Understanding the Erosion – Corrosion Behaviour of Generic Types of Stainless Steels in a CO2 – Saturated Oilfield Environment

Using of Corrosion Resistant Alloys (CRAs) specifically stainless steels is considered as one of the most effective corrosion control strategies in the oil and gas industry when aggressive environments such as carbon dioxide and chloride ions may be present. This is due to presence of a compact and protective passive film on their surfaces which acts as a barrier between the substrate and the surrounding corrosive environment. However, presence of sand particles in the flowing fluid can reduce the superior corrosion resistance of these alloys because of passive film removal by sand particles impact leaving the substrate exposed directly to corrosive environments. This phenomenon is commonly known as “erosion-corrosion”. Sand particles impact may also lead to significant surface and subsurface changes and the latter has a great influence on the erosion and erosion-corrosion resistance of stainless steels knowing that the latter vary in their chemical composition and their mechanical properties. For this reason, it is important to understand how these materials will behave under erosion and erosion-corrosion conditions.
The effect of the static corrosion behaviour on the erosion-corrosion resistance of stainless steels as a function of temperature was investigated. Also, how stainless steels degrade under erosion and erosion-corrosion conditions and specifying the factors contribute to their failure have been addressed. Moreover, the study has investigated how the percentage of contribution of total weight loss components of stainless steels changes with impact angles.
Gravimetric and electrochemical measurements in addition to post-test surface analysis including micro indentation hardness test, surface optical profilometry (Bruker- NPFLEX), Scanning Electron Microscopy (SEM), Focused Ion Beam (FIB), Transmission Electron Microscopy (TEM) were used to explain the degradation behaviour of the studied materials under erosion-corrosion conditions.
It has been found that there is a good correlation between the static corrosion behaviour and the erosion-corrosion resistance of stainless steels. For example, a good link between the repassivation ability under static conditions (i.e. (Eb-Er) and imax) and erosion-enhanced corrosion was existed. Also, the same parameters linked well with the repassivation time under erosion-corrosion conditions. Moreover, results revealed that the change in hardness can be used as a prediction parameter to erosion resistance of stainless steels in severe conditions. Furthermore, impact angle has a significant effect on the percentage of total weight loss component contribution. It was found that the percentage of the corrosion-enhanced erosion contribution to be responsible for a distinct erosion-corrosion resistance of stainless streels.