Pipe Color Codes: ASME A13.1, ISO 14726 & BS 1710

Quick Reference

Pipe color coding identifies pipe contents for safety. Key specs: ASME A13.1 (USA), PFI ES-22 (by material grade), ISO 14726 (international), BS 1710 (UK). Colors: Yellow=oxidizing, Brown=flammable, Red=fire protection, Blue=compressed air, Green=potable water, Orange=toxic/corrosive, White/Gray=user-defined (steam).

Why pipe color coding matters: Correct pipe identification prevents injuries, chemical exposures, and fatalities. Emergency responders, maintenance crews, and operators rely on visual pipe markings to identify contents instantly, without consulting drawings. OSHA recognizes ASME A13.1 as the consensus standard for pipe marking in the United States.

ASME A13.1 pipe color coding reference

ASME A13.1: The US Standard for Pipe Identification

The ANSI/ASME A13.1 standard, titled Scheme for the Identification of Piping Systems, defines the pipe color coding and labeling requirements used throughout industrial facilities in North America. Originally published in 1928 and last revised in 2020, this standard establishes how to identify pipe contents and functions using color-coded labels with text and flow direction arrows.

ASME A13.1 classifies piped substances into hazard-based categories, each assigned a specific color combination. This approach differs from European and international standards that assign colors based on the specific substance rather than the hazard category.

According to the ASME A13.1 specification, fluids are classified into:

• Flammable: fluids and vapors that may ignite and burn in the air
• Oxidizing: gases or liquids that may contribute to the combustion of other materials when combined with oxygen
• Toxic and corrosive: media that are corrosive or toxic to personnel
• Fire-quenching: water, foam, and CO2 used in sprinkler systems and firefighting systems
• Compressed air: non-hazardous pressurized gases
• Combustible: substances that can burn but are not classified as flammable (higher flash point)

ASME A13.1 Color Code Chart

The background color indicates the general hazard category of the fluid or gas within the pipe. The label text color provides contrast for legibility.

Category	Background Color	Text Color	Pantone Ref.	Examples
Flammable fluids	Brown	White	4515	Natural gas, diesel, crude oil, LPG, gasoline
Oxidizing fluids	Yellow	Black	109	Oxygen, hydrogen peroxide, ozone
Toxic/corrosive fluids	Orange	Black	151	H2S, sulfuric acid, caustic soda, ammonia, chlorine
Fire suppression	Red	White	186	Fire water, deluge systems, sprinkler, foam, CO2
Compressed air	Blue	White	540	Instrument air, plant air, nitrogen
Non-hazardous water	Green	White	335	Potable water, cooling water, condensate
User-defined	Per facility	Per facility	Per facility	Steam, specialty chemicals, custom services

Pantone References

ASME A13.1 specifies Pantone color numbers (not RAL codes) for consistent color matching across label manufacturers and paint suppliers. Always reference the Pantone number when ordering labels to avoid color mismatches between different areas of a facility.

ASME A13.1 pipe color marking

Label Sizing Requirements

ASME A13.1 specifies minimum letter height and label length based on the pipe outside diameter (including insulation). Labels that are too small to read defeat the purpose of the marking system.

Pipe OD Range	Min. Letter Height	Min. Label Length	Min. Arrow Size
3/4” to 1-1/4” (19-32 mm)	1/2” (13 mm)	8” (200 mm)	3” (75 mm)
1-1/2” to 2” (38-50 mm)	3/4” (19 mm)	8” (200 mm)	4” (100 mm)
2-1/2” to 6” (65-150 mm)	1-1/4” (32 mm)	12” (300 mm)	6” (150 mm)
8” to 10” (200-250 mm)	2-1/2” (64 mm)	24” (600 mm)	8” (200 mm)
Over 10” (over 250 mm)	3-1/2” (89 mm)	32” (800 mm)	12” (300 mm)

Insulated Pipes

For insulated pipes, measure the outside diameter of the insulation jacket, not the bare pipe. A 6-inch pipe with 3 inches of insulation has an effective OD of 12 inches and requires the larger label size.

Label Placement Rules and Flow Direction Arrows

Proper placement is as important as correct color selection. A label on a pipe is useless if workers cannot see it from their normal working position.

