Cracking heater radiant coils and crossovers are normally constructed and maintained at ambient conditions. As the pipes and tubes are heated from ambient to operating temperatures (in the range of 2000°F+ for the radiant coils), significant thermal expansion of the crossover and radiant tubes will occur and must be accommodated in the design of the radiant coil support system.

These supports must also accommodate creep, and since the rates and extent of creep elongation will vary with operating parameters, it may be required to make adjustments to the support systems over the life of the coil. In order to properly adjust and maintain the coil support systems, it is necessary to understand the requirements for coil expansion, with respect to the amounts and directions of the expected movements. This paper will review several typical coil configurations, their expected expansion and movements, and the associated impact on coil supports.