The Simple Pressure Vessels (Safety) Regulations 1991

8.  The manufacturer must, when designing the vessel, define the use to which it will be put, and select:

• the minimum working temperature;

• the maximum working temperature; and

• the maximum working pressure.

• However, should a minimum working temperature higher than minus 10° C be selected, the properties required of the materials must be satisfied at minus 10° C.The manufacturer must also take account of the following requirements:

• it must be possible to inspect the inside of the vessels;

• it must be possible to drain the vessels;

• the mechanical qualities must be maintained throughout the period of use of the vessel for its intended purpose;

• the vessels must, bearing in mind their envisaged use, be adequately protected against corrosion,

• and of the fact that under the conditions of use envisaged:

• the vessels will not be subjected to stresses likely to impair their safety in use; and

• the internal pressure will not permanently exceed the maximum working pressure; however, it may momentarily do so by up to 10%.Circular and longitudinal seams must be made using full penetration welds or welds of equivalent effectiveness. Dished ends other than hemispherical ones must have a cylindrical edge.