Where to Place Pipe Labels

ASME A13.1 requires labels at the following locations:

• At all valves (on both sides if accessible from two directions)
• At branch connections and tees, on each branch leg near the junction
• On both sides of wall, floor, and ceiling penetrations, so the pipe is identified in each room or area
• At direction changes such as elbows, bends, and offsets
• Near equipment connections including pumps, heat exchangers, vessels, and tanks
• On straight runs at intervals not exceeding 25 feet (7.6 m)

Flow Direction Arrows

Flow direction arrows are a mandatory element of every pipe label under ASME A13.1. The arrow indicates the direction of normal flow or the direction of pressure source in static systems.

Situation	Arrow Requirement
Single-direction flow	One arrow pointing in the direction of flow
Bidirectional flow (e.g., utility headers)	Two arrows pointing in opposite directions
Dead-end or static lines	Arrow pointing toward the pressure source
Vertical risers/drops	Arrow pointing up or down, visible from the access level

Vertical Pipes

On vertical pipe runs, place labels so that they are readable from the floor or platform level where personnel work. Use wrap-around labels that repeat the text and arrow on multiple sides of the pipe, or position the label on the side facing the approach direction.

Identification at Valves, Walls, and Floor Penetrations

Pipes passing through walls or floors are particularly critical marking points. Workers on one side of a wall have no visibility of where the pipe goes or what it carries on the other side. ASME A13.1 requires labels on both sides of every penetration.

At valves, the label should be placed near (but not on) the valve body, positioned so it remains visible whether the valve is open or closed. For valve stations with multiple valves in a manifold, each pipe entering and leaving the manifold must be individually labeled.

EN 13480: European Pipe Color Coding

The European Standard EN 13480 (Metallic Industrial Piping) addresses pipe color coding in European countries. While similar to ASME standards in principle, EN 13480 incorporates the content-based identification approach that is common in European practice.

Color	Contents / Category
Yellow	Flammable fluids or gases
Red	Fire protection systems
Blue	Compressed air
Green	Potable water
Brown	Combustible fluids
White	Steam
Gray	Non-potable water
Orange	Toxic or corrosive fluids

ISO 14726: International Pipe Color Coding

ISO 14726 (Pipelines: Identification of pipelines and associated services) is the International Organization for Standardization’s standard for pipe identification. It provides a globally recognized framework for color-coding pipelines in industrial and commercial applications. ISO 14726 uses a content-based identification system, assigning colors to specific substances rather than hazard categories.

Key Features of ISO 14726

Feature	Description
Color Bands	Specifies color bands or stripes on pipes to indicate the specific type of fluid or gas carried. Each color represents a particular substance category: water, steam, compressed air, hazardous chemicals, oils, or fire protection.
Base and Identification Colors	Defines a base color for the general fluid group and an identification color for the specific substance. For example, all water services share a green base, with secondary bands differentiating potable from cooling water.
Text and Labels	Recommends text or labels alongside color bands for additional information about pipe contents, operating conditions, or safety precautions.
Size and Placement	Includes guidelines for the size, placement, and spacing of pipe markings so they remain visible and legible under various lighting and environmental conditions.
Compliance and Maintenance	Covers ongoing maintenance and inspection of pipe markings to keep them visible, intact, and compliant with regulatory requirements.

ISO 14726 Color Assignments

Color	Substance
Green	Water (all types)
Silver-gray	Steam
Light blue	Air and compressed gases (non-flammable)
Yellow	Flammable gases
Brown	Flammable liquids (oils, fuels)
Violet	Acids and alkalis
Red	Fire protection
Orange	Toxic and harmful substances

Although ISO 14726 provides international guidance, regional standards and regulations may also apply. Always confirm which standards govern your project location before implementing pipe markings.

BS 1710: British Standard for Pipe Identification

BS 1710 (Specification for identification of pipelines and services) is the British Standard widely used in the United Kingdom, Ireland, and many Commonwealth countries. Like ISO 14726, BS 1710 uses a content-based identification system.

BS 1710 Color Scheme

Color (BS 4800 Ref.)	Substance
Green (12-D-45)	Water
Silver-gray (10-A-03)	Steam
Light blue (20-E-51)	Air
Yellow ochre (08-C-35)	Flammable gas
Brown (06-C-37)	Oils and combustible liquids
Violet (22-C-37)	Acids and alkalis
Red (04-E-53)	Fire protection
Orange (06-E-51)	Electrical services and conduits
Black	Drainage and waste
Cream (10-C-31)	Non-combustible gases (nitrogen, CO2)

BS 1710 Key Differences from ASME A13.1

Feature	ASME A13.1	BS 1710
Classification approach	Hazard-based categories	Content-based assignments
Steam	User-defined (commonly gray)	Silver-gray (dedicated)
Acids/chemicals	All grouped under orange (toxic/corrosive)	Violet for acids and alkalis specifically
Natural gas	Brown (flammable category)	Yellow ochre
Color reference system	Pantone	BS 4800
Number of standard colors	6 + user-defined	10+ content-specific

Standards Comparison: ASME A13.1 vs ISO 14726 vs BS 1710

The following table compares how the three major pipe color standards identify common industrial pipe services. This is essential knowledge for engineers working on international EPC projects.

