipe under plate and spherical indenter loads were established to study the effects of structure parameters on the pipe's mechanical behavior and failure modes. The results show that the matrix is the weakest part of the composite pipe under spherical indenter load, the failure areas of each fiber layer change for winding angle. The ultimate load decreases with the increasing of diameter-thickness ratio, and that increases with a deviation of the fiber winding angle from the axial direction, the indent depth increases with the increasing of diameter-thickness ratio. Under plate load, the final deformation of composite pipe is affected by the fiber winding angle and diameter-thickness ratio. The weak part of composite pipe changes due to the fiber winding angle, but the failure areas start from the plastic line area. The ultimate load and total absorbed energy of composite pipes under plate load is proportional to the winding angle and inversely proportional to the diameter-thickness ratio.

Abstract The deformation and dynamic response of a multilayer cylindrical shell composed of an inner shell and fourteen outer layers under external blast loads of different trinitro-toluene equivalency weights were studied. A numerical model using the thermo-viscoplastic constitutive model and considering fluid–structure coupling between explosion wave and structure was developed. The displacement in axial direction and cross section, as well as the effective strain responses, were analyzed to demonstrate the potential deformation of the shell structure. Results demonstrate that different materials cause inconsistent displacement and separation to develop in the inner and outer shells. In order to address the problem that the displacement of the inner shell is hard to measure due to the shielding and covering of the outer shell, a theoretical formula for calculating the maximum displacement of the inner shell was developed. The deflection process and stress triaxiality histories of the inner shell were investigated, and the results showed that compressive stress is the primary cause of plastic deformation. Additionally, the delamination that appeared in the outer shell was discussed, and it was revealed that there are two factors of delamination: (1) Stress waves spread across adjacent layers in the opposite direction because steel belts were wound in the opposite direction between the two adjacent layers; (2) Outer layers experienced uneven compressive loads. The results will be helpful to provide a reference for the intrinsic safety design of such multilayer cylindrical structures for hydrogen storage, etc.

Abstract In recent years, the role of thermal power plants has shifted from providing a baseload to providing supplemental supply to compensate for fluctuations in the output of renewable energy sources. Thus, the operation of these plants involves frequent startup and shutdown cycles, which lead to extensive damage caused by creep and fatigue interactions. In addition, the piping utilized in thermal plants is subjected to a combined stress state composed of bending and torsional moments. In this study, a high-temperature fatigue testing machine capable of generating such a bending-torsional loading was developed. Creep-fatigue tests were conducted on P91 steel piping with weldment. The results clarified that the creep-fatigue life was reduced by the superposition of the torsional and bending moments and that it was further reduced by a holding load. It was shown that the creep-fatigue life of piping with weldment can be estimated accurately using the equivalent bending moment, which is composed of the torsional and bending moments. It was also confirmed that crack occurred in the heat-affected zone (HAZ) of the welded part, which has been often observed in actual thermal power equipment. From the finite element analysis, it was identified that cracking was initiated in the HAZ due to the accumulation of creep strain and increase in the hydrostatic pressure component during a holding load.

Abstract Predicting creep crack growth (CCG) of flaws found during operation in high-temperature alloy components is essential for assessing the remaining lifetime of those components. While defect assessment procedures are available for this purpose in design codes, these are limited in their range of applicability. This study assesses the application of a local damage-based finite element methodology as a more general technique for the prediction of CCG at high temperatures on a variety of structural configurations. Numerical results for stainless steel 316H, which are validated against experimental data, show the promise of this approach. This integration of continuum damage mechanics (CDM) based methodologies, together with adequate inelastic models; into assessment procedures can therefore inform the characterization of CCG under complex operating conditions while avoiding excessive conservatism. This article shows that such modeling frameworks can be calibrated to experimental data and used to demonstrate that the degree of triaxiality ahead of a growing creep crack affects its rate of growth. The framework is also successfully employed in characterizing CCG in realistic reactor pressure vessel geometry under an arbitrary loading condition. These results are particularly relevant to the nuclear power industry for defect assessment and inspections as part of codified practices of structural components with flaws in high-temperature reactors.