Line Sizing — Companion Article
Line sizing picks a pipe diameter from a flow and a velocity. It tells you how fast the fluid is moving, which common size is the first one at or below a velocity you set, or how much flow a chosen size can carry at that velocity.
It does not choose the wall thickness, the schedule, or the pipe class. Those decide whether the pipe can hold the pressure and what material and fittings belong on the line. A fast line can still be too thin, and a thick line can still be too small for the flow. Use Wall Thickness for the pressure calculation, and Pipe by Wall Thickness when you already have a wall and want the matching size and schedule. The line number and the pipe class are a naming and specification choice. The article Introduction to Line Numbering is the place for that.
1. What this tool does
The page reports one of three results, depending on the mode you pick:
- the mean velocity in one pipe
- the first listed size whose velocity is at or below a limit you set
- the maximum flow through one pipe at that limit
An advisory panel, Typical velocity ranges, can fill the velocity limit from a service. The panel is labelled advisory guidance, not a code requirement. The number stays editable.
An optional future-flow margin adds a percent to the flow before the velocity and the minimum size are calculated.
2. When to use it
Use it when you have a volumetric flow, or a velocity you do not want to exceed, and you need a diameter check before you freeze the line size on the line list.
Use Wall Thickness when the question is pressure and corrosion allowance. Use Pipe Volume when the question is how much the line holds. Use the unit converter when the only job is to change m3/h into US gpm, or m/s into ft/s.
3. Inputs
- Choose a mode.
- Flow to velocity. One size and a flow. The result is the mean velocity.
- Flow and velocity limit to minimum size. A flow and a limit. The result is a list of sizes. The first size at or below the limit is highlighted. If a smaller size has no inside diameter, the page does not declare a minimum.
- Size and velocity limit to maximum flow. One size and a limit. The result is the largest flow that stays at that velocity.
- Choose a schedule, and a nominal size when the mode uses one pipe.
- Read the outside diameter. Change it if the pipe in front of you is different. If the record has no wall and no inside diameter, type a wall thickness or a bore. If you type both, the bore is used. Inside diameter is outside diameter minus twice the wall, unless you typed the bore itself.
- In the minimum-size mode, one wall thickness can apply to every candidate that has no stored wall or inside diameter. A bore or wall typed on a row replaces that for the row.
- Enter the flow in m3/h, L/s, or US gpm.
- Enter the velocity limit in m/s or ft/s, or choose a service in Typical velocity ranges and then edit the number if you need to.
- Optional. Enter a future-flow design margin in percent. Blank means the flow you typed is the flow that is used.
- Optional. Enter density and dynamic viscosity if you want Reynolds number, the flow regime, and the erosional velocity. Optional pressure drop per 100 m uses a roughness that starts at 0.045 mm. You can change it.
4. How it works
The running page is the calculation. The relation is the ordinary one between area and velocity.
Mean velocity = volumetric flow / internal area
Internal area = π × (inside diameter)² / 4
So flow = area × velocity. A larger bore gives a lower velocity for the same flow. The page converts the units you pick. The factors are the usual exact ones: 1 in = 0.0254 m, 1 ft = 0.3048 m, and 1 US gallon = 0.003785411784 m3.
A future-flow margin of N percent uses a design flow of the entered flow × (1 + N/100). Velocity and the minimum-size list use that design flow. The maximum flow of a chosen size is still the velocity limit times the area. With a margin, the page also shows the smaller flow that leaves that margin spare.
Reynolds number is density × velocity × inside diameter / dynamic viscosity. Below 2300 the page calls the regime laminar, from 2300 to 4000 transitional, and above 4000 turbulent. Those are the usual Moody-diagram bands. They are not a code limit.
The erosional velocity on the page is C divided by the square root of density, with density in lb/ft3 and the result in ft/s. C starts at 100. Confirm C for the fluid and the edition you use.
Optional pressure drop uses the Darcy–Weisbach equation over 100 m. The friction factor is the Swamee–Jain approximation, and only inside the range stated on the page.
5. Understanding the result
Read the sentence for the mode you chose.
In the minimum-size mode, the highlighted row is the first listed size at or below the velocity limit. A smaller size with no inside diameter blocks that claim. Type a wall or a bore for that size before you treat a larger size as the minimum.