Pipe Service	ASME A13.1 (USA)	ISO 14726 (International)	BS 1710 (UK)
Fire water	Red	Red	Red
Potable water	Green	Green	Green
Cooling water	Green	Green (with secondary band)	Green (with secondary band)
Compressed air	Blue	Light blue	Light blue
Instrument air	Blue	Light blue	Light blue
Steam	User-defined (gray)	Silver-gray	Silver-gray
Natural gas	Brown	Yellow	Yellow ochre
Crude oil	Brown	Brown	Brown
Diesel fuel	Brown	Brown	Brown
Sulfuric acid	Orange	Violet	Violet
Caustic soda (NaOH)	Orange	Violet	Violet
Ammonia	Orange	Orange	Yellow (as toxic gas)
Oxygen	Yellow	Light blue (with “O2” label)	Light blue (with “O2” label)
Nitrogen	Blue	Light blue	Light blue
Hydrogen	Brown	Yellow	Yellow ochre

Standards Comparison

When working on international projects, be aware that ASME A13.1 (USA), EN 13480 (EU), ISO 14726 (international), and BS 1710 (UK) share similar color conventions for major categories (red=fire protection, green=potable water, blue=compressed air) but differ significantly for steam, chemicals, and hydrocarbons. Always confirm which standard applies to your specific project location and jurisdiction.

PFI ES-22: Color Coding by Material Grade

PFI ES-22 stands for the “Pipe Fabrication Institute Engineering Standard No. 22.” This standard is published by the Pipe Fabrication Institute (PFI), an organization focused on pipe fabrication and installation quality in industrial construction.

PFI ES-22 addresses “Color Coding Recommendations for Process Piping.” Unlike ASME A13.1, which identifies pipe contents, PFI ES-22 identifies the pipe material grade using color bands painted on the pipe end or body. This is used in fabrication shops, laydown yards, and during construction to prevent material mix-ups.

Note that, in addition to the colors specified in the table, welded pipes shall show an additional white stripe.

PFI Standard ES-22: Pipe Color Coding Recommendations

Carbon Steel Pipes

Material	Material Grade	Band / Strip Color
Carbon Steel, Electric Resistance Welded Pipe	A53 Gr. B/API	1 solid white
Carbon Steel, Smls, specified tensile strength under 70,000 psi (483 MPA)	A53 Gr. B	No Marking
Carbon Steel killed steel	A106 Gr. B	1 solid green
Carbon Steel, specified tensile strength 70,000 psi (483 MPA) and over	A106 Gr. C	2 solid green
Carbon Steel, low temperature (impact tested)	A333 Gr. 6	1 solid red

High Yield Carbon Steel Pipes

Material	Material Grade	Band / Strip Color
52,000 min. yield	API 5L X-52	1 solid yellow, 1 solid green
60,000 min. yield	API 5L X-60	1 solid yellow, 1 solid pink
65,000 min. yield	API 5L X-65	2 solid yellow
70,000 min. yield	API 5L X-70	1 solid yellow, 1 solid orange

Low Alloy Pipes

Material	Material Grade	Band / Strip Color
C-Mo steel	A335 Gr. P1	1 solid orange
1 Cr-1/2 Mo Steel	A335 Gr. P12	1 solid orange, 1 solid blue
1 1/4 Cr-1/2 Mo Steel	A335 Gr. P11	1 solid yellow
2 1/4 Cr-1 Mo Steel	A335 Gr. P22	1 solid blue
5 Cr-1/2 Mo Steel	A335 Gr. P5	1 solid blue, 1 solid yellow
9 Cr-1/2 Mo Steel	A335 Gr. P9	2 solid orange

Ferritic and Martensitic Pipes and Tubes

Material	Material Grade	Band / Strip Color
Type 405	A268 TP405	1 solid green, 1 solid black
Type 410	A268 TP410	1 solid green, 1 solid red

