Flow diagrams describe in a schematic drawing format the flow of fluids and gases through a unit or an entire plant. By using symbols to represent various pieces of equipment, the flow diagram provides the piping designer with an overall view of the operation of a facility.

The flow diagram used in this lesson is representative of the types used by many companies in the piping industry.

While actual symbols may vary slightly from one company to the next, the ‘look and feel’ of flow diagrams is the same throughout the piping industry.

You must become familiar with the piping, equipment, instrumentation symbols and abbreviations used on flow diagrams, in order to be able to ‘read’ and interpret them.

One of the most difficult concepts for students to comprehend is the absence of scale in the preparation of flow diagrams. The flow diagram should be laid out in a very simplistic and logical order and be read from left to right. It guides the draughtsperson and designer in the same manner a road map guides a traveler.

Uses of Flow Diagrams

The flow diagram is used by the piping group to develop and layout the plot plan. When developing the plot plan, the arrangement of the equipment in the facility reflects, in part, the logical sequence of flow depicted on the flow diagram. However, many other factors such as code requirements, client standards and preferences, worker safety, and cost also influence the positioning of equipment.

Once the plot plan is finalized, the piping designer routes the pipe between two vessels as indicated by the flow diagram using piping specifications and accepted design practices. The flow diagram is usually highlighted as each line is completed and incorporated into the design.

Type of Flow Diagrams

Process engineers are responsible for developing flow diagrams. In many medium to large engineering companies, an entire department is dedicated to the development of flow diagrams.

Today almost all flow diagrams are laid out with CAD, using third-party piping packages such as ProFlow or individually developed company packages.

Flow diagrams used in a piping project are:

• Process flow diagram;

• Mechanical flow diagram; and

• Utility flow diagram.

Refer to the Student Portal for additional resources related to this module.