A result that uses a wall or a bore you typed is marked that way. It is the bore you entered.
If you set a future-flow margin, the velocity at the entered flow is still shown, and a second velocity is shown at the design flow. The minimum-size list uses the design flow.
The velocity limit, including a number filled by a service choice, is a ceiling you set. The page will say whether the result is at or below it. That comparison is not a code check.
6. Engineering considerations
Typical velocity ranges
The panel is advisory guidance, not a code requirement. Choosing a service writes a number into the velocity limit. You can type over it.
The figures below are the ones the page fills. They come from Crane Technical Paper No. 410 (2010 reprint), Appendix A, page A-10, and from NORSOK P-001 Edition 5 (September 2006), sections 6.2 and 6.3. Where those publications do not set the same ceiling, the page fills the lower one and the note on the panel says so.
| Service | What the page fills | What the publications say |
|---|---|---|
| Pump suction | 2.13 m/s (7 ft/s) | Crane: 4 to 7 ft/s for pump suction and drain lines. NORSOK: suction is sized on net positive suction head, with a carbon-steel liquid ceiling of 6 m/s and tighter pressure-drop guides for subcooled and boiling liquid. The ceilings are not the same. |
| Pump discharge | 3.05 m/s (10 ft/s) | Crane does not list discharge on its own. General-service water is 4 to 10 ft/s. NORSOK allows up to 6 m/s on carbon-steel discharge, with a pressure-drop guide up to 0.9 bar per 100 m. 10 ft/s sits inside that higher ceiling. |
| Cooling water | 3.05 m/s (10 ft/s) | Crane general-service water is 4 to 10 ft/s. NORSOK caps untreated seawater in carbon steel at 3 m/s and deoxygenated seawater in carbon steel at 6 m/s. |
| General process liquid | 3.05 m/s (10 ft/s) | Crane general service is 4 to 10 ft/s. NORSOK lists 6 m/s as the carbon-steel maximum for liquids. The page uses the lower ceiling. |
| Corrosive or slurry | 4 m/s (13.12 ft/s) | NORSOK lists 5 m/s for carbon steel carrying sand, 4 m/s for large amounts of mud or silt, and 10 m/s for corrosive carbon-steel multiphase flow. Crane page A-10 has no slurry row. The page fills 4 m/s, the lowest of those figures. |
| Saturated steam | 30.48 m/s (100 ft/s) | Crane page A-10: 4,000 to 6,000 ft/min for saturated steam on short heating lines at 0 to 25 psig, and 6,000 to 10,000 ft/min at 25 psig and up. The page fills 6,000 ft/min. Raise it toward 50.8 m/s only for the higher-pressure band. |
| Superheated steam | 101.6 m/s (333.33 ft/s) | Crane page A-10: 7,000 to 20,000 ft/min at 200 psig and up, on boiler and turbine leads. The page fills the top of that band because the field is a ceiling. Pressure drop often keeps the line slower. |
| Process gas | 60 m/s (196.85 ft/s) | NORSOK: where pressure drop is not critical, stay below 175 / (density to the power 0.43), or below 60 m/s, whichever is lower. Density is in kg/m3. The page fills the 60 m/s ceiling. Denser gas needs a lower number. |
| Compressor suction | 60 m/s (196.85 ft/s) | NORSOK treats compressor suction as pressure-drop critical, and still applies the gas ceiling above. 60 m/s is the noise ceiling. It is usually too high for a suction line. Lower it. |
Checks before you accept a size
- The velocity used the inside diameter. An outside diameter is larger, so a velocity based on it is too low and the pipe you pick is too small.
- The flow includes the later increase you already know about. The margin box is there for that percent. Blank means you sized the flow you typed and no more.
- A pump suction line is on the tighter band. The pump suction choice fills 7 ft/s. A discharge limit on a suction line is a common way to lose net positive suction head.
- The unit on the flow matches the unit you were given, and the unit on the velocity limit matches the band you meant. 3 m/s and 3 ft/s are different limits. The Unit Converter will change one into the other if you want to see both.
- Wet gas, and steam that still carries water, can erode a bend while the average velocity still looks comfortable. Use the erosional check on the page, with a density and a coefficient you have confirmed, and do not treat a dry-gas ceiling as a wet-gas ceiling.
