Design pressure of a pipe 1

[Indy]

Hi,
I have a question regarding the design pressure of a pipeline. I believe the design pressure is the maximum pressure of which the process equipment can handle. So for example we have a document which says the design pressure of a pipe is 250 barg but also says that 300 barg may be experienced for short periods. I believe then that the 300bar should be the design pressure ?

Thank you.

 

[LittleInch]

Depends on the design code.

Most "pipeline" codes allow up to 10% above design pressure for short term overpressure events. There's often very little definition of how long the overpressure lasts for our how often but the normal judgement is less than an hour once or twice a year.

Piping codes like B31.3 can allow up to 30% over design pressure.

So for your line I would expect up to 275 barg to be ok, but otherwise yes you would need to raise the design pressure. A lot depends on the details of how long and how often this overpressure occurs.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MJCronin]

In my opinion, this is the wrong forum to discuss this issue. The "Pipelines, piping and Fluid Mechanics" is more appropriate

First, your use of the term "pipeline" can mean many things to many people.

It is much better to identify the system by code of record and function. You should talk about "ASME B31.1 Steam system" or a "ASME B31.3 Nitric acid piping system"

Once you identify the code for the system, you can discuss maximum pressures.

Second, you must consider both the maximum pressure AND the coincident temperature at the time of the pressure. Piping systems can withstand a higher pressure in the cold condition than when they are hot because metals have a lower allowable stress level at elevated temperature.

Third, you must watch terminology. ASME piping codes use "Maximum Allowable Working Pressure" which is commonly understood to mean the maximum pressure that the system is EVER expected to see ..... PLUS a margin. Margins of 25 to 100 psig are typical .... 'It would be also typical for a process engineer to define a maximum operating pressure based on the dead head of a pump and then have the pressure margin added to determine to the MAWP.... Keep in mind that before a piping wall thickness can be selected, ASME and other codes require a Corrosion Allowance to be considered by the piping Engineer for the specific system Using the above systems as an example, it would be expected that a nitric acid piping system would require a greater wall thickness than a steam system of the same maximum design pressures and temperatures.

The ASME Gods have found it to be to their advantage to use the similar but confusing term MAOP (maximum allowable operating pressure) for Pressure Vessel design. The ASME Pressure Vessel Code, Section VIII as well as many governmental regulations refer to MAOP

There have been many. many discussions on Eng-tips regarding MAOP and MAWP for pressure components

Don't know if this clears things up .... but I gave it a shot !!!

MJCronin
Sr. Process Engineer

 

[MJCronin]

https://www.eng-tips.com/viewthread.cfm?qid=439153

https://www.eng-tips.com/viewthread.cfm?qid=420786

https://www.eng-tips.com/viewthread.cfm?qid=245245

MJCronin
Sr. Process Engineer

 

[LittleInch]

MJC,

As you show very well in your collected posts, there is great confusion about the terminology.

The codes I'm familiar with are B 31.3, .4 and .8

Each has a little section at the start,
namely
B 31.3 - 301.2.1
B 31.4 - 401.2.2.2 and 400.2 (definition of Max Operating Pressure)
B 31.8 - 805.2.1

In my search through these codes the ASME PIPING and pipeline codes do not use MAWP. They use design pressure and sometimes MOP or MAOP.
PIPING fitting codes (e.g. B 16.5, section 2.1)) and ASME VIII does use MAWP

So Indy - to reiterate - quote which DESIGN CODE you are using and we can make a judgement.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MJCronin]

A couple of books to consider regarding this topic ...

https://www.amazon.com/Process-Piping-Complete-Guide-B31-3/dp/0791802868

https://www.amazon.com/Power-Piping-Complete-Guide-B31-1/dp/0791860140

MJCronin
Sr. Process Engineer

 

[chrysa1975]

Dear all, I think there is a confusion here. Indy refers to a document that defines the design pressure to be 250 barg. This is a project requirement rather than a fundamental problem to solve.
In reply to Indy's query for the applicable design pressure, the correct approach is to consider Design Pressure=250 barg, while the value of 300 barg falls into para 302.2.4 of ASME B31.3.
In reply to LittleInch and MJCronin, allow me with all the respect to say that:
MAWP term is met in ASME VIII Div.1 and it is usually calculated by the fabricator of the pressure equipment based on procured and used plate material. This value may be equal or higher than the design pressure defined for the project, it can never be less.
For pipes the term that is commonly addressed is the maximum internal pressure. It is calculated for the wall thickness of the pipe minus the corrosion allowance and the mill tolerances, using the applicable allowable stresses and formulas of each code.

 

[LittleInch]

Who said it was B31.3??

Indy said "pipeline", but no code.

MAWP higher than design pressure for pressure vessels boggled my mind when I first came across it, but I get it now.

Whilst you can reverse engineer pipes to a certain extent, once you test the pipe in its final configuration that often sets the highest design pressure unless you retest the system. It's the lowest rates thing attached to the pipe which sets the design pressure as well. That could be a flange, a valve or another component.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[chrysa1975]

LittleInch I agree with you. In a system, there are limitation items that someone has to consider.
Anyhow, I do not see any reply from Indy, hence I hope he has his problem solved.

 

[Indy]

Apologies. I spoke to the process engineer. There is no issue 250barg is the design pressure for the system.

Thanks for the replies.

 

[LittleInch]

So what was the 300 barg??

If it can see 300 then 250 barg for design is too low.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.