If you are not familiar with the process of defining relationships between activities in Primavera P6 Enterprise Project Portfolio Management (EPPM) Web, read on.
Once activities and activity durations have been added in Primavera P6 EPPM, connecting activities with relationships is important for finding the true length of the project. Precedence diagramming is the foundation of these activity relationships. Experienced schedulers thoroughly understand the precedence relationships between Activities enabling them to compute accurate project duration, and also helping them ensure that the project duration is as short as possible.
This article describing how to apply relationships to your activities in Primavera P6 EPPM, so you can compute the overall length of the project.
Before we begin defining activity relationships, let’s first make certain we understand the precedence diagramming method. The precedence diagramming method is implemented to show activity dependencies. In this method rectangular bars represent activities, and arrows between bars show activity dependencies. There are four types of relationships you can use to define the inner workings between activities.
- Finish-to-Start (FS): This is the most common type of relationship where one activity cannot start until another associated activity has finished. An example is that pour concrete activity cannot begin until the set forms activity is complete.
- Start-to-Start (SS): This is a relationship where one activity cannot start until another activity has begun. An example is that remove damaged piping activity cannot proceed until the implement safety plan effort has commenced.
- Finish-to-Finish (FF): In this relationship one activity cannot finish until another related activity has finished. An example from the research industry is that documentation cannot complete until experimental testing described by that documentation has finished.
- Start-to-Finish (SF): In this not so common relationship one activity cannot finish until another activity has begun. An example is the run generator activity cannot cease until the activate power activity is complete.
Lags and Leads
Lags and leads also have a significant impact on the length of the schedule. A lag describes a required time between activities. In the FS relationship this means that the second activity cannot commence until a scheduled period of time has elapsed after the completion of the first activity.
The most common example is concrete, in which a lag is inserted between activities to allow the concrete time to cure before the successor activity can proceed. A lead has the opposite effect on the schedule. A lead is the amount of time that a activity can start before the completion of the first activity. Many schedulers refer to lead as a negative lag. Note that the use of leads is discouraged by scheduling guidelines.
Repair & Improve Piping Schedule
This article describes a Repair & Improve Piping project to show how to use the various features in Primavera P6 EMMP to model relationships between activities. The list of activities and corresponding durations for our Repair & Improve Piping project is displayed in Figure 1.
Note the milestone activities Notice to Proceed, Project Start, and Project Complete. Also, note work breakdown structure (WBS) elements Demolition Piping, Installation Piping, Installation Thrust Block, and Quality Assurance.
To add a relationships tab to the activities page view first click on any activity to invoke the Activity Details tabs at the bottom of the page. Right-click on any of the tabs in the bottom layout area. Select Relationships from the corresponding menu, Figure 2.
Assigning Start-to-Start Relationships
The first relationship we want to assign is a Start-to-Start relationship between activities Notice to Proceed and Project Start. Highlight Notice to Proceed then select the Relationship tab. In the corresponding Successors dialog area select add successor icon, Figure 3.
From the resulting Select Successor Activity dialog select and assign Project Start, Figure 4.
Project Start will appear in the Successor dialog area. Change the Relationship Type to Start-to-Start, Figure 5.
Now highlight Project Start and assign Project Management and Drain Piping Systems as the successors, Figure 6.
Again, change the Relationship Type for both of these activities to Start-to-Start, Figure 7.
Assigning Finish-to-Start Relationships
The process for assigning the standard Finish-to-Start relationship is less involved. We first highlight all the activities as displayed in Figure 8.
Right-click on any of these selected activities and choose Link Selected Activities from the following menu, Figure 8. This assigns a Finish-to-Start relationship between all these activities.
Assigning Concrete Cure Time Lag
Now we want to assign a lag between Pour Concrete and Strike Forms to give the concrete thrust block time to cure before we remove the forms. Because our lag describes the cure time of concrete it is a “round-the-clock” 24-hours a day lag.
To set the lag to a 24-hours per day lag select the Schedule icon, Options button in the Schedule Project dialog, and 24 Hour Calendar for the Calendar for scheduling Relationship Lag option in the Scheduling options dialog, Figure 9.
Now it works best in Primavera P6 if you enter the cure time lag in hours instead of days, and let P6 compute the equivalent time in days. This is because for a standard 8-hours per day schedule P6 will consider each 8-hour time period out of your 24-hour “round-the-clock” calendar as one day.
So one 24-hour cure time period will be 3-days cure time lag. A 5-day cure time or 120-hours computes to a 15-day cure time lag. We want the cure time to be 120-hours, so enter ‘120h’ for the Lag of Pour Concrete, Figure 10.
Assigning a Finish-to-Finish Relationship
Now our Insulate Piping activity will be performed in parallel with the Pour Concrete and Strike Forms activities. To model these activities in parallel we define the relationship between Strike Forms and Insulate Piping as a Finish-to-Finish relationship, Figure 11.
To fully define the Insulate Piping activity we assign the additional Finish-to-Start relationship between Test Piping System at Pressure and Insulate Piping, Figure 12.
As displayed in Figure 12 we highlight the Insulate Piping activity and in the relationship tab predecessors’ dialog area add Test Piping System at Pressure as a predecessor to Insulate Piping with the standard Finish-to-Start relationship. So the Insulate Piping activity may commence after the completion of the Test Piping System at Pressure activity and completes shortly after the completion of the Strike Forms activity.
The Finish-to-Finish (FF) relationship allowed us to begin insulation of the piping while waiting for the concrete to cure. It, thus, enabled us to compress the schedule by performing activities in parallel, which is called fast tracking.
Round Out the Schedule
Continue the schedule by assigning a Finish-to-Start relationship between the remaining activities, Figure 13.
Additionally, assign a Finish-to-Finish relationship between Final Quality Assurance Inspection and Project Complete, Figure 14.
Finally, close out the schedule with a Finish-to-Finish relationship between Project Complete and Project Management, Figure 15.
Now click the Schedule icon and select the Schedule button. And the schedule with critical path will be as displayed in Figure 16.
You now have the true length of the schedule, which is compressed slightly via the activities performed in parallel.
Primavera P6 EPPM provides up to four types of relationships allowing you to model activities both in series and parallel. Parallel activities allow you shorten the schedule through compression. Lags allow you to model delays between activities, and the 24 Hour Calendar option, in particular, enables you to describe cure time delays.
The standard Finish-to-Start relationship is very popular, and Primavera P6 EPPM provides a quickly accessed menu selection to insert this relationship. There is more than one way to insert a relationship in Primavera P6 EPPM. The relationship tab method is preferred as it displays and enables changes to both the predecessors and successors of the highlighted activity.