Shale Oil Companys Aston, Ohio, manufacturing complex comprises several operating units. These units process the crude oil that is pumped through and transform it into a multitude of hydrocarbon products. The units run 24 hours a day, 7 days a week, and must be shut down for maintenance on a predetermined schedule. One such unit is Distillation Unit No. 5, or DU5. Studies have shown that DU5 can operate only 3 years without major equipment breakdowns, and excessive loss of efficiency. Therefore, DU5 is shut down every 3 years for cleaning, inspection, and repairs.

DU5 is the only distillation unit for crude oil in the Aston complex, and its shutdown severely affects all other operating units. Some of the production can be compensated for by Shale refineries in other locations, but the rest must be processed and stored before the shutdown. Without proper planning, a nationwide shortage of Shale gasoline could occur. The time of DU5s shutdown is critical, and the length of time the unit is down must be kept to a minimum to limit production loss. Shale uses PERT as a planning and controlling tool to minimize shutdown time.

The first phase of a shutdown is to open and clean the equipment. Inspectors can then enter the unit and examine the damage. Once damages are determined, the needed repairs can be carried out. Repair times can vary considerably, depending on what damage the inspection reveals. Based on previous inspection records, some repair work is known ahead of time.

Thorough cleaning of the equipment is also known to improve the units operating efficiency. The table below lists the many maintenance activities and their estimated completion times.

Question:

1. Prepare a network diagram and table showing activity times use, event early start, early finish, late start, late finish and event slack.
2. Determine the critical path
3. Project duration
4. Determine the probability that the shutdown can be completed 1 week earlier.
5. What are the probabilities that Shale finishes the maintenance project 1, 2, 3, 4, 5 or 6 days earlier?

6. Preventive Maintenance of DU5
   Activities		Time Estimates (in Days)
   		Optimistic	Most Likely	Pessimistic
   1-2	Circulate wash water throughout unit	1	2	2.5
   2-3	Install blinds	1.5	2	2.5
   3-4	Open and clean vessels and columns	2	3	4
   3-5	Open and clean heat exchangers; remove tube bundles	1	2	3
   3-6	Open and clean furnaces	1	2	4
   3-7	Open and clean mechanical equipment	2	2.5	3
   3-8	Inspect instrumentation	2	4	5
   4-9	Inspect vessels and columns	1	2	3
   5-10	Inspect heat-exchanger shells	1	1.5	2
   5-11	Inspect tube bundles	1	1.5	2
   6-12	Inspect furnaces	2	2.5	3
   6-17	Retube furnaces	15	20	30
   7-13	Inspect mechanical equipment	1	1.5	2
   7-18	Install new pump mechanical seals	3	5	8
   8-19	Repair instrumentation	3	8	15
   9-14	Repair vessels and columns	14	21	28
   10-16	Repair heat-exchanger shells	1	5	10
   11-15	Repair tube bundles; retube	2	5	10
   12-17	Repair furnaces	5	10	20