Maintenance outages, turnarounds, or plant shutdowns are complex, and can involve hundreds or even thousands of temporary workers, and are very costly. In our work we have been successful applying non stop critical path analysis in helping reduce large facility outage duration. The immediate benefits are increased process availability and corresponding revenue and profit. Typical outages are planned and scheduled months in advance and last anywhere from a week to a month or more. Outage duration tactics include streamlining processes such as the shutdown and startup processes, improving the decision making and communications methods, and controlling scope. Another tactic is externalizing tasks, which is by doing work before or after the process goes down, tasks such as pre staging tools and materials, preparing the work site. We’ve also been working to better understand the nature of planning and executing Critical Path work.
We believe that a shorter critical path means an overall shorter outage. To get a shorter critical path you often have to add additional resources which increases turnaround costs. What we want to better understand are the conditions where a shorter outage actually costs less. Typical contractor schedules are 2 ten hour shifts per day. Productivity is believed to drop off significantly after 10 hours due to additional breaks and fatigue. We have applied longer shifts to the critical path and have seen overall duration reduction. We have also had mixed results with the concept of Non Stop Critical Path, also referred to as “tool to tool”. Some types of work are machine rate based, for example tasks such as pipe welding or sand blasting. For this type of work the value is in the “wrench or tool time”. The concept is that the tool never stops. The welder stays on the tool until someone comes, taps the worker on the shoulder, takes the welding rod and keeps on welding. While working spotters make sure the value adding worker never has to go searching for weld rod; an assistant keeps the worker supplied. The tool never takes a lunch break, or goes on treasure hunts; the tool works as close to 24 hours as possible. To do this we have spotters filling in for the workers when they take their breaks, and stagger crew start times.
Shutdowns can have a range of % critical path work. Sometimes the critical path is almost the entire outage work scope; in other cases the critical path work can be as little as 5% of the overall outage effort. We believe that when the critical path is narrow, or a small portion of the overall work, then applying additional labor to the critical path can greatly reduce the overall cost and duration of the outage.
Staffing Non Stop Critical Path of course takes more resource and is a higher operating expense then the normal 2 ten hour shifts. Non Stop Critical Path provides not only an additional 4 hours of shift time compared to 2 Tens, it also adds back two lunches, 6 breaks, and 2 sets of getting to and from the work face, or some 7 or more hours of tool time per day.
The combination of shift patterns, over time, mix of critical path work, equipment rentals, etc. makes it difficult to apply a general rule for all turnarounds as to whether extending shift length or adding labor to the critical path increases or decreases overall outage expenses. So a model is needed to answer the question of under what conditions does applying extra labor to get a shorter outage actually cost less.