Specifications

November 19, 2009

A specification is an explicit set of requirements to be satisfied by a material, product, or service. [1] Should a material, product or service fail to meet one or more of the applicable specifications, it may be referred to as being out of specification;[2] the abbreviation OOS may also be used.[3]

A technical specification may be developed privately, for example by a corporation, regulatory body, military, etc: It is usually under the umbrella of a quality management system [4]. They can also be developed by standards organizations which often have more diverse input and usually develop voluntary standards: these might become mandatory if adopted by a government, business contract, etc.

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Use

In engineering, manufacturing, and business, it is vital for suppliers, purchasers, and users of materials, products, or services to understand and agree upon all requirements. A specification is a type of a standard which is often referenced by a contract or procurement document. It provides the necessary details about the specific requirements.

Specifications may be written by government agencies, standards organizations (ASTM, ISO, CEN, etc), trade associations, corporations, and others.

A product specification does not necessarily prove a product to be correct. An item might be verified to comply with a specification or stamped with a specification number: This does not, by itself, indicate that the item is fit for any particular use. The people who use the item (engineers, trade unions, etc) or specify the item (building codes, government, industry, etc) have the responsibility to consider the choice of available specifications, specify the correct one, enforce compliance, and use the item correctly. Validation of suitability is necessary.

Guidance and content

Sometimes a guide or a standing operating procedure is available to help write and format a good specification.[5], [6], [7]. A specification might include:

Process capability considerations

A good engineering specification, by itself, does not necessarily imply that all products sold to that specification actually meet the listed targets and tolerances. Actual production of any material, product, or service involves inherent variation of output. With a normal distribution, the tails of production may extend well beyond plus and minus three standard deviations from the process average.

The process capability of materials and products needs to be compatible with the specified engineering tolerances. Process controls must be in place and an effective Quality management system, such as Total Quality Management, needs to keep actual production within the desired tolerances.

Effective enforcement of a specification is necessary for it to be useful.

 

Piping & Instrumentation Diagram

November 19, 2009

A piping and instrumentation diagram/drawing (P&ID) is a diagram in the process industry which shows the piping of the process flow together with the installed equipment and instrumentation.

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Contents and Function


An example of a P&ID.

A piping and instrumentation diagram/drawing (P&ID) is defined by the Inst...


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Process Flow Diagram

November 19, 2009

A process flow diagram (PFD) is a diagram commonly used in chemical and process engineering to indicate the general flow of plant processes and equipment. The PFD displays the relationship between major equipment of a plant facility and does not show minor details such as piping details and designations. Another commonly-used term for a PFD is a flowsheet.

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Process Design

November 19, 2009

Process design is the design of processes for desired physical and/or chemical transformation of materials. Process design is central to chemical engineering and it can be considered to be the summit of chemical engineering, bringing together all of the components of that field.

Process design can be the design of new facilities or it can be the modification or expansion of existing facilities. The design starts at a conceptual level and ultimately ends in the form of fabrication and construc...


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