Specifications and quality control

This chapter discusses the importance of specifications for composition of materials and their quality analysis. Specifications may relate to materials, components, or end products, some of which may be complex units that are manufactured from standard materials and components. They fall into two main groups: dimensional that defines form and shape and quality. The most widely used system internationally for designating carbon and alloy steels is the American Iron and Steel Institute (AISI). The situation with plastics is very different, with the formulations proprietary to the manufacturers. Property values in data sheets must be used with caution, paying particular attention to the test standards that are used. The fourth class of standard is a code of practice. In British terminology, this embodies the accepted principles of good practice and sets out the methods of erection or installation, or the suitable conditions of use to give performances as intended. A converse criticism is that standards, by their nature, tend to reduce all to a common denominator, thereby restricting enterprise and development of new materials.