Difference between MAWP and Design Pressure with respect to ASME BPVC & BS EN 12952

[coolniks37]

Hi

Can you explain the difference between MAWP and Design Pressure as per ASME & BS EN 12952 ?
For example, the drum in my boiler is having a pressure of 100 bar and my safety valve is set at 105 bar?

What is the MAWP as per BS EN 12952 and ASME BPVC?
What is the Design Pressure as per BS EN 12952 and ASME BPVC?

If both are same, why ASME says
"No boiler shall be operated at a pressure higher than the maximum allowable working pressure, except when the pressure valves are discharging, at which the MAWP shall not be exceeded by 6% ?

If MAWP and design pressure are same, then what is this 6% margin? Because in this situation, the safety valve should open at MAWP itself.
Pls clarify.

 

[Duwe6]

Look around on your boiler. Unless they are tiny, ASME boilers are required to have at least 2 PSV's installed. The set pressures are typically staggered; on yours I would expect one at 100BAR and one at 105BAR.

Design Pressure can be higher than MAWP, but typically they are the same. Design vs. MAWP rational gets 'interesting'; I keep it simple; Design = MAWP.

 

[metengr]

MAWP is clearly defined in Section I (2013 Edition);

See PG-21
PG-21 MAXIMUM ALLOWABLE WORKING
PRESSURE
The maximum allowable working pressure is the pressure
determined by employing the allowable stress values,
design rules, and dimensions designated in this Section.
Whenever the term maximum allowable working pressure
is used in this Section of the Code, it refers to gage
pressure, or the pressure above atmosphere.

Design pressure is used by other code book sections, but when dealing with Section I design rules, MAWP is what is used, and working pressure is below this value.