Page 334 - Hydrocarbon Exploration and Production Second Edition

Production Operations and Maintenance 321

Capacity: 12,000 b/d 40,000 b/d 12,000 b/d
oil
process export
facilities pump
oil
storage
tank

production
potential
10,000 b/d

Figure 12.5 Criticality of equipment.

could be maintained in a different way, such as allowing one to run to failure and
then switching to the spare pump whilst repairing the failed one.
Criticality in the above example is set within the context of guaranteeing
production. However, a similar analysis will be performed with respect to the
criticality of guaranteeing safety and minimum impact on the environment.
The failure mode of an equipment item describes the reason for the failure, and is
often determined by analysing what causes historic failures in the particular item.
This is another good reason for keeping records of the performance of equipment.
For example, if it is recognised that a pump typically fails due to worn bearings after
8000 h in operation, a maintenance strategy may be adopted which replaces
the bearings after 7000 h if that pump is a critical item. If a spare pump is available as
a back-up, then the policy may be to allow the pump to run to failure, but keep a
stock of spare parts to allow a quick repair.

12.3.1. Maintenance strategies

For some cheap, easily replaceable equipment, it may be more economic to do
no maintenance at all, and in this case the item may be replaced on failure or at
planned intervals. If the equipment is more highly critical, availability of spares and
rapid replacement must be planned for.
If maintenance is performed, there are two principal maintenance strategies:
preventive and breakdown maintenance. These are not mutually exclusive, and may
be combined even in the same piece of equipment. Take for example a private
motor car. The owner performs a mixture of preventive maintenance (by adding
lubricating oil, topping up the battery fluid, hydraulic fluid and coolant) with
breakdown maintenance (e.g. only replacing the starter motor when it fails, rather
than at regular intervals).
Figure 12.6 summarises the alternative forms of maintenance.
Breakdown maintenance is suitable for equipment whose failure does not threaten
production, safety or the environment, and where the cost of preventing failure
would be greater than the consequence of failure. In this case, the equipment would
be repaired either on location or in a workshop. Even with this policy, it is assumed
that the recommended lubrication and minor servicing is performed, just as with a
motor car.