Oil, gas and petrochemical facilities, as well as other facilities that handle potentially hazardous materials are required to provide two levels of containment in processing and storage operations to ensure that no materials escape to the environment. Primary containment consists of the receptacles (i.e., tanks, feed piping, pumps and process equipment) that are designed to hold materials during their normal use and processing, while secondary containment covers structures that serve an important backup role. These structures (e.g., concrete pads, fluid basins, sumps and trenches) surround primary containment assets and are designed to contain any hazardous materials that may spill from those assets and prevent their escape to the environment.

In the event of a spill, secondary containment areas or structures are the last line of defense for facility operators. The Federal Clean Water Act requires that they be “designed, installed and operated to prevent any migration of wastes or accumulated liquid out of the system to the soil, ground water, or surface water.” Thus, secondary containment areas are relied upon to direct, and safely contain, hazardous and/or corrosive material spills so they can be neutralized or cleaned up. In the event of a spill, secondary containment assets are vital to keeping personnel safe, minimizing spill-related facility disruption, reducing the risk of regulatory exposure or fines, and preventing expensive environmental cleanup.

Other Clean Water Act requirements for secondary containment areas (SCAs) include:

• Materials: SCAs must be constructed of or lined with materials that are compatible with the contents to be placed in primary containment vessels.
• Capacity: SCAs must have capacity to contain 100% of the largest capacity tank, or 10% of the total capacity of all tanks at the location, plus a 25-year, 24-hour rainfall event.
• Structure: SCAs must have a structurally sound foundation and provide a structure that surrounds tanks completely and is sloped to drain to a sump.
• Leaks: SCAs must be equipped with a leak detection system that notifies operators so they can initiate cleanup procedures.
• Containment: SCAs must be able to contain the wastes or liquids for a minimum of 72 hours to allow time for neutralization or cleanup of the spill.

Most secondary containment areas are built primarily of concrete, masonry bricks or blocks, or steel. To function effectively for secondary containment, they must not only be able to contain a spill when it happens, but also prevent leakage or escape of the hazard for the entire period of the cleanup process. They must also ensure containment despite potential exposure to multiple leaks – and ordinary structural weathering, wear and tear – over many years to come.

Meeting these requirements can be a challenge, since downstream oil, gas, and petrochemical processes frequently use corrosive fluids, including highly corrosive organic acids. For example, high-concentration sulfuric acid (75%-plus) and hydrofluoric acid are the most common alkylation catalysts in refinery processes that modify the octane levels of gasolines. Hydrochloric acid is widely used as a reagent in industrial chemistry, is vital to metal production and finishing processes, and is essential for everything from water treatment to the production of cleaning agents. Of the common fluids used in processing, hydrofluoric acid is the most corrosive – a 5-10% concentration can begin to damage or penetrate unprotected concrete and steel used in secondary containment areas in matter of hours.

Fortunately, there are a wide range of resin-based coating and laminate systems that can provide cost-effective, long-term protection for secondary containment areas. The process of selecting the right coating/lining system for your facility’s needs often begins with an inspection by coatings experts, who can then recommend a customized coating solution based on the processes and materials used at your site.

Their recommendation will offer solutions with the required chemical resistance and protection for your secondary containment areas over a predictable service life, typically with options that can be tailored to your maintenance concerns and budget. Because chemical resistance characteristics are critical to product selection, the makers of coating/lining systems offer detailed performance information for each product. When more information is needed, application-specific testing is generally available.

Key Considerations for Coating/Lining System Selection

While the proper chemical resistance characteristics are essential, many other factors and considerations go into the optimal coating/lining selection for a secondary containment area. These include:

• The temperature of the commodity or process to determine if the SCA coating/lining system must tolerate thermal shock in the event of a primary containment spill
• The impact and abrasion resistance of the coating/lining system to ensure it can handle the flow turbulence from a spill, especially if solids are included in that flow
• The condition of the secondary containment substrate/structure, including:
  -    Whether it’s new or existing
  -    Its structural makeup (e.g., concrete, steel, brick, etc.)
  -    Its structural stability and potential for movement and/or thermal expansion
  -    Any structural defects such as cracks, seams, bug holes or other substrate deficiencies requiring repairs
• The flexibility of the coating/lining system and its ability to fill cracks
• The permeation resistance of the coating/lining system
• Whether the surface is conductive or static-dissipative
• The presence of foot or vehicular traffic, as you may require an anti-slip or compression-resistant surface
• The accessibility of the area and if it can accommodate applicators and equipment
• Downtime requirements to apply the protective coating/lining system
• The total installed cost of the system

Among all of these factors, two deserve additional mention – flexibility and crack bridging capabilities – because they greatly affect the long-term performance of the system.

