Why Fireproofing is used?

Typically, fireproofing is designed to protect the structural steel which supports high risk or

valuable equipment. The failure point is generally considered to be 1000°F, as this is the point where steel has lost approximately 50% of its structural strength. The aim then, is to prevent structural steel from reaching 1000°F for some period of time. Tanks, pressure vessels, and heat exchangers may experience a significant cooling effect from liquid contents and so, less fireproofing protection is generally required. Some thermal insulation systems may serve a dual role as fireproofing and this is common with some pressure vessels. Piping may be insulated but it is not generally considered to be fire proofed.

Fireproofing needs to be durable to survive the rigors of every day life in the plant so that if and when a fire does occur, the fire endurance properties have been maintained and the fireproofing can be depended on to function satisfactorily. Everyday exposure may involve mechanical abuse, exposure to oil, solvents, and chemicals, and outdoor weathering for prolonged periods of twenty, thirty, forty years or more. As a coating for steel, fireproofing may provide a good measure of corrosion protection. When applied directly to steel, concrete may passivate the steel surface by providing an elevated pH. Experience has shown, however, that passivation is less than certain, especially in coastal marine environments. Corrosion under concrete fireproofing can be significant. Intumescent coatings promise better corrosion protection than concrete by virtue of their low permeability but cases of severe corrosion under fireproofing (CUF) have been reported with these materials.

Intumescent epoxies are complex proprietary materials. Concrete and some of the other materials that are used for fire protection are more familiar. The materials themselves may seem simple, but the important details of system design are often overlooked.

Risk-Based Analysis

Fireproofing is a misnomer because no material is completely fireproof. All construction materials are subject to fire damage. What we really mean is fire resistant - we seek to resist potential fire situations for a given period of time. Fireproofing is passive, built-in protection that buys time to fight the fire, shut off the fire's fuel supply and shut down the process. The aim is to minimize the overall damage incurred.

The decision to fireproof is driven by risk-based analysis. One needs to first consider the nature of the fire threat and then make an assessment of the required period of fire endurance for a wide variety of equipment including structural steel, pressure vessels, heat exchangers, pipe supports, LPG spheres and bullets, valves, and cable trays. The location of specific equipment within a process unit is important, as is a unit's location with regard to neighboring facilities.

Test Methods and required Time Rating

No fire test method is going to be typical of a real fire situation and so, there is no single correct or "best" fire test method. Standardized testing simply provides a frame of reference for relative comparisons of fireproofing materials and designs.

In the 70s, ASTM E119 "Fire Test of Building Construction Materials" was the only internationally accepted standard for investigating the performance of fireproofing materials. This test method, however, was designed to measure the fire performance of walls, columns, floors, and other building members in solid fuel fire exposures. It does not simulate the high intensity of liquid hydrocarbon-fueled fires.

Where fireproofing is required, the level of fireproofing varies with the application in the plant. Typical protection requirements for a refinery or petrochemical plant might be as follows:

• For structural steel, a facility may require a fire test rating of two or three hours. Poured-in-place concrete or gunite is most common with a specified minimum thickness of 2.0 to 3.0 inches (50-75 mm). Lightweight cementitious products may also be used.
• For steel vessels, a facility may require a fire test rating of one to two hours. Gunite applied at 1.5 to 2.0 inches (40-50 mm) may be required. Alternative fireproofing materials that provide a comparable fire resistance rating may be used, including systems that function as both thermal insulation and fireproofing.
• Plate and frame exchangers are a special concern because of the rubber gasketing material between plates. These exchangers are provided with a protective enclosure designed to prevent the exchanger from exceeding its maximum operating temperature for an hour or so. The maximum operating temperature is vendor specified and typically less than 300°F (150°C).
• Electrical and pneumatic components (including manual initiators, valve actuators, aboveground wiring, cable, and conduit) essential to emergency isolation, depressurization, and process shutdown are generally fireproofed to achieve a rating of at least 15-20 minutes. This equipment needs to function properly in the first few minutes of a fire

Source:http://www.wermac.org/materials/fireproofing.html