We simplify the specification of the Standard EN1591 as follows:

- we use a specific flange type: Welding-neck flange with cylindrical tube

- we use only three operating states I:
    I=0: mounting state (or installed condition)
    I=1: testing state
    I=2: charge state

- we use a specific mounting method:
    screw tightening method = measurement of torque (torsional, turning moment)

- systematic error induced by the inaccuracy of the screw tightening is unknown

- we ignore external forces and moments

- we do not use washers

- we use the k_B approximation in D.5