Environmental Engineering Reference
In-Depth Information
• unavoidable deviations of the given parameters;
• unacceptable increase of operating costs.
For some subjects, the limiting state is the final stage in its operation,
i.e. object is removed from service, and for others it is a certain phase in
the operating schedule requiring repair work.
In this context, objects can be:
•
non-recoverable
, for which performance in the event of failure cannot
be restored;
•
recoverable
, their performance can be restored, including by
replacement.
The non-recoverable objects include, for example: anti-friction bearings,
semiconductor products, gears, etc. Objects consisting of many elements,
such as metal-working machines, automobiles, electronic equipment, are
restorable since their failure is associated with damage to one or a few
elements that can be replaced.
In some cases the same object depending on the features and stages of
operation or purpose may be recoverable or non-recoverable.
Failure
- an event consisting of the breach of the operational state of
the object.
Failure criterion
- the distinguishing feature or a combination of
features used for establishing the moment of failure.
Types of failure are sub-divided into:
• functioning failure (the objects stops fulfilling the core functions, e.g.
broken gear teeth);
• parametric failures (some object parameters are changed in unacceptable
limits, such as loss of precision machine tools).
Reliability measure
quantifies the extent to which this object has certain
properties ensuring reliability. Some reliability measures (e.g. technical
resources, operating life) may have a dimension, a number of others (for
example, the probability of failure-free operation, availability factor) are
dimensionless.
Assigned operating lifetime
- the total operating time of the object after
which operation should be terminated regardless of its condition.
Useful lifetime
- calendar duration of service (including storage,
maintenance, etc.) from its beginning to the limiting state.
Figue 1.1 shows the graphical interpretation of these indicators, in
particular:
t
0
= 0 - the beginning of operation;
t
1
,
t
5
- points at which operatin is
interrupted for technical reasons;
t
2
,
t
4
,
t
6
,
t
8
- the moment when service
of the object is restarted;
t
3
,
t
7
- the moment when the objected is to
be repaired;
t
9
- the moment of cessation of operation;
t
10
- the time of
reaching thee limiting state.
Technical operating life
T
t
=
t
1
+ (
t
3
-
t
2
) + (
t
5
-
t
4
) + (
t
7
-
t
6
) + (
t
10
-
t
8
).
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