- Corrosive gases cause significant damage to the structure and function of industrial plants and equipment.
- Infrastructure like pipelines, tanks, and machinery can get corroded.
- Corrosion of the electrical and electronic process monitoring and control equipment is another significant area of damage.
- Air monitoring is central to any program to reduce concentrations of corrosive gases in industries.
The global cost of corrosion in industries was estimated to be USD 2.5 trillion or 3.4% of the world’s GDP in 2013. Corrosion is one of the most significant concerns in industries, and one of the leading causes is some industrial gases, which are highly reactive and corrosive. These gases are a safety concern that causes causalities, environmental impact, costly repairs, and downtime.
What is Corrosion?
According to ISO standard 8044, corrosion is metal deterioration due to physiochemical reactions with the environment or the technical system it is part of.
Gases cause corrosion, and the reaction is accelerated by high temperature and humidity. Relative humidity above 80% can corrode metals regardless of gas concentrations. The most common example is rust on iron due to humidity and oxygen.
During corrosion, the metals that are bases react with the acidic gases and water to form a chemical buildup. The buildup can form insulating layers over electrical and electronic components, causing short circuits or failures. Other forms of corrosion are pitting and metal loss, weakening infrastructure.
Corrosion can be external or internal.
- External corrosion: This type of deterioration occurs due to high temperature, humidity, and corrosive gases, such as sulfur dioxide, affecting electrical equipment.
- Internal corrosion: It is the deterioration occurring due to stored or transported gases and fluids. Continuous exposure can corrode metals in the presence or absence of oxygen. For example, oil contains hydrocarbons and dissolved corrosive gases that corrode pipelines.
Corrosion can be localized or uniform. Besides gases, additional factors can be involved in causing galvanic corrosion (between two metals) and stress corrosion (where tensile stress and corrodent are involved).
Corrosion Damage in Industries
Corrosion is damaging and expensive, as it causes structural degradation and equipment failure in industries. Some of the consequences are as follows:
Operational safety: It weakens pipelines, machinery, and structures that can cause leaks, decreased efficiency, malfunction, and accidents. These damages constitute a risk to operational safety and plant infrastructure. The leaks caused by corrosion can lead to fires, explosions, or human exposure to toxic gases. Several corrosive gases like chlorine, sulfur dioxide, and ammonia are stored in cylinders, and the compression pressure can exacerbate the dangers of these gases.
Increased costs: Corrosion also reduces the lifespan of operating machinery, necessitating replacement. It involves direct and indirect costs in repairs, downtime, lost production, and labor health care expenses.
Health risks: Corrosion that affects high voltage systems can harm personnel managing them. Leaks and accidents due to compromised infrastructure will increase human exposure to corrosive gases. These corrosive gases react chemically with living tissue to alter permanently or destroy them. Inhalation and skin contact can cause respiratory, skin, and eye problems specific to each gas.
Environmental damage: Corrosion-caused accidents and incidents can release hazardous gases into the environment, polluting air, water, and land and affecting neighboring communities.
Industries Affected by Corrosion
Corrosive gases are found in many manufacturing industries. Gases are the foremost problem that damages control and process equipment used to increase production speed and quality in modern manufacturing. Corrosive gases are a growing problem in processes such as oil and gas, refining, steel, paper and pulp, plastics, tires, food and beverages, chemicals, textiles, etc. These industries use batch or continuous production processes that generate the gases that affect the equipment.
Corrosive Gases
Gases are corrosive because they are very reactive and interact with metal. The gases are corrosive due to three types of reactions- acidic, caustic, and oxidation. The acidic gases are most harmful and inflict damage even in small amounts. Some gases can be acidic and oxidative in action, like hydrogen chloride.
- Active sulfur compounds: These include elemental sulfur (S), hydrogen sulfide (H2S), and organic sulfur compounds, which are the most common gases in process industries. Even at low parts per billion (ppb) concentrations, these gases swiftly interact with iron, copper, silver, and aluminum. The severe corrosion by H2S is called sour corrosion. The presence of moisture and chlorine and nitrogen compounds accelerate their reactions.
- Sulfur oxides: Sulfur dioxide (SO2) and sulfur trioxide (SO3) are formed due to combustion of fossil fuels. Lower ppb levels of sulfur oxides retards corrosion, but higher levels dissolved in moisture form acids to attack some metals.
- Nitrogen oxides: These oxides, nitrous oxide (NO), nitrogen dioxide (NO2), etc., are also formed due to fossil fuel combustion and contribute to the formation of atmospheric ozone. They form nitric acid in contact with moisture to attack common metals. These oxides catalyze base metal corrosion by acting with chlorides and sulfides.
- Chlorine compounds: Elemental chlorine and compounds, chlorine dioxide (ClO2), and hydrogen chloride (HCl) combine with moisture to release ions that react with iron, copper, tin, and silver alloys, even at low ppb. At higher levels, these gases oxidize the metal.
