Maximum friction losses are 5% in pipes. Who said it first?

[Hug0]

In my experience in pipeline design, it has always been said that the maximum recommended friction loss for water pipes is 5%. The recommendation is not to exceed this value. But what would be the source of this recommendation? Is it in an ASME standard or an ANSI/HI standard? There are hundreds of recommendations within the field that have no official source and are considered based on the know-how that companies already have. And does this recommendation apply only to pipelines? Or also to pipes within the process plant? It would be very helpful if a fellow engineer could indicate the source of this recommendation.

 

[Snickster]

5% of what? What kind of water pipe systems you are talking about?

 

[Hug0]

Hi Snickster, by "percentage" I mean the ratio of frictional losses (in meters of fluid column) to the length of the pipe or it would also be understood as head gradient.

 

[LittleInch]

I'm taking a WAG here that that is a plant design guide so that you don't use too small or too big and pipe, but its one I've never heard before now.

And yes, 5% of what? Pressure/head?

Pipelines often lose 100% of their start energy if pumping into atmospheric tanks or ponds

 

[IRstuff]

I would suggest that this might a rule of thumb so that you don't waste all of your pump efficiency on overcoming friction, rather than moving product. There may be ancillary benefits, such as reduced clogging from product moving too slowly due to friction.

 

[Snickster]

I think he means head loss per 100 feet of pipe like 5 ft per100 ft friction loss. That sounds about a reasonable friction loss resulting in a velocity of 7 to 10 ft/sec. I myself never used that rule of thumb but just try to maintain a velocity of 7 to 10 ft/sec.

It is my understanding that velocities in this range give the most economical pump/piping system when you look at first capital cost versus lifetime operational cost.

 

[LittleInch]

I think he means head loss per 100 feet of pipe like 5 ft per100 ft friction loss. That sounds about a reasonable friction loss resulting in a velocity of 7 to 10 ft/sec. I myself never used that rule of thumb but just try to maintain a velocity of 7 to 10 ft/sec.

It is my understanding that velocities in this range give the most economical pump/piping system when you look at first capital cost versus lifetime operational cost.

Not sure about that.

For 1km, that's 3300 ft. That would be 165 ft head loss or 50m or 5 bar if that's water. That's a HUGE frictional loss for pipeline. 1 bar/ 10m per km would be more like it for a pipeline.

I agree with the velocity range. Most long distance pipelines end up at about 1.8 to 2.2 m/sec or 6 to 8 ft/sec.

Piping is higher optimum velocity as the distances are a lot lower and cost of fittings, valves etc are a lot higher percent of the total.

 

[Snickster]

Yeah looking at the head loss tables for 6", 8" and 10" 5 ft/100 feet loss is about 10 ft/sec, 13 ft/sec and 14 ft/sec, which is kind of high. I usually just stick to close to 7 ft/sec or 9 ft/sec maximum.

 

[pierreick]

Hi,
Most Engineering companies have developed their own standards based on velocity and nature of the product flowing in the pipes.
Sometimes the results are expressed in head loss (m of Ft) per 100 (m or ft) of pipe.
The % you mentioned will be an indication not an engineering practice.
Pierre

 

[bimr]

There isn't a universally mandated rule of thumb "5%" rule for maximum friction loss

Reasonable water pipe velocities depend on the application. There is no correct velocity for all applications. Here is a general guideline.

Reasonable Velocities for the Flow of Water through Pipe:

Boiler Feed.............8 to 15 ft/sec
Pump Suction ............4 to 7 ft/sec
General Service.........4 to 10 ft/sec
City.......................to 7 ft/sec
Transmission Pipelines...3 to 5 ft/sec

Go to a basic hydraulics book. Cranes Technical Paper 410 is a reference for the above velocities.