7. Example
Both examples use bores you would type. The page does not look them up. They are schedule 40 inside diameters: NPS 3 is 3.068 in, NPS 4 is 4.026 in, and NPS 6 is 6.065 in. Section 8 says how to treat those figures. The velocities below are the arithmetic the page uses, shown to four significant figures, which is how the page prints a result.
Cooling-water line
Flow 80 m3/h. Velocity limit 3.05 m/s, the number the cooling water choice fills (10 ft/s on the Crane general-service band). No future-flow margin yet.
NPS 3, bore 3.068 in, mean velocity 4.659 m/s (15.29 ft/s). That is above 3.05 m/s.
The next larger common size is NPS 4, bore 4.026 in, mean velocity 2.706 m/s (8.877 ft/s). That is at or below 3.05 m/s, so the minimum-size list highlights NPS 4.
The maximum flow of that NPS 4 at 3.05 m/s is 90.18 m3/h.
With a future-flow margin of 20%, the design flow is 96 m3/h. NPS 4 then runs at 3.247 m/s, which is above 3.05 m/s. NPS 6, bore 6.065 in, runs at 1.431 m/s and is the size the list highlights.
Saturated steam line
Flow 600 m3/h. Velocity limit 30.48 m/s, the saturated-steam choice (6,000 ft/min).
NPS 3, bore 3.068 in, mean velocity 34.94 m/s (114.6 ft/s). That is above 30.48 m/s.
NPS 4, bore 4.026 in, mean velocity 20.29 m/s (66.58 ft/s). That is within the limit, so the list highlights NPS 4.
The maximum flow of that NPS 4 at 30.48 m/s is 901.2 m3/h.
600 m3/h is a volume, not a mass. If the process data are in kg/h, convert with the specific volume at the steam pressure before you type the flow. This steam check uses the low-pressure Crane band. Steam above 25 psig has a higher reasonable band on that same page, up to 50.8 m/s. Raise the limit only when that band is the one you mean, and still check pressure drop.
8. Standards/references (licensed vs interim)
The velocity panel cites two publications. It does not copy their tables, and it does not turn them into a code requirement.
Crane Co., Flow of Fluids Through Valves, Fittings, and Pipe, Technical Paper No. 410, 2010 reprint, Appendix A, page A-10. The water bands and the steam bands on the panel are taken from that page. This is published design guidance. It is not licensed Crane text stored on the page.
NORSOK P-001, Edition 5, September 2006, sections 6.2 and 6.3. The liquid ceilings, the gas formula, and the compressor-suction pressure-drop guide on the panel are taken from that edition. Published design guidance. Not a copy of the standard.
Where Crane and NORSOK do not set the same ceiling, the panel states both and fills the lower one.
The bores in section 7 are schedule 40 inside diameters for those nominal sizes. Interim data for ASME B36.10, not licensed ASME text. Verify against the current edition of ASME B36.10 before use. The line-sizing page does not store that table. You type the bore.
The erosional relation and the Swamee–Jain friction factor are named on the page. C and the roughness are values you enter.
9. Limitations/disclaimer
- A service choice is a starting number. It is not an acceptance test, and it is not a substitute for the pump curve, the compressor data, or the project line-sizing rules.
- Compressor suction filled at 60 m/s is a noise ceiling. Lower it to the pressure drop you can spend.
- The gas formula needs a density. 60 m/s is only the cap.
- Superheated steam filled at 101.6 m/s is the top of a wide band. Pressure drop often governs first.
- Density, viscosity, roughness, and the erosional coefficient are what you type. The page does not store a fluid table.
- Pressure drop is not calculated outside the friction-factor range stated on the page.
- A typed wall or bore is your figure. Confirm it against the pipe you will buy.
- This page does not calculate wall thickness, schedule, pipe class, or a line number.
The result is a sizing check. It still needs a review by the person responsible for the line.
10. Use the tool
Calculate now: Line Sizing
Related tools
- Wall Thickness for the pressure thickness.
- Pipe by Wall Thickness when you have a wall and want the size and schedule.
- Pipe Volume & Weight Calculator for what the line holds.
- Unit Converter for m3/h, US gpm, m/s, and ft/s.
- Introduction to Line Numbering for the line number and the pipe class on the line list.