What methods are used to design the expansion vessels produced by Zilmet SpA?

In accordance with the Pressure Equipment Directive PED 2014/68/EU, the design method used for expansion vessels, whose product between the maximum operating pressure and volume is less than 6000 bar x litre, is the experimental method: for the expansion vessels mentioned above, design calculations are not carried out, but rather tests supervised by the Competent Body to certify compliance with the specifications. For expansion vessels whose product between maximum operating pressure and volume is equal to or greater than 6000 bar x liter, the design method is the calculation method together with the experimental method.