Effect of flow pattern at pipe bends on corrosion behaviour of low carbon steek and its challenges

Recent design work regarding seawater flow lines has emphasized the need to identify, develop, and verify critical relationships between corrosion prediction and flow regime mechanisms at pipe bend. In practice this often reduces to an pragmatic interpretation of the effects of corrosion mechanisms at pipe bends. Most importantly the identification of positions or sites, within the internal surface contact areas where the maximum corrosion stimulus may be expected to occur, thereby allowing better understanding, mitigation, monitoring and corrosion control over the life cycle. Some case histories have been reviewed in this context, and the interaction between corrosion mechanisms and flow patterns closely determined, and in some cases correlated. Since the actual relationships are complex, it was determined that a risk based decision making process using selected ‘what’ if corrosion analyses linked to ‘what if’ flow assurance analyses was the best way forward. Using this in methodology, and pertinent field data exchange, it is postulated that significant improvements in corrosion prediction can be made. This paper outlines the approach used and shows how related corrosion modelling software data such as that available from corrosion models Norsok M5006, and Cassandra to parallel computational flow modelling in a targeted manner can generate very noteworthy results, and considerably more viable trends for corrosion control guidance. It is postulated that the normally associated lack of agreement between corrosion modelling and field experience, is more likely due to inadequate consideration of corrosion stimulating flow regime data, rather than limitations of the corrosion modelling. Applications of flow visualization studies as well as computations with the k-ε model of turbulence have identified flow features and regions where metal loss is a maximu

Multi-fluid approach for the numerical prediction of wall erosion in an elbow

Multiphase pipelineflows are widely used in the oil and gas industry to transport solid-liquid or gas-solid mix-tures. Erosion caused by the impact of solid particles is a major challenge for equipment maintenance and safety,especially in complex geometries such as elbows. In this work, a CFD study on wall erosion in a 90° standardelbow has been performed using a multi-fluid approach, also called Euler/Euler, for poly-dispersedfluid-particleflows. A model is used for the erosion prediction taking into account particle turbulent kinetic energy obtainedfrom the Euler-Euler approach. A good agreement with experiments is observed. The effects of wall roughnessand solid massflow rate on the erosion rate are also investigated. For a certain amount of sand passing throughthe pipe elbow, there exists a solid massflow rate for which the particle impact damage is most dramatic

Effects of fluid flow on corrosion behaviour in pipe bends

Correlation on flow induced corrosion (FIC) for straight pipes and bends have been obtained by researchers via a two-dimensional numerical method and experimental techniques. However, for pipe bends, the correlations require further improvements as the flow in bends are more complicated. The objective of this research is to obtain more accurate correlations for FIC in bends using twodimensional and three-dimensional numerical and experimental techniques. In the numerical and experimental approach, several important parameters such as Reynolds number and selected discrete particle model (DPM) were used to obtain erosion rate for miter and smooth bend models. Validations for the modellings were compared with experimental results and locations of the eroded sections were observed to be in agreement. Then, the erosion rates were extracted and analyzed using shooting method. Finally, the new coefficients for the correlations were obtained. When the new equations were applied to the same two-dimensional models, it was shown that the previous two-dimensional models had over-predicted the mass transfer values. Furthermore, when comparisons were made between smooth and miter bends results under the same flow conditions, it was observed that mass transfer values calculated from miter bend models were much higher than that of smooth bends. Experimental results also showed similar behavior, when the surface morphology was examined under Field Emission Scanning Electron Microscope (FESEM). From numerical and experimental approach conducted, it is concluded that the inner diameter bends were the areas with the highest FIC behaviour for 300 and 450 smooth and mitre bends

Numerical study of erosion in critical components of subsea pipeline: tees vs bends

Elbows are a vulnerable part of piping systems in erosive environments. Traditionally, plugged tees are used instead of elbows when the erosion rate is high. However, the advantage of plugged tees over elbows in large-scale pipelines is unclear. A comprehensive computational fluid dynamics study was carried out to predict the erosion rate in plugged tees and elbows. A numerical method was first used for aluminium elbows and tees with available experimental data through which the accuracy of the numerical solution was verified. After validating the model, numerical modelling was used to compare the erosion rates of plugged tees and elbows in varying geometrical conditions, ranging from 0.0254 to 0.6 m diameter carbon steel pipes transmitting multiphase gas/sand flow. The effects of internal flow velocity and sand particle size on erosion rates were also investigated. The numerical results revealed that the erosion ratio between plugged tees and elbows strongly depends on the internal diameter of the pipe, the flow velocity and particle size. Hence, the influence of these parameters should be considered for proper selection of the fittings to be used. Finally, numerical modelling of erosion in two subsea jumpers outfitted with standard elbows and plugged tees was presented

An Eulerian–Eulerian formulation for erosion modelling: an alternate approach.

