P&IDs show the interconnectivity and flow of process piping.  Piping is used to convey anything that can flow: liquids, gases and/or solids from one location to another. It has been used to do so in one form or another for over two thousand years.

Industrial process piping (and accompanying in-line components) can be manufactured from wood, glass, steel, aluminum, plastic and concrete. The in-line components typically sense and control pressure, flow rate and temperature of the transmitted fluid, and usually are included when one discusses the concept of piping design. Process piping is not what you see under your sink.

"Plumbing" is the form of piping that most non-technical people are familiar with, as it constitutes the form of transportation that is used to provide liquids (water) and gases (natural gas used for heating and cooking, for example) to their homes. Piping also removes waste from the household in the form of drainage.

Piping also has innumerable other industrial applications, which are crucial for moving raw and semi-processed fluids for refining into more useful products. Some of the more exotic materials of construction are titanium, chrome-moly and various other steel alloys. Typical process piping sizes range from 1/2" to 30" in diameter. The engineering discipline of piping design is that which gets the fluid to where you need it, whether it is water, gasoline, hydrogen, fuel oil, or any other flowing medium you can think of.

Process piping consists of primary (or main or major), secondary (or minor) and utility pipes.  Primary lines indicate pipe carrying a process (or product or commodity).  The major processes are determined from the associated PFDs.  Plant utilities include Water/Steam, Sewage, Electric and Air.  The links below explain process piping in great detail.



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Text Box: P&IDs—From The Drafter’s Perspective
Guide To Drafting Piping and Instrumentation Diagrams

P&ID Components—Process Piping

P&IDs - From The Drafter’s Perspective—Guide for Drafting Piping and Instrumentation Diagrams

Links to Piping Line Format for P&ID Drawings


PIP Example   Go To Sht. 5, Section & Sht. 6, Section & Sht. 9, Section 4.4


AA Standard   Go To Sht. 2, Section 2.3


P&ID Standard Notations  Scroll To Line Symbols Section


Line Widths  Go To Sht. 6— Paragraph 4


Cheat Sheet Tips


Line Conventions 


Introduction To Line Numbers


About Line Numbers


Where Do Line Numbers Change?


Line Designations—Detailed Descriptions


Piping Line List



Links To Information on Pipe Codes and Standards


Piping Service Classes


ASME B31.1 Power Piping  Article


ASME B31.3 Process Piping


ASME B31.4 Pipeline Transportation Systems for Liquid Hydrocarbons and Other Liquids  Article


Pipe Codes and Standards—American, British and Indian


Design Codes 



Links to Process Piping Information


Definitions and Details of Pipe


What is a Refinery? 


Key Facts on Process Piping Design


Engineering Fluid Diagrams and Prints—Piping Systems 


PFD & P&ID Diagrams  Go To Sht. 3 Section E


PME Primary/Secondary Piping  Article


Beyond Primary/Secondary Piping  Presentation


Flexible Piping Systems 




Design Codes—Pipework—Article


Refinery Process Descriptions—Documentation


Petroleum Refinery—Description


Plumbing Design Considerations—Applies To Process Piping Engineering


Piping Systems  Go To Sht. 59 & 78


Pipe Engineering  Go To Sht. 4


Different Piping Arrangements  Article


What is a Pipe Rack?


Pipeline Design  Article


How To Become A Piping Designer


Industrial Pipe Racks and Process Design Piping  Video


Pipe and Tube Information  Go To Sht. 11


Process Control Fundamentals

Disclaimer:  The web has been scoured to provide as much information about P&IDs as possible on this site.  This information comes from many sources and many different countries.  Reviewing it all will increase a person’s knowledge but it is the reader’s responsibility to insure that the information contained herein is verified by proper authorities as valid for use in any intended application.

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