Critical path analysis is one of the most important concepts in scheduling. It demonstrates the duration and the finish date of the schedule. According to The Project Management Body of Knowledge (PMBOK), The Critical Path is “the sequence of scheduled activities that determines the duration of the project.” In a wokschedule many activities are tied with relationship lines. These connections create several paths and each path has a duration. But the critical path is the longest path of the network diagram. Primavera P6 Critical Path calculations are useful for determination of the shortest time possible to complete the project. In this article we will review the basics of critical path analysis and see how to display critical path of a schedule in Primavera P6.
Critical Path Analysis
The critical path analysis is used to plan and control large and complex projects since the beginning of 1960’s. It was developed by by Morgan R. Walker of DuPont and James E. Kelley Jr. of Remington Rand. The critical path analysis determines the critical path of the network system and critical activities of the activity network and calculates the earliest possible completion time of the project. Unlike the PERT Method, activity durations are deterministic in Critical Path Method.
The Critical path analysis is widely used almost in all industries such as construction, defence, software, IT, aerospace, product development etc.
Basic Steps of Critical Path Analysis
Critical path analysis creates a model to represent the project execution. Below are the basic steps of critical path analysis.
- Listing All the Activities : Before to list the project activities and tasks, it is a good idea to analyze the Work Breakdown Structure and Project Scope (or Product Scope). The best way of determinig activities is to make a comprehensive analysis.
- Defining Activity Relationships: Basically there are four types of activity relationships which are FS (Finish to Start), SS (Start to Start), FF (Finish to Finish) and SF (Start to Finish). It is better to determine predecessor and successor activities before to assign activity relationships. Lags can be used if needed to delay of the successor activity.
- Visualizing Critical Path Schedule (or Drawing Network Diagram): In order to visualize the schedule, network diagram should be drawn. This diagram will be used to make forward and backward calculations before to determine the critical path.
- Estimating Activity Durations: Activity durations have an impact upon the project durations. So that it is critical to estimate the activity durations properly. Expert judment, analogus and parametric estimating are the techniques used to determine the activity durations.
- Critical Path Identification : After completing all the steps above, Critical Path Identification phase comes. Forward Pass and Backward Pass calculations are performed and the total float of each path is determined to identify the critical path.
Primavera P6 Critical Path Analysis
The figure below shows a sample pipeline project. (Figure 1). Activies are detailed under Engineering, Procurement, Construction, Above Ground Installations and Commissioning Work Breakdown Structure levels. Mainline actvities including clearing and grading, stringing, bending, welding, trenching, backfilling etc. are listed. Above Ground Installations include civil, electrical and mechanical activities of the Block Valve Stations.
In this sample, all the relationships are assigned to the activities and the project is scheduled.
In Oracle Primavera P6, critical path activities are defined by total float value. Activities that have total float values equal to or less than zero are critical. As shown in the Figure 2, critical path activities are red and their total float is zero.
Let’s assume that your project’ s completion date is 25-Feb-2019. But contractual finish date is 1-Mar-2019 and you insert the “Must Finish By” date as 1-Mar-2019. (Figure 3)
You see all of your activities have a total float value greater than 0 and they are non-critical activities. (Figure 4)
Now, in order to determine the critical path, you must change the critical path definition of P6. Select Tools | Schedule from the main drop down menu at the top of the screen. This will display the Schedule window. Then select “Options” button and change the critical path definition as shown in the below figure. (Figure 5)
If you add the “Longest Path” and “Critical” columns, you can see that the critical activities are on the longest path. (Figure 6)
Primavera P6 Schedule options window enables you to change the definition of the Critical Path of your project. Activities on the Critical Path can not be delayed. Analyzing the activities on the longest path or Critical Path helps you to understand your project’s current situation. If the activity relationships are not correct and lags are wrong, the Critical Path will not demonstrate the real conditions of the project.