One of the least understood technical concepts, yet potentially the most impactful opportunity for organic growth of the mechanical insulation industry, is passive fire protection (PFP). Engineers and asset owners can realize significant benefits in terms of safety, reliability, environmental compliance, operational efficiency, and compounding savings on energy inputs and insurance expenses. Manufacturers, distributors, fabricators and contractors can benefit from installing insulation and metal jacketing within industrial plants on assets that may have never been insulated.

The first concept to understand is the difference between the two primary types of PFP: structural versus pressure-relieving systems. Historically, these two design methodologies have often been conflated in marketing and technical bulletins, causing confusion among stakeholders.

Structural PFP is designed to protect structural steel skeletons that support pipe racks, vessels, and equipment above ground level (see Figure 1). Typically specified materials used for structural PFP are cementitious or intumescent epoxy coatings, spray-applied to steel elements such as I-beams, columns, and girders. Endothermic wraps or fire- protection boards are less common and more costly, but they are removable for corrosion under fireproofing (CUF) inspection. Structural steel loses about half of its load-bearing capacity at 1,100°F. Therefore, structural engineers must specify the number of minutes (typically 120 to 240 minutes) the steel skeletons can withstand a fire event so firefighters can evacuate well before a catastrophic collapse of the structure.

There are two test methods regarding fire protection for structural steel: UL 1709 – Rapid Rise Fire Tests of Protection Materials for Structural Steel and ASTM E1529 – Standard Test Methods for Determining Effects of Large Hydrocarbon Pool Fires on Structural Members and Assemblies. Simply stated, these tests answer the question: How many minutes will it take to increase the temperature of a specific steel member protected with a specific thickness of PFP material from ambient to 1,000°F inside a 2,000°F furnace? Thicker/heavier steel requires thinner PFP material and thinner/lighter steel requires thicker PFP material to achieve the same number of minutes of fire protection.

The second application for PFP—pressure-relieving system applications—is much less
understood, and it is the focus of the balance of this article. It is incumbent on the industry to understand and be clear when discussing this topic with engineers and facility operators by not conflating unrelated structural steel PFP test methods such as UL 1709 with pressure-relieving system applications. With few exceptions, mechanical insulation and metal jacketing is not historically specified for structural steel PFP, in favor of the more labor-friendly and cost-effective solutions mentioned above. In short, we should focus efforts on pressure-relieving applications to create organic and long-term sustainable demand for more mechanical insulation, metal jacketing, and skilled labor to install them.

The American Petroleum Institute (API) is an industry association of more than 600 member companies. According to www.api.org, “API represents all segments of America’s oil and gas industry,” and “API’s mission is to promote safety across the industry globally…” API publishes numerous consensus standards documents to assist engineers and plant operators to increase safety and promote best practices to decrease risk. One such document is titled “API Standard 521 Pressure-Relieving and Depressuring Systems.” This copyrighted document must be purchased from API or one of its authorized distributors.

API 521 is the governing document when discussing PFP that involve pressure-relieving systems. First, one needs to understand the concept in simple terms. If a fire breaks out in an industrial plant, there are many highly volatile and explosive fluids (liquids or gases) that will get hot very quickly. What happens when fluids heat up? They expand, which increases pressure inside the pipe or storage vessel. This excess pressure needs to be released, and the fluids quickly conveyed away from the fire, using specialized and costly pressure-relieving valves (PRVs) to avoid an explosion and further propagation of the fire (see Figure 2).

In industrial plants, traditional methodology assumes that during a fire outbreak, an emergency pressure-relieving event is inevitable due to the rapid heating and vaporization of stored volatile fluids. This time-tested system ensures the rapidly heated stored fluids are quickly released by PRVs into liquid knockdown drums and flashback seal drums, with the excess gases quickly burned off by a flare stack (see Figure 3).

A good analogy to this concept is a pressure cooker like those that can be found in many kitchens. These mini sealed pressure vessels quickly cook foods like beans, potatoes, and beef stew by combining heat and above-atmospheric pressure. The key to this kitchen gadget is a small PRV on the lid that sputters and emits steam with a pleasant, rhythmic hissing sound I remember fondly from my childhood. A PRV is also installed on home water heaters to release excess pressure, which prevents your water heater tank from becoming a missile and blowing a hole in your roof!

One of the lesser known and understood sections of the API 521 standard document is section 4.4.13.2.7 External Insulation. It states (bold emphasis added):

Credit for thermal insulation is typically not taken because it usually does not meet the fire-protection insulation requirements given in 4.4.13.2.7.2 through 4.4.13.2.7.4. If these requirements are met, a reduction in fire input can be obtained by using the environmental factor.

While it is true that most industrial insulation systems do NOT meet the requirements, it is also clear that systems CAN be designed with the correct components to withstand the extreme fire-protection conditions listed in the report.

