How was PED/97/23/EC test pressure coefficient 1.43 derived? 7

[CuMo]

I couldn't find another topic for this so here's the question.

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.

Thanks!

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.

 

[DBreyer]

Durgin 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 durgin 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.

 

[XL83NL]

Excellent DBreyer, a star for you

 

[CuMo]

Thanks DBreyer!
I will ask our senior engineer the same thing and see what he says. He-he.

 

[zeusfaber]

Careful, he might be a regular visitor here himself.

 

[CuMo]

Nope, he didn't know the answer.
There's always something new a person can learn.

 

[chicopee]

1.43 seems to be an interesting departure from the 1.5 required by the National Board for hydro static tests.

 

[JohnGP]

ASME VIII Div 1 now requires minimum 1.3 x MAWP test pressure. Interestingly Div 2 opts for 1.43 x MAWP minimum test pressure.
I found on one project subject to the PED that some non-European based vessel manufacturer's had an issue with testing their ASME vessels using the higher factor. I think at that time Lloyd's were of the view that the requirement in the construction code should prevail, but eventually came around to the general consensus adopted by other notified bodies, of using the PED factor of 1.43.
Cheers,
John

 

[OSIRIS7]

At ambient temperature normally the yield strength is leading for the allowable stress, normally Re/1.5, but there are exceptions. By hydrotesting at 1.43*PS you reach 1.43*Re/1.5=approx. 95% yield strength.

Just another vision on what DBreyer wrote. I thought it might help.

Kelly