Connection of Fittings with Different Schedule

Yes, it is possible to connect different pipe schedules to one another. For any given pipe size, the OD and threads (if threaded) are the same. However, you need to be careful about such mixing-and-matching. If one part of a piping system requires a certain schedule to handle the pressure, chances are that all parts of the system will need similar pressure-handling capabilities, and thus the same schedule. This will not always be the case, but you should be prepared to justify any schedule differences.

Thank You, sir!

But what mean this "This will not always be the case, but you should be prepared to justify any schedule differences."

While one could do it, one must be ready to explain why one wants to.

Dear Bojo,

In my opinion what Tornado is saying is that when you connect items with different schedules and similar outside dimensions you should adapt the wall thickness of the thicker part in such way that they fit perfectly together at the weld area with a smooth transition to the thicker part.

Please note that piping codes, such as ASME B31.1 and ASME B31.3 contain details on this matter.

To be in compliance with these codes, an internal "taper" must be machined into the thicker component when the mismatch exceeds a certain amount.

The internal "taper" or slope helps to ensure a smooth flow path.......

To give an example, a high-pressure Schedule 80 line might enter a PRV (pressure reducing valve). The downstream pressure could then be low enough that Schedule 40 pipe would suffice. However, you would want to be sure that a failure in the valve would not result in over-pressure in the downstream line.

In a pressure reducing valve if you supply a fluid at low pressure to the LP side,will you get fluid at high pressure at HP side? Has anybody tried this?

To the first question, no; to the second, probably yes, but unsuccessfully.

Is there any simple mechanical device (without using external power)available to increase the pressure?

Yes, there are hydraulic pressure intensifiers. For example, if the rod in a hydraulic cylinder is half the area of the piston, the rod can be used as a secondary piston to produce twice the pressure at half the flow (minus frictional losses). Please note that although the pressure increases, the power and energy do not, on account of the decreased flow and the losses.

Thank you.Could you please give a brand name or technical specs for such a device?

Sorry, I don't know offhand of any manufacturers; I've only heard or read of the concept. Maybe a Google on "pressure instensifier" would turn up something, such as 868,000 hits in 0.29 seconds.

Thanks.If we install a bell type reducer in the pipe and connect it to a smaller pipe,will there be an increase in pressure?

No.

(Except for relatively slight pressure differences if the fluid is flowing.)

In connection with flow of water in pipes I like to narrate an incident which happened in Saudi Arabia. A deep well submersible pump when commissioned didn't deliver water.Some technicians who did the installation said that our manager went there brought a bowser of water and after pouring some water into the vertical pipe work and restarted the pump,it started to deliver water.Can you shed some light on this?. in fact I wanted to replace a few lengths of pipe with smaller diameter ones.

In a piping system, if you reduced the pipe cross-section by any means (such as a reducer, ... etc.), the velocity will be raised and the pressure will be reduced resulting in higher friction loss. At this situation and if you need to maintain the same flow rate, may be you have to get another pump with a higher pumping pressure to overcome the friction loss (pressure drop) in the piping system.

In the attached figure, a crude petroleum flowing in different diameters of pipelines, you can obviously notice that the friction loss (pressure drop) in smaller diameter is higher than that in larger diameters.

Example: For crude oil with a Specific Gravity 1 (^OAPI 10), flowrate 2000 Barrels/hour, and viscosity 100 (Say Bolt Universal seconds), the friction loss shall be:

• 18" NPS ..... 2.7 PSI/mile

• 14" NPS ..... 8.8 PSI/mile

• 10" NPS ..... 35 PSI/mile

Can can imagine how much the pressure drop and intern the pump(s) required for 50 mile pipeline to fulfil the same flowrate:

• 18" NPS ..... 135 PSI

• 14" NPS ..... 440 PSI

• 10" NPS ..... 1750 PSI (may be you need 2 or more pump stations)

..........................

Bojo if your piping system requires Xray this may fail.

I heard that electrical conduits are specified by OD and water pipes by ID.If OD is same for different schedule nos of water pipes and thickness varies the internal diameter and hence the cross section of useful area will vary. In that case for a sch 40 & sch 80 pipes (say 3")the flow (Q) will not the same.Will sch no dictate selection of pipe size?

Yes, it can. Various pressure drop tables, charts, and programs take pipe schedule into account, so that effectively they work by I.D.

I suggest to machine down the ends of biggest schedule to get the same ODs & IDs. Otherwise, it will be difficult to pass the weld radiographic test.

consrning the flow, there is no majeur effects.

there will be obstruction of flow because the wall thickness of shedule 4o pipe is greate than shedule 30 even though the ouside diameter is the same on both. in a preasurized envelope the pressure will remain constant