(e) For this heat treatment, the drum shall be placed in a furnace sufficiently larger to accommodate the whole drum. The furnace shall have proper means of temperature measurement and control and shall be capable of heating the whole of the drum to a uniform temperature. It shall be so designed as to prevent direct impingement of flame on the drum. The temperature of the furnace at the time the drum is placed in it shall not be higher than 300°C.

For carbon steel a stress relieving heat treatment shall be performed by heating the part to at least 600 ± 20°C.

When required by the characteristic of the material, different temperatures may be necessary to obtain proper stress relieving.  The part to be stress relieved shall be brought up slowly to the specified temperature and held at that temperature for a period proportioned on the basis of at least 2 ½ minutes per millimeter of the maximum thickness of the part (approximately one hour per 25mm of the thickness) and shall be left to cool in the furnace to a temperature not exceeding 400°C.  For carbon steels and when stress relieving temperature is at least 615 ± 20°C, the soaking time shall be 2 ½ minutes per mm of thickness up to 50mm and 15 minutes for every additional 25mm thickness over 50mm and shall be left to cool in the furnace to a temperature not exceeding 400°C

Alternative procedure for the heat treatment of the drum may be submitted to the Inspecting Authority for approval.

In special cases it may be permissible to heat treat the test plates separately from the drum, provided the Inspecting Authority is satisfied with the means adopted to ensure that the following factors will be the same for the drum as far the test plates.