API RP 579, Recommended Practice for Fitness-For-Service, provides guidance for conducting a fire damage assessment. The most important aspect of the assessment is to identify the temperatures or "Heat Exposure Zones” within the fire area. This is the most critical activity of the assessment since all inspection plans and fitness-for-service evaluations follow from this.

Remember that the Heat Exposure Zone temperatures refer to the external temperature in the fire regions, not necessarily the equipment or piping metal temperature. The metal temperatures that the equipment and pipe actually reached determine the extent of metallurgical damage and the need for replacement. By metallurgical examination of affected areas we can determine the extent of the damaged and whether or not the vessel/equipment has to be replaced. 

Once the shock of a major process plant fire has subsided, the pieces must be put back together. The structured fire damage assessment approach contained in API RP 579, plus additional practical application methods, can help minimize reconstruction costs and allow safe resumption of unit operation as fast as possible.