- Hydrogen fluoride: The compound (HF), a halogen, reacts similarly to inorganic chloride compounds.
- Ammonia and derivatives: Ammonia (NH3), amines, methylamine, and ammonium in fertilizer and chemical plants react with copper and its alloys.
- Carbon dioxide: The gas carbon dioxide (CO2) causes sweet corrosion and is present in the oil and gas industry. Dry CO2 is not corrosive, but when it mixes with water, it forms carbonic acid that causes pitting in metals and mesa attacks on low alloy metals.
- Photochemical species: This group includes several unstable gases in the atmosphere formed by the reaction of chemicals with sunlight and moisture. These have short lifetimes as they get involved in reactions quickly. Examples are ozone, nitrogen oxide, sulfur oxides, etc. Thus, the corrosion from these gases affects outdoor installations, and metals are not affected much. However, ozone (O3) acts as a catalyst for many corrosive gases.
Each site will have a different combination of corrosive gases in varying concentrations. Corrosion can be rapid or gradual, apparent after many years, depending on gas combinations and their concentrations.
Air Quality Standards
To control the levels of corrosive gases, established standards require optimal control room design and information on air quality. Some of the standards are:
- The “ISA-S71.04-1985 ‘Environmental Conditions for Process Measurement and Control Systems: Airborne Contaminants’ from the Instrument Society of America (ISA).
- The “International Electrotechnical Commission (IEC) Standard, IEC 60654-4 (1987-07) ‘Operating Conditions for Industrial-Process Measurement and Control Equipment. Part 4: Corrosive and Erosive Influences’ of 1987.”
Such standards define and categorize environments on their corrosion potential. The ISA-S71.04 has identified four corrosion severity levels:
- G1 levels are mild, and corrosion is not a danger in this environment.
- G2, G3, and G4 indicate increasing corrosive potential in an environment, with G4 being the most severe.
Air Monitoring
Air monitoring is crucial for any program aiming to control corrosion. It can provide short-term data to manage levels and prevent damage and safety risks. In the longer term, it provides data to ensure air quality.
Tools are chosen based on their sensitivity, complexity, and costs.
- Sensitivity: The tools must be capable of measuring traces of gases at ppb levels when corrosive action by the gases starts.
- Complexity: the tool must also be simple enough to be used by personnel and not require extensive training and skill. The results must provide actionable insights. In some cases, portability will be an issue.
- Cost: The cost of gas analyzers will be considered, as a facility will require several to cover the entire facility.
Interscan offers fixed and portable gas analyzers for common corrosive gases. The tools are simple to use and give precise results in real-time.
- The small portable model GasD® 8000 Portable Gas Monitor allows workers to carry it anywhere needed, including confined spaces.
- The fixed gas monitors AccuSafe Fixed Point Gas Detection allows monitoring 24 x 7 year-round and can be connected to system management software. Several sensors measuring different gases can be integrated and connected to a central unit to handle gas mixtures.
Corrosion Control
Besides air monitoring, corrosion control requires several other measures. These are listed below.
Gaseous contaminant control: Three standard methods to control corrosive gas levels in an industrial facility are source control, ventilation, and removal.
Avoiding the source should be explored first. However, it can be difficult in industries where corrosive gases are produced due to the manufacturing processes. In these cases, ventilation dilutes gases and reduces their concentrations. The last resort is removal when ventilation is not enough. Standard removal methods include air filtration systems, which bring corrosive gas levels back to acceptable levels.
Handling and storing: Simple steps during storing and handling gas cylinders can control corrosive gas levels.
- All gas cylinders must be labeled.
- Use cylinder caps and other restraints when the cylinder is not used.
- Mechanical devices like forklifts and trolleys ensure the cylinders remain upright.
- Ventilate corrosive gas stores to prevent buildup in case of leaks.
Use of Personal Protective Equipment (PPE): Personnel must wear appropriate PPE to avoid contact with corrosive gases and prevent health issues.
Emergency decontamination: Despite best efforts, accidents and leaks can occur. So, each facility must have emergency decontamination equipment in work areas with corrosive gases. These could include eye-wash and shower stations.
Planning for Safety
Controlling corrosive gases begins with a proper industrial hygiene and safety program, which identifies the risks in any business first. Choosing materials resistant to corrosive gases, and treating them with paints and other surface treatments can protect infrastructure. Air monitoring and other control measures specific to a facility’s individual or combination of gases will be necessary during operation. Training people about the dangers, proper handling of daily activities and emergencies, and regular inspection and maintenance of plants and equipment are other crucial aspects of reducing corrosion and its safety risks in the workplace.
Learn more about how Interscan’s customized solutions can help reduce your facility’s corrosion potential.
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