Stages of Corrosion
Corrosion is a dangerous threat that can cause catastrophic damage to the strongest equipment. This process is a natural reaction that causes the gradual degradation of metal, and while corrosion is naturally occurring, there are preventative measures that can slow the process down completely.
To ensure smooth flow and production in the oil and gas industry, it’s imperative that designers, engineers and field operators are conscious of corrosion at every stage. Here’s a closer look at some of the most effective ways to prevent corrosion.
Material Selection
Choosing the right material for your application is the first step in avoiding future corrosion. While steel is a widely used metal in the oil and gas industry for its excellent strength and resistance properties, there are many other metals that effectively resist corrosion as well, including:
- Nickel
- Copper
- Titanium
- Chromium
Fiberglass is often used in the industry for water disposal, holding chemicals and storing crude oil. Fiberglass, along with certain plastics, such as polyethylene and polyvinyl chloride, are great non-metal options for highly corrosive applications.
Protective Coatings
Protective coatings, such as paint can be applied to the exterior of pipes and other metal components to effectively prevent corrosion over an extended period of time. Inside pipelines and tanks, additional layers of coating may be applied to prevent corrosion that may occur internally.
Some metal materials, such as galvanized steel and stainless steel do not require a protective coating to avoid corrosion. For these materials, oxidation and rust may lightly build up on the surface and form a natural protective coating that is not strong enough to cause leak paths.
Using Inhibitors
Inhibitors are chemicals used to protect the surface of metals in oil and gas applications. These chemicals reduce the risk of corrosion by binding to the metal surface or reacting with impurities in the environment. Corrosion inhibitors may:
Restrict the rate of corrosion by blocking active sites on the metal surface
Increase the chemical potential of metal to create a natural oxide film
Contribute to the formation of a thin protective layer on the surface that stifles the corrosion process
When using an inhibitor, you should consider toxicity, environmental impact, availability and cost. These compounds can be pricey and the right inhibitor for your application can be difficult to get a hold of. When selecting an inhibitor, keep in mind that organic compounds are less toxic and have been proven more effective than inorganic inhibitors.
Corrosion Monitoring and Inspection
Corrosion monitoring provides a direct measurement of corrosion rate and metal loss in an application. Effective inspection can be done by measuring wall thickness frequently and assessing corrosion rates in vulnerable areas. To monitor the interior of pipes and tanks, electronic probes are often used to measure changes in electrical resistance. Additionally, there are multiple pigging operations, such as magnetic flux and ultrasonic pigs that travel along pipelines and detect internal corrosion.
