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Pipe Size Selection and Several Criteria of Pipe Size

Someone in my office asked me if there is a criteria for pipe size selection, in other words, pipe sizing criteria. One basic document that every process engineer produce in the beginning of engineering stage is process design basisIn the document, pipe size criteria shall be stated clearly.

I have involved in at least two engineering projects. Those two projects have different pipe size criteria. Which one is correct?

I personally don’t know which one is true. And if this true, does it make the other one wrong? I don’t know.

One of my client ever told me that in his previous company, they used pipe size criteria based on good paper. Their senior and expert staffs evaluated some papers and gave justification that these papers can be used as references. In the end, it actually lowered piping cost.

I don’t know if this post will help you. But my intention to write this post is to present several sources of pipe size criteria. Hope you find something relevant.

When we size pipe, we look into two criteria: flow velocity and pressure drop. I usually consider these two criteria, but in some case I just consider one criteria. I will divide pipe size criteria based on fluid state: liquid and gas.

Pipe Size Criteria for Single Phase Liquid Lines

I have collected several sources of pipe size criteria for liquid lines. Hope you find this useful.

#1 Pipe size criteria based on ISO 13703 

I got this standard for free from this link. The keys of pipe size criteria based on this ISO 13703 are:

  • Single phase liquid lines shall be sized base on flow velocity primarily
  • If transportation from one vessel to another vessel is conducted by differential pressure, maximum velocity should not exceed 5 m/s at maximum flow rate
  • Flow velocity should not be less than 1 m/s to minimize sand deposition
  • Table below can be used as preliminary criteria for sizing suction and discharge of pump
Typical pipe size criteria based on ISO 13703
Typical pipe size criteria based on ISO 13703

#2 Pipe size criteria based on API 14E

Pipe size criteria based on API 14E is the same as that ISO 13703. Except they used imperial unit instead of SI unit.

#3 Pipe size criteria based on Norsok Standard

I got Norsok standard for free from this link. The keys of pipe size criteria based on this Norsok standard are:

  • Velocities shall be low enough to prevent problems

#4 Pipe size criteria based on BS MA-18

British Standard Marine Series 18 (BSMA-18) provides specification for salt water piping systems in ship. The standard stated maximum velocities of seawater pipeline as a function of pipe bore. For pipe with  bore equal to and more than 100 mm, maximum velocity are (for continuous flow basis):

  • 5 m/s for cast iron
  • 4 m/s for CuNi 70/30
  • 3.5 m/s for CuNi 90/10
  • 3 m/s for steel galvanize
Maximum velocities of seawater for continuous flow
Maximum velocities of seawater for continuous flow (source: BS MA 18)

Pipe Size Criteria for Single Phase Gas Line

#1 Pipe size criteria based on ISO 13703

  • Gas line should be sized so that resulting end pressure is high enough to satisfy the requirement of next piece of equipment
  • Excessive noise may result from restriction such as control valve, orifice, etc, from velocities higher than 25 m/s. However this value should not be used as absolute criteria

#2 Pipe size criteria based on API 14E

The point of pipe size criteria gas single phase gas line in API 14E is the same as ISO 13703. However the velocity limitation is 60 ft/s.

#3 Pipe size criteria based on Norsok Standard

In line where pressure drop is not  limitation, gas velocity shall not exceed limits which may create noise or vibration problems. As a rule of thumb velocity should be kept low:

Sizing gas line based on Norsok Standard
Sizing gas line based on Norsok Standard

Reference:

  1. ISO 13703 petroleum and natural gas industries – design and installation of piping systems on offshore production platforms
  2. Norsok standard – process design

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