How should thermal expansion be specified for industrial heating elements?

Thermal expansion of an industrial heating element should be calculated from the maximum operating temperature minus ambient, the sheath alloy's coefficient of expansion, and the effective heated length, never estimated on site by rule of thumb. The drawing must mark the fixed point, the free end and the permitted travel direction, and the flange hole or furnace wall opening needs axial clearance sized to the calculated growth so cold assembly dimensions are not locked when hot, which could bend the element or crack a weld. At purchase, ask the supplier for its expansion calculation, then verify watt density, sheath material and insulation resistance at design temperature, and confirm mounting clearance will not interfere with the thermal cut-out or any travel stop.