TWI Frequently asked questions
by Alan Smith
The Pressure Equipment Directive (PED) requires a manufacturer to subject each item of pressure equipment that he will place on the market to a 'conformity assessment procedure'.
The conformity assessment procedure prescribes inspection and quality assessments appropriate to the level of hazard and environmental impact should a failure occur. The steps involved are outlined below:
- Consider the fluid group to discriminate between dangerous fluids and more benign fluids. Group 1 fluids include explosive, highly flammable, toxic and oxidising fluids. Group 2 fluids comprises all other fluids includingsteam.
- Assess the stored energy in the vessel in terms of pressure and volume or, for pipes and pipework, pressure and nominal diameter.
- Derive the risk category from tables and reference to charts (see Fig.1).
- Choose a conformity module using either an inspection or quality system route most suitable to meet the requirements of the situation (see Table 1).
Fig 1. Typical chart illustrating risk categories for vessels containing Group 2 gasesCat 1 PxV between 50 and 200barlitres
Cat 2 PxV between 200 and 1000barlitres
Cat 3 PxV between 1000 and 3000barlitres
Cat 4 PxV over 3000barlitres FAQ: Who is responsible for conformity to the Pressure Equipment Directive?
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