N2 amount for pipeline pressure test

[sabadean]

I really appreciate if somebody can help me to calculate how much amount of N2 gas needed to do pressure test for 3" diameter schedule 40 pipe with 100 meters in length. Test pressure is 89.1 bar.

Thanks in advance for inputs.

 

[quark]

Neglecting temperatures and using P1V1 = P2V2 you can get this.

ID of Sch. 40 3" pipe is 3.068" (77.92mm). The volume of 100 m piping is 0.4769 cu.m

So the final volume is 90.1 x 0.4769 = 42.96 cu.m (approximately)

 

[Montemayor]

sabadean:

First, go to:

http://webbook.nist.gov/cgi/fluid.c...it=Btu/lbm&WUnit=ft/s&VisUnit=cP&STUnit=lb/ft

Copy the HTML table of N₂ properties and paste it into a spreadsheet. You also know:

A 3” sch 40 pipe has 0.05130 ft² of transverse internal area;

100 meters = 328.08399 ft (according to Katmar’s Econeer);

1 lb-mole of N₂ = 28.016 lbs = 379.49 standard cubic feet (Scf) @ 60 ^oF & 14.696 psia.
Of course, you failed to tell us what temperature you are testing the pipe at, so I had to assume a range that includes 4 temperatures – as shown in the table. If you have a different temperature, you will have to use the free NIST database to give you the true thermo values.

On the same spread sheet you can now quickly calculate the Scf of N₂ required at each of the 4 base temperatures, using the given N₂ density. I obtain:

@ 70 ^oF = 1,454 Scf;
@ 80 ^oF = 1,422 Scf;
@ 90 ^oF = 1,392 Scf; and,
@ 100 ^oF = 1,363 Scf.

Of course you should order a contingency amount of N₂ over that calculated to make up for losses, leaks, and flawed measurements. I believe this method is as accurate as you're going to get.

 

[sailoday28]

Montemayor
I went to the above website.
Could you explain how to get N2 data for other pressures?

Regards

 

[Zapster]

This is the NIST site for thermophysical properties

http://webbook.nist.gov/chemistry/fluid/

 

[Montemayor]

sailoday28:

Zapster has given you the correct webpage to access in order to initiate your database request through NIST.

In the #1 drop-down box select Nitrogen as your working fluid; don’t forget to right-click your mouse outside the drop-down box. If you don’t , the fluid you selected remains high-lighted and will change identity when you start to fill in the other information boxes.

Next, choose the units you wish to use. In your case, its Nitrogen.

Now, chosse the desired type of data. You can choose one of five options:

1. Isothermal properties
2. Isobaric properties
3. Isochoric properties (constant density)
4. Saturation properties - temperature increments
5. Saturation properties - pressure increments

Lastly, click “Press to Continue”

If you select isobaric (as in your case), state your fixed pressure and the range of temperatures you want to limit the data to. Click on “Press for Data”.

The calculations will be done almost instantaneously; click on “View data in HTML table” and you will get a table that can be copied and pasted to a spreadsheet.

I hope this source helps you out as much as it has me.

 

[sailoday28]

Zapster/ Montemayor: Thanks for the response.
Neglecting what is in the pipe originally (air, etc.)The mass of N2 will also depend upon the source conditions.


With adiabatic conditions and const To source
Ufinal-Uinitial= ho mass(mass final-mass inital)

U is internal energy ho, stag enth. of source

For simplicity-Consider perfect gas const specific heats
and treating initial air in a "closed pipe of volume V" as N2.

Cv(Tfinial-Tinitial)=Cp(mfinal-minitial)To

Pf/mf-pi/mi=gammaR/V(mf-mi)To

where p is pressure, m mass gamma=Cp/Cv R gas const
V closed volume. T temp

subscripts o, source f final condition
i, initail condition
For this simplified case---knowing Pf, Pi, To and mi allows determination of mf.

Regards

 

[sabadean]

Thanks guys for your response, it help me a lots