As stated in the beginning of this chapter regarding the new design thickness stress multipliers, a number of important factors must be considered in determining the thickness required for heads under internal pressure, such as stress values, quality factors, and joint efficiencies, according to the degree of radiographic examination. Many designers have difficulty in determining these factors.

It should be remembered that the ASME Boiler and Pressure Vessel Code is a progressive, viable code and that when necessary, changes are made. Therefore the latest edition of the Code should always be used.