MAWP 1

[H Cameron]

Hi Guys,

If MAWP can be higher than Design Pressure in a pressure vessel?
why? or why not?

 

[XL83NL]

Yes it can. Because you can never design a vessel, using (mostly) standard sizes for all product forms like flanges, heads, plate and pipe, to exactly match, all at once, the required design pressure. There's always margin, because the supply market for these products forms like pipe, plate, heads, caps, elbows etc has standardized on standard sizes, or supplies products with a fixed rating, which never equlas your specific design pressure.

 

[H Cameron]

1- Doese it mean it can be work higher than design pressure??

2-In this case we have to calculate hydrotest based on MAWP or Design Pressure?

 

[TGS4]

In ASME Section VIII, Divisions 1 and 2, you can set the MAWP to be equal to the Design Pressure without performing any calculations. If you wish to "re-engineer" the vessel to determine the actual MAWP, then you are free to do so. More can be seen from UG-98 in VIII-1 or 4.1.5.2(b) in VIII-2. You may not operate (work) at a pressure higher than the design pressure, but you may re-certify to a higher design pressure based on the MAWP calculation. Most owner/user/operator standards have guidance on this.

In either case, the MAWP is used in the pressure test - see UG-99(b) in VIII-1 or 8.2.1(a) in VIII-2.

 

[H Cameron]

Thanks TGS4

1- Where can I find the clause that allow me to use design pressure for that in the code DIV 1?
2- if we have MAWP more than Design Pressure then we have to use MAWP for hydro test pressure calculation (1.3*MAWP)?

 

[jte]

H Cameron-

Two things: First, read TGS4's post, seeking answers to the two questions which you asked above. Second, read ASME Section VIII Div. 1 - at least the pertinent parts.

Your 18 posts in two months, 12 in this forum alone, are symptomatic of a vessel designer (are you an engineer?) who does not want to study and merely wants us (an unidentified group of people on an internet forum giving free advice and opinions) to do your work for you. Develop your own competence, and contribute to the site rather than simply asking novice questions an average of over once per week.

If you are truly interested in this issue of optimizing vessel design, you may be interested in two papers published at the ASME PVP conference in July (I don't see them available for purchase yet on the ASME web site). One common form of optimizing the design is to increase the pressure after the nominal thicknesses have been chosen. Another common form of optimization is that of the designer's time in which case no optimization of the design takes place. But one can also optimize temperature and corrosion allowance.