Laboratory Development of a Corrosion Inhibitor for a North Sea Main Oil Line Offering Enhanced Environmental Properties and Weld Corrosion Protection

Abstract The use of chemical inhibitors for mitigation of corrosion has been a tried and tested method of corrosion control in the oil industry for many years. However, in recent years there have been requirements identified for these inhibitors that were not considered when they were designed in the past. One of these requirements is based on the environmental regulations being imposed on oilfield production, especially in offshore production facilities in the North Sea. This requires inhibitors to be approved by local environmental bodies using various notification schemes. A performance issue identified is the ability of corrosion inhibitors to inhibit preferential corrosion seen in 1% nickel welds. Past experience has shown that inhibitors can have detrimental effects on these welds if the inhibitor is used at the wrong concentration or has been formulated without taking into account this type of attack. Therefore, the formulation of inhibitors to overcome this form of attack can be key for the integrity of pipeline systems to be maintained. This paper deals with the laboratory investigations carried out in order to replace non environmentally acceptable corrosion inhibitors in a Main Oil Line system in the North Sea. The testing carried out involved the use of routinely used laboratory methods such as aqueous and partition bubble testing, employing Linear Polarization Resistance (LPR) and Rotating Cylinder Electrode (RCE) tests. The testing involved the study of the products in respect to preferential weld attack and considered how the new environmentally acceptable products maintained inhibition. After laboratory studies were carried out, a new product offering an improved environmental profile whilst maintaining good weld inhibition properties was recommended for field evaluation. This paper reviews the experimental work conducted in this development.