scope:

General

Erosion is defined by NACE International as "The progressive loss of material from a solid surface resulting from mechanical interaction between that surface and a fluid, a multicomponent fluid, or solid particles carried with the fluid."

Erosion has two main consequences for the Oil and Gas Industry:

Operating conditions can lead to erosion and damage to equipment and potentially loss of primary containment. These consequences can have an impact on safety, environment, and operations.

Production rate can be limited to avoid erosion. If these limits are set too low, the consequence is significant and unnecessary production loss or deferment.

Erosion problems are frequently caused by solids. These solids may come from the following sources:

• Unconsolidated reservoirs. The rate of sand produced from reservoir is influenced by the following factors:

ο Reservoir management

ο High drawdown from subsurface artificial lift systems: ESPs, PCPs, sucker rod pump (SRPs)

ο High drawdown due to well high flow rate in naturally produced wells.

ο High Flow rates

ο Sand/Proppant used in fracking operations

• Corrosion products such as FeCO3, FeS, Fe(OH)2. See section 4.1.3.8.

• Inorganic solids from scaling water with tendency of producing carbonate scales and/or others

• The requirement to maintain and increase production.

• The occurrence of multiphase flow (i.e. slugging in the transport of production fluids in both existing and new projects).

• Continued development of sand-production-prone reservoirs.

Many flow dependent wastage mechanisms are termed "erosion." For produced fluids, there are three main mechanisms to be considered:

• Erosion by fluids through liquid droplet impact. This requires very high fluid velocities in gas-dominated multiphase flow.

• Erosion by non-corrosive fluid carrying solid particles. Also applicable to low corrosivity fluids overwhelmed by the mechanical action of the metal removed by the solid particle impingement.

• Erosion-corrosion by a corrosive medium containing solid particles. For conditions where both erosion and corrosion are recognized as important contributors to the total metal wastage. Erosion-corrosion can also happen at high velocity in presence of droplets.

High flow rates may enhance corrosion by increasing mass transport of corrosion products and reactants, but this is not to be confused with erosion-corrosion as no mechanical removal of material is involved.

There are cases when small content of solids, even below typical detection limits, may trigger erosion-corrosion as per mechanism described in the third bullet point in 1.1.4.

These definitions can easily be distinguished on paper by degradation mechanisms, but in real practice these mechanisms are often not absolute, and they may be distinguishable and defined by the significance of the contribution of either corrosion or erosion and the consequent mitigation method used to minimize the wastage. For example, an erosion-corrosion problem on carbon steel subject to nominally solid free corrosive production (per EEMUA 194 definition) might be effectively resolved using a corrosion resistant alloy (CRA), hence for practical purposes the damage mechanism is often classified as Corrosion.

Erosion and corrosion can be independent of each other, in which case the total wastage is the sum of the wastage produced by each mechanism in isolation, or synergistic, in which case the total wastage is greater than the sum of the independent processes of erosion and corrosion taken separately.

Erosion caused by cavitation occurs as result of the formation and collapse of bubbles at or near the surface which result in material removal. Cavitation is a threat in high velocity fluid flow with sudden changes in pressure.