What You Need to Know About Stress Corrosion Cracking
Corrosion costs are a huge drag on the profitability of refineries. In 2016, the estimated costs for corrosion and associated downtime rose to over $1.1 trillion. Battling corrosion is a top priority for the oil & gas industry.
We’re going to examine one specific type of corrosion called stress corrosion cracking, as well as some strategies for dealing with it.
What Is Stress Corrosion Cracking?
Stress Corrosion Cracking (SCC) is a silent killer of carbon steel assets. If not caught in time, it can cause sudden failure in pipes and tanks. This type of corrosion starts off as microscopic cracks inside of metal. Often there is no visible corrosion or loss of metal before there are visible cracks, or worse, failure of the component. Part of what makes this type of corrosion so dangerous is its unpredictable timeline; it may cause failure of equipment in as little as a few hours, or remain undetected for months or years before triggering an issue.
SCC is a rather complex problem with many contributing factors, but there are three elements that must be present:
- A metal, most often an alloy.
- A corrosive environment for that metal.
- Stress on the metal, usually well below the tensile limits.
Variations in these factors make SCC a tricky problem to solve. Worse, the equipment doesn’t have to be in a highly-corrosive environment for SCC to occur. For instance, even buried pipes can fall prey to SCC. The soil pH can create the right environment for corrosion and the weight of the soil can put enough stress on the pipe to cause SCC to form.
Carbon steel assets are sturdy and widely used in the oil & gas industry, but they are unfortunately prone to corrosion. Most companies use an anti-corrosion coating as their chosen prevention method. But if a coating fails or is compromised for any reason, SCC can grow fast. Corrosive elements can become trapped between the coating and the metal. Worse, the remaining coating could hide the cracks, leaving your company unaware of the growing issue until suddenly your equipment fails.
What To Do if You Identify Stress Corrosion Cracking on Your Assets
SCC can be detected in several ways, including hydrostatic testing, in-line testing, and direct observation of collections of deep and long scratches on an asset’s surface. If SCC has advanced far enough before being noticed, replacement of the part or asset is the only option. If it’s caught in the early stages, the corrosive elements and stresses on the steel asset must be reduced before failure occurs.
Corrosion control is performed in several ways, including:
- Coating inspection and replacement
- Using corrosion inhibitors during cleaning
- Reducing the sources of corrosion below the metal’s limit.
Metal stress is relieved through heat treatment and controlling the temperature of the metal. If a part has to be replaced, it may be wise to take time to see if the design can be improved to reduce stress — especially if it’s a part that fails often.
Preventing Stress Corrosion Cracking
Preventing SCC is a far better tactic than fixing it after discovery. This is usually done by applying coatings to carbon steel assets to protect them from corrosive elements. Unfortunately, traditional coatings fail over time due to environmental abrasion, internal stressors caused by the coating’s formula, or exposure to various chemicals. Repairing these coatings requires additional equipment downtime, as the old coating often has to be removed. If some corrosion or flash rust is already present, the surface may also have to be abrasive blasted to create an even, clean layer for the new coating.
EonCoat’s inorganic coating was designed to mitigate these problems. EonCoat® is a plural component coating applied via spray gun that delivers a dual-layer of protection against corrosion. The first layer chemically bonds with carbon steel to create a thin alloy layer, which passivates the surface of the steel to prevent corrosion. As opposed to traditional coatings that sit on top of the surface, EonCoat’s chemical bond with the steel actually pulls the coating into the valleys of the substrate leaving no coverage gaps for stress corrosion cracking to occur.
The top, ceramic layer forms over the iron phosphate alloy layer and guards against environmental elements and mechanical damage. This top layer is far more abrasion resistant than traditional coatings. It simultaneously acts a phosphate reservoir, leaching phosphate if necessary to re-alloy the steel.
The combination of these two layers makes EonCoat® resistant to abrasion, environmental stressors, mechanical damage and chemical reactions that cause other coatings to fail. Thanks to its self-healing nature, which keeps the alloy intact under the toughest of conditions, EonCoat® prevents corrosion — including stress corrosion cracking — for decades without the need for reapplication.
Detecting and mitigating stress corrosion cracking early is crucial to minimize equipment downtime and production losses. Protect your assets from corrosion from the very beginning by coating your carbon steel equipment with state-of-the-art corrosion protection. Contact EonCoat to learn more about our patented coating for long-lasting protection against corrosion.