There was a time when “CPM scheduling” (critical path management) used to be the favorite buzz phrase in turnaround scheduling. People realized improper management of the critical path activities could have a serious impact on their bottom line. These days, it seems the favorite buzz phrase is “priority level scheduling.” As we become more efficient at managing turnarounds, there remains less waste we can squeeze out.
One place where there is still significant opportunity to squeeze is in how we man-age manpower. Generally, we have learned to avoid ramping up too soon because we will lose money through lack of productivity while we are waiting on equipment to be turned over. We have learned staffing up too slowly means we risk losing money by extending the end date. But we can also lose money by saturating a space with more workers than the space can productively accommodate. We can also over allocate our manpower — that is, we can have more work scheduled than our limited manpower can address in the specified timeframe. For example, if we have six mechanics scheduled to do six oil changes in 30 minutes, but the shop only hired three mechanics, guess what? Those six oil changes are going to take an hour — twice as much time as the schedule indicated.
Once the critical path is optimized and you have squeezed down its duration as much as possible, it is then time to squeeze savings out of the near-critical work and the noncritical work. So, how does priority leveling help me? First of all, proper leveling only applies to work that is not on the critical path. Leveling only looks at the noncritical activities because they have float in them, which means there is a certain amount of flexibility to move them into other time slots that fit your manpower better.
When you tie logic into a schedule and time analyze it, there are unnecessary peaks and valleys in the manpower staffing before you level it. If we hired and laid off according to a staffing plan that has not been leveled, we could be hiring on day one, laying off on day two and rehiring the same people on day three with that same pattern running all throughout the turnaround. Leveling allows us to somewhat average our staffing levels and keep them more constant. Another feature of leveling is that it takes into account whatever resource limits have been assigned and helps to avoid over allocating those resources by moving work into time slots that can better accommodate the available manpower.
Another place where leveling is a great help is where activities are driven more by a certain time window than they are by logic sequence. For instance, who cares in what order a lot of the valves and piping jobs are done? The same is true of much of the instrumentation and electrical work. So, why go through the trouble of tying lots of logic to hundreds or thousands of activities that are not driven by logic? Why not just level them within a constrained time frame?
We get into priority leveling when we assign priority codes to activities to tell the software which activities are the first to receive available resources, which activities are second in line to receive available resources and so on. Using priority leveling is akin to using logic loosely but without having to make a lot of logic ties. And when work is done out of sequence, which inevitably occurs during every turnaround, it is much faster and easier to change leveling priorities than to untie and retie logic relationships.
One thing to watch when leveling is the creation of gaps between activities within the same job. If a crew is halfway through a job at the end of the day and it is not on the schedule the next day because it got pushed out by leveling, that would not inspire confidence in the integrity of the schedule. Priority leveling is a great tool as long as it is not pushed too far. Someone said managing a turnaround is like holding a dove in your hand — squeeze it too much and you can hurt it; don’t squeeze enough and it can get away from you.
For more information, contact Mike Bischoff at (281) 461-9340, email sales@tamanagement.com or visit www.tamanagement.com.
