Maximum allowable working pressure 1

[johngladstone]

Dears,
I looking for your help for following terminology

1- what is difference between MAWP and MAOP?
2- leak test pressure require for pipe is it related to design pressure or MAWP?
3- what is mean MAWP of pipe is 1750PSI?

Thank you in aDvance

Best regards
John gladstone

 

[LittleInch]

All in the definition of the relevant code you're using.

However as a basic guide:
1- what is difference between MAWP and MAOP?
MAWP tends to be a pressure vessel thing which is, as it says, the maximum allowable working pressure of the vessel. in general there is no allowance for any over pressure within this.

MAOP on the other hand is a pipeline thing where the test pressure sets the MAOP as some sort of fraction. Not all pipeline codes use MAOP.
2- leak test pressure require for pipe is it related to design pressure or MAWP?
You need to read the code to which your "pipe" refers. As said MAWP is normally a pressure vessel thing

3- what is mean MAWP of pipe is 1750PSI?
Well it means the maximum pressure (other than test) is 1750 psis.

Some context might help here.

LI




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[GD2]

MAWP is used in Vessel. It's stamped in the vessel name plate. Design Pressure is always less or equal to MAWP.
In piping world MAWP means Design Pressure. Design pressure is a term used in codes like B31.1, B31.3.
As LI stated, MAOP is used in pipeline world.

Ganga D. Deka, P. Eng
Canada

 

[johngladstone]

Dears,
Thank you gentlemen.
Ohk regarding relation between leak test pressure and flange rated pressure.
Is it require the test pressure was lower than flange rated pressure?

Please advice
John Gladstone

 

[LittleInch]

Is it require the test pressure was lower than flange rated pressure?

No. Flange rated pressure allows for test pressures on the associated piping system to 1.5 times the 38C rating ( section 2.6 of ASME B 16.5.

Other flange design codes may say something different, but most permit test pressures to exceed the flange rating by at least 1.25 or 1.3 and many are 1.5.

Note: flanges themselves do not need to be tested, only as part of an assembled piping system.

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[johngladstone]

Ohk, when the test pressure exceed flange rated pressure it will not harmful Piping flange?

Ex :- Regarding B31. 3 is it allowed to be test pressure above or below Flange rated pressure?

According my information test pressure above 1,5 design pressure but at same time lower than flange pressure..

Am I missing something?

 

[LittleInch]

Para 1 Correct

Para 2 Above by 1.5 times the flange rating for asme 16.5 flanges

Para 3. Not correct- see above

Para 4. Yes. Test pressures are different to MAWP or MAOP or flange MWP limits

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[johngladstone]

I appressiTe little inch

In summarize test pressure will be 1.5 flange pressure rating.

My question now relation between flange rated pressure and design pressure of pipe?

 

[GD2]

Johngladstone,

If you had selected the correct flange P-T rating in relation to the design pressure and temp conditions, you need not worry about overshooting the flange test pressure. Suppose you are testing a pipe spool with flanges, the flange will be the weaker part and the test pressure will be limited by the flange test pressure which is 1.5 times the design pressure x the temp correction factor. If you are using ASME B16.5 flanges, the design pressure = Working Pressure in the P-T tables corresponding to the Temp (first left column) = design temp. Flanges are rated in terms of Class ex Class 150, 300 etc. etc.

It looks like you are very confused with so many pressure terms.

Ganga D. Deka, P. Eng
Canada

 

[racingwind]

Just be cautious that for high pressure systems, such as Class 1500 or higher, hydrotest at 1.5 times the flange pressure rating at 100F might produce hoop stress that is exceeding the yield stress, especially for large pipe.

 

[KevinNZ]

Racingwind

Your piping will have a design pressure. This will not be higher than the flange P/T rating, but could be lower.

Test pressure is lower of
1.the requirement of the piping code. Design pressure * factor (this will not over stress the pipe)
2. the maximum test pressure for the flanges and other components in the system

 

[johngladstone]

Thanks for whole gentlemen for your inputs.

If I suppose design pressure of Piping was 280psi which CS flange must select class I select 150#or 300#?

Is there rule of thumb for example that flange rate pressure must be higher than with 10% or something like this?

 

[KevinNZ]

The piping system design pressure can be the same as the flange class P/T rating

 

[johngladstone]

Even there is hammering option, quick closing valve, startup pressure?

 

[KevinNZ]

The design pressure has to allow for all sources of pressure.

Piping codes do have an extra allowance for short acting pressure above the "design" pressure. But flanges and valve codes may not have this allowance.

for example
B16.5
Pressure–temperature ratings are maximum allowable
working gage pressures..
(no mention of transients)

B16.34
2.5.2 Other Variances. Damage that may result from
subjecting a valve to other operating variances (transients)
in excess of its pressure rating is solely the responsibility
of the user.

You need to calculate the maximum pressure including transients and check with each code what allowance above design pressure you can have for transients.

 

[LittleInch]

It depends on your working temperature and material class of flange.

Group 1.1 no higher than 38C the class 150 flange rating is 284 psi.

You don't need any margin as Kevin NZ says.

Although there is no transient pressure clause in B 16.5, B 31.3 allows varying levels of overpressure of the piping system (which includes valves and flanges) to between 10 to 305 depending on the duration of the over pressure.

But regular overpressure (i.e. every start or stop) > 10% above design pressure is not a good idea.



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[johngladstone]

Thank you very much gentlemen for whole your valuable inputs.

@littleinch
For testing pipe system @1,5 flange rated pressure for how many hours if it's liquid or pneumatic test? And for how much permissible pressure drop ?

@kevinnz

Is there any practical example document to understand calculation of transient pressure @16.5 & 16.35

 

[LittleInch]

There's noo real limit for a "test" - that's up to the piping design code. Usually min 1 hour to 4 hours, but pipeline can be 24 hours test.

No pressure drop permitted that cannot be explained by temperature change and expansion / contraction of liquid.

Piping codes often want all pipework to be visually examined for leaks.

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Also: If you get a response it's polite to respond to it.

 

[johngladstone]

@littleinch after I calculate design pressure of Piping system I found that will be 320psi @38 c in this case I will select flange rated #300?
am I right?

 

[LittleInch]

Yes

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