Fireproofing Materials

Concrete

The excellent fire protection afforded by concrete has been demonstrated time and time again over 90 years of experience in the petrochemical industry. The high mass and low thermal conductivity of concrete make it very effective at reducing heat input to the underlying structure. Poured-in-place concrete, using forms, is common for columns and beams. Gunite is pneumatically applied to spheres and other structures where the use of forms for poured-in-place concrete is impractical. The principal drawback with gunite application is that it can be very messy.

Post-fire inspections have shown that concrete spalls to various degrees but the general conclusion is that concrete/gunite performs satisfactorily with the steel structures well protected. Wire reinforcement is commonly used. Reinforcement does not prevent cracking and spalling of the concrete but it does minimize the loss of fractured material during a fire exposure.

Excellent Fire Endurance of 30 Year Old Concrete

A refinery fire initiated at a gas oil line from a crude distillation unit and burned for about 12 hours. The main pipe rack near the crude tower at the center of the fire was damaged beyond repair. The support structure for the crude tower overhead equipment was severely damaged.

The aluminum jacketed thermal insulation on vessels and exchangers was destroyed (aluminum melts at about 660°C) but most pressure vessels and heat exchangers, showed no visible signs of permanent damage, primarily due to the cooling effect of liquid contents. Gaskets that had been damaged and high strength bolts that had been tempered by the fire exposure, had to be replaced.

Thermal expansion and contraction on structural support columns near ground zero caused a good deal of cracking and de-lamination of the concrete fireproofing; however, no evidence of deep damage to the concrete was found. The main concern was for the support structure of the crude distillation tower as the refinery is located in a seismic zone.

The radiant heat and direct fire exposure caused spalling of the 30 year old concrete cover on the exterior of the vessel skirt. Firewater cooling added to the spalling problem. Some rebar was exposed at the crude tower foundation, most notably on the side of the tower that faced the fire. Concrete was removed for inspection of the crude tower skirt and anchor bolts. No heat buckling of the skirt or distortion of the bolt seatings was observed. Bolts were checked for cracks and hardness measurements were made to confirm strength. The concrete fireproofing had prevented any permanent damage to the vessel skirt and anchor bolts. The 30 year old concrete was now a mess but it had served its function.

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