OBSOLESCENCE
Matee Nuserm/Shutterstock
for some assets obsolescence of the
component parts may play a greater part
in assessments of residual life.
For example, where nowadays would
you go to source a replacement for an
Intel 8008 microprocessor or some of
the older memory chips? Perhaps eBay?
But what would be their provenance?
That said, some electronic components
such as electrolytic capacitors have seen
general improvements – for example
being routinely available to higher rated
temperatures. Routine replacement
of electrolytic capacitors in control
electronics and power supplies could bring
real benefits for life extension because
overheating is a major cause of failure,
especially where drives are used in dusty
conditions, as they often are.
In contrast, obsolescence tends not
to be a very significant factor for the life
expectancy of cables. There are many
recorded instances of cables which are
over 100 years old and still providing useful
service. This is of course dependent on
factors such as the quality of manufacture
and installation, as well as use within
specification in a benign environment.
Environmental factors can result in service
life being a lot less – perhaps 20 years.
Ultraviolet exposure, minor manufacturing
defects and inconsistencies, partial
discharge and water treeing may all be
significant degradation factors.
Cable insulation and construction
Other advice on ageing equipment
Over the last five years, a new methodology of hazard identification has
emerged that aims to pick up on hazards caused by the accumulation of many
small changes – so-called ‘creeping change’. A guide was published in 2017
by the Petroleum Institute (see www.is.gd/cojebo). It says: “The CCHAZID
methodology covers both engineering (including process safety; mechanical
engineering, and electrical, control and instrumentation (EC&I)) and human/
organisational changes.” It argues that the techniques, which were developed
for high-hazard industries, are applicable to any industry, and should be used
to regularly review plant risks in terms of safety, environment and commercial
aspects. The subject continues to be taught by HSL, including in a Buxton
course in early February 2022 (see www.is.gd/iricol).
Ageing assets are a particular problem in the nuclear power industry, as
many commercial stations have had their initial operational term extended.
International nuclear agency IAEA has expanded its guidelines for long-term
operation of nuclear reactors through its peer-review process called SALTO
(safety aspects of long term operation; www.is.gd/ekiguh). The first such
mission was in 2005, and more than 40 have been carried out. -Will Dalrymple
tend to be optimised for particular types
of use, for example fire resistance or
high temperature. But optimising for
one characteristic is generally to the
detriment of others, such as flexibility
or permeability to water, which may
be particularly so for some earlier
generations of cables. There may
also be batch differences
between nominally
identically specified
cables. Again, it comes
down to knowing what
you’ve got, observing
changes, testing
as appropriate and
keeping detailed and
accurate records.
These examples have
been chosen because in
some respects they represent
extreme cases of a type of ageing
management. They are certainly not the
only assets with age-related problems.
One might mention switchgear and
protection as an example of the need for
regular maintenance activity and where
aftermarket upgrades of ageing plant may
bring real benefits, or UPS as an example
of where accurate understanding of the
original requirement may have already
determined the achievable asset life,
given good maintenance.
Mindful of many of the issues
outlined above, EEMUA has tried to
give a helping hand by producing new
guidance developed by its electrical
engineering committee, which brings
together engineers, technical authorities,
policy managers and others from across
industry. EEMUA 227, ‘Management of
ageing electrical assets’, has sections
dealing with UPS, electrical drives,
electrical protection devices,
power cables, switchgear,
transformers, and
generators and motors.
Each section
has a similar
structure: technical
introduction, typical
failure modes,
condition monitoring
techniques, expected
and acceptable values,
assessment of failure risk,
life extension methods. The guiding
principle has been not to duplicate
the content of some of the existing
excellent guidance available in standards,
from regulators, or on the internet
generally, but to give a broadly applicable
overview with pointers to more detailed
information.
Probably there aren’t too many
engineers who would deliberately set out
to be experts on ageing electrical plant.
Hopefully they won’t need to be if they
can be better equipped to understand the
issues and find the right information.
kcube - Kaan Baytur/Shutterstock
42 www.operationsengineer.org.uk Winter 2021
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/www.operationsengineer.org.uk