The Dissolve Activity feature in Primavera P6 Professional was explained project in this article, How to Dissolve an Activity. The function allows the removal an activity while maintaining the relationship connections and logic of that activity’s predecessors and successors.
In P6 Professional versions 19 and newer, the additional option to choose to retain relationship lag of the dissolved activity was added. Project managers can easily enable the relationship lag to be transferred to the new relationships.
What is Relationship Lag?
Lag is the delay between an activity and its successor. When designing the logic of the project, there is sometimes the need to start an activity a little later instead of immediately after its predecessor has completed. For example, in Figure 1 below, after pouring a concrete pad (Activity A), you will need to allow 2 days for the concrete to cure before starting the next task (Activity B).
Figure 1: Primavera P6 Relationship Lag Example
To learn more about relationship lag, we have 2 helpful articles that explains different aspects of lag.
- https://www.p6consulting.ca/blog/a-little-bit-of-lag-in-our-lives-can-be-positive-or-negative/
- https://www.p6consulting.ca/blog/q-a-how-do-you-know-when-to-use-a-constraint-or-lag/
The feature to remove or Dissolve an activity was explained in detail in this article, https://www.p6consulting.ca/blog/how-to-dissolve-an-activity-in-primavera-p6-professional/.
In Primavera P6 versions 19 and newer, the Retain lag setting is in the Calculations tab of the User Preferences Dialog box. If you choose to retain lag, the lag from the dissolved activity’s predecessor relationship will be added to that of its new successor relationship.
The steps to enable the option to Retain Lag of the Dissolved Relationship are below and shown in Figure 2.
- On the Menu Bar select Edit.
- Click User Preferences.
- Select the Calculations tab.
- In the Dissolving Activities field, check mark Retain Lag.
Figure 2: Enable Retain Lag for Dissolving Activities in Primavera P6
The project in Figure 3 shows two paths of activities.
- Path 1 of ABC where there is 5 days of lag between B and its Successor C.
- Path 2 of DEF where there is 5 days of lag between E and its Predecessor D.
Figure 3: Test project with Predecessor and Successor Lag in Primavera P6
If Activity B and E are Dissolved with the Retain Lag option activated then:
- In Path 1, Activity B’s 5 days of Successor Lag will be transferred to Activity A and C’s new Finish-to-Start relationship.
- In Path 2, Activity E’s 5 days of Predecessor Lag will be preserved between Activity E and F’s new Finish-to-Start relationship.
Figure 4 shows the steps to Dissolve an activity. First select the activity in the table to dissolve. Second, on the Menu Bar, select Edit. In the drop down menu, select Dissolve. Click Yes when prompted “Are you sure you want to dissolve the selected activity? This cannot be undone.”
Figure 4: How to Dissolve an Activity in Primavera P6
The results of dissolving both activities B and E while retaining the relationship lag are shown in Figure 5. As can be seen, both the successor lag and predecessor lag of the removed activities have been transferred to the newly connected activities.
Figure 5: Test project results after Dissolving activities in Primavera P6
Summary
Dissolving an activity in Primavera P6 versions 19 and newer has the added flexibility to transfer any relationship lag of dissolved activities to the new activity connections. The choice to retain or not keep the lag is easily toggled on and off so you are not obligated to keep the same setting for every single activity throughout the duration of the project.
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