Few points on Colour Coding and Marking Criteria of Piping System

Most of you have seen in operating process plants that pipes are coloured in various colour. There are two main reasons behind it:

  • To allow the metallurgy of each spool to be easily identified in the warehouse before erection
  • Process and utility piping can be properly and clearly identified for use by plant personnel

So colour coding will help in identifying the Piping components shipped individually to the jobsite and Material identification shall not be required for pipe spools that have been verified by the shop and have mark piece numbers associated with them.

Permanent colour pipe service markers shall be used for process and utility services. Fabricator shall provide service markers for spools produced. Placing the marker on the spool shall be done after piping has been installed, coated, or insulated if required.

Colour Coding and Marking of Systems:

Material Colour Coding:

  • Material colour coding is developed to differentiate between various grades or specifications of materials.
  • Colour markings are assigned on the basis of nominal chemical compositions.
  • Location of marking shall be as follows:
  1. Pipe shall be marked with, for example, paint, dye, or tapes for its full length
  2. Flanges shall be banded (Refer Fig. 1) on the back of the flange at the intersection of the back face and the hub
  3. Fittings shall be stripped from bevel to bevel
  4. Miscellaneous material shall be colour marked so as to provide proper identity
  5. The paint shall not cover welded surfaces, heat marks, or any other identification
Figure showing Colour Band Locations
Fig. 1: Figure showing Colour Band Locations

Pipe Service Markers:

  • Permanent colour pipe service markers shall be used for all process and utility piping systems within the plant.
  • Piping systems shall include utility pipes of any kind and, in addition, fittings, valves, and pipe coverings. Piping systems shall be painted a neutral background colour, for example aluminium or grey, which shall not detract from the high visibility of the colours and lettering of the service markers.
  • Permanent colour markers for piping systems shall be placed at the battery limit and at vertical risers at utility stations. Service markers shall be applied close to valves or flanges, and adjacent to changes in direction, branches, and where pipes pass over or through walls, floors, fences, or roads, and on straight pipe runs, sufficient for identification.
  • A service marker in English shall be used as the primary and explicit means of identification for the contents of all aboveground piping. Positive identification of the contents of a piping system shall be by lettered legend giving the name of the contents in full or abbreviated form. Arrows shall be used to indicate direction of flow. Additional details, for example temperature or pressure, shall be added as necessary to highlight the degree of hazard.
  • Shutdown, emergency, or car-sealed valves shall be labelled with P&ID and valve numbers and any descriptive labelling needed to permit easy identification. Firewater system sectionalizing block valves shall be identified by their firewater system identification number.
  • Contrast shall be provided between colour field and legend for readability. For identification of materials in pipes of less than 3/4 inch (19 mm) in diameter, and for valve and fitting identification, the use of a permanently legible tag is recommended. The size of the service marker letters shall neither be less than 13 mm, nor be greater than 89 mm, varying in size depending on the outside diameter of the pipe.
  • For piping 2 inch NPS and smaller running between equipment, where the total length is less than 15 m, no service marking shall be necessary. For piping on pipe racks, service marking shall be oriented in a way that it is visible from grade level and from any nearby platform.
  • The colour of the service marker letters shall be black or white, whichever provides the greater contrast to the background colour.
  • Pipe markings shall be clearly visible. Where pipe lines are located above or below the normal line of vision, the lettering shall be placed below or above the horizontal centreline of the pipe.
  • Marking materials for stainless steel and nickel alloy piping shall not contain any harmful substances, for example chlorides, fluorides, sulphur, and low melting point metals.

Execution Process:

  • Surface Preparation: Surfaces to be colour coded or marked shall be free from oil, grease, dirt, and other surface contaminants that might be detrimental to the adhesion of the paint used for colour coding and marking.


  1. Whenever colour coding or marking paint is to be applied to a primed surface, the primer shall be dried completely before the colour coding or marking paint is applied.
  2. Colour coding, marking, and identification paint shall be applied to dry, clean surfaces in accordance with manufacturer’s instructions.
  3. Unless otherwise recommended by the manufacturer, colour coding and marking shall not be undertaken when the ambient temperature is less than 10 °C (50 °F), or the relative humidity is more than 90 percent.
  4. Colour coding and marking paint shall be applied in 1 coat.


Anup Kumar Dey

I am a Mechanical Engineer turned into a Piping Engineer. Currently, I work in a reputed MNC as a Senior Piping Stress Engineer. I am very much passionate about blogging and always tried to do unique things. This website is my first venture into the world of blogging with the aim of connecting with other piping engineers around the world.

Leave a Reply

Your email address will not be published. Required fields are marked *


Recent Content

Subscribe For Latest Updates

Signup for our newsletter and get notified when we publish new articles for free!