Intumescent fire protective coating.docx

7/27/2019 Intumescent fire protective coating.docx

1/5

Intumescent fire protective coatingDefinition

A coating which reacts to heat by swelling in a controlled manner to many times its original thickness to

produce a carbonaceous char, which acts as an insulating layer to protect the steel substrate. It is a form

of passive fire protection which attempts to contain or slow the spread of the fire in steel strutures.

Intumescent fire protective coatings are widely used as passive fire protection in oil and gas industries,

civil buildings, chemical plants and other facilities in developed countries. Intumescent coatings are

composed of three fire retardant additives: an acid source (such as ammonium polyphosphate), a

carbon source (such as pentaerythritol), and a blowing agent (such as melamine) bound together by a

binder. The formulation of the coating has to be optimized in terms of physical and chemical processes

in order to produce an effective protective char layer upon exposure to fire.

Types of intumescent coatingThere are two types of intumescent coating:

1) Thin film intumescent coating

2) Thick film intumescent coating

Thin film intumescent coatingThin film intumescent coating is composed of 3 components: a primer, a basecoat(the chemical which

will react upon contact with fire) and a sealer coat.

The basecoat comprises of the following ingredients:

A catalyst which decomposes to produce a mineral acid such as phosphoric acid. A carbonific such as starch which combines with the mineral acid to form a carbonaceous char. A binder or resin which softens at a predetermined temperature. A spumific agent which decomposes together with the melting of the binder, to liberate large

volumes of non-flammable gases. These gases include carbon dioxide, ammonia and water vapour.

The production of these gases causes the carbonaceous char to swell or foam and expand to provide

an insulating layer many times the original coating thickness.

Thin film intumescent coating is mainly used in buildings where the fire resistance requirement are 30,

60 and 90 minutes. Later, researchers have been able to develop thin intumescent coating of 120

minutes resistance. Both on site and off site application is possible.


2/5

In general, most on-site application is carried out using water based materials. However, where the

structure to which the material is applied is not to have an end use in a dry, heated environment,

solvent based materials are commonly used. Solvent based materials also tend to be able to cover a

wider range of section factors than water based materials and can be used on-site to protect smaller

sections requiring high thicknesses.

Typical expansion ratios are about 50:1, i.e. a 1mm thick coating will expand to about 50mm when

affected by fire.

Thick film intumescent coatingThick film intumescent coatings are epoxy based and have a much higher dry film thickness than thin

film. These materials are tough and durable and were originally developed for use with hydrocarbon

fires, where the test heating regime is much more severe than that used for most industrial and

commercial applications. A number of manufacturers have modified their materials for use in cellulosic

fires. These modified materials are usually used in situations where the benefits of intumescent coatings

in terms of appearance, weight and thickness are required but where circumstances are too severe, or

maintenance too difficult, to allow the use of thin film materials . Typical recent examples have occurred

in external steel in high rise buildings and exposed marine environments.

INTUMESCENT CHAR FORMATIONEpoxy resin filled with active ingredients which react (intumesce) and swell in a fire (typically expanding

5 to 10 times in volume), producing a tough, carbonaceous char insulating layer.

This char formation restricts the rate of temperature increase of the steel & prolongs its load bearing

capacity.


3/5

INTUMESCENT EARLY STAGES OF FIRE

INTUMESCENT INTERMEDIATE STAGES OF FIRE


4/5

INTUMESCENT FINAL PHASE OF FIRE


5/5

Before & After Fire Exposure

The intumescent coating behaviour is characterized by expansion and mass loss, producing a foam char

with a volume that varies from 5 to 200 times its original volume. Heat transfer analysis through the

protection material, during the initial stage and its intumescence, assumes great importance to defineand design this thermal protection.

Documents

Intumescent fire protective coating.docx