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CO2 Steel Pipe Sizing

Three main lines — MT suction, LT suction, and liquid. Drag evaporators into position, connect one line to another, and click any line to set its length.
R744 · MT -8.0 °C · LT -32.0 °C · 26.50 kW

System Data

Evaporating temperature for each circuit and liquid receiver temperature. The liquid temperature also sets the flash-gas share, and with it the mass flow.
Useful superheat at evaporator outlet. Real vapor is less dense than saturated vapor — suction lines are sized based on the lower density.
Installed compressor capacity for comparison with connected evaporator loads. Enter compressor power for total heat rejection.
Directly controls pipe sizing — higher velocity yields smaller pipes.
Pipes that can't meet this pressure are marked ⛔ and never chosen automatically. The defaults follow common EN 378 reference values (32°C ambient) for a transcritical booster system — CO2's standstill pressure often governs more than the running temperature. Adjust for your own system.
Advanced – Margins & Pipe Material
Increases the length in the pressure-drop calculation — shows up in the Δp column in the “Main Headers”/“Evaporator Branch Connections” tables below, not in the pipe size or the cards at the top.
Adds ordering margin to the Bill of Materials and Insulation Schedule totals only (offcuts, mistakes) — a different thing from “Extra length for fittings” above, and does not affect the pipe size or Δp.
Low-temperature steel for CO2 — plain carbon steel (P235/P265GH) is not impact-tough at LT temperatures. Impact tested to −40 °C (EN 10216-4); below that, check EN 13480-2 Annex B or use stainless steel. Heavy wall and high pressure rating. Needs external corrosion protection.
What pressure each size can take: see the table at the bottom ↓
Pipes smaller than this threshold will never be selected automatically.
Select insulation specification (thickness/color) per header for the material bill.

Evaporators

Name Circuit kW
A pipe stub contains only ONE line (liquid, MT, or LT). An MT/LT stub can be converted to an evaporator by assigning a kW load.
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Project

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Options · Units

Changes how values are shown and entered — all calculations still run in the background as before.

Flow Diagram

MT Suction Liquid LT Suction Tapped off another pipe
100% 100%
Drag an evaporator freely to position it. Click any pipe segment to set its length or manually override size.
Click here, then on a pipe run, to place a power meter.
— m Size:
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Bill of Materials

Lengths include the waste allowance above, but not the fitting length allowance (which only affects Δp).

Insulation Schedule

Insulation types are selected under 'Advanced' in System Data.

Evaporator Branch Connections

"Own Load" is the evaporator's own kW value. "Load in Pipe" is the accumulated flow through that specific pipe — larger if other evaporators/pipes are tapped onto it. Never sum the "Load in Pipe" columns for a grand total; use "Own Load" instead.

