Hastelloy and Incoloy: Fasteners for Oil Field Corrosion

Oilfields are constantly exposed to a variety of corrosive agents, including carbonic acids, hydrogen sulfide (H2S), and chemicals used in hydraulic fracturing like hydrochloric and hydrofluoric acids. Naphthenic acids and organic acids are also present during crude oil extraction. Alongside these acids, the environment contains abrasive substances such as sand, which can lead to erosion and accelerate corrosion through a process known as erosion-corrosion. Additional factors like water injection, high temperatures, and high-pressure conditions further exacerbate this corrosive environment. Standard stainless steels like 304 and 316 typically cannot withstand these harsh conditions, making it necessary to use specialty nickel-based alloys instead. This article will explore the advantages of using specialty alloy fasteners, which play a critical role in preventing corrosion in oil fields and reducing equipment failures. Among the most commonly used nickel alloys is the Hastelloy family. Hastelloy C276 bolts are frequently employed in sour gas environments and can handle pressures up to 8,000 psi H2S and temperatures up to 400°F. The following chart shows the corrosion resistance of Hastelloy C276 fasteners in H2S/CO2 environments without elemental sulfur. Corrosion rates remain below 0.05 mm/yr (2 mils per year), with no stress cracking or stress corrosion. Sulfur has been shown to cause significant pitting and catastrophic cracking, even in many nickel alloys. Hastelloy C276 fasteners excel in preventing sulfur-induced stress cracking, which is vital since minor corrosion can lead to fastener failure. C276 also offers exceptional protection against carbonic acid, organic acid, and water-related corrosion, and it is resistant to CO2 corrosion, which is common in well operations. Hydrochloric acid, another aggressive agent found in fracking and well stimulation, is also effectively managed by Hastelloy C276. These bolts are resistant to all concentrations of hydrochloric acid at room temperature and can be used up to approximately 120°F. For more extreme conditions, materials like Hastelloy C2000 and tantalum are recommended. Incoloy 825 and 925 are popular options for protecting against sour gas corrosion, even at elevated temperatures. Incoloy 825 provides excellent resistance to H2S, while Incoloy 925 bolts are ideal when both high strength and corrosion resistance are required. Incoloy 925 bolts boast a tensile strength of 167.3 ksi, making them suitable for high-pressure applications. They also offer protection against chloride-related corrosion that can occur. Hydrofluoric acid, another corrosive agent used in fracking, can even corrode solid tantalum, which is generally resistant to most acids. To counteract hydrofluoric acid, we suggest using Monel 400 or Hastelloy C2000. These materials are among the few that can endure such an aggressive environment. In summary, the right choice of specialty alloys can significantly reduce corrosion issues in oil fields, ensuring safer and more reliable operations. Proper material selection is key to minimizing costly failures and maintaining efficient production.

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