Austenitic Stainless Steel Pipes

Material	Material Grade	Band / Strip Color
Type 304	A312 TP304	1 solid black
Type 304L	A312 TP304L	2 solid black
Type 304H	A312 TP304H	1 intermittent black
Type 309	A358 Gr309	1 solid black, 1 solid brown
Type 310	A358 Gr310	1 solid green, 1 solid orange
Type 316	A312 TP316	1 solid gray
Type 316L	A312 TP316L	2 solid gray
Type 316H	A312 TP316H	1 intermittent gray
Type 317	A312 TP317	1 solid brown, 1 solid green
Type 317L	A312 TP317L	1 solid brown, 1 solid red
Type 321	A312 TP321	1 solid pink
Type 321H	A312 TP321H	2 solid pink
Type 347	A312 TP347	1 solid brown
Type 347H	A312 TP347H	2 solid brown

Nickel-Alloy Pipes

Material	Material Grade	Band / Strip Color
Nickel 200	—	1 solid black, 1 solid pink
Incoloy 800	—	1 solid black, 1 solid orange
Incoloy 800H	—	1 solid gray, 1 solid red
Incoloy 825	—	1 solid gray, 1 solid blue
Inconel 600	—	2 solid blue
Inconel 625	—	1 solid blue, 1 solid pink
Hastelloy Alloy 8-2	—	1 solid red, 1 solid orange
Hastelloy Alloy C-276	—	1 solid red, 1 solid blue
Hastelloy Alloy C-22	—	2 solid red
Hastelloy Alloy G	—	1 solid red, 1 solid yellow
Carpenter Alloy 20 C 8-3	—	1 solid black, 1 solid blue
Monel 400	—	1 solid black, 1 solid yellow

Practical Implementation Guide

Implementing a pipe color coding system across a facility requires planning, coordination, and sustained maintenance. The following steps outline a practical approach for new facilities and retrofits.

Step 1: Select the Applicable Standard

The standard depends on the project location, owner requirements, and local regulations:

Location / Context	Primary Standard	Notes
United States	ASME A13.1	OSHA-recognized consensus standard
United Kingdom	BS 1710	Widely adopted; may be supplemented by owner specs
European Union	ISO 14726 or EN 13480	Country-specific codes may also apply
Middle East (EPC)	ASME A13.1 or project-specific	Many operators specify ASME A13.1
International projects	ISO 14726	Used as a neutral baseline when standards conflict

Step 2: Develop a Pipe Marking Specification

Create a project-specific document that defines:

1. The color code for every service in the facility (referencing the applicable standard)
2. Label format: text content, font, size, and arrow style
3. Placement rules: spacing, locations, and orientation
4. Label materials: vinyl, snap-around, stenciled paint, or metal tags
5. Responsibility for initial application and ongoing maintenance
6. User-defined colors for services not covered by the standard (e.g., steam under ASME A13.1)

Step 3: Label Materials and Durability

Environment	Recommended Label Type	Expected Life
Indoor, ambient temperature	Self-adhesive vinyl or polyester	3-5 years
Outdoor pipe racks	UV-resistant laminated polyester	7-10 years
High vibration or thermal cycling	Snap-around or coiled markers	5-10 years
Offshore or corrosive atmosphere	Stainless steel tags (SS 316)	20+ years
Insulated pipes (steam, hot oil)	Applied on insulation jacket surface	Match insulation maintenance cycle

Step 4: Verification and Maintenance

Pipe marking is not a one-time activity. Labels degrade from UV exposure, chemical splash, abrasion, and temperature cycling. Include pipe marking verification in:

• Annual facility safety inspections
• Management of Change (MOC) procedures, since any piping modification must trigger label review
• Pre-startup safety reviews (PSSRs) for new or modified piping
• Turnaround and shutdown planning checklists

Common Mistakes in Pipe Marking

Even facilities with well-intentioned marking programs make recurring errors. The following list covers the most frequent issues found during audits and inspections.

Common Mistakes to Avoid

1. Relying on color alone without text labels. Approximately 8% of males have some form of color vision deficiency. Color bands without text labels leave these individuals unable to identify pipe contents. Always include written identification.

2. Not updating labels after process changes. A “POTABLE WATER” label on a pipe that was re-routed to carry process chemicals creates a life-threatening hazard. Include pipe marking in every MOC review.

3. Labels placed where they cannot be seen. Labels on top of high pipe racks, behind equipment, or facing a wall serve no purpose. Position labels to be visible from the normal approach direction and at eye level where possible.

