What is a piping drawing?

The main purpose of a piping drawing is to communicate the information in a simple way. These drawings are schematic representations and they would define functional relationships in a piping system. The drawings would help to speed up the fabrication and erection work at the site. Piping diagrams are designed in a way that will be understandable for non-technical personnel. There are different types of piping diagrams and they are process flow diagrams, piping and instrumentation diagram, orthographic pipe drawing, piping isometrics, and block flow diagrams. By the help of these drawings and also with the project installation specifications would provide good guidelines to complete the piping system. 

What are the requirements for a piping drawing?

  • Pipe length dimensions
  • Location of fittings and valves
  • Size and type of valves and fittings
  • Pipe diameter contents and identification number

The pipe lengths are determined by calculations using coordinates and elevations. The vertical lengths of the pipe can be calculated by using elevations, while the horizontal lengths are calculated by using north-south and east-west coordinates. 

How piping arrangement is done?

The process equipment and piping have priority over the piping arrangement. The primary and the secondary beams are shown as utility stations so that the most proper route for the utility can be determined. In a piping arrangement all the equipment, instrument connections with the tag numbers will be shown in a piping arrangement, important details will be on large scale.

Piping arrangement drawings

The pipelines on a piping arrangement are shown by a single line or double line. In a single line, only the centerline of a pipeline is drawn and in a double line representation, the actual size to scales are drawn with the centerline marked as a chain dotted line.

How single line pipe drawing is done?

In this type of drawing, the flanges are shown as thick lines drawn to the scaled outside diameter of the flange. In order to indicate the gaskets a small gap between the dimension lines in the flanged joints. The valves are shown by identification number with a hand-wheel. If the valve is lever operated then the movement of handle position will be given. The flanged valve dimensions are given to the flange face while the nonflanged valves are dimensioned to the center lines of their stem.

Why color codes are used in piping?

The color codes are used in piping to identify the hazardous material that the pipe carries.

Yellow – flammable material

Brown – Toxic and poisonous material

Blue – harmful material

Green – oxidizing material

Grey – Physically dangerous material

Red – Fire protection material


Process flow diagram

This diagram shows the relationship between the components in a system, this type of diagram tabulates the process design values for different operating mode components. This type of piping diagram won’t display minor components, piping systems, piping ratings, and designations. A PFD diagram would contain the process piping, major equipment symbol names and identification numbers, control valves and valves that affect the operation of the system, interconnection with other systems, major bypass and recirculation lines, the composition of fluids, and system ratings operation values like maximum flow temperature and pressure.

The process flow diagram conveys the major processing steps represented by the equipment

  • It is very useful to convey the heat and material balances
  • It is also useful for conveying the major piece of equipment
  • It would convey the process condition
  • Useful for conveying utilities

Block flow diagram

The block flow diagram is also called a schematic diagram and it is a non-scaled single line diagram. This diagram is a simplified diagram of the piping system at the initial stages of the design process. The equipment in the piping network is represented by simple shapes such as rectangles, circles, etc. This diagram can be considered as a theoretical or conceptual layout of a system and its operations. This diagram acts as a guide for the process flow diagram.

Orthographic pipe drawing

This type of drawing would show single pipes either straight or bent in one plane. This type of drawing is mostly a single line drawing and it is drawn by drawing the centerline of the pipe as a thick line and add valves and fittings, or double line drawings, where we can draw each valve and fittings. The single-line method is mostly used where speed is an important factor. Mostly the double line drawings are used for applications such as catalogs, where visual appearance is more than the drawing time. This type of drawing is mostly used for complex piping systems. The orthographic diagram shows only one side and because of that multiple drawings are required to show the complete piping arrangements.

Isometric drawing

The isometric drawing is a type of piping drawing and it shows the piping system in three dimensions (length, width, & depth). So in this drawing three sides of an object can be viewed. This drawing is widely used for industries because it can be drawn easily and it would display the object in a realistic way. This diagram shows both the horizontal and vertical planes. These drawings are used in pipelines that have bent more than in one place. We can use either the single line or double line method. The finished isometric drawings are easier to understand in practical format than an orthographic line drawing. Mostly the piping isometrics are created from orthographic drawings and this will be really useful for engineers. The isometric drawings are really helpful for the complex or the larger piping system. The piping isometrics are used for the stress analysis and it is very useful for the draftsmen to create the shop fabrication spool drawings.

The isometric drawing can be described as a pictorial representation that combines the height, width, depth, length, into a single view 30 degrees from its horizontal plane. The line diagram shows certain details such as operating and design temperature, operating and design pressure, insulation required, hydro test pressure, pipe support location, point of weld, and its type.

Information on an isolation diagram

  • Pipe support & elevation
  • Coordinates of the reference items
  • Piping section elevation and their angle with reference to the horizontal and vertical
  • Piping class
  • Test media and test pressure
  • Insulation requirements
  • Inline instruments and valve number, size, type
  • Weld positions and welding specifications
  • Operating temperature and pressure

Piping and instrumentation drawings

This diagram is widely used in the process industry and it would show the piping of the process flow together with the installed equipment and instrumentation. This diagram would show the functional relationships among the system components. The P&ID shows the graphical representation of the equipment, piping, and instrumentation. In order to understand the P&ID one should understand the equipment, instrumentation, and technology. The process symbol list of the pant must be memorized so that we can determine the instruments while checking the diagram. This diagram would also help the constructors to develop the other construction input documents. The P&ID would provide the direct input to the field for the physical design and installation of the field run piping. This diagram ties together the system description, the system flow diagram, the electric control schematic, and the control logic diagram.

The P&ID would show the following

  • Mechanical equipment
  • It shows all the valves which are associated with the process piping
  • Vents and drains
  • Special fittings
  • Sampling lines
  • Permanent start-up and flushing lines
  • Instrument designations
  • Equipment names and numbers
  • Valve and pipeline identification
  • Direction of flow
  • Reducers, increasers, and wages, etc
  • Annunciation inputs and plant computer inputs

What are the advantages of P&ID?

  • It shows the key piping and instrumentation details
  • Control and shutdown schemes
  • Safety and regulatory requirements
  • Basic start-up and operational information
  • Instrumentation and designations
  • Mechanical equipment with names and numbers
  • All valves and their identification and also shows process piping, sizes, and identification.
  • This diagram plays an important role in the maintenance and modification of the process it describes
  • During the design stage, this diagram would provide the basis for the development of the system control schemes, thus allowing for further safety and operational investigations such as the hazard

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