Succinctly stated, a properly designed and professionally installed insulation system can be utilized to dramatically limit the rapid heat gain in a system during a fire. In a real sense, one can buy time to “slow the pot from boiling” in the first place. As Benjamin Franklin said, “An ounce of prevention is worth a pound of cure.”

Section 4.4.13.2.7.2 clearly outlines the requirements of the insulation SYSTEM for it to qualify as “fire-protection” for the purposes of reducing the potential of a rapid expansion of stored fluids during a fire outbreak. The system includes insulation, attachment method, metal cladding, and any accessories to help the system remain attached and intact, to protect the vessel from rapid heat gain during a fire. This method may allow for a reduction in the cost and footprint of the pressure-relieving and flaring system.

Section 4.4.13.2.7.2 states that the physical property requirements of the insulation system are as follows:

• The system must be able to function effectively at temperatures up to 1,660°F for up to 2 hours.
• Corrosion under insulation must be considered when installing any insulation.
• The system must remain intact and not be dislodged by high-pressure water streams during firefighting operations.
• The insulation system must be able to withstand direct flame impingement.
• The insulation system must be attached with stainless steel bands and then clad with stainless steel jacketing.
• Aluminum banding and/or jacketing is NOT acceptable because it will melt at 1,220°F.

According to several metal jacketing suppliers, about 90% of mechanical insulations installed in industrial plants are clad with aluminum jacketing due to the lower cost compared to stainless steel jacketing (25 to 30% Δ). This fact explains the statement in API 521, “Credit for thermal insulation is typically not taken because it usually does not meet the fire-protection insulation requirements.” By specifying T-304 stainless steel bands, wing seals, and cladding with a melting point greater than 2,500°F, this ensures the insulation system can withstand the extreme temperatures and hold the insulation on the asset (see Figure 4.) Stainless steel expansion or compression springs installed on the outer bands of large vessels keep the bands tight during operations and can help the insulation remain attached during a fire event.

Table 6 of API 521, reproduced here in Figure 6, lists five different types of generic insulations (Figure 5). Please note that Table 6 should not be considered an “approved list” or all-inclusive of every type of generic insulation material that could be specified by an engineer in conjunction with stainless steel jacketing for this application. At the same time,
certain other types of insulations that cannot withstand extremely high temperatures should not be considered for this application. In this author’s experience, the most common error in the engineering community in specifying “fire protection insulation” per API 521 is confusing maximum continuous operating temperature versus a 2-hour excursion temperature of 1,660°F during a fire event, as listed in the API requirements. If one misunderstands this key difference, then the only insulation that would apparently suffice would be type II calcium silicate with a continuous operating temperature of 1,700°F. API’s Table 6 lists several other generic types of insulation with maximum continuous operating temperatures between 900°F and 1,200°F that will all survive a 2-hour excursion event when attached/clad with stainless steel bands/jacketing. Several other generic types of insulation not listed in Table 6 could also be specified as a component in a fire-protection insulation system per API 521. Hybrid systems using more than one type of generic insulation also could be considered. Engineers should contact manufacturers of materials not listed in Table 6 for specific performance and recommendations for this specialized application.

For the purposes of this overview, which focuses on benefits to the insulation industry and its end users, we will not discuss in detail the process for determining the thickness required to slow the rapid heat gain during a fire or to potentially reduce the cost and footprint of pressure-relieving systems. At a high level, engineers must calculate the anticipated heat gain at much higher mean temperatures that often exceed the required maximum mean temperatures to be reported per the various ASTM material standards (typically 700°F mean or lower). One specific takeaway to consider is for insulation manufacturers promoting their materials for API 521 applications to invest in testing and publishing measured thermal conductivity values at higher mean temperatures—perhaps up to 1,100°F mean, as an example.

Here is a concrete illustration of how utilizing a properly designed fire-protection insulation system per API 521 can provide immediate and long-lasting return on investment (ROI) for an industrial plant operator. The average age of an oil refinery in the United States is 74 years old. As safety standards have increased over time, insurance carriers have also increased their fire-protection requirements for owners. One such refinery in the western United States was faced with a costly expansion of their pressure-relieving system as a condition of their insurance carrier continuing coverage. The refinery had a large pressure vessel with one 2”-thick layer of type I calcium silicate insulation, which was clad with aluminum jacketing. By employing the design methodology in API 521, plant engineers were able to plan and execute a project that removed the aluminum jacketing and added one more layer of 2”-thick insulation that was then clad with new stainless steel jacketing. Using this smart strategy, the owner was able to meet the insurance company’s new requirements without upgrading to larger PRVs along with an expanded flare disposal system. The owner reported the cost difference between the two options was over a million dollars and improved the thermal efficiency of the pressure vessel!

Conclusion

Mechanical insulation is well known for its myriad benefits, including process control, worker protection, and reduced energy consumption and greenhouse gas emissions—all while providing extremely short payback periods and compounding ROI. Fire-protection insulation systems per API 521 provide one more valuable benefit for owners to consider as part of their overall risk management strategy.