Identification of Pipe Line Number in P&ID

  • The P&ID plays a very important role in the operation, maintenance, and modification or expansion of every process industry and power plant.

  • The P&ID demonstrates the physical sequence of each and every piece of equipment connected and its control system.

  • These P&IDs provide basic information on systems for plant development and allow for operational safety.

  • The pipeline number should not be repeated for various lines. It means each and every pipe connected must have different line numbers.

  • The lines can be numbered based on the fluid type.

  • Process fluids lines can be numbered from 001 to 100.

  • Utility lines can be numbered from 101 to 200.

  • This piping line number specification is defined by the American Society of Mechanical Engineers (ASME) or American Petroleum Institute (API) using American standards.

What is the Pipeline number?

  • A pipeline number is a unique number assigned to every pipe.

  • A line number is a combination of a sequence of characters (alphabets and numerical) text provided to identify a pipe used for particular applications.

  • Every line must have a different line number i.e. the number must not be duplicated.

What is the purpose of line numbers?

  • The process industry consists of several pipelines for the transfer of fluids such as water and steam gas from one point to another point.

  • But all the pipelines are not similar to each other, but the pipeline number indicates the detailed information of that pipe.

  • Generally, a pipeline number is similar to a tag number that is used to identify the type of the instrument.

Representation of Piping Number on P&ID

The piping number on a P&ID diagram is indicated as



10” – Represents the size of the line in inches, the line size is 10 inches.

PL – Represents the service fluid.

12007 – The first two digits (12) of 12007 represent a unit area or facility number. And the last three digits (007) of 12007 represent the serial number or line number.

B12B – Represents pipe classification or service class of piping.

We can further divide the class of piping service B12B as shown below

B – Represents the rating of the flange.

12 - Represents the material used for piping

B - It is a suffix to qualify the piping material.

IA – Represents the type of insulation.

50 - Represents thickness of the insulation

Piping Attributes in P&ID:

Piping attributes in a P&ID diagram represent a line identification number for every segment of pipe to describe its identity and installed area including line size, insulation type, insulation thickness, service class (material and its schedule), etc.

Process and Utility Fluid:

  • Process pipelines are made to convey various fluids.

  • These fluids are further divided into process fluids and utility fluids.

  • The process fluids include raw materials, intermediate process streams, the process by-products, and the final product.

  • Utility fluids include Auxiliary cooling water, process condensate, chilled water, main steam, thermic fluids, soft water, and De-Mineralized water.

  • The nomenclature for each line indicated specific codes depending on the fluid handled.

  • CWS denotes Cooling Water Supply.

  • CWR denotes Cooling Water Return.

  • De-Mineralized Water Supply is denoted by DMS.

Location or Area:

  • The nomenclature also consists of another parameter location that indicates the origin of any streams at various plant locations.

  • The various plant locations such as raw material storage, intermediate product storage, final product storage, water treatment plant, utility section, by-product storage, and waste treatment section.

Material of Construction:

  • The nomenclature for materials of constructions can be shown as MOC.

  • The commercial pipes used for fluid transfer are available with various materials of construction. The most commonly used materials are carbon steel, AISI 304, AISI 316, copper, PVC, etc.

  • AISI 304: AISI 304 is the most commonly used austenitic chromium-nickel stainless steel. This is highly corrosion-resistant with excellent drawing properties and very good formability. AISI 304 stainless steel is used to make sinks, and kitchen appliances such as pans, containers, etc.

  • AISI 316: AISI 316 is the second most widely used type of stainless steel after AISI 304. SS 304 serves great success in most situations. Both AISI 304 and AISI 316 are typically used in industry. AISI 316 can be used in harsh environments where there

  • Corrosion resistance is high.

  • High tensile strength at higher temperatures

  • The resistance property of AISI 316 to chloride-rich conditions is better than SS 304

AISI: American Iron & Steel Institute.

Line Size:

  • Sizing of the process line must be done by the piping engineer or project engineer

  • The commercial pipes are available as nominal bore (NB) based or outer diameter (OD) and material of construction (MOC).

  • The standard pipe size mentioned in the nomenclature is based on

  • Nominal Bore are 25, 50, 80,100,150,200 etc.

  • Outer Diameter are 33.4, 60.3, 88.9, 114.3, 168.3, 219.1 etc.

The Phase of Process Fluid:

  • In process plants, the materials handled exist in various phases.

  • Generally, fluid flow can be categorized as single-phase flow, two-phase flow, and three-phase flow.

  • Single phase flow indicates the flow of only one phase they may be either solid, liquid, gas, or vapor.

  • Two-phase flow indicates the combination of any two phases such as solid & liquid, solid & gases, liquid & vapor and so in.

  • Three-phase flow indicates the combination of any three phases.

  • This parameter in the nomenclature is considered an optional means that may or may not be included.

  • If included in nomenclature it makes it easy to clarify and control in case of two phases or three phase flow through various lines in the plant.

  • The phases can be shown by letters such as S for Solid, L for Liquid, G or Gases, and V for Vapours.


  • The process equipment and pipelines must be properly insulated to prevent loss of heat to the surrounding environment or to prevent heat gain from the surrounding environment.

  • Hot insulations and cold insulations are two types of insulations used for processing equipment and pipelines.

  • The term “H” is used to indicate hot insulations.

  • The term “C” is used to indicate cold insulations.

  • The nature of insulation varies based on the internal temperature of the pipe and its surroundings.

  • The insertion of this parameter in the nomenclature is essential to indicate the fluid nature inside the pipe that is mainly required for personnel safety in the plant.