Mechanical Technology July 2016

⎪ Structural engineering materials, metals and non-metals ⎪

Materials engineering in practice: musings on standards

In this month’s Materials engineering in practice column Tony Paterson talks about standards, their history, role and value.

E ngineering 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

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 19 th 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

A diagram illustrating the relationship between the engineering designer, standards and support systems.

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Mechanical Technology — July 2016