The Most Destructive Corrosive Element in Process Control and Equipment Rooms

Corrosion of contacts and components on circuit boards accounts for between 30 and 40 percent of all equipment failures in process control and equipment rooms. This corrosion is caused by an unmanaged environment that makes it susceptible to harmful elements such as temperature and humidity. However, the number one most destructive element in process control and equipment rooms is corrosive gas.

How Corrosive Gas Affects Process Control and Equipment Rooms

In the context of electronic equipment, corrosion is defined as the deterioration of a base metal resulting from a reaction with its environment. Gaseous contaminants cause a chemical reaction that leads to this corrosion of metals. Heat and moisture accelerate the corrosion process, but corrosive gasses are generally the main driver.

As chemical reactions continue in the environment, products can form insulating layers on circuits which can lead to thermal failure or short-circuits. Pitting and metal loss can also occur.

The Danger of Corrosive Gasses

Corrosive gasses have been and continue to be a growing problem in the process industries. Petrochemical (oil, gas, and hydrocarbon processing), refining, pulp and paper, steel making (blast and electric furnaces), and other processing produces chemical compounds that can wreak havoc with electronic equipment reliability. In fact, significant quantities of corrosive gasses are being generated by these processes and the equipment required to maximize process efficiency is being adversely affected.

Corrosion will remain a threat for the foreseeable future, thanks in part to the advancement of technology. The processing capacity for some industries is increasing at the same time that electrical and electronic equipment is becoming more sophisticated and complex—which only makes it more sensitive to environmental conditions. The result for many processing plants is direct and indirect costs incurred due to corrosion-based equipment failures. The United States alone sees several hundred thousand dollars a year lost to corrosion in its processing plants.

Beyond cost, corrosion is also an increasing safety concern, particularly on higher voltage systems. Should corrosion cause delicate systems such as circuit breakers to fail, personnel responsible for the use and management of these systems could face critical injury.

What Are the Major Destructive Corrosive Gasses in Process Control and Equipment Rooms?

Three types of gasses are the prime culprits in the corrosion of electronics:

Acidic gasses such as hydrogen sulfide, sulfur and nitrogen oxides, chlorine, and hydrogen fluoride
Caustic gasses such as ammonia
Oxidizing gasses such as ozone.

Of the gasses that can cause corrosion, the acidic gasses are typically the most harmful. For instance, it takes only 10 parts per billion (ppb) of chlorine to inflict the same amount of damage as 25,000 ppb of ammonia. However, all these types of gasses can cause serious destruction of equipment.

Each site may have different combinations and concentration levels of corrosive gaseous contaminants. Performance degradation can occur rapidly or over many years, depending on the particular concentration levels and combinations present at a site.

Let’s take a deeper look at each of the top corrosive gas types.

Acidic Gasses

Active sulfur compounds (H2S)

This group includes:

Hydrogen sulfide (H2S)
Elemental sulfur (S)
Organic sulfur compounds such as the mercaptans (RSH)

When present at low parts per billion levels, these gasses rapidly attack copper, silver, aluminum, and iron alloys. The presence of moisture and small amounts of inorganic chlorine compounds and/or nitrogen oxides greatly accelerate sulfide corrosion. Note, however, that attacks can still occur in low relative humidity environments. Active sulfurs rank with inorganic chlorides as the predominant cause of atmospheric corrosion in the process industries.

Sulfur oxides

Oxidized forms of sulfur (SO2, SO3) are generated as combustion products of sulfur-bearing fossil fuels. Low parts per billion levels of sulfur oxides can passivate reactive metals and thus retard corrosion. At higher levels, however, they will attack certain types of metals. The reaction with metals normally occurs when these gasses dissolve in water to form sulfurous and sulfuric acid.

Nitrogen oxides (NOX)

NOX compounds (NO, NO2, N2O4) are formed as combustion products of fossil fuels and have a critical role in the formation of ozone in the atmosphere. They are also believed to have a catalytic effect on corrosion of base metals by chlorides and sulfides. In the presence of moisture, some of these gasses form nitric acid which, in turn, attacks most common metals.

Inorganic chlorine compounds

This group includes:

Chlorine (Cl2)
Chlorine dioxide (ClO2)
Hydrogen chloride (HCl)

Reactivity will depend upon the specific gas composition. In the presence of moisture, these gasses generate chloride ions which react readily with copper, tin, silver, and iron alloys. These reactions are significant even when the gasses are present at low parts per billion levels. At higher concentrations, many materials are oxidized by exposure to chlorinated gasses.

Particular care must be given to equipment which is exposed to atmospheres which contain chlorinated contaminants. Sources of chloride ions, such as bleaching operations, sea water, cooling tower vapors, and cleaning compounds should be considered when classifying industrial environments. They are seldom absent in major installations.

Hydrogen fluoride (HF)

This compound is a member of the halogen family and reacts like inorganic chloride compounds.

Ammonia and Derivatives

Reduced forms of nitrogen (ammonia (NH3), amines, ammonium ions (NH₄⁺)) occur mainly in fertilizer plants, agricultural applications, and chemical plants. Copper and copper alloys are particularly susceptible to corrosion in ammonia environments.

Photochemical species

The atmosphere contains a wide variety of unstable, reactive species which are formed by the reaction of sunlight with moisture and other atmospheric constituents. Some have lifetimes measured in fractions of a second as they participate in rapid chain reactions.

Some common photochemical species are:

Ozone (O3)
Hydroxyl radical
Radicals of hydrocarbons
Oxygenated hydrocarbons
Nitrogen oxides
Sulfur oxides
Water

Because of the transient nature of most of these species, their primary effect is on outdoor installations and enclosures. In general, metals are only slightly susceptible to photochemical effects. However, ozone can function as a catalyst in sulfide and chloride corrosion of metals.

Strong oxidants

This includes ozone plus certain chlorinated gasses (chlorine and chlorine dioxide). Ozone is an unstable form of oxygen which is formed from diatomic oxygen by electrical discharge or by solar radiation in the atmosphere. These gasses are powerful oxidizing agents. Photochemical oxidation—the combined effect of oxidants and ultraviolet light (sunlight)—is particularly potent.

Hydrogen sulfide (H2S) from pulping, sulfur dioxide (SO2) from power plants, and active chlorine compounds (Cl2, HCl, and ClO2) from bleaching operations and cooling towers have all been shown to cause significant corrosion in electrical and electronic equipment at concentrations of just a few parts per billion in air.

Even at levels that are not noticed by or harmful to humans, these gasses can be deadly to electronic equipment. Most of the odor threshold levels are much higher than the levels at which corrosive damage will occur.

Protect Your Precious Equipment with Purafil Corrosion Solutions

Computer process and control systems need not be exposed to the threat of corrosive damage. Purafil’s corrosion monitoring and chemical air filtration technologies have developed to the point where corrosive gasses can be accurately measured in real-time and controlled effectively and economically.