Corrosion, Cost and Loss of Containment

Corrosion is the deterioration of a material, usually a metal, by chemical or electrochemical reaction with its environment. On an oil and gas or process facility, the metal is mostly carbon steel and the environment is produced water, wet gas, seawater, soil or the atmosphere. Steel was made by putting energy into iron ore. Corrosion is the steel slowly returning to an oxide or sulphide, which is a more stable state. It cannot be stopped forever. It can only be slowed, controlled and watched.

This is why corrosion is a management subject, not only a chemistry subject. Every facility is losing wall thickness somewhere, every day. The question is whether the organisation knows where, how fast, and how much margin is left.

The three costs of corrosion

• Safety. Corrosion thins or cracks the pressure boundary. When the remaining wall can no longer hold the pressure, the result is a loss of primary containment (LOPC): an unplanned release of process fluid from its pipe, vessel or tank. A release of hydrocarbon can ignite. A release of hydrogen sulphide (H2S) can kill.
• Environment. A leak from a corroded pipeline can pollute soil, groundwater or the sea for years.
• Business. Unplanned shutdowns, emergency repairs, lost production, replacement of equipment early, fines and damage to reputation.

A study published by NACE International in 2016 (the IMPACT study) estimated the global cost of corrosion at about US$2.5 trillion a year, about 3.4% of global gross domestic product (GDP). The same study estimated that good corrosion control practice could save about 15–35% of that cost. The figure is an estimate built from national studies, so treat it as an order of magnitude, not an exact number.

Corrosion as a barrier problem

Most major-accident thinking uses the idea of barriers: things that stop a hazard becoming an event. The pressure boundary is the first barrier, and corrosion attacks it directly. Corrosion management keeps the pressure boundary healthy by combining many smaller barriers: the right material, a coating, cathodic protection, chemical treatment, process limits, monitoring and inspection. When one weakens, another must still hold. The rest of the course follows this logic.