Main Headers

Show calculation

Calculation per pipe

PipeMass flow [kg/s]Density [kg/m³]Inner diameter [mm]Velocity [m/s]RefLength (+ allowance) [m]Δp [kPa]Δp per metre [Pa/m]Pipe type, PS
#1 DN15 · Liquid: Refrigeration unit → Cold Room 10.1043972.416.10.52771,7000.02786 (+1.8)1.82233P265NL · PS 60 bar
#2 DN15 · Liquid: Cold Room 1 → Freezer 10.07272972.416.10.36750,0000.02856 (+1.8)0.906116P265NL · PS 60 bar
#3 DN15 · Liquid: Freezer 1 → Cold Room 20.05316972.416.10.26936,6000.02936 (+1.8)0.49863.9P265NL · PS 60 bar
#4 DN15 · Liquid: Cold Room 2 → Freezer 20.02948972.416.10.14920,3000.03156 (+1.8)0.16421.1P265NL · PS 60 bar
#5 DN15 · Liquid: Freezer 2 → MT Display Case0.01579972.416.10.079710,9000.03486 (+1.8)0.05226.69P265NL · PS 60 bar
#6 DN15 · MT Suction: Refrigeration unit → Cold Room 10.0710370.2616.14.97406,0000.02616 (+1.8)111,410P265NL · PS 52 bar
#7 DN15 · MT Suction: Cold Room 1 → Cold Room 20.0394670.2616.12.76226,0000.02656 (+1.8)3.43439P265NL · PS 52 bar
#8 DN15 · MT Suction: Cold Room 2 → MT Display Case0.0157970.2616.11.190,3000.02746 (+1.8)0.56872.8P265NL · PS 52 bar
#9 DN15 · LT Suction: Refrigeration unit → Freezer 10.0332632.816.14.98216,0000.02656 (+1.8)5.22669P265NL · PS 30 bar
#10 DN15 · LT Suction: Freezer 1 → Freezer 20.0136932.816.12.0588,8000.02746 (+1.8)0.917118P265NL · PS 30 bar
#11 DN15 · Line to Cold Room 1 · Liquid0.03157972.416.10.15921,7000.03125 (+1.5)0.15623.9P265NL · PS 60 bar
#12 DN15 · Line to Cold Room 1 · MT Suction0.0315770.2616.12.21181,0000.02665 (+1.5)1.84283P265NL · PS 52 bar
#13 DN15 · Line to Cold Room 2 · Liquid0.02368972.416.10.1216,3000.03255 (+1.5)0.091314P265NL · PS 60 bar
#14 DN15 · Line to Cold Room 2 · MT Suction0.0236870.2616.11.66135,0000.02695 (+1.5)1.05161P265NL · PS 52 bar
#15 DN15 · Line to MT Display Case · Liquid0.01579972.416.10.079710,9000.03485 (+1.5)0.04356.69P265NL · PS 60 bar
#16 DN15 · Line to MT Display Case · MT Suction0.0157970.2616.11.190,3000.02745 (+1.5)0.47372.8P265NL · PS 52 bar
#17 DN15 · Line to Freezer 1 · Liquid0.01956972.416.10.098813,5000.03355 (+1.5)0.06439.89P265NL · PS 60 bar
#18 DN15 · Line to Freezer 1 · LT Suction0.0195632.816.12.93127,0000.0275 (+1.5)1.53236P265NL · PS 30 bar
#19 DN15 · Line to Freezer 2 · Liquid0.01369972.416.10.06929,4200.03585 (+1.5)0.03365.17P265NL · PS 60 bar
#20 DN15 · Line to Freezer 2 · LT Suction0.0136932.816.12.0588,8000.02745 (+1.5)0.764118P265NL · PS 30 bar

Basis of the calculation

Method
Each pipe is sized for the smallest size that keeps the velocity at or below the target and is rated for its PS; the pressure drop is calculated with Darcy–Weisbach.
Equations
  • ṁ = Q / (h″(t₀) − h′(t_liq))
  • v = ṁ / (ρ · π·d²/4)
  • Re = ρ·v·d / μ
  • f = 0.25 / [log₁₀(ε/(3.7·d) + 5.74/Re^0.9)]² (Re ≥ 2300); f = 64/Re (Re < 2300)
  • Δp = f · (L/d) · ρ·v²/2, L = length × (1 + allowance %)
Friction factor
Swamee–Jain (explicit form of Colebrook–White)
Fluid data
CoolProp, Span–Wagner EOS (R744) 8.0.0
Standards
EN 378-2 (PS) · EN 10220 (outside diameters) · EN 13480-3 (p = 2·f·z·e / (D − e)) · EN 10216-4 (P265NL, f = 170 MPa) · EN 10216-5 / EN 10217-7 (1.4404, f = Rp1.0/1.5 = 150 MPa)
Notes
  • Mass flow from the cooling capacity and the enthalpy difference between saturated vapour at the evaporating temperature and liquid at the liquid temperature; suction lines with the given superheat.
  • Static height differences and the pressure drop of valves and fittings beyond the allowance are not included.

