Abstract: Apparatus for determining the corrosion rate of petroleum distillation equipment so that corrosion inhibitors may be effectively utilized to control corrosion. The apparatus includes a water box having a coil arranged in the box through which hydrocarbon vapors are directed. Cooling water is forced through the box in a counterflow direction to cool the vapors and simulate cooling that will take place in heat exchange units. Corrosion and temperature probes are arranged along the coil to determine corrosion rates at the various temperature levels of the hydrocarbons so that a corrosion profile can be established and related to the temperature of the vapors at various locations in the heat exchange units of the equipment.