Types of Maintenance

THE TYPES OF MAINTENANCE 
what they are & when to use them
ROAD TO RELIABILITY™

Preventive
Maintenance
vs
Corrective
Maintenance
before a failure
has occurred
after a failure
has occurred

Maintenance
Deferred Emergency
Corrective
Maintenance
Time
Based
Failure Finding
Condition
Based
Risk
Based
The Types of Maintenance
Predictive
Preventive
Maintenance

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“9 Types of Maintenance”

Time Based Maintenance
Considered Preventive Maintenance
Task Type Scheduled Overhaul / Replacement
Objective Restore or replace regardless of condition
Interval
Fixed time or usage interval
e.g. 1 month, 1,000hrs or 10,000 km
When to use Age related failure modes, compliance tasks

Failure Finding Maintenance
Task Type Functional Test
Objective Determine if hidden failure has occurred
Interval
Fixed time interval
(can be set based on risk assessment e.g. SIL)
When to use Protective functions, hidden failure modes

Condition Based Maintenance
Task Type Measurement of condition
Objective
Restore or replace based on a measured condition
compared to a defined standard
Interval Fixed interval between condition assessments
When to use
Random failure modes
(i.e. those with constant probability of failure)

FunctionalPerformance
Time
P = change in condition or performance
detected
F = functional
failure
The P-F Curve
smooth
running
impending
failure
limited
functionality
PF Interval = lead time to failure
further
degradation

Predictive Maintenance
Task Type Calculation and extrapolation of parameters
Objective Determine if failure is imminent and intervention is required
Interval
Continuous online monitoring of parameters, intervention as
required
When to use Well understood failure modes with significant consequences

Risk Based Maintenance
Task Type Inspection or Test
Objective
Determine condition, conduct risk assessment and establish
when next inspection, test or intervention is required
Interval
Time based interval between tasks and scope of task is
based on risk assessment
When to use
Often used for pressurised equipment (vessels, piping etc.)
and can be used for pressure relief valves

Deferred Maintenance
Considered Corrective Maintenance
Task Type Repair / Replace
Objective
Restore or replace following failure. Result of a Run to Failure
Strategy or an unplanned failure.
Interval
Not applicable, but intervention is deferred to allow for proper
planning & scheduling.
When to use As part of a Run-to-failure strategy

Emergency Maintenance
Considered Corrective Maintenance
Task Type Repair / Replace
Objective Restore or replace following unplanned failure.
Interval
Immediate intervention required, breaks into the Frozen
Weekly Schedule
When to use Avoid

Comparison of Maintenance Types
Maintenance Type
Preventive Maintenance Corrective Maintenance
Time
Based
Maintenance
Failure Finding
Maintenance
Condition Based
Maintenance
Predictive
Maintenance
Risk
Based
Maintenance
Deferred
Maintenance
Emergency
Maintenance
Task Type
Scheduled
Overhaul /
Replacement
Functional Test
Measurement of
condition
Calculation and
extrapolation of
parameters
Inspection or Test Repair / Replace
Repair / Replace
Objective
Restore or replace
regardless of
condition
Determine if
hidden failure has
occurred
Restore or replace
based on a
measured
condition
compared to a
defined standard
Determine if failure
is imminent and
intervention is
required
Determine
condition and
conduct risk
assessment to
determine when
next inspection,
test or intervention
is required.
Restore or replace
following failure.
Result of a Run to
Failure Strategy or
an unplanned
failure.
Restore or replace
following
unplanned failure.
Interval
Fixed time or
usage interval e.g.
1 month, 1,000hrs
or 10,000 km
Fixed time interval
(can be set based
on risk assessment
e.g. SIL)
Fixed time interval
for condition
measurements /
inspections
Continuous online
monitoring of
parameters,
intervention as
required
Time based
interval between
tasks and scope of
task is based on
risk assessment
Not applicable, but
intervention is
deferred to allow
for proper planning
& scheduling.
Immediate
intervention
required.

And what about
Planned vs Unplanned Maintenance?
or
Proactive vs Reactive Maintenance?

Planned vs Unplanned Maintenance
This is all about whether you have
planned, i.e. properly prepared,
your maintenance such that
you can execute it efficiently.

Planned
Maintenance
Work that has been prepared
in advance by a planner.
All preventive maintenance
should be planned maintenance
Almost all of your corrective
maintenance should be planned
maintenance.
Unplanned
Maintenance
Work that is executed
without advance preparation.
This should only be the most
urgent corrective maintenance
i.e. emergency maintenance.
Emergency maintenance
should be < 2% of total
maintenance workload.
vs

Reactive vs Proactive Maintenance
This is really a differentiation
in maintenance culture.
Are you chasing failures
or continuously improving?

Proactive
Maintenance
A maintenance culture that is
focused on continuously
improving.
Preventive maintenance is
executed on time.
Defects when detected are
eliminated. Improvements are
made by all.
Reactive
Maintenance
A maintenance culture that is
dominated by failures.
The organisation is caught in a
vicious cycle of equipment
breakdowns.
Firefighting is the norm. There is
no time for improvement.
vs

make your plant more reliable, more profitable and safer

Types of Maintenance

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