Ever more stringent environmental regulations make it increasingly difficult to obtain satisfactory corrosion inhibitors which are effective while being compatible with marine life. Toxicity towards aquatic organisms is a major concern and environmental constraints have been imposed on the types of compositions used in the North Sea in order to protect marine organisms. Many available inhibitors cannot meet the environmental criteria while maintaining effective corrosion inhibition.

For sweet / carbon dioxide corrosion, imidazoline based inhibitors are traditionally effective but they have an imperfect environmental profile. Here we describe how the environmental properties have now been improved by alkoxylation of a traditional inhibitor. This not only improves the environmental aspects but also increases the hydrophilicity of the inhibitor making it more suitable for water based applications and increasing its solubility in the water phase where corrosion usually takes place.

Organic phosphate esters are also effective corrosion inhibitors with a broad field of application in sweet and sour corrosion.

Here we describe laboratory-based corrosion testing on an innovative range of mixed imidazoline / oligophosphate ester inhibitors which show synergy in corrosion inhibition ability, especially at low dosages. The alkoxyimidazoline protects the cathode of the electrochemical cell and the oligophosphate protects the anode – this dual mechanism promotes synergy and increases confidence that the inhibitor will continue to give corrosion protection even in extreme situations where one of the components might have failed.

These mixed corrosion inhibitors are therefore applicable to a wide range of water based systems used in the oil and gas industry.

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