A successful coating/lining system must be engineered to move with the underlying substrate. This is vital because movement of the substrate, caused by thermal expansion and contraction, can damage the bond at the coating/substrate interface and result in premature system failure. Substrate movement is measured by the Coefficient of Linear Thermal Expansion (CLTE) of the substrate material. The key to long-lasting coating adherence is to modify the CLTE of the coating system (typically, by selective addition of specific aggregates) until it more closely matches that of the substrate material. This modification enables the coating to respond to thermal expansion/contraction in essentially the same way as the substrate: when the substrate moves, the coating moves with it. Therefore, the coating system shouldn’t fail due to substate movement.

Another important factor is the degree of crack bridging/filling that the coating system needs to provide, since any underlying defects in the substrate must be thoroughly repaired prior to or during the coating system installation. Improper or inadequate sealing of structural cracks, seams, joints and transitions in the secondary containment structure is the second preventable cause of coating system failures. With careful pre-application inspection and product selection, as well as a high-quality application job, these essential details can be easily addressed, assuring maximum service life for the protective coating system.

Coating/Lining System Materials

Coating/lining systems can be comprised of a variety of materials. These six are the most common:

Liquid Coatings. There are three basic types of resin-based liquid coatings used in primary and secondary containment structures. Depending on their ingredients, they may be applied either as primers, or as base or topcoats. All may be “flake-reinforced” with aggregate materials to add or modify chemical resistance and other desirable characteristics, improve strength and reduce permeability. They are frequently modified with co-reactants to improve coating adhesion, resist moisture or ensure proper curing in varied temperatures.

The three types of liquid coatings include:

• Epoxies and related resins are general purpose products that offer a moderate degree of flexibility and bond well to steel or masonry surfaces. These include many epoxies and vinyl esters.
• Polyurethanes and polyureas are characterized by a very high degree of flexibility. These products are often used on substrates that are subject to cracking or movement, or as part of a system to repair structures that have cracks or damage.
• Internally flexible epoxies are special epoxies that never fully harden, so they provide a maximum level of flexibility. These coatings are ideal for use in repairing or patching large cracks or sealing large structural or surface joints.

Urethane Concrete. This material is a slurry of concrete and urethane, specially designed to be applied over “green” concrete. This combination bonds strongly to the underlying concrete, yet tolerates the moisture and outgassing that occurs as the concrete cures. Once urethane concrete sets up, other coating/lining system materials can be added to complete the protection system. These will not be affected as the underlying concrete substrate continues to cure.

Aggregates. Aggregates are flaked minerals that are added to liquid coatings or concrete slurries to add vertical depth, reduce CLTE, add structural reinforcement, reduce permeability and/or add other valuable protective characteristics. (See “Medium Films” below.)

Laminates. When structures require additional structural strength or abrasion resistance, “laminate” or “reinforced laminate” systems may incorporate one or two layers of woven, mat-like materials, between 1 mil and 10 mils in dry film thickness (DFT). These laminate mats can be made of woven or stranded fiberglass, polyester or even carbon-reinforced fibers. Such laminates are typically used in the middle layer of the protection system, affixed by a glue-like saturant to the adjacent coating layers.

Coating/Lining System Options

The above materials can be combined into a variety of coating/lining systems to meet facility requirements and owner budgets. System options include:

Thin Films (10-20 mils DFT) consist of a primer coat, base coat and topcoat. They are typically used to protect new steel or concrete tanks or existing tanks that show no sign of wear or erosion. The primer coat seals the substrate, while the epoxy base and topcoat provide chemical resistance and the ability to bridge very small cracks or surface defects.

