An aromatic polyurethane is applied to a concrete clarifier

I frequently get to build forts in my basement with my three kids, and the designs of these epic creations can be daunting. Are the chairs tall enough? Will the clothespins be sufficient to hold the blankets? Do we have enough floor space for activities? All of these details are critical to the success, longevity and awesomeness of the fort.

In the industrial coatings world, there’s a similar type of environment where attention to detail very much affects its success, longevity and, yes, even awesomeness. Much like an epic fort, secondary containment systems can be daunting to design. There are many factors that come into play during the design process, such as:

  • To which chemical commodity is the containment system being exposed?
  • What physical stress will the system incur throughout its lifetime?
  • Are there pipe or other mechanical penetrations that could result in a possible leak of the containment?
  • Are there joints that could cause potential seepage into the ground?
  • Is reinforcement needed to help mitigate the stress of concrete flexing on the coating system?

These are just a few examples of the many considerations that exist when designing a secondary containment system. However, to simplify the design process, we can break the system’s design down into three basic components—chemical exposure, physical requirements, and joint and penetration details.

(Note: If you haven’t read Steve Harrison’s recent article on industrial coating systems for secondary containment, it is a fantastic starting place for any discussion relating to the “why” behind secondary containment systems.)

  • 1. Chemical Exposure

    In simple terms, a secondary containment area is defined as the containment of a leak or spill of a commodity that is being held in a primary containment unit, such as a tank or vessel. In order to properly specify a secondary containment lining, we must first know the commodity/chemical and storage temperature of what is being stored in the primary containment. Estimating either of these factors could result in a catastrophic failure of the secondary containment lining.

    Generically, there are a few different chemistries when it comes to linings that provide varying levels of protection to secondary containment areas. Amine epoxies, such as Carboline’s Semstone 140 lining system, provide basic-level chemical resistance to a wide variety of chemicals. Novolac epoxies, such as Semstone 145, offer increased chemical resistance to more highly concentrated chemicals and acids. Vinyl esters, like Carboline’s Semstone 870 lining system, also cover chemical attack from a broad range of aggressive chemicals, while utilizing a slightly different chemistry than a true epoxy lining.

  • 2. Physical Requirements

    Choosing the right lining chemistry to combat chemical attacks is certainly important. However, evaluating the physical stress to which the lining system will be subjected is of equal significance. In secondary containment environments, foot traffic can be very mild. An example of this is what one might find in a very small pit that is surrounding a primary containment tank. It may only see light foot traffic or, on the opposite end of the spectrum, it might be subjected to consistent semi-truck traffic where loading and unloading of chemicals constantly occurs.

    On the mild side of things, a secondary containment system often referred to as a “neat coat” might be all that is needed. Within the realm of Carboline’s secondary containment systems, this is referred to as Semstone NC. The low physical stress that is created on this basic system allows it to perform adequately in mild environments. In more moderate exposures that might see heavier foot traffic or wheeled carts, an aggregate filled system like Semstone AFC might be appropriate. The strength imparted to the system by the aggregate and two layers of coating make it more than suitable for this type of environment.

    Finally, in the most aggressive of environments where vehicular or fork lift traffic is a constant factor, an aggregate filled reinforced system, typically reinforced with an engineering fabric, will impart ultimate strength to the system and protect the substrate from both chemical attack and extreme physical stress. Semstone AFRC is a tried and true system that incorporates fabric reinforcement and broadcast aggregate to deliver ultimate protection to a secondary containment system.

    Carboline’s Semstone System Selector is a great interactive tool that helps to provide considerations for both chemical resistances and physical considerations all in one place.

  • 3. Joint & Penetration Details

    While protection against chemicals and physical stress is examining a secondary containment system on a macro level, considering the details of the environment is deep diving into the micro aspects of the system’s design—equally as important as these big-picture considerations.

    The most common details come from either joints, such as expansion joints, control joints or, in the case of refurbishments, stress cracks; transition areas, such as horizontal to vertical transitions; or penetrations into and through the concrete via pipes or other mechanical structures.

    When it comes to addressing these details, one size does not fit all. Each detail is important to consider, with a specific coating system needed to properly address it. Within Carboline’s secondary containment resources, a set of construction details exists to address many of these specific situations. Most commonly, a flexible coating like the Semstone 805 epoxy polymer is used to coat the substrate and provide flexibility to accommodate for the movement often found in these locations.

Although this blog post offers a basic overview of the design factors for a secondary containment system, there are often more details that emerge needing specific attention. In this case, a local sales representative from Carboline’s Technical Service team can provide an in-depth review of a secondary containment system’s design to make sure your system will hold down the fort.

Want to Explore Our Secondary Containment Systems?

Check out Carboline’s new interactive hub of secondary containment sales tools.