The pipe color code calculator tells you which marking colours, legend size and flow arrows a pipe needs. Pick the fluid or hazard and the pipe outside diameter, and it returns the ASME A13.1 colour scheme and label dimensions, with BS 1710, IS 2379 and PFI ES-22 reference data, a label generator and a line-number builder.
How pipe identification colour codes work
Pipe marking exists so that operators, maintenance crews and emergency responders can identify a line’s contents and hazard at a glance. Under ASME A13.1 the colour of the label is set by the hazard of the fluid, the legend names the contents, and an arrow shows the direction of flow. The label size grows with the pipe outside diameter so it stays readable from a normal distance.
ASME A13.1 colour schemes
| Fluid hazard | Legend / background | Typical services |
|---|---|---|
| Flammable fluids | Black on yellow | Hydrocarbons, fuel gas, hydrogen, solvents |
| Combustible fluids | White on brown | Lube oil, diesel, heavy fuel oil |
| Toxic and corrosive fluids | Black on orange | Acids, caustic, ammonia, chlorine |
| Fire-quenching fluids | White on red | Fire water, foam, sprinkler lines |
| Compressed air | White on blue | Plant and instrument air |
| Other water | White on green | Cooling water, potable water, boiler feed |
| User-defined | Purple, white, grey or black combinations | Facility-specific services |
Legend and colour-field size by pipe OD
| Pipe OD incl. insulation | Letter height | Colour field length |
|---|---|---|
| 19–32 mm (¾–1¼ in) | 13 mm (½ in) | 200 mm (8 in) |
| 38–51 mm (1½–2 in) | 19 mm (¾ in) | 200 mm (8 in) |
| 64–150 mm (2½–6 in) | 32 mm (1¼ in) | 300 mm (12 in) |
| 200–250 mm (8–10 in) | 64 mm (2½ in) | 600 mm (24 in) |
| Over 250 mm (over 10 in) | 89 mm (3½ in) | 800 mm (32 in) |
Always size from the outside diameter of the insulation or cladding, not the bare pipe.
Worked example: 4-inch hydrogen line
- Hazard: hydrogen is a flammable gas, so ASME A13.1 assigns the flammable scheme – black legend on yellow.
- Size: a bare 4-inch pipe has an OD of 114.3 mm, which falls in the 64–150 mm band: 32 mm letters on a 300 mm colour field. If the line is insulated to, say, 220 mm OD, step up to 64 mm letters and a 600 mm field.
- Legend: “HYDROGEN” with a flow arrow at each end; add the line number (for example 4-H2-1001-A1) if your project requires it.
- Placement: next to valves and flanges, at branches and changes of direction, both sides of wall and floor penetrations, and along straight runs so a marker is always in view.
ASME A13.1 vs BS 1710 vs IS 2379 vs PFI ES-22
- ASME A13.1 – hazard-based labels; common in North America and on US-specified projects.
- BS 1710 – contents-based basic colour bands (green for water, silver-grey for steam, brown for oils, light blue for air) with code-indication bands; common in the UK, Middle East and Commonwealth countries.
- IS 2379 – Indian practice with ground colours and secondary bands by service.
- PFI ES-22 – fabrication-shop colour coding of pipe and fittings by material grade to prevent mix-ups; it is not an operational hazard-marking system.
The systems are not interchangeable. Adopt one marking standard per facility and record it in the project piping specification.
Assumptions and limitations
ASME A13.1 colours and sizes are implemented from the published scheme; BS 1710, IS 2379 and PFI ES-22 data are representative reference values. On-screen colours are sRGB approximations – match paint, tape or labels to a physical RAL or BS swatch named in your specification, and verify against the governing standard edition.
Related tools and guides
- Piping colour codes and identification standards – full guide
- Piping specification & component calculator
- All engineering calculators
Frequently asked questions
What is ASME A13.1?
ASME A13.1 is the American standard for the scheme for the identification of piping systems. Since the 2007 revision it assigns marking colours by the fluid hazard rather than the fluid type, using six designated colour combinations plus user-defined ones, and it sets the legend letter height and colour field length by the pipe outside diameter.
