Differences between PMA and PLK Item Types

Pipe segments in AVEVA P&ID are drawn using AutoCAD entity type POLYLINES or MLINES. The internal item types of these pipe segments will be either PLK or PMA. Below are the differences between the two item types that users must be aware when deciding to use one or the other for constructing their pipe lines.

• Lines of item type PMA are drawn using ribbon options "Draw Pipelines" and "Process links".

  

  These options will draw pipelines with the following characteristics:

  • They will have a unique identification (Branch ID).

  • Properties configured in the project for pipes will be set against them and user will be able to modify them.

  • Pipe lines modelled as branches in the drawing will contain the branch ID of their owner pipe line and they will inherit properties from pipe owner following rules set against them in the project.

  • They will include head and tail and flow direction concepts.

  • They will be available in the reporting database as part of the line list with their names, source, destination and other key properties.

  • They can optionally have arrow heads to indicate flow direction.

• Lines of item type PLK will draw secondary pipe lines or tubing that in most instances do not deserve a unique identification or name in a project, they are drawn using ribbon option Instrument Link.

  

  These lines have the following characteristics:

  • They do not have a Head and Tail or concept of flow direction.

  • They are effectively unnamed items in the project and no unique identification recognizable by users is set against it.

  • They are not part of the line list in the reporting database.

  • The main objective in drawing these lines is to connect offline engineering items such as drain or vents valves, flow or temperature or pressure instrument indicators etc. attached to their owner’s pipeline or equipment making it possible for them to inherit key properties from their parent named pipe lines.

  • Because of the above mentioned characteristics instrument links (PLK) should NOT be used to draw complex pipe networks that include for instance:

    Networks with multiple branches

    Example of incorrect use of instrument link to construct a pipe network:

    

    The correct approach for this scenario will be as follows: