In the process industry, chemical industry, manufacturing industry, and other commercial and industrial contexts, pipe marking is used to identify the contents, properties and flow direction of fluids in piping. It is typically carried out by marking piping through labels and color codes. Pipe marking helps personnel and fire response teams identify the correct pipes for operational, maintenance or emergency response purposes.

Pipes are used extensively in commercial and industrial buildings and on industrial plant (e.g. oil refineries) to transfer fluids between items of plant and equipment.^[1] Positive identification assists operations personnel to correctly identify plant when carrying out routine or maintenance activities, and for emergency personnel when responding to emergencies. Pipe marking is particularly important for identification where pipes run along pipe racks, through walls and bulkheads and through floors.^[2]

A range of corporate, national and international codes, standards and regulations are in use around the world.

In the United States, Occupational Safety and Health Administration regulations recommend following American Society of Mechanical Engineers Standard A13.1-2015 - Scheme for the Identification of Piping Systems.^[3]

The standard states that labels should be placed where easily viewed by a person standing near the pipe at any of the following points:^[4]

A13.1-1996 ^[4]

Meaning	Background Color	Text Color	Example
Hazardous materials[a]	Safety Yellow	Black	Acetylene
Non-hazardous liquids	Safety Green	White	Stormwater
Non-hazardous gases	Safety Blue	White	Nitrogen
Firefighting materials	Safety Red	White	Sprinkler Water

A13.1-2007/2015^[4]

Meaning	Background Color	Text Color	Example
Flammables[b] & Oxidizers[c]	Safety Yellow	Black	Acetylene
Combustible Fluids[d]	Safety Brown	White	Lubricating Oil
Toxic and Corrosives	Safety Orange	White	Ammonia
Water	Safety Green	White	Stormwater
Compressed air/Non-hazardous gases	Safety Blue	White	Compressed Air
Firefighting materials	Safety Red	White	Sprinkler Water
Custom - Defined by user	Safety Purple	White	Fluid Name
Custom - Defined by user	Safety Grey	White	Fluid Name
Custom - Defined by user	White	Black	Fluid Name
Custom - Defined by user	Black	White	Fluid Name

2015 revisions added oxidizing materials to the existing 'Flammables' classification. The other major change allowed and encouraged labels to incorporate the GHS signal word, hazard pictograms, and hazard statements. This addition helped identify additional dangers when dealing with materials that fit into multiple categories, like hydrogen sulfide, which is both flammable and toxic.^[4]

In 2014, the International Institute of Ammonia Refrigeration introduced a specialized label design for use when marking pipes associated with refrigeration systems using ammonia, including information such as the physical state, pressure and purpose in the system.^[6]

The National Fire Protection Association have a special labeling system in the standard for Health Care Facilities, such as hospitals and dentistry offices. This standard puts more emphasis on gases found in Medical gas supply systems, which consist of both oxidizing gases and gases that displace oxygen.^[7]

Gas	Background Color	Text Color
Carbon Dioxide	Gray	Black or White
Helium	Brown	White
Medical Air	Yellow	Black
Oxygen	Green	White[e]
Oxygen/Carbon Mixtures	Green	White
Nitrogen	Black	White
Nitrous Oxide	Blue	White
Waste Anesthetic Gas Disposal	Purple	White
Medical Surgical Vacuum	White	Black
Non-Medical Air	Yellow/White Diagonal Striped	Black
Non-medical and Level 3 Vacuum	Black/White Diagonal Striped	Black (In box)
Laboratory Air	Yellow/White Checkerboard	Black
Laboratory Vacuum	Black/White Checkerboard	Black (In box)
Instrument Air	Red	White

In the United Kingdom there are three principal regulations that mandate the marking of equipment and piping:

• Classification, Labelling and Packaging of Chemicals (Amendments to Secondary Legislation) Regulations 2015,^[8]
• Health and Safety (Safety Signs and Signals) Regulations 1996,^[9]
• Provision and Use of Work Equipment Regulations 1998,^[1]

The regulations require that vessels containing hazardous substances together with the pipes containing or transporting such substances must be labelled or marked with the relevant hazard pictograms or pipe marking. The labels used on pipes must be positioned visibly in the vicinity of the most hazardous points, such as valves and joints; at both sides of bulkheads and floor penetrations; and at reasonable intervals.

The regulations do not specify a specific marking system, but BS EN ISO 1710 Graphical symbols — Safety colours and safety signs is often used.