Pressure rating per size

Allowable pressure (bar) for every size and pipe type, with wall thickness. Green is enough for all three stems' design pressure (MT suction 52, LT suction 30, liquid 60 bar). Amber is enough only for the stems named in the cell. Red ⛔ is enough for none of them. – means the pipe type is not made in that size.
SizeP265NL – carbon steel, seamless (EN 10216-4)
selected pipe type		316L (1.4404) – stainless, seamless (EN 10216-5) 316L (1.4404) – stainless, welded thin-wall (EN 10217-7)
DN10 17.2 mm451 bar
2.30 mm		340 bar
2.00 mm		233 bar
1.60 mm
DN15 21.3 mm407 bar
2.60 mm		269 bar
2.00 mm		185 bar
1.60 mm
DN20 26.9 mm314 bar
2.60 mm		243 bar
2.30 mm		144 bar
1.60 mm
DN25 33.7 mm308 bar
3.20 mm		217 bar
2.60 mm		144 bar
2.00 mm
DN32 42.4 mm273 bar
3.60 mm		170 bar
2.60 mm		113 bar
2.00 mm
DN40 48.3 mm237 bar
3.60 mm		148 bar
2.60 mm		99 bar
2.00 mm
DN50 60.3 mm204 bar
3.90 mm		132 bar
2.90 mm		79 bar
2.00 mm
DN65 76.1 mm207 bar
5.00 mm		104 bar
2.90 mm		62 bar
2.00 mm
DN80 88.9 mm198 bar
5.60 mm		98 bar
3.20 mm		53 bar MT, LT
2.00 mm
DN100 114.3 mm172 bar
6.30 mm		85 bar
3.60 mm		41 bar LT
2.00 mm
DN125 139.7 mm140 bar
6.30 mm		77 bar
4.00 mm		33 bar LT
2.00 mm
DN150 168.3 mm130 bar
7.10 mm		72 bar
4.50 mm		36 bar LT
2.60 mm
DN200 219.1 mm112 bar
8.00 mm		77 bar
6.30 mm		28 bar ⛔
2.60 mm
DN250 273.0 mm99 bar
8.80 mm		62 bar
6.30 mm		26 bar ⛔
3.00 mm
DN300 323.9 mm94 bar
10.00 mm		59 bar MT, LT
7.10 mm		21 bar ⛔
3.00 mm

P265NL – carbon steel, seamless (EN 10216-4): Low-temperature steel for CO2 — plain carbon steel (P235/P265GH) is not impact-tough at LT temperatures. Impact tested to −40 °C (EN 10216-4); below that, check EN 13480-2 Annex B or use stainless steel. Heavy wall and high pressure rating. Needs external corrosion protection.

316L (1.4404) – stainless, seamless (EN 10216-5): Acid-resistant stainless steel with a medium wall. No external corrosion protection needed and tough at low temperatures.

316L (1.4404) – stainless, welded thin-wall (EN 10217-7): Light thin-wall pipe, rated with a weld joint factor of 0.85. Only the smaller sizes handle CO2's pressure — see the ⛔ mark against your design pressure.

Source and method: EN 13480-3, p = 2·f·z·e / (D − e), where e is the minimum wall (nominal less the tolerance: −12.5 % seamless, −10 % welded), f the allowable stress (P265NL 170 MPa, 1.4404 150 MPa, Rp1.0/1.5 on the safe side) and z the weld joint factor (0.85 for welded). The walls are common stock sizes – check with your supplier before ordering.

Other countries

The pressure ratings above follow European practice (EN 378, EN 13480-3). In other markets refrigerant piping is designed and approved to these codes instead. This calculator has not been checked against them – use the code that applies where the system is installed.

