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When to use Elgiloy over 316 stainless steel

A question that comes up frequently is whether, when using a spring energized seal, should the spring material be Elgiloy or will 316 stainless steel suffice. The following post will detail the specific media that will determine when you should make this consideration. This information should also be contemplated for other equipment and tools used in oilfield applications. 

First, before we detail the specific media, it is of value to appreciate what Elgiloy is: Elgiloy is a high-performance, cobalt-based superalloy known for its excellent mechanical properties and corrosion resistance. Its composition includes cobalt, chromium, nickel, iron, molybdenum, and manganese, which all contribute to its impressive qualities.

For oilfield applications in particular, one should consider Elgiloy over 316 stainless steel if the following media is present:

  1. Hydrochloric Acid (HCl): Used in acidizing wells to stimulate oil and gas production, hydrochloric acid can be very corrosive. Elgiloy offers good resistance to this acid, especially compared to standard stainless steels.
  2. Sulfuric Acid (H2SO4): While less common in direct oil and gas operations, sulfuric acid can still be encountered in associated processes. Elgiloy has demonstrated superior resistance to sulfuric acid under various conditions.
  3. Hydrogen Sulfide (H2S): While not strictly an acid, hydrogen sulfide is a sour gas that can have corrosive effects similar to those of strong acids. It’s frequently encountered in the oil and gas industry, particularly in sour gas wells. Elgiloy provides excellent resistance to environments containing H2S. The concentration of sour gas that Elgiloy can handle depends on various factors, including temperature, pressure, and the specific environment it is exposed to. Generally, Elgiloy performs well in sour gas environments containing H2S concentrations up to 1,000 ppm (parts per million).
  4. Organic Acids: Organic acids, such as acetic acid (CH3COOH), can also be found in oil and gas operations, especially in the presence of certain types of bacteria. Elgiloy generally offers good resistance to many organic acids.
  5. Carbon Dioxide (CO2): CO2 can combine with water to form carbonic acid, which can be corrosive. Elgiloy can offer superior resistance to environments with CO2 compared to some other alloys.

It’s important to note that the exact resistance of Elgiloy to these and other corrosive substances can depend on a variety of factors, including the concentration of the acid, the temperature and pressure, and the presence of other substances. As always, it’s essential to consult with materials experts or refer to relevant industry standards to guide materials selection for a specific application.

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