Sand is commonly produced besides petroleum fluids and it presents a major erosional hazard leading to pipe failures. Particle erosion is a complex process in which material is removed due to the repeated particle impacts. Conventionally, a CFD flow solver and computationally intensive lagrangian particle tracking sub–routines, known as Eulerian–Lagrangian (E–L) model, along with empirical erosion equations are used to predict the erosion rates. The present work introduces an Eulerian–Eulerian (E–E) approach in which the multiphase granular model resolves the solid phase and obviates the need of particles tracking. Particle–laden turbulent flow across a flow restrictor, based on an experimental study, is chosen for validation. Numerical experiments are done in Simcenter STAR–CCM+. Comparison with the experimental data demonstrate a good agreement and in particular, the E–E model yields reliable predictions of impact wear locations, erosion rates as those of E–L model. A 90° square bend is also simulated and comparison of erosion rates on the concave wall demonstrate that E–E model can be used as an alternate to computationally expensive approaches

Viscosity effects on sand flow regimes and transport velocity in horizontal pipelines

Solids transport in multiphase systems is one of the issues under the umbrella of ‘‘flow assurance.’ But unlike issues such as waxes and hydrates, solids transport has received relatively little interest to date. The overall aim of this research was to investigate the fluid viscosity effects on sand particle transport characteristics in pipelines. Investigations were conducted using a 3-inch test facility for oil and a 4- inch flow loop for water and CMC experiments. Three oil viscosities were used including 105 cP, 200 cP and 340 cP. The sand used had a density of 2650 kg/m3 and a median diameter of 0.2 mm. The sand loadings were 50 lb/1000 bbl and 200lb/1000bbl. Based on the King et al (2000) sand minimum transport condition definition, the sand transport velocity for water, CMC solutions and oil (105 cP, 200 cP and 340 cP) were determined by visual observation and camera. The observed sand/oil flow regimes were compared. For oil/sand tests, it was observed that the dominant regime when approaching the critical sand transport velocity was the sliding sand bed, sand dunes were notably absent. However, for water and 7 cP CMC solution, sand dunes and sliding sand bed regimes were observed when approaching the sand transport velocity. For 20cP CMC solution, it was observed that the sand particles in the region between the main dunes were very active compared to those within the dunes

Particle Attrition Mechanisms, their characterisation, and application to horizontal lean phase pneumatic conveying systems: A review

Understanding particle attrition is vital to the optimisation of a wide range of industrial processes. Lean phase pneumatic conveying is one such process, whereby the high energy particle impacts can cause undesirable loss in product quality or change in bulk behaviour. The attrition process is resolved into a material function and a process function; the combination of these functions dictates the attrition mechanism present, and the magnitude of failure observed. Subsequently, the forces applied to the particles are examined within the context of lean phase pneumatic conveying. Finally, empirical and numerical models are reviewed along with comments on experimental method. To summarise some of the findings of this review: the requirement of standardised test equipment is recognised in order to compare the wide variety of particulate materials under comparable loading conditions; stronger correlation between the results obtained from different particle attrition test methods is required; and finally, seldom are the manufacturing conditions (where applicable) linked to the particulate attrition behaviour

Pressure drop and flow characteristics for the pneumatic transport of fine particles through curved and straight circular pipes

The initial results of an investigation into the flow properties of a gaseous suspension of fine particles are reported. The objective of the work has been the acquisition of extensive experimental data, the analysis of which provides a better understanding of the pressure drop and flow characteristics of pneumatically transported solid particles. The versatility of the test rig is demonstrated by the diversity of the investigations performed during this study. Quantitative results were acquired for the flow of different-sized alumina particles flowing through vertical and horizontal pipes of different diameters, and around six bends of varying geometry. Dimensional analysis is profitably applied to the correlation of the experimental. data and the ensuing deductions examined critically. These conclusions were either substantiated or refuted by a visual appreciation of the nature of the flowing suspension. Investigations into bend erosion have explained the mechanism of the erosion process, and the data analysis has produced an equation which defines the mean wear rate as a function of the mean air velocity and the solids-to-air mixture ratio. This study has revealed the need for extensive study of topics not yet fully examined. Suggestions for further work are included at the end of Chapters 5, 6, ? and 8

Recent progress in CFD modeling of powder flow charging during pneumatic conveying

Thus far, Computational Fluid Dynamics (CFD) simulations fail to predict the electrostatic charging of particle-gas flows reliably. The lack of a predictive tool leads to powder operations prone to deposits and discharges, making chemical plants unsustainable and prime candidates for explosions. This paper reviews the rapid progress of numerical models in recent years, their limitations, and outlines future research. In particular, the discussion includes CFD models for the physics and chemistry of particle electrification. The condenser model is most popular today in CFD simulations of powder flow electrification but fails to predict most of its features. New experiments led to advanced models, such as the non-uniform charge model, which resolves the local charge distribution on non-conductive particle surfaces. Further, models relying on the surface state theory predicted bipolar charging of polydisperse particles made of the same material. While these models were usually implemented in CFD tools using an Eulerian-Lagrangian strategy, recently Eulerian methods successfully described powder charging. The Eulerian framework is computationally efficient when handling complete powders; thus, Eulerian methods can pave the way from academic studies to application, simulating full-scale powder processing units. Overall, even though CFD models for powder flow charging improved, major hurdles toward a predictive tool remain.Comment: arXiv admin note: substantial text overlap with arXiv:2205.0821