Mechanical Technology July 2016

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32 Mechanical Technology — July 2016
⎪ Structural engineering materials, metals and non-metals ⎪
Engineering is taught as a
science. Simplified, but not
always simple, models that
apply to specific circumstances
are often reduced to numeric descrip-
tors. On the worksite, the young engi-
neer finds that reality is more complex.
Models are overlaid, model edges are
less certain and judgement and/or
compromise are required. This is the art
of engineering, learned and developed
through experience.
The Engineer is often legally respon-
sible for safety. If a structure fails and
people are adversely affected, engineer-
ing decisions fall under the magnifying
glass. Choices are guided by competence
based on training and experience, under-
pinned by standards within the scope of
local, regional and national legislation.
This is outlined below.
Are standards recipes, a set of instruc-
tions that yield a satisfactory result for
the layman? Are standards the same as
operating procedures used in companies,
bureaucratic procedures that are applied
to ensure predictable behaviour under
specific operating circumstances? No
and no.
However quality standards such as
ISO 3834: Quality requirements for fu-
sion welding, as part of the ISO 9001
suite of quality management standards,
are closer to operating procedures than
are design and fabrication standards.
Compiled by experts, these use a com-
bination of repeatable science experience
and history to draw up recommenda-
tions. But cultural and commercial
influences may play a role. So whilst
standards make a valuable contribution
to decision making, they cannot possibly
cover all eventualities – they must be
generic in nature.
Compliance with standards is a
starting point, a guide, not a goal.
Consequently, being very familiar with
relevant standards, engineers also need
to understand the philosophy and think-
ing behind the standards. BS 5700 notes
In this month’s Materials engineering in practice column Tony Paterson talks
about standards, their history, role and value.
A diagram illustrating the relationship between the engineering designer, standards and support systems.
Materials engineering in practice:
musings on standards
that ‘compliance with a British Standard
does not in itself confer immunity from
legal obligations.’ Whilst there is no
excuse for being unfamiliar with relevant
standards, Engineers Australia (March
2009) notes that ‘Engineers cannot
avoid liability in negligence by simply
relying on a current or published stan-
dard or code.’
In principle, the failure to guard
against a foreseeable risk, even a small
one, via a means that involves little
difficulty or expense, will generally be
regarded as negligent.
Where did standards come from?
The Industrial Revolution – the move
from an agrarian to an industrial base
and the transition to new manufacturing
processes – developed country by country
in the period from about 1760 in England
to sometime between 1820 and 1840.
This led to the need for clients to specify
what they required.
The increased use of high-precision
machine tools led to a need for inter-
changeable parts and, in 1800, the
first industrially practical screw-cutting
lathe began the standardisation of
screw thread sizes. In 1841 Joseph
Whitworth’s screw thread measurements
were adopted as the first (unofficial) na-
tional standard by UK companies – and
other countries soon followed.
By the end of the 19th century, differ-
ences in standards between companies
were making trade increasingly difficult
and strained. Efforts were being made to
standardise electrical measurement, for
example, with a large range of different