How Does Hydrogen Sulfide Affect Metal Components In Oil & Gas Industry?

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1911

H2S is a dangerous and destructive chemical compound. 

There is no denying this fact. Hydrogen sulfide (H2S) is not only deadly to living things, it can cause significant damage to infrastructure, from processing equipment for oil and gas producers, to pipelines and tanks for midstream companies. Also known as sour gas, H2S is naturally occurring both from a geologic and biologic perspective, and when paired with certain materials, it can be highly corrosive. H2S can be found downhole in hydrocarbon producing zones, and along static or flowing crude oil and natural gas pipelines, it is present in wastewater ponds at refineries, dairy digesters, or generated in biogas. All of these industries are prone to excessive and catastrophic corrosion if not properly accounted for, managed, and treated. 

When H2S comes into contact with carbon steel pipes or other infrastructure not properly coated or treated, it can wreak havoc on them and destroy their structural integrity making them weak and brittle. This not only comprises the oil purification processes but also increases the chances of the H2S gas leaking inside a facility.

H2S Corrosion and Its Impact on Infrastructure

One of the most hazardous forms of corrosion is Wet H2S cracking inside pipelines. The location makes detecting such corrosions all the more complex until it is too late. 

In these dominantly liquid process environments, hydrogen is generated from corrosive reactions that weaken the structural integrity when coming in contact with steel pipelines. There are multiple kinds of H2S cracking found in pipelines or the chambers of oil refineries, and these include Hydrogen Induced Cracking (HIC), Stress-Oriented Hydrogen Induced Cracking (SOHIC), and Sulfide Stress Cracking (SSC).

HIC forms a blister or pocket of concentrated hydrogen ions that create iron sulfides. Isolated HIC may not cause widespread damage; however, when these HIC events compound and stack upon themselves or create larger patches of blisters, then they become the larger threat. SOHIC will form cracks and exacerbate HIC formation. SSC failures are found at high stress boundaries such as triaxial or other complex adjoining steel components exposed to H2S. If prevention is not paramount in the design parameters, embrittlement will be expected and only H2S treatment will slow this inevitable process.

Besides damaging the metal equipment in refiners, H2S leaks constitute a significant safety concern for the facility. Undetected corrosion in the pipelines and various steel vessels can result in spills that can indefinitely bring the entire operation to a halt.

Besides incurring downtime, the cleanup process and equipment repairs are time-consuming and expensive. While there are various methods and ways to detect H2S leaks, they are quite costly and tend to give better results in the lab than when they are tested in real-world scenarios.

H2S Removal Solutions for the Oil and Gas Industry

Several preventive measures are available to stop H2S leaks, such as corrosion inhibitors, anodic and cathodic protection, alloys, and internal coatings. These actions will restrict the H2S from coming in contact with the metal chambers and pipeline, thus preventing corrosion. These solutions must be planned far in advance, because applying some of these measures once miles of pipeline are laid or entire facilities are built, can be quite an expensive and time-consuming undertaking. 

Cathodic Protection

This is an effective approach for preventing metal corrosion. It works by converting active regions of a metal surface into passive regions, that is, making them the cathode of an electrochemical cell. Variations of cathodic protection are implemented in most modern designs; however, these preventive measures are not always fully implemented at construction and therefore belie the overall protective effort.

Galvanic Anode Cathodic Protection (AKA: Sacrificial Anodes)

It consists of joining the metal to be protected with another metal that is more susceptible to corrosion to act as an anode. Zinc, aluminum, and magnesium are metals commonly used as anodes. The most active metal (also the least noble) becomes the anode of the others, and “sacrifices” itself by corroding to protect the cathode.

Impressed Current Cathodic Protection (ICCP)

This technique works by connecting a DC power supply between the metal to be protected and the cathodic protection anode. Unlike GACP, the cathodic protection current is supplied by the DC power source, not by the corrosion of the anode.

Chemical Inhibitor

The most potent and widely used preventive technique, chemical inhibitors, use H2S scavenger chemicals to eliminate the toxic vapor from basins and refineries. These chemical inhibitors or H2S removal solutions are scavengers that efficiently eliminate traces of the corrosive and poisonous gas from gas and oil.

In the effort to increase the netback value of certain hydrocarbons afflicted with H2S, chemical H2S scavengers are commonly used by oil and gas producers, midstream companies, refinery operators, and traders. Some scavengers have been developed to reduce chemical usage by 50 to 75 percent compared to traditional H2S removal methods like MEA Triazine. Another benefit of using H2S removal solutions is that you can monitor and track injection rates and H2S readings in tanks in real-time through apps. 

Conclusion

Prevention of hydrogen sulfide corrosion in pipelines and tanks for oil and gas equipment is critical in maintaining the operational integrity of this industrial infrastructure. Coupled with prevention efforts, treating afflicted volumes for H2S is nearly as important. Apart from equipment and infrastructure damage, H2S leaks are detrimental to human health and compromise the safety of all the employees working in the facility.