FAQ: How do line groups, line segments, and linked line segments differ?

Schematic lines are represented in the program in two ways: as line groups, which are conceptual representations (or types) of lines (such as sewage lines or hot water pipes), and as line segments, which are actual purchasable pipes.

You can link a line segment to another line segment. When a line is linked, it assumes the tag information of the line to which it is linked. If you link a line belonging to one group to a line in another group, the line leaves its original group and joins the new group.

Note: You can link lines only within a drawing. To link lines across drawings, use an off-page connector.

Each time you add a line to a drawing, you are prompted to continue the line group, start a new line group, or link the line to another line segment.

The following chart explains the important differences between the three choices.

Prompt	Action	Result and Tag	Data Manager
Continue sline group	You are prompted to select an existing line group to which the new line segment will be added	The new line segment assumes the tag of the selected line group	No change to the pipe line group A new row is created for the new pipe line segment
New sline group	The new line segment becomes part of a newly created group	A new group is created, and the new line segment tag is empty	A new row is created for the new pipe line group A new row is created for the new pipe line segment
Link sline segment	You are prompted to select an existing line segment to which the new line segment will be linked	The new line segment: assumes the tag of the selected line segment is added to selected segment’s group assumes the tag of the line group	No change to the pipe line group No new row; the new segment is represented by the same row as the segment to which it is linked

Segments in a group inherit properties from that group. By default, a pipe line segment tag gets its service and line number from its pipe line group. The uniqueness of pipe line segments and groups is controlled by the pipe line group tag.

P&ID Line Groups

You can use slregoup to set the unassigned line to an existing line number (line group tag value).

The above image shows line number 101 with unassigned (?) line selected.

Use the Select Line Group dialog box to specify 101 for the selected (unassigned) line.

The unassigned line number is now in line group 101, which sets the line segment tag.

With the addition of slregoup, you can no longer specify an existing line group tag in the Assign Tag dialog box. This avoids accidentally joining (and possibly modifying) existing line groups.

Note: Pipe lines are not automatically added to existing groups if you assign identical tags. Instead, a Tag Already Assigned dialog box displays and the tag assignment is cancelled. Also, you cannot connect to an unassigned line. However, you can connect an unassigned line to an assigned line.

For more information, see About P&ID Line (SLINE) Grouping.

Line Group Tag Management

No two different schematic line groups can have the same tag because the tag identifies the group. This can prevent you from assigning an existing line number to a line segment.

If an operation attempts to assign an existing tag and cannot be interrupted, a question mark ( ? ) is added to the tag temporarily. You can later use the assigntag command or Data Manager to resolve this.

You can use the slgroupedit command to add lines to an existing line. If the default tag format is used, any lines added to the group are assigned the same Line Number.

You can use Project Setup to modify the tag format of the pipe line group or the line segment.