The Impact of Low Concentration of H2S on Carbon Steel Pipelines

Hydrogen sulfide (H2S) is known to have a detrimental effect on carbon steel pipelines and processing facilities. At even low concentrations, H2S can induce pitting corrosion and accelerate other forms of corrosion through its interaction with oxygen and carbon dioxide. This article explores how low concentrations of H2S specifically impact carbon steel, especially in the context of oil and gas transportation and processing.

Induction of Pitting Corrosion by H2S

H2S can induce pitting corrosion in carbon steel pipelines by acidifying the water. The presence of H2S in the water leads to the formation of corrosive acids, which further accelerate the process of corrosion. This acidity can lead to the formation of small pits on the surface of the carbon steel, weakening its structure and potentially leading to catastrophic failure.

When oxygen and carbon dioxide are added to the corrosion reaction, the rate of corrosion is further accelerated, leading to a significant reduction in the service life of pipelines and processing facilities. The higher the concentration of these gases, the more pronounced the effects. In oil and gas industries, where high pressures and temperatures are common, this can be particularly problematic.

Corrosion Acceleration by Velocity and Turbulence

Higher turbulence, which is often associated with higher velocity, can significantly impact corrosion rates. The mixing of gases within the solution is enhanced, leading to a more efficient and rapid formation of corrosive species. This has a direct impact on both the rate of bare steel surface corrosion and the rate of iron carbonate precipitation. High velocity promotes the rapid dissolution of oxygen and carbon dioxide, accelerating the corrosion process before any protective layer can be established.

The creation of a protective layer, such as a passivation film, generally occurs at much slower rates, which are insufficient to keep up with the accelerated corrosion caused by high velocities. This leads to a situation where the steel is continuously exposed to corrosive environments, ultimately leading to the failure of the material.

Effects of Sulfide Stress Cracking

Low concentrations of H2S can also cause sulfide stress cracking (SSC) in carbon steel. SSC is a form of embrittlement where hydrogen sulfide causes the material to become more brittle, leading to potential failure by a brittle fracture. The process does not require high temperatures, making it a significant concern at ambient conditions. If a low carbon material is exposed to significant levels of H2S, it can lead to a brittle failure of the material.

Hydrogen embrittlement, a related phenomenon, can also contribute to the failure of carbon steel under H2S exposure. This embrittlement can occur at ambient temperatures and is a result of hydrogen atoms diffusing into the steel matrix, weakening the material's structure.

Tackling the Problem: Scrubbing and Chemical Inhibitors

Given the potential risks associated with H2S exposure, it is crucial to implement strategies to mitigate the effects. One common method is the scrubbing of H2S from the gas stream. Various technologies and processes can be used to reduce the concentration of H2S to safe levels. For example, amine gas treating is a widely used technique for removing H2S from natural gas streams.

There are also quick and simple tests to detect low concentrations of H2S. One such test involves using lead acetate. By wetting a test paper with a solution of lead acetate and observing whether it turns black, one can determine the presence of H2S. This test is useful for preliminary screening and can alert operators to the need for further action.

Chemical inhibitors can also be used to retard the corrosion process. These inhibitors form a protective layer on the steel surface, reducing the rate of corrosion. However, it is important to note that chemical inhibitors have a limited lifespan and must be replenished periodically to maintain their effectiveness.

For more information on H2S corrosion, you may refer to the following resources:

Siddhagiri Metals Tubes Total Materia Hydrogen Sulfide Corrosion

Carbon steel is known to be very sensitive to sulfur, and even low concentrations of H2S can cause significant damage. By understanding the mechanisms behind H2S-induced corrosion and stress cracking, industry professionals can take proactive measures to protect their pipelines and processing facilities.

Keywords: H2S, Carbon Steel, Pitting Corrosion, Sulfide Stress Cracking