USA

  • ASME B31.5 – Refrigeration Piping and Heat Transfer Components: pipe design, design pressure and test pressure
  • ANSI/ASHRAE Standard 15 – Safety Standard for Refrigeration Systems: safety requirements for refrigerating systems

Canada

  • CSA B52:23 – Mechanical refrigeration code: refrigeration code; refers to ASME B31.5 for piping

Australia and New Zealand

  • AS/NZS 5149 – Refrigerating systems and heat pumps — Safety and environmental requirements: safety requirements for refrigerating systems
  • AS 4041 – Pressure piping: pipe design, design pressure and test pressure

CO2 steel piping – frequently asked questions

How do you size steel pipe for CO2 (R744)?

Each line is sized from its mass flow and the allowed velocity: MT suction, LT suction and liquid. The calculator works out the mass flow from cooling capacity, evaporating temperature and superheat, picks the smallest DN size that meets the target velocity and shows the pressure drop section by section.

Calculate in the tool above ↑CO2 (R744) pipe sizing – copper →

What is the pressure rating of the steel pipes?

The allowable pressure is calculated to EN 13480-3 (p = 2·f·z·e / (D − e)) using the minimum wall after the mill tolerance: −12.5 % for seamless and −10 % for welded pipe. The calculator shows the pressure rating of every size and warns with ⛔ when a pipe cannot take the design pressure you entered.

Calculate in the tool above ↑

P265NL or 316L stainless steel – which should I use?

P265NL (EN 10216-4) is a seamless carbon steel, impact tested for low temperatures, and the usual choice for CO2 plants; plain P235GH/P265GH is not intended for LT temperatures. Stainless 1.4404 (316L) comes seamless (EN 10216-5) and longitudinally welded (EN 10217-7). It needs no painting, but welded pipe has a thinner wall and a lower pressure rating. P265NL is impact tested to −40 °C (EN 10216-4); below that, check EN 13480-2 Annex B or use stainless steel.

Calculate in the tool above ↑

Which pipe sizes does the calculator cover?

DN10 to DN300 with outside diameters to EN 10220, from 17.2 to 323.9 mm. The wall thickness follows the selected pipe type, and the bill of materials gives the order designation, for example "DN25 · 33.7 × 3.2". Check the wall thickness with your supplier before ordering.

Calculate in the tool above ↑

When should I use steel instead of copper?

K65 copper tube is available up to 2-1/8″ (54 mm). Larger lines, industrial CO2 refrigeration and parts with a high design pressure are therefore usually built in steel. For smaller systems there is the copper calculator, and a project file opens in both with the drawing kept.

Calculate in the tool above ↑CO2 (R744) pipe sizing – copper →

Assumptions: Saturated liquid line, subcritical CO2 (R744) between −50 and +10 °C. Pipe sizes are DN with outside diameters to EN 10220; wall thicknesses are common stock sizes. Pressure ratings are calculated to EN 13480-3 using the minimum wall thickness. Verify wall thickness, material and design pressure against EN 378/PED and the supplier's data before installation. Mass flow is based on the net refrigerating effect, h_g at the evaporating temperature minus h_f at the liquid temperature, so flash gas from expansion is included. Superheat enthalpy and pump overfeed are not counted.

Disclaimer: This tool does not guarantee correct results. Always verify pipe wall thickness, pressure rating, and other values manually before installation.

Help – how to use the calculator

The calculator sizes the pipes in a CO2 (R744) refrigeration system: MT suction, LT suction and liquid. Enter the system data, build the plant in the flow diagram, and read off pipe sizes, pressure drops and the bill of materials. The load of each evaporator determines the flow in every pipe run, and pipes are chosen so that the velocity does not exceed the target velocity.

