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Abstract
Erosion and corrosion are usually behind the failure and damage of complex pipeline configurations. Corrosion is caused by the oxidation of carbon steel pipe wall while erosion is affected by inertial impaction of the high velocity liquid droplets and solid particles. The pipelines always contain fittings such as elbows. Erosion and corrosion rates are higher in elbows than in straight sections due to the complex flow in elbows.
The objective of this thesis is to develop general mathematical models that are able to predict multi-phase flow characteristics, mass transfer controlled corrosion rate, particulate flow and erosion rate in complex pipeline configurations using commercially available computational Fluid Dynamic code. The numerical calculations are performed for three-dimensional turbulent multi-phase flows through complex pipeline configurations. The turbulent flow field was obtained by solving Reynolds Averaged Navier-Stokes equations. Different turbulence models are examined and the most appropriate one is obtained. A mass transfer model is used to calculate the transfer of oxygen and hydrogen sulfide species from the flow to the pipe wall and is extended to calculate corrosion rates. For the particulate phase a Lagrangian approach is used to obtain particle trajectories. Finally, the erosion rate is determined by using the suitable erosion equation. The prediction models are validated using the available experimental data from open literature. Generally, the comparison between model predictions and experimental data showed good agreement. The present prediction models are applied to the case study of a complex pipeline configuration which exists in Assiut Oil Refining Company (ASORC) to determine corrosion and ersion rates qualitatively and quantitatively. The effect of different parameters such as inlet velocities, water volume fractions and concentration of species (i.e. hydrogen sulfide) on corrosion and erosion are investigated. The effect location of elbows is taken into consideration as well. It was found that increasing the inlet velocity and water volume fraction in the pipeline increases the corrosion rates. It is found also that elbows have great effect on the flow field, and thus on the distribution of corrosion rates. The maximum corrosion in elbows occurs always at the other surface of the elbows at the exit. The numerical model provided detailed information on the flow and the assdociated phenomena affecting corrosion rates. Since the flow through the seiected pipeline of ASORC does not contain particulate material injected from the inlet, the particulate phase is considered in this study as the corrosion products which are released from the elbows. The corrosion products are mainly ferrous hydroxide Fe(OH)2 and iron sulfide FeS which are formed as a result of the corrosion process. The prediction for the particulate phase indicated that intertial effects cause denser particles to be distributed near the outer wall. The predicted results of erosion indicated that the erosion rate increases by increasing the velocity. It is also found from the calculation of the cavitation coefficient that no cavitation would be expected to occur under the conditions of ASORC case.
This developed mathematical model describing three-dimensional multi-phase turbulent flow through complex pipeline configurations should be very useful in design and operation.