How Alberta's Oil and Gas Operations Can Achieve Better Corrosion Prevention

Steam-assisted gravity drainage (SAGD) operations involve corrosive fluids and abrasive media that can threaten the reliability of rotating equipment. When dealing with these harsh fluids in oil and gas, corrosion prevention is a major concern, and material selection is critically important. Materials that may be adequate for light crude operations can leak or fail under SAGD conditions.

Metallurgical quality can be the difference that keeps your rotating equipment running efficiently, with less downtime and fewer leaks—even in the harsh environments of SAGD operations. High-quality alloy composition and surface treatments are two aspects of tubing and component metallurgy that can prevent corrosion and improve equipment reliability.

High-Quality Stainless Steel Exceeding Industry Standards

SAGD oil contains water, chlorides, heavy metals, hydrogen sulfide (H₂S), and debris that can be extremely damaging to metals used for piping, tubing, and any other components that contact process fluids. Stainless steel is a common material in SAGD processes because of its resistance to corrosion and oxidation. However, not all stainless steel is the same—even when the same grade is specified.

Stainless steel is an alloy of iron, chromium, and sometimes other elements. The addition of chromium gives stainless steel its superior corrosion resistance compared to other types of steel. When chromium is added to steel, it forms a passivation layer of chromium oxide on the surface, which protects the steel from corrosion. Stainless steel contains between 10.5% and 30% chromium, depending on the type. In general, the more chromium, the better the corrosion resistance.

Many common stainless steel grades, like 304 and 316, also include nickel as an alloying element. Adding at least 8% nickel improves stainless steel’s corrosion resistance considerably. Higher nickel content further improves corrosion resistance, especially in acidic environments like those found in SAGD operations.

The composition of stainless steel alloys is specified by industry standards maintained by organizations like SAE and ASTM. For example, ASTM A240 specifies that 316 stainless steel must contain between 10% and 14% nickel and between 16% and 18% chromium. This means that even within a specific grade of stainless steel like 316, there can be considerable differences in properties from one product to another. An 18% chromium stainless steel is significantly more resistant to corrosion than a 16% chromium stainless steel.

Because elements like nickel and chromium are expensive, most stainless steel is made with the lowest allowed percentages, making it more vulnerable to corrosion. Swagelok's specifications for chromium and nickel content in stainless steel are at the high ends of the ranges specified by ASTM standards, which means Swagelok metallurgy offers better properties like corrosion resistance compared to similar products from other sources, even when they specify the same grade of steel.

Unlike most 304 and 316 stainless steels, Swagelok 304 and 316 are not cross-listable. Many manufacturers sell a stainless steel composition that meets specifications for both 304 and 316. However, because Swagelok’s stainless steels are made to tighter specifications, Swagelok 316 tubing and other components are superior to typical cross-listed 304/316.

Oil and Gas Corrosion Prevention and Consistent Weldability

Another element commonly found in stainless steel is sulfur. Unlike chromium and nickel, sulfur is usually undesirable because it diminishes stainless steel’s corrosion resistance and weldability. Industry standards specify the allowable sulfur content in an alloy as a maximum amount—typically about 0.030%. Unfortunately, sulfur’s negative effects can still be significant at these levels.

Because sulfur impurities solidify at a lower temperature than steel’s other components, they remain molten for some time after the metal has solidified. These molten spots draw chromium from the surrounding steel, diminishing its ability to form the protective oxide layer. This can lead to localized defects known as pitting that weaken the steel, often with catastrophic consequences for applications like pipes and pressure vessels. Additionally, welding components with high sulfur levels yields poor weld results. The sulfur content creates a weld bead shift which compromises the quality of the weld.

As with chromium and nickel, Swagelok specifies a tighter tolerance for sulfur content than what is specified by ASTM for stainless steel. This results in better resistance to pitting corrosion and H₂S and more consistent weldability compared to stainless steels with broader sulfur tolerances.

Surface Treatments for Maximum Corrosion Resistance

How components are finished has a significant effect on their corrosion resistance as well. In general, a rougher surface finish is more prone to corrosion because abrasive particles and corrosive fluids can become stuck in microscopic surface imperfections where they continue to damage the metal. A smoother surface finish promotes more effective flushing to remove any corrosive residue from the component’s inside surface.

One surface finishing technique for steel is passivation. In this process, free iron is removed from the surface of the material in an acid bath, leaving an inert chromium oxide layer that further enhances its corrosion resistance.

Swagelok’s seal support system technology includes a variety of surface treatment options for components like valves and tubing, including passivation, to protect them from highly corrosive SAGD chemicals and ensure reliability and prolonged life.

Look to Local Experts for the Best Metallurgy for Oil and Gas Corrosion Prevention

If you have questions about which components and materials are best for your SAGD operation, Edmonton Valve & Fitting can help. Our expert Field Advisors can perform an onsite assessment to understand your process and make sure you get the right materials and components for your process. We can also make specific recommendations regarding panel layout, instrumentation, and custom components to boost efficiency and reliability.

In oil and gas, corrosion prevention is key. Our goal is to ensure you have the best available metallurgy for your components so you don’t have to worry about corrosion. All our products are backed by Swagelok’s industry-leading Limited Lifetime Warranty, so you can rest assured that you’re covered if anything does go wrong.