Pipework erosion is becoming an increasing issue within the oil and gas industry. New, high-rate subsea wells and associated topsides tie-ins are particularly vulnerable to erosion, and the consequences of failure are considerable.
Accurate prediction methods can be used to improve pipework design, inspection regimes and operating limits. This paper assesses the accuracy of erosion predictions made using simple equations, conventional computational fluid dynamics (CFD) erosion simulations and high-resolution CFD methods.
Correlation-based prediction methods, such as those in DNV RPO501, are effective for screening purposes, but they only deal with simple pipe fixtures such as single bends. CFD is often used to assess more complex layouts such as manifolds or flow lines. However, the standard CFD approach typically assumes a steady state flow and a homogeneous multiphase mixture. Recent comparison with large-scale tests has shown that CFD can effectively predict the flow-induced vibration forces caused by liquid-gas mixtures. In this work, the same liquid-gas modelling techniques have been used, with an additional sand particle phase, to assess pipework erosion.
In wet gas flow, a thin annular liquid film typically coats the pipe walls. Test work has shown that wall-films can significantly reduce erosion rates by slowing and redistributing sand impacts. The homogeneous approach used in most correlations and typical CFD studies ignores this effect and these methods tend to over-estimate erosion rates. This ultimately results in overly-conservative pipework design and production limits. It was found that high-fidelity CFD simulations that explicitly model the liquid, gas and sand correctly predict a reduction in erosion when a liquid film is present. The predicted flow regime is consistent with physical observations and the gas-liquid-sand model more closely predicts experimental test results.
This work demonstrates the benefits of explicitly modelling separate gas, liquid and sand phases, comparing predictions with published test data and showing the effects of higher-resolution simulations in a typical subsea pipework configuration.