How Was PED/97/23/EC Test Pressure Coefficient 1.43 Derived

Does anyone know how was the hydro test coefficient of 1.43 in PED/97/23/EC derived and why?
Why not 1.42 or 1.44 for example?
Where did that 1.43 come from?

Just curious.

Here’s an extract from PED/97/23/EC:

Hydrostatic test pressure
For pressure vessels, the hydrostatic test pressure referred to in 3.2.2
must be no less than:

  • that corresponding to the maximum loading to which the pressure
    equipment may be subject in service taking into account its
    maximum allowable pressure and its maximum allowable temperature, multiplied by the coefficient 1,25, or
  • the maximum allowable pressure multiplied by the coefficient 1,43,
    whichever is the greater.


During normal operation a safety margin of 1.5 between actual stress and yield strength has to be maintained.
During hydrotest the safety margin is reduced so that fabrication failures and/or material inhomogenities lead to leakages and are thus detected before the vessel starts its operation.
A certain safety margin to the yield strength (which has also some fluctuation)shall also be maintained during pressure testing. It was decided that the safety factor during pressure testing shall at least be 1.05.
So 1.5/1.05 gives you 1.43 as test pressure coefficient to have at least a safety of 1.05 during pressure testing.

Above is a snippet.