# Flow in a Pipe

Guys...need a little help
Given
Internal fluid Pressure P (Not Pressure Drop)
flow rate Q
Length
Assume all the required parameters like viscosity, fluid density, temperature of the fluid, surface roughness and all losses (both major and minor) etc...
I need to find the internal diameter of the Pipe.
Is there any formula to find that?

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JBA
Gold Member
The pressure in a pipe can be the same regardless of the diameter of the pipe. It is the strength of the pipe material and the wall thickness that determine how much pressure can be contained within a given pipe diameter.
What determines the size of a pipe for a given flow rate Q is the flowing pressure drop that will provide the required pipe outlet pressure for the for a given pipe inlet pressure.

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Thanks guys...but think of it like this

I need to carry a fluid which is at Pressure P and flowing at a flow rate Q,
What is the internal diameter of pipe I should use?

jack action
Gold Member
It is all based on recommended flow velocity.

Quick references:
More general:
And the referred guideline in the previous link that should cover any of your need:

It is all based on recommended flow velocity.

Quick references:
More general:
And the referred guideline in the previous link that should cover any of your need:
Could you please tell me how did they find those velocity ranges for various Pressures in pipes?

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jack action
Gold Member
If you read carefully the last link, you'll see it depends on the fluid in use and it seems based on experience more than anything. For example:

For liquid lines:
• For lines transporting liquids in single phase from one pressure vessel to another by pressure differential, the flow velocity should not exceed 15 feet/second at maximum flow rates, to minimize flashing of the control valve.
• If practical, flow velocity should not be less than 3 feet/second to minimize deposition of sand and other solids. (If you don't have solids in your fluid, this is not a concern)
For pumps:
• Velocity in discharge piping should not exceed three times the velocity in the suction piping. This velocity will normally result in an economical line size for all pumps, and will minimize pulsations in reciprocating pumps.
For gas/liquid lines:
• Erosional Velocity. Flowlines, production manifolds, process headers and other lines transporting gas and liquid in two-phase flow should be sized primarily on the basis of flow velocity. Experience has shown that loss of wall thickness occurs by a process of erosion/corrosion. This process is accelerated by high fluid velocities, presence of sand, corrosive contaminants such as C02 and H2S, and fittings which disturb the flow path such as elbows. The following procedure for establishing an "erosional velocity" can be used where no specific information as to the erosive/corrosive properties of the fluid is available. The velocity above which erosion may occur can be determined by the following empirical equation: ##V_e = \frac{c}{\sqrt{\rho_m}}## where ##V_e## = fluid erosional velocity (feet/second), ##c## = empirical constant, ##\rho_m## = gas/liquid mixture density at flowing pressure and temperature ( lbs/fts). Industry experience to date indicates that for solids-free fluids values of ##c## = 100 for continuous service and ##c## = 125 for intermittent service are conservative. For solids-free fluids where corrosion is not anticipated or when corrosion is controlled by inhibition or by employing corrosion resistant alloys, values of ##c## = 150 to 200 may be used for continuous service; values up to 250 have been used successfully for intermittent service. If solids production is anticipated, fluid velocities should be significantly reduced, Different values of "##c##" may be used where specific application studies have shown them to be appropriate. (You can appreciate here how experimental data is of importance. The fluid composition, pressure and temperature (i.e. density) will all affect the optimum fluid velocity.)
• Minimum Velocity. If possible, the minimum velocity in two-phase lines should be about 10 feet per second to minimize slugging of separation equipment. This is particularly important in long lines with elevation changes.
Other considerations:
• The fundamental approach to noise control in piping systems should be to avoid or minimize the generation of harmful noise levels. Methods that may be effective in avoiding such levels in piping systems include: (i) Minimize fluid velocities. The noise levels generated by the recommended velocities in Section 2 should be acceptable.
In the first link, which talks about hydraulic systems and where values agree with most other following links, it says:
• A tube that is too small causes high fluid velocity, which has many detrimental effects. In suction lines, it causes cavitation which starves and damages pumps. In pressure lines, it causes high friction losses and turbulence, both resulting in high pressure drops and heat generation. High heat accelerates wear in moving parts and rapid aging of seals and hoses, all resulting in reduced component life. High heat generation also means wasted energy, and hence, low efficiency.
So you won't find a «one fit all» theoretical equation to estimate fluid velocity. They are just too many variables to consider.

If you read carefully the last link, you'll see it depends on the fluid in use and it seems based on experience more than anything. For example:

For liquid lines:
• For lines transporting liquids in single phase from one pressure vessel to another by pressure differential, the flow velocity should not exceed 15 feet/second at maximum flow rates, to minimize flashing of the control valve.
• If practical, flow velocity should not be less than 3 feet/second to minimize deposition of sand and other solids. (If you don't have solids in your fluid, this is not a concern)
For pumps:
• Velocity in discharge piping should not exceed three times the velocity in the suction piping. This velocity will normally result in an economical line size for all pumps, and will minimize pulsations in reciprocating pumps.
For gas/liquid lines:
• Erosional Velocity. Flowlines, production manifolds, process headers and other lines transporting gas and liquid in two-phase flow should be sized primarily on the basis of flow velocity. Experience has shown that loss of wall thickness occurs by a process of erosion/corrosion. This process is accelerated by high fluid velocities, presence of sand, corrosive contaminants such as C02 and H2S, and fittings which disturb the flow path such as elbows. The following procedure for establishing an "erosional velocity" can be used where no specific information as to the erosive/corrosive properties of the fluid is available. The velocity above which erosion may occur can be determined by the following empirical equation: ##V_e = \frac{c}{\sqrt{\rho_m}}## where ##V_e## = fluid erosional velocity (feet/second), ##c## = empirical constant, ##\rho_m## = gas/liquid mixture density at flowing pressure and temperature ( lbs/fts). Industry experience to date indicates that for solids-free fluids values of ##c## = 100 for continuous service and ##c## = 125 for intermittent service are conservative. For solids-free fluids where corrosion is not anticipated or when corrosion is controlled by inhibition or by employing corrosion resistant alloys, values of ##c## = 150 to 200 may be used for continuous service; values up to 250 have been used successfully for intermittent service. If solids production is anticipated, fluid velocities should be significantly reduced, Different values of "##c##" may be used where specific application studies have shown them to be appropriate. (You can appreciate here how experimental data is of importance. The fluid composition, pressure and temperature (i.e. density) will all affect the optimum fluid velocity.)
• Minimum Velocity. If possible, the minimum velocity in two-phase lines should be about 10 feet per second to minimize slugging of separation equipment. This is particularly important in long lines with elevation changes.
Other considerations:
• The fundamental approach to noise control in piping systems should be to avoid or minimize the generation of harmful noise levels. Methods that may be effective in avoiding such levels in piping systems include: (i) Minimize fluid velocities. The noise levels generated by the recommended velocities in Section 2 should be acceptable.
In the first link, which talks about hydraulic systems and where values agree with most other following links, it says:
• A tube that is too small causes high fluid velocity, which has many detrimental effects. In suction lines, it causes cavitation which starves and damages pumps. In pressure lines, it causes high friction losses and turbulence, both resulting in high pressure drops and heat generation. High heat accelerates wear in moving parts and rapid aging of seals and hoses, all resulting in reduced component life. High heat generation also means wasted energy, and hence, low efficiency.
So you won't find a «one fit all» theoretical equation to estimate fluid velocity. They are just too many variables to consider.
Thank You so much..