The oil and gas industry is characterized by the usage of materials used in equipment and pipelines under conditions that are harshest in the world. Sour service environments, where hydrogen sulfide (H2S), carbon dioxide (CO2), and other corrosive elements are found, challenge the integrity and safety of such materials. In order to avoid corrosion and material failure, strict guidelines are established that include limitations on the nickel content in materials used for sour service applications. This article explores the reasons why nickel (Ni) is restricted to a maximum of 1% for sour service.
Importance of Nickel restriction to maximum of 1% for sour service
Stress Corrosion Cracking (SCC)
SCC is one of the common problems found in sour service environments. SCC takes place when the corrosive environment along with tensile stress results in crack initiation and propagation within the material. Hydrogen sulfide has been shown to make nickel-rich alloys prone to SCC.
Nickel (Ni) is restricted to a maximum of 1% in sour service due to its tendency to form brittle intermetallic with other metals in the presence of hydrogen sulfide (H2S). This phenomenon is particularly concerning in sour service applications, where H2S is present in high concentrations and can cause corrosion and degradation of the metal. The formation of brittle intermetallics can reduce the toughness and ductility of the metal, which makes it more prone to cracking and failure. Moreover, high concentrations of Ni can also increase the susceptibility of the metal to corrosion in sour service environments.
Limiting nickel content to 1% or lower helps mitigate the risk of SCC and ensures the long-term integrity of equipment and pipelines.
Sulfide Stress Cracking (SSC)
Sulfide stress cracking is another failure mechanism commonly seen in sour service conditions. This type of cracking can result in sudden, catastrophic failure, thus posing a significant safety risk. Low-nickel materials are less susceptible to SSC, and this is why nickel content is restricted to a maximum of 1% in sour service applications.
Hydrogen Embrittlement
One of the primary concerns in sour service environments is hydrogen embrittlement. Hydrogen, generated during the corrosion of materials in the presence of H2S, can diffuse into the metal’s lattice structure and weaken its mechanical properties. Nickel is particularly susceptible to hydrogen embrittlement, making it essential to limit its content in materials used for sour service to reduce the risk of catastrophic failures.
Conclusion
The nickel content will be restricted to a maximum of 1% for sour service applications due to factors such as nickel’s susceptibility to hydrogen embrittlement, stress corrosion cracking, and sulfide stress cracking and the need for cost control. In addition, adherence to standards and regulations set by the industry is important to ensure safety and reliability of equipment and pipelines in sour service environments. By limiting nickel content, industries can ensure the long-term integrity of their infrastructure and protect against potentially catastrophic failures.