Abstract

The nature and distribution of residual stresses are invariably critical for fatigue life with dissimilar material joints often inducing high tensile residual stresses. A fatigue-resistant concept of weld cladding process pipelines, producing compressive residual stresses, is under investigation to examine how these stresses may be influenced. Simplified weld cladding simulations have successfully illustrated the development and distribution of residual stresses through the joint. The study has highlighted the importance of accurate material data for clad and substrate materials with current analysis assumptions in a simple thick-walled pipe discussed. Experimental validation, using ICHD, measured residual stresses with depth on weld clad specimens, resulting in good correlation between simulation and experiment for a nickel-chromium-based superalloy clad on low alloy carbon steel as discussed. Future work, including a full 3D representation of the cladding process and a comparison of residual stress measurement methods, are also discussed.

Abstract

In this study, the limit load, shakedown and ratchet limit of a defective pipeline subjected to constant internal pressure and a cyclic thermal gradient are analyzed. Ratchet limit and maximum plastic strain range are solved by employing the new Linear Matching Method (LMM) for the direct evaluation of the ratchet limit. Shakedown and ratchet limit interaction diagrams of the defective pipeline identifying the regions of shakedown, reverse plasticity, ratcheting and plastic collapse mechanism are presented and parametric studies involving different types and dimensions of part-through slot in the defective pipeline are investigated. The maximum plastic strain range over the steady cycle with different cyclic loading combinations is evaluated for a low cycle fatigue assessment. The location of the initiation of a fatigue crack for the defective pipeline with different slot type is determined. The proposed linear matching method provides a general-purpose technique for the evaluation of these key design limits and the plastic strain range for the low cycle fatigue assessment. The results for the defective pipeline shown in the paper confirm the applicability of this procedure to complex 3-D structures.

Abstract

Impact forces generated in the load transfer area of railway crossing panels lead to a range of degradation modes from wear and fatigue of the contacting materials, fatigue of supporting components to ballast/subgrade deterioration. A simplified modelling approach has been developed to first analyse the geometrical problem of the axle rolling through the crossing geometry, and in a second step to predict the vertical dynamic force produce from the interaction between the wheel unsprung mass and the track system. The force is analysed in the frequency domain to estimate the level of damage in different parts of the track system. A parametric analysis of wheel shapes was carried out showing that the axle lateral displacement has a significant influence on the produced level of damage and also that characteristics such as the wheel flange thickness and the equivalent slope in the area of contact also leads to increased damage. It is suggested that such a measure in combination with the simplified algorithms developed here could be used, possibly in combination with track side monitoring system, to highlight traffic instances leading to increased asset damage.

Abstract

Turnouts are a key element of the railway system. They are also one part of the railway system with the highest number of degradation modes and failures for a number of reasons, including dynamic loads generated from non-linearities in the rail geometry and track support stiffness. It is therefore necessary to optimise the performance of the system in terms of its dynamic behaviour taking into account effects on long-term term damage evolution. The main aim of this study is to optimise the rail-pad stiffness in the crossing panel in order to achieve a decrease in the main indicator for ballast settlement, which is ballast pressure. A three-dimensional vehicle/track interaction model has been established, considering a detailed description of the crossing panel support structure. Genetic algorithm has been applied to find the optimum rail-pad combination for a specific case where variation in travelling speed and support conditions have been considered.

Abstract

—Asphaltene deposition in wellbores/pipelines causes serious production losses in the oil and gas industry. This work presents a numerical model to predict asphaltene deposition in\\ud wellbores/pipelines. This model consists of two modules: a Thermodynamic Module and a Transport Module. The Thermodynamic Module models asphaltene precipitation using the Peng-Robinson Equation of State with Peneloux volume translation (PR-Peneloux EOS). The Transport Module covers the modeling of fluid transport, asphaltene particle transport and asphaltene deposition. These\\ud modules are combined via a thermodynamic properties lookup-table generated by the Thermodynamic Module prior to simulation. In this\\ud work, the Transport Module and the Thermodynamic Module are first verified and validated separately. Then, the integrated model is\\ud applied to an oilfield case with asphaltene deposition problem where a reasonably accurate prediction of asphaltene deposit profile is\\ud achieved