Medium Films (20-40 mils DFT) consist of a primer coat and a “flake-filled” epoxy or vinyl-ester topcoat. Flake reinforcement reduces the CLTE of the coating, relieves shrinkage stress of coating resins and reduces permeability by creating a “barrier” of overlapping mineral plates. Specific types of reinforcing flakes may be selected to add additional protective properties to coatings, including:

• Micaceous Iron Oxide: Ideal for use in primers used on steel surfaces
• Muscovite Mica: Increases the depth of the coating system
• Zinc: Provides steel with cathodic protection
• Glass: Increases resistance to thermal, mechanical and undercutting damage to the coating system
• Graphite: Enables conductivity, offers thermal and mechanical benefits similar to glass, and adds chemical resistance to sodium hypochlorite, fluoride compounds and hot caustics that attack glass and silica-based compounds

Mortar Systems (1/8"-1/4") and Slurry Systems (1/16"-1/8") are specifically designed to resurface and protect degraded concrete in production and other high-traffic areas. These systems begin with a primer coat, then add a layer of aggregate-filled mortar, topped by grout and finished with a flake-filled topcoat. The resulting systems bond extremely well with existing concrete, while providing low permeability and excellent resistance to chemicals, wear and thermal shock. Aggregate fillers may include quartz silica, carbon, metallic oxide, ceramic and others. These materials are generally used to reduce curing shrinkage and lower the coating system’s CLTE, while increasing abrasion resistance and compressive strength.

Laminate Lining Systems (55-120 mils DFT, single or double layers) are the first of three systems that can be used to repair, renew and strengthen steel or concrete storage tanks or secondary containment structures. These systems feature a primer coat, topped by one or two layers of saturant/laminate mat/saturant, and finished with a topcoat. The laminate mats consist of woven fiberglass, polyester or carbon fiber and can range from 1 mil to 10 mils thick. Laminate systems are often used for tank-bottom renewals, tank repairs and linings, and secondary containment structures because they add structural reinforcement with moderate abrasion resistance and can also bridge small structural cracks.

Mortar Laminate Systems (90-120 mils DFT) are the second of three systems that can be used to repair steel or concrete tanks. These systems also begin with a primer coat, but use a layer of mortar rather than saturant as the base for the laminate mat, with a flake-filled topcoat to follow. Because mortar laminate systems offer extremely high abrasion resistance, they are an excellent alternative for renewing steel or concrete vessels that are subject to highly turbulent or erosive flows.

Flexible Basecoat Glass-Reinforced Mortar Laminate Systems offer the ultimate renewal/repair solution for steel and concrete tanks and secondary containment areas because they not only offer chemical resistance with superior abrasion and shock resistance, but also offer excellent crack bridging/filling. The ingredients in this system include a primer, a highly flexible base coat, a laminate mat and a saturant layer, with several options for the finish layer: an aggregate-filled mortar, a self-leveling flake-filled topcoat or a medium-film flake-filled topcoat.

Specifying the Right Coating/Lining System

In the event of a hazardous leak or spill, secondary containment areas must be able to contain the hazard and prevent escape to nearby soil or groundwater. Yet, leaks of commonly used chemical products, including corrosive organic acids, may be able to penetrate weathered or damaged concrete containment areas within a matter of hours, putting facility owners at risk for personnel injuries, regulatory action and even fines and cleanup costs. The same can be true if the applied coating/lining system is not compatible with spilled contents from primary containment vessels. For these reasons, it is essential that oil, gas and petrochemical facility operators consider the value of coating/lining systems that resist chemical spills while renewing and protecting the long-term integrity and durability of containment structures. Expert assistance from coating and lining system experts is available to help facility owners consider their needs and options and select an excellent alternative.

ABOUT THE AUTHOR

Rodney Cressionnie is Business Development Manager – Petrochemical Market for Sherwin-Williams Protective & Marine. His responsibilities include serving as a corrosion specialist and engineering support for owners in the midstream and downstream petrochemical market, particularly in the Southeast United States and Caribbean. Cressionnie has 14 years of industry experience, including 11 years with Sherwin-Williams. He has previously served the coatings industry as a store manager, outside sales representative and product manager. Cressionnie is a NACE International Level 2 Certified Coating Inspector and a board member for the Louisiana Coating Society. He has a bachelor’s degree from Spring Hill College with a major in business administration and minors in chemistry and biology. He can be reached at rodney.cressionnie@sherwin.com.