The temper process for steel consists of heating the steel to below a critical temperature. The time and temperature depends on the steel and composition. In general for most carbon based steels, the tempering process allows some of the carbides in the martensite to change size and structure. This process changes the brittleness of the steel and increases the steels toughness. Toughness is a term to represent resistance to fracture. The overall strength of the pipe decreases but the ability to deform within an elastic region is considered toughness. This provides the best of both worlds. The pipe has high tensile strength, but if overstressed it will deform but return to its origional dimensions.
The process of tempering requires a consistent, controlled temperature. Furnaces to accomplish this must be designed to provide a high degree of uniformity. The greatest problem that pipe producers face is getting the steel to the correct temperature and making sure it is uniform from one end to the other. In large furnaces, balancing and tuning the burners is important in achieving these goals.
ESG promotes the use of walking beam furnaces for this use. The furnaces are specially designed to create hot gas circulation to provide uniformity throughout the furnace. In addition, for the high uniformity possible we promote preheating the pipe prior to entering the furnace.