What are the ASME A13.1 pipe colours?
The six designated ASME A13.1 schemes are: flammable fluids, black legend on yellow; combustible fluids, white on brown; toxic and corrosive fluids, black on orange; fire-quenching fluids, white on red; compressed air, white on blue; and other water, white on green. Four further user-defined combinations using purple, white, grey and black are available for facility-specific services.
What colour should hydrogen piping be under ASME A13.1?
Hydrogen is a flammable gas, so under ASME A13.1 it takes the flammable scheme: a black legend on a yellow colour field, with a flow-direction arrow. The legend size follows the pipe outside diameter, and many facilities add the word FLAMMABLE and hazard details as a user-defined enhancement.
How big should a pipe label be?
ASME A13.1 sizes the marker by the pipe outside diameter including any covering. For 19 to 32 mm pipe the letters are 13 mm and the colour field 200 mm; for 64 to 150 mm the letters are 32 mm and the field 300 mm; for 200 to 250 mm the letters are 64 mm and the field 600 mm; and for pipe over 250 mm the letters are 89 mm and the field 800 mm.
Which direction should the flow arrow point?
The arrow points in the direction of normal flow and is shown at each legend location. Where flow can occur in both directions, arrows are shown pointing both ways. Arrows are placed at each end of the legend so the marker reads correctly from either approach.
What is the difference between ASME A13.1 and BS 1710?
ASME A13.1 is hazard-based: the background colour is set by the fluid hazard. BS 1710 is contents-based: it uses a basic identification colour for the pipe contents (for example green for water, silver-grey for steam, brown for oils, light blue for air) with additional code-indication colour bands. They are different systems and are not interchangeable, so a plant should adopt one standard consistently.
What is BS 1710?
BS 1710 is the British Standard for the identification of pipelines and services. It applies a basic identification colour band for the pipe contents, with code-indication colour bands placed between two basic bands to give more detail, plus safety colours for hazards. It is widely used in the UK, the Middle East and Commonwealth countries.
What is IS 2379?
IS 2379 is the Indian Standard code of practice for colour code for identification of pipelines. It defines ground colours for the main pipe contents with secondary colour bands to indicate the specific service, and is commonly specified on projects in India and South Asia.
What is PFI ES-22?
PFI ES-22 is the Pipe Fabrication Institute Engineering Standard for the recommended practice for colour coding of piping materials. It is used in fabrication shops to mark pipe and fittings by material grade during fabrication so that materials are not mixed up, which is distinct from the operational hazard marking of ASME A13.1.
How often should pipe markers be placed?
Markers should be visible from the normal points of approach. Common practice places them adjacent to valves and flanges, at branches and changes of direction, on both sides of wall, floor and ceiling penetrations, at battery limits and equipment connections, and at intervals along straight runs, typically every 8 to 15 metres so at least one marker is always in view.
What is a line number?
A line number is the unique identifier of a piping line on a P&ID and isometric. It typically combines the nominal size, a service or fluid code, a sequential number and a piping material specification, for example 6-CWS-1001-CS1. Projects define the exact format, and this tool lets you compose and validate line numbers to a chosen convention.
Are the on-screen colours exact?
The on-screen colours are sRGB approximations of the standard marking colours and are intended for design and visualisation. For procurement of labels, paint or tape, match the colour to a physical reference such as a RAL or BS colour swatch specified by your project, because screen rendering and printer output vary.
Is this pipe colour code tool free and standards-compliant?
The tool is free and works offline in the browser. The ASME A13.1 colour scheme and sizing are implemented to the published standard. BS 1710, IS 2379 and PFI ES-22 data are representative engineering values to be verified against the actual standard, and all colours are on-screen approximations. Confirm the final marking against the governing standard edition and project specification before application.
Written by Muhammad Raza
Founder of Aienginear. Engineering and digital solutions professional with 26+ years managing projects, plant shutdowns and turnarounds in oil & gas, petrochemical and power generation.
