Mechanical Technology Archive

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

Tony Paterson Wits Engineering materials in practiceEngineering is taught as a science. Simplified but not always simple, models that apply to specific circumstances are often reduced to numeric descriptors. On the worksite, the young engineer 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 responsible for safety. If a structure fails and people are adversely affected, engineering decisions fall under the magnifying glass. Choices are guided by competence based on training and experience, underpinned by standards within the scope of local, regional and national legislation.

Standards diagramAre standards recipes, a set of instructions 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 fusion 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 combination of repeatable science experience and history to draw up recommendations. 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 thinking 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 standard 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 interchangeable 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) national standard by UK companies – and other countries soon followed.

By the end of the 19th century, differences 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 standards and systems being used by electrical engineering companies.

The Engineering Standards Committee was established in London in 1901 as the world's first national standards body. It subsequently extended its standardisation work and, in 1918, became the British Engineering Standards Association, adopting the name British Standards Institution (BSI) in 1931. National standards were adopted universally throughout the country. These enabled markets to act more rationally and efficiently, with increased levels of cooperation.

After the First World War, similar national bodies were established in other countries. The Deutsches Institut für Normung (DIN) was established in Germany in 1917, followed by its counterparts, the American National Standard Institute (ANSI) and the French Commission Permanente de Standardisation (CPS), both in 1918.

Because specification authorities developed separately, the nature and philosophy of specifications was affected by the cultural traits of the country or countries responsible. These traits include choices such as professionalism versus statutory control; uniformity versus flexibility; conservatism versus optimism; and secrecy versus transparency – philosophies that are also reflected in the education systems of different countries and in national ways of thinking.

As an example, the US standards for welded fabrication tend towards method specifications. Provided the methodology is followed correctly, the risk of failure is taken by the client. Inspection is easy. On the other hand the European EN codes tend towards performance standards. Whilst more design and fabrication flexibility is given, the risk is carried by the designer/fabricator. Not surprisingly, the EN codes appear more lenient but require more skilled interpretation and more competent engineering. More specific information gathering and testing may be required and inspection is more complex.

Initially countries were largely isolated in terms of technology development with specifications developing separately in different countries. Over time organisations seeking common approaches emerged.

The League of Nations, first proposed by US president Woodrow Wilson as part the plan for an equitable peace in Europe, was created in 1920 to provide a forum for resolving international disputes. The United States never became a member, but the United Nations Organisation (UN) was founded after the Second World War with similar but broader objectives.

As international trade increased the need for common specifications developed. The International Standards Organisation (ISO) was founded in February 1947 to promote ‘worldwide proprietary, industrial and commercial standards’. The USA has never been a member.

The GATT agreement of 1948 dealt with regulation of trade between participating countries by providing a framework for negotiating trade agreements and a dispute resolution. The World Trade Organisation (WTO) was formed in 1995 to take over GATT responsibilities.

The European Union grew from the 1951 Coal and Steel treaty between six countries to manage heavy industries. These countries agreed on a common market in 1957. Membership was expanded in 1973 and the single European act of 1987 expanded common market flexibility paving the way for the common EN specifications and standards we see today.

Working in conjunction to simplify understanding, the ISO and EN specifications have moved closer together. There is a gentleman’s agreement that attempts to make all EN standards into ISO standards and vice versa, but this does not work for all standards.

Harmonised EN Standards apply only to those that are considered relevant to satisfying European Safety Requirements (ESR) in products (such as pressure vessels) in support (such as welding) and engineering material directives. Harmonised standards contain an appendix Z, which defines which directives and ESRs the standard meets. For example, EN ISO 15614 for the specification and qualification of welding procedures will be harmonised, but other routes for weld procedure approval may not be, such as EN ISO 15610, EN ISO 15611, EN ISO 15612, etc.

From time to time, various countries’ standards clashed. Why? First, the base philosophy differs, between method-based requirements (input – what to do); and end-specifications or performance-based philosophies (output – what the project or element should do). The choice reflects local culture and the practical consequences lie in risk apportionment.

Specifications, standards and codes

In principle a standard is a document, prepared and published in accordance with established procedures that applies collectively to codes, specifications, recommended practices, classifications, test methods, and guides. Standardisation refers to the process of establishing, by common agreement, the criteria, terms, principles, practices, materials, items, processes, equipment, parts, sub-assemblies, and assemblies appropriate to achieve the greatest practicable uniformity of products and practices.

Standards ensure a minimum feasible variety of such items and practices.


•          A specification document is generally considered to be a working or business document, developed by one entity, which may use content from one or more standards and may alter the said content to meet whatever needs. They are intended to clearly and accurately describe the technical requirements of any given product or process.

•          A standard is a set of technical definitions and guidelines covering specific narrow topics that function as input for designers, manufacturers, operators, or users of equipment – an agreed way of doing something. Whilst standards rarely cover all known exceptions for all circumstances, they are typically at the heart of quality management and control systems such as ISO 9000.

•          Codes are a mandatory collection of standards, adopted by one or more governmental bodies, or incorporated into a business contract. Codes are enforceable by law.

Standards are powerful tools that can help drive innovation and increase productivity. They can make organisations more successful and people’s everyday lives easier, safer and healthier. They represent the distilled wisdom of people with expertise in their subject matter and who know the needs of the sectors they represent.

The purpose of a standard is to provide a reliable basis for people to share the same expectations about a product or service.

Standards help to facilitate trade; provide a framework for achieving cost effectiveness, efficiency and interoperability; and they enhance consumer protection and confidence.


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