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Pipe Fittings (Threaded)

06/01/2012 4:38 AM

What is the difference between Class 300 and Class 3000 malleable iron threaded black steel pipe fittings, in terms of their pressure ratings, applications where each is generally used, and whether used with Schedule 40 and Schedule 80 pipes.

Which is more suited for LPG piping from gas storage tanks to the kitchen and for FM200 and CO2 Fire Fighting piping?

Thanks.

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Guru
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#1

Re: Pipe fittings (threaded)

06/01/2012 4:41 AM

The difference in the classes is the wall thickness.

The difference in use lies with appropriate selection by the piping system designer.

It sounds as though the issue needs to be delegated to a qualified and experienced piping specialist, and the design reviewed by the Engineer/Surveyor from the company supplying fire/loss protection and indemnity insurance for the facility to make sure that insurance cover will be provided once the systems are complete and commissioned in accordance with an approved design.

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#2

Re: Pipe fittings (threaded)

06/01/2012 5:17 AM

Pressure rating is a function of the temperature of the process fluid. Generally, the higher the temperature, the lower the pressure rating.

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#3

Re: Pipe fittings (threaded)

06/01/2012 6:15 AM

Hi solidspaces,

A quick "Google" showed Class 300 are Cast Malleable Steel fittings rated at 300 psi while the Class 3000 are Forged Steel rated at 3000 psi. Applications are vast and various and the pipe schedule used should be of a comparable pressure rating.

Best regards,

John

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#8
In reply to #3

Re: Pipe fittings (threaded)

06/04/2012 9:23 AM

This is the old go-by that us graybeards use, but it is not technically correct.

There is a reason fittings are no longer referred to as 300psi, or 300#. This was changed back in the '70's to be read as "class 300." Old rules die hard when they are easier to remember. Most folks in the field today still say "300 pound" fittings.

PWSlack is most correct when he says the rating is a function of pressure and temp. Unfortunately, he didn't say what the rating is. That is a much harder thing to do. It requires a graph, not just a number.

I am providing the below information for reference purposes only. For actual application data, please consult your pipe spec.

-A-

Gage Pressure

(psi)

Temperature

(oF)

Flange Class
15030040060090015002500
< 1002857409901480222037056170
2002606759001350202533755625
3002306558751315197032805470
4002006358451270190031705280
5001706008001200179529954990
6001405507301095164027354560
6501255357151075161026854475
7001105357101065160026654440
750955056701010151025204200
80080410550825123520603430
8506527035553580513402230
900501702303455158601430
95035105140205310515860
1000205070105155260430
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#4

Re: Pipe Fittings (Threaded)

06/01/2012 8:30 PM
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#5

Re: Pipe Fittings (Threaded)

06/01/2012 10:35 PM

The same difference as between 300 psi and 3000 psi or 900%.

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#6

Re: Pipe Fittings (Threaded)

06/02/2012 1:41 AM

Class of pipe fittings represent pressure rating. Pipe schedule is selected based on maximum pressure, temp and fluid it is intended to be subjected. So, normally higher class fittings for higher schedule pipe.

For gases like LPG or acetylene, even though maximum operating pressure and temp may suggest schedule 40 pipe is OK, but schedule 80 is selected referring to other standards for explosive gases.

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#7

Re: Pipe Fittings (Threaded)

06/03/2012 9:31 AM

1. Class 3000 can be used with sched 40 or 80 pipe.

2. LPG to kitchen...domestic or industrial ? Manifold/ header ? Consult your local gas supplier ....

3. FM 200/ CO2 fire-suppression: there are very good reasons for you not to try any home-grown design solutions here, given the basic nature of your queries.

FM 200 design and flow calculations are proprietary, developed by experts eg Hughes Associates and certified independently by various bodies (UL etc..). These systems are designed per application and the stored pressure may be at 25bar or 42bar. The pipe schedule is provided by the manufacturer/ distributor. I hesitate to provide you too much info, since it may do more harm than good! Suffice to say that the manifolds should be sched80 and the screwed fittings 3000#. The nozzle pipe sched is dependent on the minimum discharge temperature eg lowest temperature for sched 40 would be minus (-) 28 C / 82.4 F. The extinguishing effectiveness is entirely dependent on the discharge time, which is a product of the proprietary calculations...

CO2 systems are more common/standardised but also subject to expert calculation and design. Note that this is a smothering agent, not an extinguishant.

An important concept for you to take from here, is that internal pipe diameters between sched 40 and sched 80 differ, and that this affects the discharge calculations. These installations cannot be left to amateurs.....so sorry.

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#9

Re: Pipe Fittings (Threaded)

06/05/2012 9:00 AM

solidspaces some differences between the two that should be also considered are class 300 fittings are a cast product made of malleable iron class 3000 are made of a steel forging which are machined. Cast products have had porosity issues (leaks) but are less costly. Forged steel fittings do not have porosity issues but are more expensive. Sometimes forged steel is used for the integrity of the fitting (less chance of leaks) and the structural strength of the material. Pressure ratings 300# MI is 2000 psi @ 150F for sizes 1/4"- 1" and 1500 psi thru 2", 3000# forged steel is 3000 psi for cold water oil or gas. Steel pipe is interesting because plain end pipe has a higher pressure rating than threaded pipe. For instance Continuous welded 1" Sch.40 plain end is rated 1,290 psi, threaded 490 psi, Sch.80 plain end 1,790 psi, threaded 950 psi. ERW pipe 1" Sch.40 plain end 2,440 psi and Sch.80 3,370 psi. Malleable iron fittings are generaly used with welded pipe forged steel fittings are used with seamless pipe. In your situation have seen forged steel and seamless pipe used with LPG gas and 300# MI fittings and welded pipe used in the CO2 equipment.

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