A widely used British Standard (BS) for marking equipment is:

• BS 1710:2019 Graphical symbols — Safety colours and safety signs — Registered safety signs

The Standard stipulates the colours to be used. These are as follows:^[2]

BS 1710 Basic identification colours for pipes

Contents	Colour	BS 4800 colour[10]
Water	Green	12 D 45
Steam	Silver-grey	10 A 03
Oils	Brown	06 C 39
Gases	Yellow Ochre	08 C 35
Acids and Alkalis	Violet	22 C 37
Air	Light Blue	20 E 51
Other liquids	Black	00 E 53
Electrical & Ventilation	Orange	06 E 51

In addition to the basic colours, certain safety colours are used:

BS 1710 Safety colours for pipes

Safety service	Colour	BS 4800 colour[10]
Fire fighting	Red	04 E 53
Warning	Yellow	08 E 51
Fresh water	Auxiliary Blue	18 E 53
User defined	User defined

The arrangement of markings is for the safety colour to be between bands of the basic colour.^[2]

Firewater service would be:

The pipe contents must be identified adjacent to the banding.^[2] This can be done by giving either:

• The full name
• Abbreviation
• Chemical symbol
• Refrigerant number
• Coloured bands (user specified)

The direction of flow should also be identified near the banding.^[2]

Examples using this system are as shown.

The Indian Standard IS 2379 provides for a ground colour and a coloured band on piping to identify material.^[11]

IS 2379 ground colours^[11]

Substance	Ground colour
Water	Sea green
Steam	Aluminium
Oils and combustible liquid	Light brown
Acids	Dark violet
Air	Sky blue
Gases	Canary yellow
Alkalise	Smoke grey
Other gases and liquids	Black
Hydrocarbons/organic compounds	Dark aluminium grey

Colour bands of 25 mm to 100 mm width are placed at locations such as battery limits, intersections, near valves, at walls, starting and terminating points. There is a large range of bands which define the contents of the line. For example, for oils.

IS 2379 Oil colours^[11]

Substance	Ground colour	Band colour
Light diesel	Light brown	Brilliant green
High speed diesel	Light brown	None
Paraffin oil	Light brown	Signal red
Quenching oil	Light brown	Canary yellow
Furnace fuel	Light brown	French blue
Lubricating oil	Light brown	Light grey
Hydraulic power	Light brown	Dark violet
Transformer oil	Light brown	Light orange

Pipes, ducts and conduits are identification by the Australian Standard AS 1345—1995 “Identification of the contents of pipes, conduits and ducts”^[12]

Australian Standard AS 1345^[12]

Service	AS 2700 Colour
Water	G21 Jade
Steam	N24 Silver Grey
Oils, flammable liquids	X53 Golden Tan
Gases	Y44 Sand
Acids & alkalis	P23 Lilac
Air	B25 Aqua
Other Liquids	N61 Black
Fire Services	R13 Signal Red
Electric Power	X15 Orange
Communication	N14 White
Dangerous Materials	Y14 Golden Yellow + N61 Black

Ships and marine facilities must conform to an international standard for piping systems identification. This is ISO 14726:2008 Ships and marine technology — Identification colours for the content of piping systems.^[13]

This is a two-colour banded marking system. The main colour shows what the fluid is being used for. This is on either side of the secondary colour which indicates what the substance actually is. The main colours are as follows:^[13]

•   Black - Waste media
•   Blue - Fresh water
•   Brown - Fuel
•   Green – Sea water
•   Grey - Non-flammable gases
•   Maroon - Air and sounding pipes
•   Orange - Oils other than fuels
•   Silver - Steam
•   Red - Fire fighting
•   Violet - Acids, alkalis
•   White - Air in ventilation systems
•   Yellow - Flammable gases

International Standard ISO 20560-1:2020 Safety information for the content of piping systems and tanks — Part 1: Piping systems was intended to replace the variety of regulations and standards across countries and regions. Basic identification colours and warning symbols identify the pipe contents and any hazards.^[14]

Pipe markers consists of 4 basic elements:

• Basic identification (background) colour, see table below, e.g. yellow for hazardous substance
• Name of the substance/content, e.g. NATURAL GAS
• Flow direction indicator arrows, ⇒
• Warning symbols, e.g. GHS symbol

Colours and substances are typically as follows:^[14]

ISO 20560-1:2020 Colours and substances

Substance	Background colour		Text colour
Hazardous substances		Yellow		Black
Gas (liquid or gaseous)		Grey		White
Liquids & solids (powder/granulate)		Black		White
Acids		Orange		Black
Alkalis		Violet		White
Fire fighting medium		Red		White
Water		Green		White
Air		Blue		White

International Standard ISO 20560-2 Safety information for the content of piping systems and tanks — Part 2: Tanks, provides a similar colour scheme for tanks.

RAL colour standard charts are used by architects, construction industry and road safety.^[15]

The pipe identification colours are as shown in the table.

Pipe Identification Colours^[15]

Type	Reference	RAL Colour Code	Colour
Steam	2114	9006	White aluminium
Air	2123	5012	Light blue
Water	2138	6010	Grass green
Gas	2149	1004	Golden yellow
Acid	2163	4001	Red lilac
Liquid Spirits	2173	8001	Ochre brown
Other Liquids	2179	9005	Jet black

• Piping
• American National Standards Institute
• American Society of Mechanical Engineers