MAWP on Nameplate
MAWP on Nameplate
(OP)
Hi,
I've just received an order for building 1 vessel acc. to ASME VIII Div.1, Stamp U.
It's a very simple vessel, sort of filter, made from pipe and caps, carbon steel.
On the drawing it's written 10 bar as design pressure, and 23 bar as MAWP. Hydrostatic test is according to UG-99(b).
Calcs (given me by the client) were made using design pressure as reference for estimating minimum thickness of components. However, in one page is reported the MAWP as written on the drawing.
My question is: what MAWP do I have to stamp on the nameplate? Usually my AI advises me to put DP=MAWP, but in this case? if I wrote 23 bar on the nameplate, wouldn't this imply that the vessel is verified for an higher pressure, higher than the real one (10 bar)? Do I have to redo calcs at 23 bar?
Thank you
I've just received an order for building 1 vessel acc. to ASME VIII Div.1, Stamp U.
It's a very simple vessel, sort of filter, made from pipe and caps, carbon steel.
On the drawing it's written 10 bar as design pressure, and 23 bar as MAWP. Hydrostatic test is according to UG-99(b).
Calcs (given me by the client) were made using design pressure as reference for estimating minimum thickness of components. However, in one page is reported the MAWP as written on the drawing.
My question is: what MAWP do I have to stamp on the nameplate? Usually my AI advises me to put DP=MAWP, but in this case? if I wrote 23 bar on the nameplate, wouldn't this imply that the vessel is verified for an higher pressure, higher than the real one (10 bar)? Do I have to redo calcs at 23 bar?
Thank you





RE: MAWP on Nameplate
RE: MAWP on Nameplate
RE: MAWP on Nameplate
If the thickness is indeed higher than the minimum required for design, that's irrelevant. It's what the design is that matters.
Does this thing have any flanges or other pressure rated components?
If you want to stamp it 23barg @ X deg C, then design it for 23 barg at X deg C. Simple.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: MAWP on Nameplate
RE: MAWP on Nameplate
Regards.
RE: MAWP on Nameplate
I apologize.
RE: MAWP on Nameplate
RE: MAWP on Nameplate
MAWP has to be higher than design pressure, otherwise the unit would not pass CODE.
ElCid,
You can either stamp 10 bar or 23 bar on the nameplate, but have to provide calculations showing that the MAWP that you mark on the nameplate passes CODE.
RE: MAWP on Nameplate
For "passes" do you mean, for example, to substitute the pressure in the calculation of minimum thickness of all components with the MAWP, and then verify that this "new" min.thk is < adopted thk (considering undertolerance, corrosion, etc...)?
RE: MAWP on Nameplate
This post gives most of the answers. http://www.eng-tips.com/viewthread.cfm?qid=229469
Basically as far as I can figure out - to start with MAWP is pressure at the top of the vessel and design pressure the pressure at the bottom including any liquid head. This is used to design the vessel with min thicknesses of plates etc.
However if you then build it with thicker components, you can take the corroded thickness ( assumed of course at the start of design) and back calculate the MAWP of each main component. The lowest MAWP becomes the MAWP of the vessel.
For small diameter simple vessels you can easily need to use thicker pipe than you need for practical purposes.
However you can only stamp MAWP of any figure if you've got the design data to prove it.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: MAWP on Nameplate
Welcome to pressure vessel design! Yes, it's a tad different than piping, and even more removed from pipeline work.
You almost got it right in your summary above: The Design Pressure of the vessel is what the process engineer specifies at the top of the vessel. The design pressure of a given component takes the process DP and adds any hydrostatic head and then the component is designed. That's all well and good. The code, since the original Boiler Code of 1914, has included the premise of optimizing the design. In most cases when optimization is performed, it takes the form of MAWP which is the back-calculated maximum pressure of the vessel as designed. You might think of this as a "pre-stamping rerate". However, as others have noted above, Section VIII Div. 1 has allowed for a lack of optimization of the steel, specifically in that there is no requirement to go back and rerate the vessel to determine the MAWP.
One crucial point you miss in your post above is that all components, not just the main components must pass muster with VIII-1 design requirements and the one with the lowest pressure rating then sets the MAWP for the entire vessel. Many company spec's have a statement to the effect of "minor components shall not govern" but this is a (good, in my opinion) user's decision, not a code mandate.
ElCid-
It is not clear to me what your contractual obligations are in this case. From my perspective, if I were to place an order with you and state in the data sheets that I want or expect a 23 bar MAWP, then that's what I expect to see on the nameplate. The 10 bar design pressure is of value only in that it indicates to future engineers what the process engineer decided that they need. This may be what the relief system is designed around, but it doesn't change the fact that I asked for a 23 bar MAWP. As Afox88 points out above, it is the manufacturer's (i.e. your) responsibility to provide design calc's that back the 23 bar MAWP.
RE: MAWP on Nameplate
Glad I got it nearly correct, most of the time I don't get involved in PV discussions for obvious reasons, but this one I couldn't help myself - it was useful to understand how it works though and that's the value of this site - it forces you to go and find something out that you didn't know before.
for me normally Design pressure is King, nothing should normally exceed it (hydro and intermittent excepted). Clearly PVs work a little differently.....
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: MAWP on Nameplate
I. Chemical as Afox88 design pressure is their used pressure. That's the controversy. I stand that the specifier shall be contacted to clarify the MAWP.
But it seems that the order came from Chemical so the calculations should be to the higher pressure. When the poster, ASME engineer does the required re,calc then he can see if the vessel Comply to the higher pressure or not. Real simple.
Regards to all. Gen blr.
RE: MAWP on Nameplate
Yep, the very same reason I try to stay out of pipeline issues. Different environment, different code philosophies.
jt
RE: MAWP on Nameplate
In my case, as he says, stamping on the nameplate 23bar as MAWP is correct because:
1) 23 bar is the lowest MAWP among all the items (as ASME required)
2) DP is lower than MAWP, which means that the vessel is built with "extra-tickness", not only with the strictly minimum required. Using DP as MAWP would mean undervaluing the "potentiality" of the vessel.
RE: MAWP on Nameplate
23 bar is significantly higher than 10 bar, so this vessel is likely way overdesigned. But if that's the case, then so be it. The nameplate should be stamped based on what the hydrotest pressure was assuming there are calculations to support that pressure. If it was hydrotested at 1.3*10bar, then you can not stamp the MAWP at 23 bar into the nameplate.
RE: MAWP on Nameplate
RE: MAWP on Nameplate
RE: MAWP on Nameplate