What Causes Internally Influenced Corrosion and How Can It Be Mitigated?
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 third video, Buddy Damm, senior scientist of metallurgy, explains what internally influenced corrosion is, what types of it exist, and how an operator can prevent or mitigate it.
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BETH NIESER:
Hello and welcome to Ask Swagelok. I'm Beth Nieser, and I'm here with Buddy Damm, who's a senior scientist of metallurgy here at Swagelok.
So, Buddy, you've been telling us about corrosion in offshore oil and gas environments. And you talked to us a little bit about externally influenced corrosion. Can you talk about internally influenced corrosion? What are some of the different types of it and what can mitigate it?
BUDDY DAMM:
Internally influenced corrosion occurs because of the fluid that you're pulling out of the well—the fluid, liquid or gas. Each well can be different in composition, so there's a broad range. The deeper a well is drilled, the higher the pressures and the higher the temperatures, so these environments keep getting more and more severe. The components and the composition of the well can have hydrogen sulfide; it can be acidic; it can contain seawater and therefore chloride ions. The operators may also be protecting components through something called cathodic protection, and that can result in hydrogen being present. This becomes a very complex environment where many different types of corrosion can act together, and the term that we use to describe that is environmentally assisted cracking.
BETH NIESER:
So the fact that we're containing pressure—we're under a tensile load, and we have this complex environment that is accelerating the corrosion problem.
BUDDY DAMM:
To mitigate this problem—the best way to address it, because it's so complex, is to go to the NACE MRO 175 or ISO 15156 standard, which describes the limits for material use in oil and gas sour well environments. This standard will describe the limits of the types of alloys you can use as a function of temperature, pH or acidity, the chloride concentration, the hydrogen sulfide concentration; it puts limits on whether or not the material’s been heat treated a certain way or what strength it is. It also puts limits on whether it's for general use or for downhole, because it's complicated.
BETH NIESER:
You know, having a strong understanding of your environment is the first part. And then working closely with, for example, your Swagelok Sales and Service Center, or Swagelok technical service experts, allows you to manage the complexity of this NACE standard. We also have NACE compliant components that are in our catalog and listed as NACE compliant to help.
So it sounds like the NACE standards really provide critical guidance in order to select the right materials and for heat treatment in order to prevent corrosion to begin with.
BUDDY DAMM:
Absolutely. Yeah, a very useful tool.
BETH NIESER:
Okay, great. Well, thank you for that. And thank you all for joining us for Ask Swagelok.