Abstract

life-cycle cost analysis model is developed in this study, to examine the effects of particle size distribution of the solid particles to be\\ud transported on the optimal sizing and lifetime of the pipelines used for transportation of solid-liquid mixtures. The method determines the lifetime of the pipe corresponding to the least annual total cost per unit length of the pipe. The optimum diameter is obtained so that the total\\ud cost per unit pipe length per unit volume of the transported mixture throughout this lifetime is minimum. The total cost includes manufacturing\\ud and repair cost of pipe, cost of pumping power as well as the cost of power required for the crushing of particles from an initial size distribution to a desirable particle size distribution. The repair cost of pipe and cost of pumping power increase as the pipe becomes older due to more frequent pipe breaks and due to the pipe wear that makes wall roughness, and thereby pressure drop, greater. These costs together with the cost of power for crushing must be considered for through life costing of pipelines. Since the transportation of solid-liquid mixtures is maintained by several pumping stations in long pipelines, the spacing between two successive pumping stations must also be determined. The study shows interdependence of parameters such as the lifetime, the optimum diameter, the corresponding spacing for a given pumping power and the particle size distribution of solid particles transported in the pipeline. Furthermore, the method also provides the interrelation between the total length of pipeline when crushing is economical and the different particle size distributions. Document type: Article

Abstract

Hydraulic capsule pipelines (HCPs) are the third generation pipelines transporting hollow containers, known as capsules. These capsules are filled with material/cargo to be transported. The shape of these capsules has a significant effect on the hydrodynamic flow characteristics within HCPs. As the variations in the pressure distribution within HCPs are directly linked to and the flow characteristics within pipelines, it is essential to critically evaluate the effect of capsule shape on the pressure drop across the pipeline. Published literature is severely limited in terms of establishing the effects of the shape of the capsules on the flow characteristics within pipelines. Hence, the present study focuses on using a well-validated Computational Fluid Dynamics tool to numerically simulate the flow of capsules of various shapes quantified in form of a novel shape factor in hydraulic capsule pipelines. Both on-shore and off-shore applications of such pipelines have been investigated in the present study, along-with pipe fittings, such as bends. Variations in flow related parameters within these pipelines have been discussed in detail for a wide range of geometrical parameters associated with the capsules and the pipelines. Pressure drop values have been used to develop novel semi-empirical prediction models as a function of the shape factor and other flow and geometric variables of the capsules. These prediction models have been embedded into a pipeline optimisation methodology, which has been developed based on Least-Cost Principle. The resulting novel optimisation methodology can be used for hydraulic capsule pipeline design. Performance charts for practical applications have been developed for easy implementation of the design methodology for the designers of hydraulic capsule pipelines transporting capsule of different shapes. Document type: Article

Abstract

"jats:p"Corrosion damage is reported to be one of the leading causes of steel pipeline failure causing significant financial losses to operators and damage to the surrounding environment. As part of a rising confrontation to pipeline integrity management, researchers are continuously seeking better ways to assist on how to identify, assess, and prevent such incidents. Thus, there is a crucial need to establish a connection between assessment of pipeline condition and its structural stability. To achieve this, a three-dimensional finite element (FE) model is developed. The effects of geometry parameters such as defect thickness and spread angle are considered. Results show that thicker pipelines with corrosion groove perform better structurally than slender equivalents. The impact of corrosion damage is assessed to be significant on pipe stability with pipelines experiencing higher displacement and wall stresses with increasing defect depth and spread angle. A protective measure has been proposed using the buried pipes bedding system. The most critical spread angle is at 60 deg for unprotected pipe sections and 90 deg for bedded protected sections.

Abstract

integrity management (AIM) is crucial at each stage of offshore energy development in order to maintain the integrity and enhance the safety of critical assets. Risk-based integrity is a widely used approach in AIM which aims to assess the potential risks of infrastructure damage, on the basis of likelihood of failure and magnitude of consequences. This paper develops a risk-based integrity model for offshore energy infrastructures with particular application to subsea oil and gas pipelines. The likelihood of failure is estimated using the Bayesian prior-posterior analysis as well as expert elicitation methods. The consequences associated with failures are also evaluated in terms of a 'cost' function which includes the costs of inspection, maintenance and repair. Our presented model is then applied to assess the potential risk of damage to an oil export pipeline. The results indicate that 'corrosion' is the most common cause of failure for pipelines, followed by external influences and human and operational errors. In accordance with the consequence analysis carried out, cost of inspection and preventive maintenance is evaluated to be significantly less than the costs associated with pipeline replacement. Finally, three mitigation strategies are suggested to minimise the risks of pipeline damage.

Abstract

When production facilities reach the end of their economic life in the offshore oil and gas industry, field owners must decide whether to replace, extend the life of, or decommission assets. The decommissioning of deep and ultra-deep water oil and gas pipelines has become a serious issue in recent years because it is a complex process and presents challenges to stakeholders. In this paper, we review the current practices of pipeline decommissioning in different regions of the world and then highlight issues and challenges related to such activities in deep and ultra-deep waters. These issues and challenges can be broadly categorised into technical (e.g., selection of appropriate decommissioning procedures for handling hazardous pipelines), financial or economic, health and safety legislation, environmental, and human or organisational issues (such as lack of requisite skills, knowledge and expertise). In order to address the challenges identified in the study, some directions for future research are suggested. [Received: December 7, 2016; Accepted: October 17, 2017]