Hydrogen sulfide (H2S) is a highly toxic and corrosive gas that poses significant challenges to the oil and gas industry. When in the presence of moisture, H2S can cause severe damage to equipment and infrastructure, leading to:
- Safety hazards
- Production disruptions
- Costly repairs
In this article, we will provide an overview of:
- Wet H2S damage
- Identify susceptible areas
- Materials and systems
- Discuss types of damage
- Explore non-destructive testing (NDT) detection methods
- Outline prevention/mitigation strategies
We will delve into the relevant API (American Petroleum Institute) and NACE (National Association of Corrosion Engineers) codes used to inspect and determine wet H2S.
Areas Susceptible to Wet H2S Damage
Several oil and gas systems areas are particularly vulnerable to wet H2S damage. These include:
Pipelines and Flowlines:
H2S can corrode the internal surfaces of pipelines and flowlines. This can lead to metal loss, pitting, and stress corrosion cracking.
Wet H2S can attack casing and tubing in wellbores. This causes sulfide stress cracking and hydrogen-induced cracking.
Equipment such as separators, vessels, and tanks are susceptible to wet H2S damage. This is from exposure to corrosive environments.
Certain materials are more prone to wet H2S damage than others. These include:
Carbon steel is widely used in the oil and gas industry but is highly susceptible to wet H2S damage. It can suffer from corrosion, cracking, and embrittlement.
Low Alloy Steels:
Low alloy steels, particularly those with higher sulfur content, are susceptible to wet H2S damage.
Cast iron components may experience accelerated corrosion in the presence of wet H2S.
Susceptible Oil and Gas Systems:
Several oil and gas systems are at risk of wet H2S damage, including:
Sour Gas Systems:
Systems handling sour gas containing high concentrations of H2S are susceptible to wet H2S damage.
Sour Crude Oil Systems:
Crude oil containing H2S can corrode pipelines, storage tanks, and other equipment in sour crude oil systems.
Types of Wet H2S Damage:
Wet H2S damage manifests in various forms, including:
Uniform metal loss occurs on the surface due to the reaction between H2S and moisture.
Localized corrosion is characterized by forming small pits on the metal surface.
Stress Corrosion Cracking (SCC):
Cracking is induced by the combined action of tensile stress and the corrosive environment.
Hydrogen blistering occurs when atomic hydrogen diffuses into the metal substrate. This forms hydrogen-filled blisters beneath the metal surface. In the presence of wet H2S, hydrogen blistering can be more severe. The blistering can cause disbandment. This weakens the metal and potentially leads to catastrophic failures.
Hydrogen-Induced Cracking (HIC):
HIC is a form of hydrogen embrittlement. It occurs when atomic hydrogen enters the metal lattice and causes cracking under tensile stress. In the presence of wet H2S, the susceptibility to HIC is heightened. As a result, cracks associated with HIC can propagate rapidly and result in structural failure.
Stress-Oriented Hydrogen-Induced Cracking (SOHIC):
SOHIC is a specific type of hydrogen-induced cracking. It occurs in areas where high tensile stresses are present in combination with the presence of H2S. It is observed in welded regions, such as heat-affected zones or weld metal interfaces. The combination of:
- Tensile stress
- Susceptible materials
can lead to crack initiation and propagation. This results in equipment failure.
NDT Detection Methods:
Non-destructive testing methods are crucial for detecting wet H2S damage. As well as, assessing the integrity of the equipment. Some commonly used NDT techniques include:
Ultrasonic Testing (UT):
UT uses high-frequency sound waves to detect internal flaws such as corrosion and cracks.
Magnetic Particle Testing (MPT):
MPT is employed to detect surface-breaking cracks in ferromagnetic materials.
Liquid Penetrant Testing (LPT):
LPT involves applying a liquid dye to the surface of a component to detect surface defects.
Prevention and Mitigation:
To prevent and mitigate wet H2S damage, you can implement several measures:
Chemical inhibitors can be injected into the system to reduce the corrosive effects of wet H2S.
Applying a sacrificial anode or impressing a direct current can provide cathodic protection to mitigate corrosion.
Utilizing materials with improved resistance to hydrogen embrittlement, such as:
- Low sulfur
- Low-strength alloys
can help reduce the susceptibility to these damages.
Control of Hydrogen Charging:
Implementing measures to minimize hydrogen exposure, such as:
- Properly controlling H2S content
- Minimizing moisture
- Managing operating conditions
can mitigate the risk of these damaging phenomena.
Post-Weld Heat Treatment (PWHT):
Performing PWHT on sensitive materials and welded joints can alleviate residual stresses. It can also improve resistance to hydrogen-induced cracking.
Employing cathodic protection systems can help mitigate the risk of hydrogen-related damage. It reduces the likelihood of hydrogen entering the metal.
API and NACE Codes:
The oil and gas industry relies on industry standards to ensure the safe operation and inspection of equipment exposed to wet H2S. The relevant API codes include:
- API RP 571 for damage mechanisms
- API RP 941 for steels in hydrogen service
- API RP 939-C for avoiding sulfide stress cracking.
Additionally, NACE MR0175/ISO 15156 NACE MR0175/ISO 15156 specify:
- Welding practices
- Inspection criteria to prevent these damages
Wet H2S damage poses a significant threat to the oil and gas industry, with:
- Potential safety hazards
- Equipment failure
- Production interruptions
- Identifying susceptible areas
is crucial for implementing effective prevention and mitigation strategies. Utilizing NDT methods and adhering to industry standards outlined by API and NACE can ensure the reliable inspection and determination of wet H2S damage. This enables the industry to operate safely and efficiently in the presence of this corrosive gas.
- Hydrogen blistering
are critical damaging phenomena associated with wet H2S exposure. Detecting, preventing, and mitigating these damages requires a combination of:
- Appropriate material selection
- Inspection techniques
- Adherence to industry codes and standards.
By implementing these measures, the industry can minimize the risks and ensure the integrity and reliability of equipment and infrastructure in H2S-containing environments.