Erosion of oil&gas industry choke valves using computational fluid dynamics and experiment

doi:10.1016/S0142-727X(98)10039-5

International Journal of Heat and Fluid Flow

Volume 19, Issue 6, December 1998, Pages 636-643

https://doi.org/10.1016/S0142-727X(98)10039-5 Get rights and content

Abstract

As part of several years research activity with erosion in chokes, Norsk Hydro ASA has developed a model to estimate erosion and lifetime of chokes by incorporating erosion models into particulate flow models. This model has been verified with the results from flow and erosion testing of two different types of chokes, Needle&Seat and External Sleeve. The erosion tests with both the modified Needle&Seat choke and the External Sleeve choke gave peak erosion rates only two or three times larger than calculated. This is assumed to be near the uncertainty of the erosion model alone. This is very satisfactory for such complex flow geometries. The model and the experiments demonstrated that the External Sleeve choke is much more prone to erosion attack, at the given low pressure conditions.

Introduction

For production of oil and gas, choke valves on each well are used to balance the pressure of each well into a common manifold. The well stream is normally a mixture of oil, gas and water, which may contain sand particles. For large pressure reductions, up to sonic velocities can be reached within the chokes. Extensive erosion is then often experienced. The expense and lost production associated with choke trim replacements will normally be high, specially for subsea location of the chokes.

As part of several years research activity with erosion in chokes, Norsk Hydro ASA has developed a model to estimate erosion of chokes by incorporating an erosion model into a particulate flow model for:

•
choke lifetime predictions for a given design,
•
optimising choke geometry to reduce erosion.

This model has been verified with the results from flow and erosion testing of two different types of chokes, the modified Needle&Seat choke and the External Sleeve choke.

Also a liquid droplet erosion model is included into the particulated flow model (Nøkleberg and Søntvedt, 1995). This article, however, will only consider erosion by solids.

Section snippets

Flow model

The particulated flow version of Fluent (Ref. Fluent user's manual, 1997) has been used to simulate the fluid flow and erosion in the chokes. Fluent is a CFD (Computational Fluid Dynamics) program for modelling fluid flow, heat transfer, chemical reaction and the trajectories of dispersed particles/droplets. It is one of 3 or 4 widely used numerical simulation programs for fluid flow.

For flow in the continuous phase it solves the discretized Reynolds and continuity equations, together with

Erosion tests – experimental conditions

The tests were performed by DNV (Det Norske Veritas) in a test facility specially built for these tests, see Fig. 1. The chokes were tested with sonic flow conditions of air and sand. A compressor supplied the air. Transmitters for pressure, temperature and gas flow rate were used to control the flow conditions in the chokes.

The test conditions for the chokes were:

•
Gas – Air,
•
Inlet pressure 6 bar,
•
Outlet pressure 2 bar,
•
Inlet temperature 60–70°C,
•
Inlet pipe diameter 88.7 mm,
•
Solid particles 0.28 mm

Results from the simulations – needle&seat choke

This choke design had been optimised with respect to internal erosion as part of a Joint Industry Project which was initiated in 1993, using this numerical flow model. A prototype was designed and fabricated using the results from previous testing by DNV (Haugen et al., 1995) and detailed flow and erosion simulations (Nøkleberg and Søntvedt, 1995), see Fig. 2.

The 3-dimensional grid representing the modified needle and seat choke comprised 99,750 control volumes. Symmetry made it sufficient to

Discussion

In simple flow geometries such as bends, the impact velocities and impact angles of solid particles can relatively easily be determined with a reasonable accuracy. Then predictions of erosion are quite simple, using the method described in section `Erosion By Solid Particles' directly. The design of chokes, however, has been optimised over a period of many years to reduce erosion as much as possible. For example the External Sleeve choke which had been expected to be very erosion resistant, has

Conclusions

Extensive erosion in chokes can lead to very short lifetimes. The model developed for erosion in chokes has successfully been verified with experiments.The erosion tests with both the modified Needle&Seat choke and the External Sleeve choke gave peak erosion rates only 2–3 times larger than calculated. This model has been used in Norsk Hydro ASA to:

•
optimise the design of a Needle&Seat choke, giving 50–100 times reduction in erosion,
•
estimate expected choke lifetime for new installations and

References (6)

K. Haugen et al.
Sand erosion of wear resistant materials: erosion in choke valves
Wear
(1995)
L. Nøkleberg et al.
Erosion in choke valves – oil and gas industry applications
WEAR
(1995)
Fluent user's manual. Fluent, New Hampshire,...

There are more references available in the full text version of this article.

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Citation Excerpt :
Erosion has been studied throughout the years in several geometries such as elbows, valves, tees, cyclones, among others [1–6].
Pipeline erosion in the production of oil and gas often occurs in elbows, tees, valves, pipes, chokes and other pipe geometries that cause a rapid change in flow direction. Liquid-dominated flows are of importance in mining and many oil fields and transportation lines carrying oil and gas including those in deep water subsea flowlines. In this study, experimental data for wall thickness losses were measured with an ultrasonic transducer in a 50.8 mm standard elbow. Experiments were conducted with multiphase flows with water, air and 300 µm average sand particles and with liquid-sand flows. Wall thickness losses were measured on the outer radius of elbows at 63 locations and for several different flow conditions. Computational Fluid Dynamics (CFD) simulation was performed using the Euler-Lagrange approach with the Reynolds Stress Model (RSM) for turbulence and Eulerian Multiphase model for multiphase flow cases. Different flow regimes were investigated in liquid-sand and multiphase flows. It was observed that maximum erosion increases as the mixture velocity increases. In addition, for liquid-sand and dispersed-bubble-sand flows the Euler-Lagrange and Euler-Euler-Lagrange approaches used in the CFD simulations were able to predict the observed maximum erosion rates, erosion locations and erosion patterns.

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