What is Corrosion and What Causes It?
In order to combat corrosion in offshore oil and gas environments, it is important to understand the challenges associated with the environment. That’s why we’ve created a three-part Ask Swagelok series that explains the types of offshore corrosion—including internally and externally influenced corrosion—and ways to mitigate it.
In this first video, Buddy Damm, senior scientist of metallurgy, explains what corrosion is at a high level and why it occurs in offshore oil and gas situations.
Video Transcript
BETH NIESER:
Hello and welcome to Ask Swagelok. I'm Beth Nieser, and I'm here today with Buddy Damm, who's a senior scientist of metallurgy here at Swagelok. Today we're going to be talking about corrosion in offshore oil and gas applications. So Buddy, can you tell me what corrosion is and what causes it?
BUDDY DAMM:
Corrosion occurs as a result of an electrochemical reaction in which electrons are lost from the metal and the metal itself reacts chemically. Corrosion scientists describe this in terms of two different half‑cell reactions.
When a metal loses electrons due to a corrosive environment, that process is called oxidation. Those electrons then travel through the metal to a nearby location and participate in a reduction reaction. Together, these are known as a redox—reduction‑oxidation—reaction.
The net result is the consumption of the metal. You may see thinning of the material, which can reduce pressure‑containing capability, or you may see pitting, cracking, or crevice corrosion—forms of damage that reduce mechanical performance.
BETH NIESER:
So then, what corrosion problems are common in an offshore platform environment?
BUDDY DAMM:
Offshore corrosion can be grouped into two categories: externally influenced corrosion and internally influenced corrosion.
Externally influenced corrosion occurs because components are exposed to a marine environment—saltwater, sea spray, and even compounds from the production process itself. These environments often involve wet and dry cycles. When something gets wet, the corrosive species may be dilute, but as the water evaporates, those species become more concentrated and the environment becomes more severe.
You can also see fretting corrosion when two components rub against each other. Normally you'd expect wear, but the corrosive environment accelerates it. Additionally, components may experience cyclic loading due to vibration or platform movement. In a corrosive environment, that can lead to corrosion‑assisted fatigue.
BETH NIESER:
Okay. And what about internally influenced corrosion?
BUDDY DAMM:
Internally, we're pulling hydrocarbons out of the ground, and these wells can contain a wide range of chemical compounds. They may include hydrogen sulfide, carbon dioxide, or other acidic components. Deeper wells tend to be higher temperature and higher pressure, making the environment even more aggressive.
Because we're containing pressure from deep underground, the combination of mechanical stress and a complex chemical environment can result in environmentally assisted cracking.
BETH NIESER:
Okay, great. Thank you for that overview. And thank you all for joining us for Ask Swagelok.
