MAWP: Max Allowable Working Pressure
MAWP: Max Allowable Working Pressure
(OP)
The datasheet provided of an atmospheric condensate storage tank was provided by a contractor:
(1) Design Temp: 70degreesC
(2) Operating Pressure: -0,05 - 0,35 barg. (I bet this means -50mbarg to 350barg)
(3) Tank MAWP [bar g] = Geodetic Height + 500mbarg Nitrogen Blanket / -20mbarg
My problem is I need to fix a design pressure based on these specifications with no clue what these contractors mean by no. (3).
What I understand of geodetic height is the level difference between the pump suction and the tank top water level, but how is it relevant in determining tank MAWP? Plus, the operating vacuum given seems to be an irrational value at -50mbarg. I've sent out an enquiry but I'm hoping someone else knows.
The tank must be a 1000m3, ~12m cylinder standing at ~10m.
Thanks!
(1) Design Temp: 70degreesC
(2) Operating Pressure: -0,05 - 0,35 barg. (I bet this means -50mbarg to 350barg)
(3) Tank MAWP [bar g] = Geodetic Height + 500mbarg Nitrogen Blanket / -20mbarg
My problem is I need to fix a design pressure based on these specifications with no clue what these contractors mean by no. (3).
What I understand of geodetic height is the level difference between the pump suction and the tank top water level, but how is it relevant in determining tank MAWP? Plus, the operating vacuum given seems to be an irrational value at -50mbarg. I've sent out an enquiry but I'm hoping someone else knows.
The tank must be a 1000m3, ~12m cylinder standing at ~10m.
Thanks!





RE: MAWP: Max Allowable Working Pressure
The operating vacuum would normally be a fraction (typically 40%) of the design vacuum, so I would wonder if one of those was in error or the two values were reversed.
RE: MAWP: Max Allowable Working Pressure
RE: MAWP: Max Allowable Working Pressure
RE: MAWP: Max Allowable Working Pressure
So would it be logical to just design the tank to withstand atmospheric pressure, while assuming that the gas blanketing system pressure will be accounted for by the pressure equalising line? It does seem quite illogical to have design thicknesses needing to cater for such high gas blanket pressures. Perhaps 500mBarg could mean the discharge pressure of the gas blanketing system and not the partial pressure of the gas in the tank itself?
I really only need to determine the thickness of the roof and shell plates which are directly affected by design pressure.
RE: MAWP: Max Allowable Working Pressure
RE: MAWP: Max Allowable Working Pressure
Using EN14015:2004 (Clause 10.4), I calculated the roof plates to be 18mm thick due to the 500mbar pressure in the space above the liquid.
=========================================================================================
3.5 Roof Plate Thickness
Material = EN S275 JR
As per EN14015, Clause 10.3.3,
Min. nominal thickness = 5 mm
Owner-specified corrosion allowance = 1.5 mm
Thus, min. required plate thickness = 6.5 mm
Adopted Roof plate thickness = 8 mm
As per contract, the roof shall be self-supporting, and not attached to roof-supporting members. Therefore, resistance towards design internal pressure is checked as follows:
3.5.1 Design Pressure Check
Minimum Roof plate thickness excluding corrosion allowance:
= PR/10SyJsin θ
= 500x5.5/1570x0.10
= 17.86 mm
where P = design pressure (mbar)
θ = roof slope angle (deg)
R = radius of the tank [m]
J = joint efficiency factor = 0.5 [double-fillet weld]
Sy = Allowable Design Stress [MPa]
3.5.2 Conclusion
Design Pressure Check = OK
Adopted Roof plate thickness = 8 mm
======================================================================================================================
With the 500mbarg, it seems that anchors are now also needed to prevent failure at the shell-to-bottom junction. I'm seeing an uplift force of 26000kN here. Certain I've not made any dimensional errors in the math...
[See Attachment]
RE: MAWP: Max Allowable Working Pressure
RE: MAWP: Max Allowable Working Pressure
Is there something naturally wrong with a design vacuum of 50mbar? On a 11m dia. tank, this is an absurd-sounding downward force of 1900kN. I understand that this is supposed to be an low-pressure storage tank (hence the design pressure of only 20mbar), so what cases justify the logic of a design vacuum more than twice the design pressure?
Is there another EN standard to be used?
I looked at API650 and this is what I read:
HELP!