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MAWP and MAOP
6

MAWP and MAOP

MAWP and MAOP

(OP)

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!
 

RE: MAWP and MAOP

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

RE: MAWP and MAOP

(OP)

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

RE: MAWP and MAOP

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

RE: MAWP and MAOP

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
 

RE: MAWP and MAOP

(OP)

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!

RE: MAWP and MAOP

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

RE: MAWP and MAOP

(OP)

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

RE: MAWP and MAOP

(OP)

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?
clown

 

RE: MAWP and MAOP

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

RE: MAWP and MAOP

(OP)

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

RE: MAWP and MAOP

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.

RE: MAWP and MAOP

Here we go again....

RE: MAWP and MAOP

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

David

RE: MAWP and MAOP

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.
 

RE: MAWP and MAOP

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!!!  

RE: MAWP and MAOP

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.
 

RE: MAWP and MAOP

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.

RE: MAWP and MAOP

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

RE: MAWP and MAOP

4
Considering all the codes I know, the nearest answer is that MAOP and MAWP are equal as zdas says in the first response.  That's why I haven't looked at this since then.  
Since these terms are not discussed equally in all codes, some codes ignore MAOP completely, I base that statement on review of B31.3, B31.4, B31.8 and CFR 49 Part 192 TRANSPORTATION OF NATURAL AND OTHER GAS BY PIPELINE and CFR 49 PART 195 TRANSPORTATION OF HAZARDOUS LIQUIDS BY PIPELINE,
 
B31.3 does not define "MAOP"

It defines "design pressure", as follows, and since 302.2.4 defines "design pressure" in terms of yield strength, its clear that "design pressure" is the pressure <= yield.  Any condition exceeding this is subject to further incidence counts, time and safety limitations given in the same pp 302.2.4.  As such, if those incidence counts, time or safety limits are exceeded, the design pressure must be increased until those overpressure excursions fall under the stated limits, similar to what is mentioned in pp V303.3.  Hence overpressure conditions are related back to pressure at yield at a design temperature.

B31.3 uses the term "Operating Pressure", but does not define it.  However, since operating pressure must be a condition, it must be <= "design pressure".  B31.3 2002 uses the term 3 times, once in conjunction with "maximum permissible normal operating pressure", which is mentioned  only to size reinforcement of a branch.

[/quote]
301.2 Design Pressure
301.2.1 General
(a) The design pressure of each component in a
piping system shall be not less than the pressure at the most severe condition of coincident internal or
external pressure and temperature (minimum or maximum)
expected during service, except as provided in
para. 302.2.4.
(b) The most severe condition is that which results
in the greatest required component thickness and the
highest component rating.

~~~~~~~~~~~~~~~~~

302.2.4 Allowances for Pressure and Temperature
Variations. Occasional variations of pressure and/or
temperature may occur in a piping system. Such variations
shall be considered in selecting design pressure
(para. 301.2) and design temperature (para. 301.3). The most severe coincident pressure and temperature shall determine the design conditions unless all of the following criteria are met.
~~~~~~~
(b) Nominal pressure stresses shall not exceed the
yield strength at temperature (see para. 302.3 of this
Code and Sy data in BPV Code, Section II, Part D,
Table Y-1).
[/quote]

B31.3 2002 uses the term "maximum allowable working pressure" in pp 322.6.3 "Pressure Relieving Devices" and sets it equal to "design pressure" for the subsections and defines a few other pressures in the footnotes,

Quote:


11 The design pressure for pressure relief is the maximum design pressure permitted, considering all components in the piping system.
12 Set pressure is the pressure at which the device begins to relieve, e.g., lift pressure of a spring-actuated relief valve, bursting pressure of a rupture disk, or breaking pressure of a breaking pin device.
13 Maximum relieving pressure is the maximum system pressure
during a pressure relieving event.

B31.4 Liquid pipeline code
"maximum allowed operating pressure" is used once in pp A451.11 Inspection.  It is not otherwise used nor is it specifically otherwise defined.

B31.4 Does define a "maximum steady state operating
pressure" of a piping system be raised to a value
higher than the "internal design pressure", thus design pressure is related to steady state pressure.
Surge pressures are defined as any nonsteady state condition that could exist and are limited to 10% over internal design pressure in ss 402.4

Quote:


402.2.3 Normal Operating Conditions. For normal
operation the maximum steady state operating pressure
shall not exceed the internal design pressure and pressure
ratings for the components used.

402.2.4 Ratings - Allowance for Variations From
Normal Operations. Surge pressures in a liquid pipeline
are produced by a change in the velocity of the moving
stream that results from shutting down of a pump
station or pumping unit, closing of a valve, or blockage
of the moving stream.
Surge pressure attenuates (decreases in intensity) as
it moves away from its point of origin.
Surge calculations shall be made, and adequate controls
and protective equipment shall be provided, so
that the level of pressure rise due to surges and other
variations from normal operations shall not exceed the
internal design pressure at any point in the piping
system and equipment by more than 10%.

Quote:


402.2.3 Normal Operating Conditions. For normal
operation the maximum steady state operating pressure
shall not exceed the internal design pressure and pressure
ratings for the components used.

"Operating pressure" is defined as,

Quote:

451.1 Operating Pressure
(u) Care shall be exercised to assure that at any
point in the piping system the maximum steady state
operating pressure and static head pressure with the
line in a static condition do not exceed at that point
the internal design pressure and pressure ratings for
the components used as specified in para. 402.2.3, and
that the level of pressure rise due to surges and other
variations from normal operation does not exceed the
internal design pressure at any point in the piping
system and equipment by more than 10% as specified
in para. 402.2.4.

~~~~~~~~
456
(c) In no case shall the maximum steady state operating
pressure of a piping system be raised to a value
higher than the internal design pressure
permitted by
this Code for a new piping system constructed of the
same materials.

[b]B31.8 Gas Transmission Pipeline Code
Design pressure: "is the maximum pressure permitted by this code"  (Therefore it obviously must be the maximum of any pressure, operating, allowed, permitted, or otherwise falling under this code.)

805.213 Maximum Operating Pressure (MOP) maximum actual operating pressure, is the highest pressure at which a piping system is operated during a normal operating cycle.

[color red] (HERE IT IS MAOP!) 805.214 Maximum allowable operating pressure (MAOP) is the maximum pressure at which a gas system may be operated in accordance with the provisions of this code.

PP 845.214 further defines MAOP in ss 1 in terms of test pressure, the maximum allowable operating pressure shall be limited to the pressure obtained by dividing the test pressure by the class factor.

MAOP do form important safety information that must be submitted by pipeline operators covered by the CFRs and definitions similar to the above can be found in the relavent sections, for which I won't bore you further with endless quotes.  There all in here if you're interested,
http://www.access.gpo.gov/nara/cfr/waisidx_02/49cfr192_02.html
and,
http://www.access.gpo.gov/nara/cfr/waisidx_02/49cfr195_02.html

OK, now that we have all of that, its still very important to note that even though the internal design pressure must produce a stress less than yield, it is not the only condition and must be taken into consideration when establishing operating pressure.  It must be considered in combination with other transverse and longitudinal stresses, such that the combined yield stress is not exceeded.  Considering that, it is possible that the operating pressure must be reduced to cause a hoop stress of much less than yield stress in certain loading combinations.

BTW, its "only when it is corroded", if a corrosion allowance was used.

 

**********************
"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/

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