Corrosion costs the pipeline industry an estimated $1.372 billion per year. That being said, metal corrosion is a serious problem, but one that can be prevented with the proper knowledge and precautions.
1. Crevice corrosion
Crevice corrosion is a type of localized corrosion that can occur when stagnant water is present within a crevice. It is highly penetrative and will either occur directly inside of or adjacent to any gaps in your metal surface--the perfect place for the corrosive agents to attack the metal, leading to rapid deterioration.
To prevent crevice corrosion, pipeliners should make sure all fittings and joints are properly sealed, and that any stagnant or low-flow water is removed from the system.
2. Intergranular corrosion
Intergranular corrosion occurs at the grain boundaries of metals. This type of corrosion can be caused by impurities in the metal, such as sulfur or phosphorus.
To prevent intergranular corrosion, pipeliners should use metals with a low concentration of impurities, and should avoid using welding or cutting processes that can introduce impurities into the metal.
3. Erosion corrosion
Erosion corrosion occurs when a corrosive liquid flows over a metal surface, dissolving or removing the metal's passive oxide layer and creating vulnerabilities.
This type of corrosion usually appears as a crater, groove, or valley in a directional pattern of a metal surface. The best way to prevent metal erosion is with protective coatings like SplashTRON or ThermoTRON.
4. Uniform corrosion
Uniform corrosion, the most common type, attacks the entire surface area where the metal was exposed to a corroding agent. It's usually caused by electrochemical or chemical reactions that consume the metal and thin it out until it's been entirely dissolved.
To prevent uniform corrosion, pipeliners should use coatings and inhibitors like SplashTRON and ThermoTRON to protect the metal from exposure to moisture and acids.
5. Stress corrosion cracking
Stress corrosion cracking is a type of corrosion that occurs when the metal is subjected to tensile stress in a corrosive environment (e.g., cold deformations, heat treatments, and welding) or along grain boundaries that are already experiencing intergranular corrosion. It appears as fine cracks in specific areas on a metal surface.
6. Pitting corrosion
Pitting corrosion is a type of localized corrosion that occurs in small pits on the metal surface. This type of corrosion is one of the most dangerous out there and is highly penetrative. It's extremely difficult to predict and can cause sudden and massive failures.
Pitting often occurs when inconsistencies are found in the protective passive film of the metal. These inconsistencies might be due to poor coating application, film damage, or foreign deposits.
7. Selective leaching
Selective leaching is a type of corrosion that occurs when one element of the alloy has deteriorated or been removed due to corrosion. This type of corrosion can be observed in the selective removal of zinc in brass alloys (dezincification).
The best ways to prevent selective leaching include selecting metals or alloys that have a greater resistance to dealloying, using impressed current cathodic protection or sacrificial anode cathodic protection, or controlling the environment to minimize the selective leaching.
8. Galvanic corrosion
Galvanic corrosion, also known as bimetallic corrosion, is a type of corrosion that occurs when two different types of metal are in contact with each other. One of the types will rapidly deteriorate and the other will be fine.
This type of corrosion is solely an electrochemical reaction driven by the electrode potential differences between two metals. Once exposed to an electrolyte, they'll form a bimetallic couple, where one metal is a cathode and the other is an anode. Like selective leaching, the farther apart the metals are in the galvanic series, the greater the corrosion rate.
Corrosion can be tricky, but your offshore structure doesn't need to fall victim to it. Mark Tool's SplashTRON coating can be applied to various areas on an offshore platform, and is most commonly used to protect risers, j-tubes, spools, bends, and more from the corrosive elements of the splash zone. Contact us today to request a quote!