Maximum speed for sea water and hydraulic fluid in pipes

[raton]

Hi All.
I have a question regarding the maximum speed in pipes for sea water and hydraulic fluids.

I have a technical specification for a marine system and it is stated the following values for speed.

Nominal Service Velocity: 2 m/s
Maximum Service Velocity: 4 m/s
Exceptional Service Velocity: 8 m/s

Do you know any standard of engineering practice related to these velocities?
Are these values correct for sea water and hydraulic systems?

Thank you very much

Jaime

 

[moon161]

Noise, turbulence, cavitation, water hammer will probably figure into an appropriate solution.

 

[zdas04]

Individual companies have their own standards. The standards are usually different for gases and liquids, but sometimes the company standards are written by people without a clue.

One number that I see pretty often is a max allowable velocity of 100 ft/s divided by the square root of density. For water this works out to a maximum velocity of 3.9 m/s. The first standard that I saw this in had an explanation that faster than that markedly increased erosion risk. I can't make those numbers work, but maybe I just haven't seen all the data. Based on that arithmetic, your velocity numbers work fine

At the end of the day someone will have to apply engineering judgement. I don't think that this issue is addressed in any industry standards or government regulations so it comes down to company documents or engineering judgement. I don't think there is going to be a lot of help here.

David

 

[hydromech]

Do these velocities relate to inlet speeds?

If so then they are governed by the pump and it's ability to fill and the diameter of the bore. Bernoulli's law dictates that the pressure will drop as the velocity increases. With the addition of the negative pressures induced by the pump, the fluid may reach its vapour point.

In other words, there are no standards.

The same goes for the pressure lines, there is no problem with going faster than the velocities specified. The penalty will be turbulent flow which will drag the systems efficiencies down. The fluid will not reach its vapour point because of the high pressure in the pump outlet line.

Many modern hydraulic systems run with linear velocities well in excess of 15 mtrs/sec. As long as there is enough power in hand to compensate for the pressure loss there will be no problem.

It's all application specific.

Hydromech

 

[MikeHalloran]

Hydraulic systems are sometimes used in acoustically quiet environments, where flow noise associated with velocity above ~15 ft/sec is undesirable.

Mike Halloran
Pembroke Pines, FL, USA

 

[zeusfaber]

Those figures are certainly familar for seawater systems.

I've seen significant erosion problems in HPSW piping running continuously at 10 m/s.

A

 

[SJones]

For the seawater velocities: British Standard MA 18 or UK Defence Standard 02-719

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04