Article Archive
Critical Moments
Intumescent coatings buy time in fire emergencies
Vol. 27 No. 3

Intumescent coatings as industrial fire protection do not prevent the spread of flames. Instead, use of these products on structural steel buys critical time against catastrophic structural failure, said Roger Williams, global market director for fire protection with The Sherwin-Williams Company.

“If the fire takes hold, intumescent coating will insulate the steel against the temperature rise, giving people time to use the emergency evacuation procedures and the fire brigade time to put the fire out,” Williams said.

The protection of life, assets and production in high-risk petrochemical facilities, both onshore and offshore, was the focus of a webinar sponsored by Sherwin-Williams Protective & Marine Coatings.

The session, “Fire Protection of Steel,” provides an overview of the causes of fires in hydrocarbon facilities, the difference between active and passive fire protection (PFP), and the essential role intumescent coatings play in achieving the fire resistance ratings required for a sound PFP system.

Intumescent coatings rapidly swell in reaction to a fire, forming a thick char barrier that protects a steel substrate by reducing heat transfer for several hours before structural failure can occur.

Williams discussed the two types of fires to which offshore platforms, refineries, terminals, pipelines and chemical plants are vulnerable. He also addressed the rigorous testing required to bring to market intumescent coating products that meet the toughest performance standards in both onshore and offshore environments, including for weatherability and corrosion protection.

“For hydrocarbon structures, PFP applications require specific coating thicknesses to achieve the time rating required by the project’s safety assessment,” said Williams. “It is essential to have the correct coating specified and properly applied. And the additional benefit is that you are applying a corrosion resistant system designed to last the life of the asset – dramatically reducing the need for expensive maintenance.”

Sherwin-Williams makes a comprehensive line of epoxy intumescent coating products under the FIRETEX brand name.

In a fire, steel begins to lose its structural strength as it heats up; it can lose around 20 percent of its structural integrity at 500 degrees Centigrade or 950 degrees Fahrenheit, Williams said. At 600 degrees Centigrade (about 1,100 degrees Fahrenheit), it will have lost over 50 percent of its structural integrity.

“I don’t mean it melts,” he said. “But it would easily flex and bend under the load it carries. You can imagine that the steel on the ground floor of a 40-story building has a lot of pressure and weight above it that it has to support.”

As the temperature continues to rise, the steel loses more and more of its strength until ultimate failure, Williams said.

 However, different types of fire behave differently. As a result, different types of intumescent materials have been developed for application to withstand various classifications of fire. Add to this the fact that fire regulations vary widely around the world and the issue becomes quite complicated.

For buildings such as schools, hospitals and offices, the fuel source is mainly cellulosic – wood, carpeting, drywall and paper. Products used on indoor structural steel grant 30 minutes to three hours of protection.

In industry, hydrocarbon fires are the greatest threat to structural steel under load, Williams said. Worse, the steel is readily exposed to some of the worst environments on earth.

“It’s no good if after two or three years the coatings start to fall off or disbond from the steel work,” Williams said. “The coatings have to be there. They have to live through the life of the assets to perform in the case of a fire.”

As opposed to a cellulosic fire, a hydrocarbon fire can reach temperatures critical to steel integrity in a relatively brief amount of time – minutes as compared to hours. Intumescent coatings can extend the life of that steel to as much as three hours.

“By varying the thickness at which we apply the product, we can vary that degree of protection,” Williams said.

Coatings are generally used on critical steel members that support inventory or process equipment, Williams said. It is also applied to pipe supports and specialty valves. Subject the coating to heat and it expands significantly before the exterior begins to char, he said.

“It’s like hard wood on a barbecue,” Williams said. “The exterior chars. Break the char away, there is fresh wood underneath.”

Hydrocarbon fires split into different categories. While a pool fire can reach high temperatures, it is under no pressure, Williams said. However, with pressurized vessels a jet fire can produce heat at a velocity that is highly erosive.

“The approximate temperature of a hydrocarbon pool fire is about 1,100 degrees Centigrade, or about 2,012 degrees Fahrenheit,” Williams said. “Typically, within five minutes, the heat flux would rise between 47,000 to 55,000 BTUs. A jet fire very quickly reaches 1,200 degrees Centigrade, probably in less than half a minute. The heat flux from this is under 100,000 BTU.”

As part of its research and development of intumescent coatings, Sherwin-Williams uses three large furnaces to assess their products, Williams said.

Holes are drilled into steel sections that will be heated. Thermocouples fitted into those holes measure the core temperature of that steel once it is heated. The steel is then coated before being heated.

Coatings designed for hydrocarbon fires typically swell to five to 10 times their original thickness of about 10 millimeters or around 2/5 of an inch, Williams said. By comparison, coatings designed for cellulosic fires go on at about 300 to 600 microns (12-24 mils) – the thickness of a piece of cardboard.

While waiting for a fire, intumescent coatings are expected to prevent corrosion in harsh environments for as much as 25 years, he said.

“The simple rule with fire protection is it has to be there to work,” Williams said. “We have 25 years of confidence in assets that were coated in the North Sea and other locations that are in perfect condition and more than capable of producing the same fire protection as when the products were first applied.”

Preparing the surface is key when applying fire protective coatings, he said.

“For hydrocarbon fire protection, steel work is typically sandblasted and primed,” Williams said. “Then we apply our first coat of FIRETEX. Typically, we would apply the first coat at up to 50 percent of the required dry film thickness. Remember, the thickness we put on will determine the fire resistance of the steel component.”

The process is similar to that used in applying fiberglass, he said. While the first coat is wet, a reinforced mesh is embedded in it.

“The reason is the different erosivity of a fire, plus the different types of velocity of a cargo,” Williams said. “There may be a jet fire requirement or even a blast requirement. There may be other requirements such as with LNG spills. So it is important that when the products foam and char up to provide insulation, it be reinforced enough to withstand any type of fire.”

Once the initial coating is dry, the remaining 50 percent of the required thickness is applied.

“It is actually a very straight forward and simple application process as long as good housekeeping rules are adhered to,” Williams said.

As opposed to fire retardant paints which are designed to prevent the spread of flames across ceiling and walls, intumescent coatings ensure that critical steel does not reach its failure temperature, Williams said.

“In the event a fire does take hold and has not been put out by the active fire system – sprinklers and extinguishers – it will give people the time to use the emergency evacuations procedures and get out.”

 
 

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