MAWP and MAOP 7

[Melimelo]

Hello,
Can somebody tell me what is the difference between MAWP (for working pressure), MAOP (for operating pressure) and design pressure?
For me, I think MAWP < MAOP < Design P, what do you think?
Thanks a lot!

 

[zdas04]

MAWP and MAOP are the same thing. Design pressure is a less formal term that sometimes means "design point" or the nominal operating pressure that the system will operate at most of the time (<MAWP) and sometimes it means MAWP depending on the country/company.

David

 

[Melimelo]

waw, are you completly sure there is no difference between MAWP and MAOP???

 

[lizking]

In my experience, MAOP is traditionally used in pipeline operations and essentially has the same "meaning" as MAWP in terms of overpressure protection.

 

[SJones]

Stick to the definition of terms stated in the design code being applied - it saves a lot of misunderstanding (and numerous threads on here)!

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[Melimelo]

Hello SJones,
You mean that these definitions can be different from a company to another one?
If I asked this question, it's exactly to know that...
(Sorry for my basic questions, I'm a novice process engineer working in my company just since 3 months...)
Thanks a lot!

 

[JoeWong88]

MAOP limited by process or proper operation of particular device in the system...

Design pressure selected to have good margin from MOP.

MAWP is where the designed / built equipment can withstand it is corroded



MAOP < Design Pressure <= MAWP

JoeWong
Chemical & Process Technology

 

[Melimelo]

OK, OK, now I understand...
Well, just something else: MOP = MAOP, isn't it?
Thanks JoeWong!
Méli

 

[Melimelo]

JoeWong,
For your last sentence, you mean:

MAWP is where the designed / built equipment can withstand WHEN it is corroded;

You have forgotten the WHEN, no?
)

 

[JoeWong88]

MOP <= MAOP.

Oui. MAWP is pressure where the designed / built equipment can withstand WHEN it is corroded.

MOP <= MAOP < Design Pressure <= MAWP

JoeWong
Chemical & Process Technology

 

[Melimelo]

OK, OK, thank you very much JoeWong!
Méli )

 

[ClaireBear]

I dont think Design pressure is the pressure at which a system is designed to operate. I think its the pressure the vessel is designed to withstand and will be substantially more than the MAWP.

 

[gr2vessels]

Here we go again....

 

[zdas04]

ClaireBear,
This is really not subject to what you think, do you have any source that you could cite to support your nonsense?

David

 

[zerosum]

http://webwormcpt.blogspot.com/

Check this site for today 13 Nov 08. Pretty good graphic comparing all the terms.

 

[Prince74]

My name is Tadese Kazeem Adegunle,
With my little understanding in process, i believe that MAWP>MAOP( These terms can be used interchangeably, depending on different company desire)
DP(Desigh=n Pressure) is less than MAOP
WP(Working Pressure) is less than equal to DP(Design Pressure)
Hence,MAWP>MAOP>DP greater than or equal to WP.
This is my submission.
Thanks for the honour given to me to participate.

 

[rconner]

Just some advice. Acronyms in general in and of themselves may be essentially worthless when dealing with important matters (in my opinion they in general should be carefully defined as well as practical in/per the specification and/or an applicable codes). I know of at least one "CEO" who has made that point very clear to some folks!!!

 

[davefitz]

I think the design codes define the MAOP. In the case of a fire , some codes may allow 20% overpressure ( 1.2 * Pd). Except for that unique emergency , some codes limit MAOP to 15% for less than 1% of the time ( as with safety valve lift events or pump dead head events).
In these above cases , Pd is the design pressure based on code calcs and as-recieved pipe or vessel wall thickness and valve or fitting class, whichever is less.

 

[djack77494]

I think that one very clear graphic way of thinking of the MAWP is that this is the pressure (at design temperature) above which the vessel may fail. Yes, I know we have our various overdesign factors and allowances, etc., but the vessel is built to be capable of withstanding the MAWP and not necessarily any more. MAWP applies to long term operation, and therefore it is under hot and corroded conditions with the permissible corrosion specified as an allowance. All other mentioned parameters would necessarily be lower than the MAWP.

 

[JoeTank]

Okay Folks, here's what ASME VIII says...
MAWP = pressure specified by the purchaser for the design of the vessel. It is the pressure at the top of the vessel in its operating position. The MAWP is what is stamped on the ASME nameplate. Additional comment at the bottom of response.
Design pressure (P)= the MAWP plus static head pressure due to liquid (if any) that is used to design each PART of a vessel.
To the best of my knowledge MAOP is not an ASME VIII Code-defined term.
There is an alternative to the value of MAWP stamped on the nameplate. Instead of using the MAWP specified by the purchaser, the MAWP of the vessel may be reported as the highest MAWP permissible, based on the the as-built thickness of each component. This requires that the vessel be designed and plate thicknesses selected. Then the calculations are "reversed" using the a-built thickness (minus CA) and determining what MAWP would be permitted for each part. The MAWP for the vessel will then be the LOWEST MAWP of each part, reduced by the appropriate static head presseure for each part.
Wow, that was quite long winded.

Joe Tank