4. Using the wrong standard for the jurisdiction. A plant in the UK using ASME A13.1 colors, or a US plant using BS 1710 colors, creates confusion for local emergency responders who are trained on their regional standard.

5. Inconsistent label sizing. Mixing label sizes or using undersized labels on large-diameter pipes reduces legibility. Follow the minimum sizing table strictly.

6. Forgetting flow direction arrows. The arrow is not optional under ASME A13.1. Without it, a maintenance technician cannot determine which valve to close upstream in an emergency.

7. Labeling only at pipe ends. Long straight runs without intermediate labels leave workers guessing about contents mid-span. Maintain the 25-foot (7.6 m) maximum spacing.

8. Missing labels at penetrations. Wall and floor penetrations are the most commonly overlooked marking points. Workers on the other side of a wall have no way to identify the pipe without labels.

Facility-Specific and Industry Standards

Some industries or facilities maintain their own color coding standards based on internal policies, safety regulations, or industry practices. These may differ from ASME/ISO/BS standards but serve the same purpose: accurate identification of pipe contents and functions.

Examples include:

• Semiconductor manufacturing: specialized gas delivery systems use proprietary color codes for ultra-high-purity gases
• Pharmaceutical plants: GMP requirements may dictate additional markings for clean-in-place (CIP) and sterilize-in-place (SIP) lines
• Nuclear facilities: NRC regulations require specific identification for safety-related, non-safety-related, and seismic-qualified piping
• Food and beverage: 3-A Sanitary Standards may supplement ASME A13.1 with requirements for product contact vs. non-contact lines

Always check the applicable standards, regulations, and facility-specific guidelines before implementing pipe color coding.

Pro Tip

Color code pipes at regular intervals and at every change of direction, valve, or penetration, not just at the ends. In an emergency, operators need to identify pipe contents quickly from any location. ASME A13.1 recommends labels every 25 feet on straight runs and at both sides of walls and floors.

Existing Facilities

When taking over operations of an existing facility, verify the pipe color coding against actual contents before any maintenance work. Facilities where color codes were never updated after process changes present a serious safety risk. Trust but verify, especially on older installations.

Frequently Asked Questions

What color is used for flammable pipes under ASME A13.1?

Under ASME A13.1, flammable fluids and gases (such as natural gas, diesel, and crude oil) are identified with white text on a brown background (Pantone 4515). Oxidizing fluids use white text on a yellow background (Pantone 109). The label must include the specific fluid name and a flow direction arrow. Do not rely on the background color alone; always include written identification of the exact substance.

What is the difference between ASME A13.1, ISO 14726, and BS 1710?

ASME A13.1 (USA) classifies pipes by hazard category (flammable, toxic, fire suppression, etc.) using 6 standard colors plus user-defined. ISO 14726 (international) and BS 1710 (UK) assign colors based on specific pipe contents (water, steam, acids, oils) and use 10 or more content-specific colors. Fire water (red), potable water (green), and compressed air (blue) are consistent across all three standards. However, steam, chemicals, and hydrocarbons are assigned different colors depending on the standard. Always verify which standard applies to your project.

How often should pipe labels be placed?

ASME A13.1 requires pipe labels at intervals not exceeding 25 feet (7.6 m) on straight runs, plus at every valve, branch connection, direction change, and on both sides of wall, floor, and ceiling penetrations. Labels must be visible from the normal approach direction and include the fluid name and flow direction arrow. BS 1710 and ISO 14726 have similar placement requirements, typically specifying 6-8 meter intervals.

Does ASME A13.1 assign a color for steam pipes?

No. ASME A13.1 does not assign a dedicated color for steam piping; it falls under the user-defined category. Most North American facilities adopt gray or silver as the background color for steam. By contrast, BS 1710 and ISO 14726 specifically assign silver-gray to steam, and DIN 2403 (Germany) uses red, which can conflict with fire water markings in other systems. Always check the project-specific pipe marking specification for steam color assignments.

Is pipe color coding required by OSHA?

OSHA does not mandate a specific pipe color standard, but it requires employers to identify pipe contents under 29 CFR 1910.261 and the general duty clause (Section 5(a)(1)). ASME A13.1 is the recognized consensus standard for compliance in the United States. Failure to identify pipe contents can result in OSHA citations and fines. Many facility owners and insurance underwriters require ASME A13.1 compliance as part of their safety management system and process safety management (PSM) programs.