Erosion

Erosion is the common issue in the oil and gas industry. Erosion damage is caused by the impact of solid particles on the surface of the pipe. Accurate erosion predictions are critical for the design and risk management of piping systems. The approaches to predict erosion include physical experimental testing, empirical models, and computational fluid dynamics (CFD) simulations.

Erosional Velocity

Flowlines tranporting multiphase fluids are particularly susceptible to erosion. When no specific information as to the erosive/corrosive properties of the fluid is available, an erosional velocity can be calcuated per API RP 14E, which is an empirical constant divided by the square root of the fluid mixuture density. The sand production rate is not considered in the erosional velocity formula. The erosion may occur if the flow velocity is above the erosional velocity. The erosional velocity is calculated for varing fluid mixture density and shown in Figure 1 (Imperial Units) and Figure 2 (SI Units).

Erosion Models

Emperical erosion models, which only address plain erosion (sand particle erosion), have been utilized to estimate erosion potential per DNV-RP-O501. These models are validated primarily for quartz sand as the erosive agent, making them applicable to subsea, topside, and onshore oil and gas production facilities. The erosion assessment is applicable to the following piping component(s):

• Smooth and straight pipe
• Weld joint
• Pipe bend (rigid or flexible pipe)
• Blinded tee
• Intrusive erosion probe
• Reducer
• Choke gallery

The design inputs for erosion assessment include piping geometry, target material properties, agent (particle) properties, and mixture flow properties. All models are based on mixture fluid properties. The mixture flow properties can be input directly for single-phase fluids (oil or gas), or calculated using a liquid-gas model, or based on a simplified black oil model with reference to allocated or measured flow rates, operating pressures, and temperatures. For single-phase fluids (liquid or gas), the respective single-phase properties should be applied. For multiphase flow, the mixture flow properties (velocity, density, and viscosity) must be established based on the properties of all phases.

For each type of piping component, the relative surface thickness loss [mm/ton] and annual surface thickness loss [mm/year] are calculated. The relative surface thickness loss increases with the particle impact velocity (equal to mixture fluid velocity), while the annual surface thickness loss is proportional to the mass rate of sand. In many cases, it is important to use the 'real-time' measured erosion rate from the probe to assess the 'real- time' amount of solids produced. The real time sand production can be determined from the measured erosion rate.

CFD

The complicated way to address erosion is to use computational fluid dynamics (CFD) simulations. CFD simulations can provide a more accurate prediction of erosion rates than empirical models. CFD simulations can model more complex piping geometries and flow conditions. CFD modeling with a high level of detail and expertise can provide detailed information on the exact location and magnitude of the erosion. Ansys-Flunt provides an erosion-MDM (Moving Deformation Mesh) coupling module to simulate the dynamiclly changing surface wall position due to erosion, which is a more advanced, less conservative, and more accurate approach to predict erosion. CFD modeling, running, and interpreting results are not provided in our cloud based modules, but can be performed offline.

References

1. DNV-RP-O501: Managing sand production and erosion
2. API RP 14E, 5th Edition, Reaffirmed September 2019 - Recommended Practice for Design and Installation of Offshore Production Platform Piping Systems