Corrosion inhibitor

What is a corrosion inhibitor?

Corrosion is the gradual destruction of metal by chemical or electrochemical reaction with its surroundings, most familiarly as rust. In pipelines, wells, tanks, boilers and cooling systems, water, oxygen, carbon dioxide, hydrogen sulfide and bacteria all drive it. A corrosion inhibitor is added to the fluid to slow that attack, usually at concentrations of parts per million.

How corrosion inhibitors work

• Film-forming inhibitors adsorb on the metal surface and form a thin barrier that separates it from the corrosive fluid. Many oilfield inhibitors, such as imidazolines and other amine-based compounds, are surface-active molecules that attach to steel through a polar head group.
• Anodic and cathodic inhibitors slow one half of the electrochemical corrosion reaction.
• Oxygen scavengers remove dissolved oxygen, a major driver of corrosion in water systems.

Where they are used

• Oil and gas production, where “sweet” corrosion from carbon dioxide and “sour” corrosion from hydrogen sulfide attack tubing, flowlines and equipment. Inhibitors are injected continuously or applied in batch treatments.
• Acid treatments, where inhibitors protect steel from the acid during acidizing.
• Industrial water systems, such as cooling towers and boilers, where inhibitor packages protect steel and copper alloys.

Corrosion inhibitors are usually part of a broader program with scale inhibitors, biocides and dispersants, because deposits and bacteria can cause localized corrosion underneath them; see fouling.

Frequently asked questions