Effect of Test Approaches & Conditions on Corrosion Inhibitor Screening

Abstract

Laboratory-based assessments of corrosion inhibitors for chemical qualification generally rely on approaches designed to replicate all key aspects of the corroding environment (ppCO2, field crude, brine composition, system temperature, pressure, wall shear, etc.). However, the time and costs associated with testing under fully field representative conditions (e.g. High Pressure/ High Temperature (HP/HT) autoclave or flow loop tests), often restrict the use of such tests to chemicals at dose rates pre-qualified by simpler screening tests, especially when many different formulations are submitted for potential qualification. This paper includes illustrative examples of how apparently small changes to the test methodology in these preliminary screening tests can have significant influence on the relative ranking and absolute performance of the chemicals tested, specifically: the effect of pre-corrosion; adjustment of brine chemistry to avoid artefacts from scale deposition; appropriate pH control (representative of the in situ field conditions where high ppCO2 may be present) partitioning between hydrocarbon and aqueous phases can be affected by minor procedural differences. The net effect is that product ranking can be significantly affected, potentially leading to the qualification of less effective products, or more significantly to the de-selection of otherwise effective products, prior to the more detailed field representative autoclaves / flow loops. More so, since many of the artefacts can be transferred from the screening tests to the field representative tests, product performance and ranking in the more field representative HP/HT tests can also be affected, if critical control of the test conditions is not adhered to. Examples are provided from both generic corrosion inhibitor formulations as well as case studies using field specific formulations. This will assist in improving the design of corrosion inhibitor screening programs and eliminating common errors and artefacts.