Page 410 - Hydrocarbon Exploration and Production Second Edition

Managing the Producing Field 397

Routinely scheduled
100% of time
testing / inspection Unscheduled
Opportunity based
servicing
breakdown+repair

enhancement

equipment
available

Figure 16.10 Availability of equipment.

a system that was designed to shutdown the process in the case of an emergency. This
causes a loss of production. Where possible, inspection and testing is designed to be
performed on-line to avoid interrupting production, but otherwise such inspections
are scheduled to coincide. The periods between full function testing of process
equipment is sometimes set by legislation.
Servicing of items is a routinely scheduled activity which is managed in the same
way as inspection, and the periods between services will depend on the design of
the equipment. The periods may be set on a calendar basis, that is every 24 months,
or on a service hours basis such as every 10,000 operating hours.
Breakdown and subsequent repair is clearly non-scheduled, but gives rise to non-
availability of the item. Some non-critical items may actually be maintained on a
breakdown basis, as discussed in Section 12.3, Chapter 12. However, an item which
is critical to keeping the production system operating will be designed and
maintained to make the probability of breakdown very small, or may be backed up
by a stand-by unit.
Enhancements to the process may be required due to sub-optimal initial design of
the equipment, or to implement new technology or because an idea for improving
the production system has emerged. De-bottlenecking would be an example of
an enhancement, and while making the changes for the enhancement, the system
becomes temporarily unavailable.
All of the above activities reduce the total availability of items, and possibly the
availability of the production system. Managing the availability of the system hinges
upon planning and scheduling activities such as inspection, servicing, enhancements
and workovers, to minimise the interruption to producing time. During a planned
shutdown, which may be for 1 or 2 months every 2 or 3 years, as much of this type of
work as possible is completed. Reducing the non-availability due to breakdown is
managed through the initial design, maintenance and back-up of the equipment.
If the planned shutdowns are excluded, then a typical up-time, the time which the
system is available, should be around 95%.