What is a Pressure System?

Pressure Systems include air receivers, pipework and hoses, boilers and steam generators, autoclaves, pressure cookers, pressurised plant and piping, compressed air systems (fixed and portable), heat exchangers and refrigeration plant,valves, steam traps and filters, pressure gauges and level indicators, pressure Dewars, nitrogen generators etc. The aim of the Pressure Systems Safety Regulations 2000 (PSSR) is to prevent serious injury from the hazard of stored energy as a result of the failure of a pressure system or one of its component parts.

A decision tree to help to determine whether a pressure system is subject to the Pressure Systems Safety Regulations 2000 (PSSR) and requires a written scheme of examination (WSE) is incorporated into the latest HSE guidance. Please note, the decision tree does not apply to pipework and systems connected to a transportable pressure receptacle (gas cylinder).

There are two types of Pressure System each with a separate set of regulations.

The Pressure Systems and Safety Regulations apply to systems comprising one or more pressure vessels with pipework and protective devices;
pipework and protective devices to which a transportable pressure receptacle (e.g. a gas cylinder) is connected or a pipeline (i.e. pipework crossing the boundaries of premises) and its protective devices which contain a “relevant fluid” such as steam at pressure, fluids at a pressure of >0.5 bar above atmospheric or a gas dissolved under pressure in a solvent contained in a porous substance (e.g. acetylene).

There are exceptions to the Regulations which include systems pressurised unintentionally or solely during leak testing; pipelines under 2 bar above atmospheric pressure; engine water cooling systems; 2 part beer kegs or containers for beer or carbonated drinks <0.252 m³ capacity and <12 bar above atmospheric pressure; vapour compression refrigeration systems with power <25 kW; portable fire extinguishers <25 bar and <23 kg weight; and hand held tools/appliances.

Systems (other than those containing steam) where the product of the pressure (in bars) and the volume (in litres) is <250 are exempt from some of the Regulations (in particular, the need for a written scheme of examination).

The Simple Pressure Vessels Regulations apply to vessels containing only air or nitrogen; with pressure between 0.5 and 30 bar; with temperature -50^oC and <300^oC (steel vessels) or <100^oC (aluminium vessels) and not intended to be exposed to flame; and specified materials/construction.

Pressure vessels that are made of non-alloy quality steel, non-alloy aluminium, or non-age hardening aluminium alloy; cylindrical component with the ends being outwardly dished or flat, or two co-axial outwardly dished ends; maximum working pressure (PS) 30 bar and maximum working pressure multiplied by capacity (i.e. PS.V) is not more than 10 000 bar litres; minimum working temperature is no lower than minus 50⁰C, and the maximum working temperature is not higher than 300⁰C (steel) or 100⁰C (aluminium) are subject to these Regulations.

They must be manufactured in accordance with sound engineering practice and must meet specified manufacturing requirements; possess a safety clearance; display the UKCA or CE mark; be accompanied by the manufacture’s instructions; be safe and be marked with
- the maximum working pressure in bar
- the maximum working temperature in degrees Centigrade
- the minimum working temperature in degrees Centigrade
- the capacity in litres
- the name or mark of the manufacturer
- the type of serial number.

Additional reading and guidance
UK Legislation and useful guidance can be found via the HSE Pressure Systems webpage.
Additional guidance and industrial standards can be downloaded from the University of Warwick Library through the Construction Information Service database, including guidance by the British Compressed Gas Association (BCGA); British Oxygen Company (BOC) have a leaflet and CD available via Safe under Pressure and Product Standards can be downloaded from the DTI Product Standards: Pressure Equipment (URN 05/1074)