3 replies to this topic

[Dtan76]

Hello all ...

I'm coming back again! Sorry so long never post message here due to overload + many papers work current now.

I'm develop hydraulic line verification report, anyone of you interest to look at please let me know or email to me.

One question here, as we know liquid line (non-compressible fluid) pipe diameter is size between 3 to 3.5 m/sec, any velocity greater than this will cause relatively high pressure drop hence may lead to overall piping pressure drop and cause pump failure.

Someone told me this statement: if you oversize your pipe, you will have expensive infrasture cost (valve/fittings) but relative low operational cost.

What do you guy understand from this statement.

Thanks!

Best regards

[pleckner]

There have been numerous articles written over the ages about optimizing pipe line sizing. Personallly, I pretty much ignore them and stick to good engineering judgement for velocity versus pressure drop.

What you are referring to is the fact that if I make the pipe size big enough, I can minmize the effects of pressure drop on the pump in terms of frictional losses so the pump won't have to work so hard. This translates into a smaller pump and motor and thus lower operating costs over the life of the pump. Smaller motor can translate into less Hp or Kw and thus lower energy costs. The key question becomes can this lower operating cost over come the total installed cost of the larger pipe? And, what is the pay back time even if it can? Too long of a pay back doesn't make much sense either.

[5.6]

Hi DTan76,

indeed many articles has been published about this. There are genral guidelines to selcect firstly the diameter of the pipe. But during optimizing the pipe system, you might need to choose diffrent diamter, also other factors like: viscosity, solids tranport, etc. Also for the first judgement you should know, if the pipe line is a long one without many armatures or relativley short and maybe with many bends and armatures. So I use always an excel sheet calculation to find out, where the real pressure loss lies, either pipe or armatures etc. As I said in the beginning, you might start with the general rule of thumb with:

<DN32 0.6... 1.5m/s
DN32..50: 1.0....2.0m/s
DN50...100: 1.2...3.0 m/s
DN100...200:1.5...4.0 m/s

As you see, small diameter change does not cost that much diffrence in installation but could make a big differecence in pressure loss; and at bigger diamter the invest from one to another diamter could have the bigger impact. So you need to be carefull all times..

cheers 5.6

[proinwv]

Also realize that you should size the valve to the application needs, not the line size. Very often, the valve size is quite adequate when less than the line size. This should ease some of your thoughts about the cost of larger piping.

Larger pipe has a lesser pressure rating for the same wall thickness. That needs to be considered also.

But as previously mentioned, you need to do an engineering analysis on the entire system.