When a segment is taken out of service in a looped or multi-source system, virtually all of the other segments remain in service. However, in tree shaped systems, removing one segment from service also takes downstream segments out of service. These downstream segments are referred to as “Outage Segments”. To determine outage segments, highlight the Outage Segments level of the left pane and click the Go arrow. This will identify all outage segments.

Viewing and zooming to outage segments is similar to these operations in regular network segments. Segments must be identified before outage segments can be identified. In most cases in looped systems, the isolating segments usually contain no elements. However, there may be some surprises which can provide some insights into the adequacy of valving in a system.

The figure below shows the network segment that is being isolated in blue and the corresponding outage segment in red. Note that the various colors assigned to elements by the program are not representative of any network attribute but are only used to differentiate adjacent segments.

This system which at first looks as if it has adequate valving and parallel piping has a serious problem because of valving in the blue segment results in a large outage segment.

Determining the outage segments for a critical valve study works the same as critical pipe/segment studies. The only difference is that the valve being closed is highlighted in green. Also note that the segments are determined differently than critical pipe/segments. In the screen capture below, ISO-4 is closed. The corresponding segment is shown in blue and the elements affected by this outage is highlighted in red.