To establish whether or not you need a pressure vessel inspection, simply multiply the vessel operating pressure (in bar units) by the vessel capacity ( in litres). For example 20 bar x 100 litres = 2000 bar/litres capacity and therefore is above the 250 bar/litres threshold. This system would require an inspection with a written scheme of examination.

LEGAL REQUIREMENTS 

There is a legal requirement for thoroughly examining pressure vessels and receivers containing steam, compressed air, and refridgerants. Any pressure vessel containing compressed gas over 250 bar/litres capacity requires inspection.