Protecting personnel from burns on hot, exposed surfaces is a top priority for process plant safety.
All it takes for skin to blister and burn is a few seconds of incidental contact with a hot surface. The U.S. Occupational Safety and Health Administration (OSHA) sets a limit of a maximum skin temperature of 140°F (60°C) after five seconds of exposure. By definition, no reportable injury will occur at this skin temperature and exposure time.
The external surfaces of process piping, ductwork, storage tanks and other equipment throughout a plant can reach temperatures well above the OSHA guideline for incidental skin contact. Systems with external surface temperatures greater than OSHA’s threshold pose a major hazard to workers’ and visitors’ safety — so plants must take steps to mitigate burn potential.
In some situations, plants can erect safety cages and fencing to keep people away from hot surfaces. More often, though, sites must insulate surfaces to ensure their temperature does not exceed the limit.
Process plants have two primary options for insulating hot, exposed surfaces for burn protection: the traditional method of covering surfaces with insulation and cladding or the emerging method of applying thermal insulative coatings. Both options enable plants to meet OSHA’s burn protection guidelines — but they differ in their cost, installation, maintenance, corrosion potential and insulation values.
Traditional systems typically feature insulation materials covered with a metal cladding to protect the insulation. These bulky systems do the job of mitigating burn potential and also offer high insulation values, especially when first applied. However, they’re prone to water infiltration, which significantly reduces their insulating properties. Worse yet, that water infiltration may cause corrosion under insulation (CUI), a hidden and costly threat to plant safety and reliability (Figure 1).
In contrast, thermal insulative coatings are spray-applied to exposed surfaces and don’t require cladding to mitigate burn potential (Figure 2). The coatings can be used almost anywhere that traditional insulation systems are. Just a few simple-to-apply layers of material make the coated surfaces safe to touch. By obviating metal cladding, the coatings also completely eliminate the threat of hidden CUI.
The coatings contain ceramic microspheres — small beads filled with air — that create a high air content in the final dried coating surface. This air acts as an ideal insulator, limiting the transfer of heat energy through the coating so exterior surfaces remain safe to touch for at least the OSHA-mandated 5-sec threshold. Even dangerously hot systems like steam piping and boiler ductwork may be coated to prevent burns to personnel.
Because many plants aren’t familiar with thermal insulative coatings, this article compares such coatings to traditional insulation systems and provides some pointers for deciding on an appropriate insulation system.
Although they offer similar capabilities for burn protection, traditional insulation systems and thermal insulative coatings differ significantly in their application and maintenance requirements — particularly in terms of plant downtime and inspection.
Downtime. To apply traditional insulation systems, plants typically must shut down operations that produce heat in the process areas being insulated. Once surfaces are cool enough, workers must remove and discard the old insulation, inspect all areas for surface corrosion, potentially abrasive blast and coat any areas that have corroded, and then rewrap the entire area with insulation and cladding. The procedure is time consuming, especially for fitting bulky insulation around curves, tight spaces and valves.
In contrast, applying thermal insulative coatings may not require shutting down any processes. Advanced single-component, waterborne acrylic insulative coatings can be put on surfaces with temperatures from ambient up to 350°F (177°C).
Maintenance staff can apply the coatings to a prepared and primed surface or directly to an intact, existing coating — so long as it’s tightly adhered, sound and compatible with the insulative coating. To ensure compatibility, personnel may need to test the coating for adhesion. They also must remove any dirt, grease and other contaminants using solvents or an abrasive sweep blast prior to putting on the coating. During application, staff must limit overspraying coatings onto surrounding equipment and surfaces, particularly in hazardous or confined areas. Sensitive components may require covering to protect from overspray. Using coatings with short dryfall distances can help minimize overspray concerns.
Each coat is approximately 20-mils thick. The number of coats required depends on the operating temperature of the substrate — for example, two to three coats may suffice for systems operating at up to 250°F (121°C) but systems reaching temperatures as high as 350°F (177°C) may need as many as five coats to ensure surface temperatures are below OSHA’s skin-contact threshold. (Confirm the OSHA compliance of the insulative coating system in the laboratory using a thermesthesiometer. A traditional surface temperature probe will not provide an accurate reading of skin temperature.) Substrates with temperatures above 350°F (177°C) exceed the temperature resistance of the acrylic resin and will require a conventional insulation and cladding system.