In discussing fire as it relates to insulation, the conversation frequently focuses on cementitious fireproofing. Cementitious fireproofing, as its name implies, is a cement-like material that is applied to structures, both building and chemical process equipment, to delay the damaging effects of elevated temperature while the fire is controlled.
The term “fireproof” is a misnomer in this case since it implies that the material renders the protected structure immune from the effects of fire. In reality, these materials are applied at a specific thickness designed to protect a specific length of time against a specific type of fire.
If the fire is not controlled before the design period is exceeded, the structure will likely fail due to the weakening of the steel as its temperature rises. Conventional thermal insulation materials such as fiberglass, mineral fiber, or calcium silicate do not generally have a role in protecting support structures in a chemical plant, but they do have a critical role in the protection of chemical process equipment during a fire. Visit here for more information acusfoc.com
Let’s consider what happens during a fire by looking at a hypothetical design example. The XYZ Chemical Company plans to manufacture a highly flammable solvent in a conventional chemical plant that will consist of feed tanks, a pressurized reactor, a distillation column, and a product storage tank.
Some of the process runs under pressure and above ambient temperature (225 F) and includes equipment that is constructed of carbon steel, stainless steel, and copper. Cementitious fireproofing to a level 30 feet above grade protects the structural steel of the enclosed process building.
XYZ’s usual insulation standards call for the use of rigid polymer foam to insulate the elevated-temperature equipment and no insulation on the ambient-temperature equipment.
They normally use the aluminum jacket on insulated equipment in non-flammable service. In this case, because the product to be made is highly flammable, the insulation design must be changed, and XYZ must use their fire-protective insulation standard.
Consider what would happen if the pump that transfers crude product from the reactor to the distillation column failed catastrophically, releasing a large quantity of flammable material into a pool surrounding the reactor and distillation column. If this pool ignites, an intense fire would occur at the base of pressurized process equipment that contains more fuel. While it is likely this plant would be protected by a sprinkler system, let’s assume for the sake of argument that it does not function properly.
The only barrier between the surface of the process vessels and the fire is the thermal insulation; so it must remain in place for as long as possible. If it doesn’t, the pressure inside the vessels will rise along with the metal temperature, which at the least will cause the vessel to relieve and at worst may lead to failure of the vessel.
The jacket and accessories that hold the jacket in place are the first lines of defense. Aluminum melts at around 650 C, well below the temperature of the fire; the usual aluminum jacket would melt quickly, exposing the underlying insulation material to the fire.
The rigid foam insulation used in XYZ’s usual standard is secured by an adhesive tape that would also quickly fail when exposed to fire. When the fire company arrives to fight the fire, the first thing it does is hit the insulated vessels with a hose stream. Since the tape has failed, the hose stream will blow the insulation off the vessel, and XYZ would have an uninsulated vessel exposed to the fire.