The schedule for a revamp project must mesh with the existing plant schedule for shutdowns and outages. So, after we have the assessment and WBS details, we must next determine how to actually do the project. The challenge of a revamp project compared to a brown- or green-field project is that the sequence of construction must be very tightly controlled. In most cases a revamp project must work within a limited shutdown window. Unlike a grassroots project where you have more flexibility, the revamp project also has to deal with construction in a running plant with all the hazards and limitations that this entails.
The schedule for the project has to allow for the fact that only a certain number of the work packages can be implemented at any one time and in the limited time and shutdowns available. There is also the fact that there is only a certain amount of physical space available in the operating plant to work in. Moreover, any change in the shutdown window can dramatically affect the project schedule since a whole series of tasks may have to be pushed forward or backward.
This means that the sequence of activities in the priority work packages of the WBS must be carefully detailed out to determine exactly what to do, when, and how long is allowed. Key to prioritizing the work packages is the wear or breakdown status of the equipment, piping, etc. that needs to be replaced.