1. System data

  • Enter the evaporating temperature for MT and LT, the liquid line temperature, and the superheat for MT and LT (superheat affects the sizing of the suction lines).
  • Set a separate target velocity for MT suction, LT suction and liquid. A higher target velocity gives smaller pipes; a lower one gives larger pipes and lower pressure drop.
  • The installed rack capacity and compressor power are optional. They are used to compare with the evaporator loads and to show the total heat rejection.
  • Under “Advanced – Margins & Pipe Material”: extra length for fittings (affects only the pressure drop, not the pipe size), pipe type, minimum allowed pipe size, and insulation per header (used in the bill of materials).
  • Pipe type and design pressure together decide which sizes are allowed — ⛔ in the tables means that size doesn't meet the pressure you entered.
  • Tick “Line to gas cooler” to also size the discharge line to the gas cooler: enter the high pressure, discharge temperature, gas cooler outlet temperature, target velocity and PS of the high-pressure side. The line is drawn above the refrigeration unit.

2. Evaporators and pipe stubs

  • Add an evaporator with “+ Add Evaporator” and enter its name, circuit (MT/LT) and load. Use ▲ ▼ to change the order and × to remove a row.
  • A pipe stub is a single line (liquid, MT or LT) that other evaporators can be tapped onto. Give an MT/LT stub a load if it should become an evaporator.

3. The flow diagram

  • Drag an evaporator to move it. Click its name to rename it and its load value to change it. Click [MT]/[LT] to switch circuit (only possible when the evaporator's suction line connects directly to the header).
  • Click a pipe to set its length, lock the length or choose the pipe size manually. A ✎ in the tables shows that the size was chosen manually.
  • In the same box you can choose the pipe type for that line alone, e.g. 316L stainless for small pipes and P265NL for the rest. Each size shows its rating (bar) in that pipe type, and ⛔ means it cannot take the stem's design pressure (PS).
  • Right-click a pipe to add an evaporator or a pipe stub at that spot.
  • The round handle at an evaporator's pipe can be dragged and dropped onto another evaporator's pipe of the same kind to tap into it, or onto empty space to connect straight to the header. The small squares are dragged along the evaporator's edge to change where the pipe enters it.
  • Select an evaporator or pipe and press Delete to remove it. Undo with “Undo” or Ctrl/Cmd+Z.

4. Navigating the drawing

  • Drag the background to pan. Zoom with the buttons, with Ctrl/Cmd + mouse wheel, or by pinching on a trackpad. A− and A+ change the text size in the drawing.
  • “Print Drawing” prints the flow diagram together with a summary.
  • Tick “Force 90° Bends” to route every pipe in clean right angles; untick it to connect and drag pipes freely, however you like.
  • Tick “Force Parallel Lines” so that pipes running directly from a stem connect in line with the evaporator's connection and become one straight line with no bend. The tap point on the stem then follows along when you move the evaporator or its connection.

5. Power meter

  • Click “Add Power Meter” and then a pipe. The meter shows how many kW flow on each side of the point.
  • Drag the dot to measure at another place, drag the box to move the readout, and click × to remove the meter.

6. Reading the results

  • The cards at the top show total cooling load, total mass flow and the pipe size of the three main headers.
  • The tables list, for each evaporator and pipe run, the load, chosen pipe size, velocity and pressure drop (Δp). The program picks the smallest pipe size that stays within the target velocity.
  • ⚠ means the flow needs a larger pipe than the largest size in the table. 🚩 means two pipes or evaporators have the same name.
  • The bill of materials and the insulation list add up pipe lengths per size, without the fitting allowance. Use them as a basis when ordering.

7. Saving and opening

  • “Save” and “Save As…” store the whole plant as a file, and “Open Project” loads it again.
  • In Chrome and Edge, “Save” and autosave write to the file you chose with Save as or Open. Other browsers download a new file with “Save”, and autosave keeps the project in the browser instead.

8. Units

  • Under “Options · Units” you choose the unit for temperature, superheat, pressure, velocity, length, power and mass flow separately. This only changes how values are shown and entered, not the calculations.
Disclaimer: This tool does not guarantee correct results. Always verify pipe wall thickness, pressure rating, and other values manually before installation.