Yes! Vacuum casings which do not have a maximum allowable pressure PS > 0,5 bar are therefore not pressure equipment in their own right.
However as structural elements attached to pressurised parts, they are part of pressure equipment and any negative effects of the vacuum casing and insulation on the pressurised parts must be taken into account and avoided.
Note: PED Article 2 (7) defines pressure relative to atmospheric pressure, i.e. gauge pressure. As a consequence, vacuum is designated by a negative value. It shall not be interpreted as “differential pressure between atmospheric pressure and absolute pressure prevailing inside the equipment” for the purposes of classification.
Inerting pressure > 0,5 bar of a pressure equipment which operates at ≤ 0,5 bar will have the consequence of including the equipment in the scope of the directive, if not otherwise excluded.
Typical application for vacuum insulated pressure vessels
Static vacuum insulated cryogenic vessels are used for the storage of cryogenic (refrigerated liquefied) industrial and medical gases.
Vessels used for the storage of cryogenic liquids consist of an inner pressure vessel, insulation, an outer jacket and the auxiliary equipment. The space between the inner vessel and the outer jacket (annular space) is under vacuum.
The gases are supplied in a liquid or gaseous phase to the customer’s point of use. The liquid or gas flow is normally achieved by pressure difference where the inner vessel and its contents are at a higher pressure than the customer’s point of use. To achieve this, the vessels are fitted with a vaporiser, normally called the pressure build up unit and a pressure regulator.
Standards for vacuum insulated pressure vessels
EN 1251: Cryogenic vessels – Transportable vacuum insulated vessels of not more than 1000 litres volume – Part 2: Design, fabrication, inspection and testing.
EN 13458-2: Cryogenic vessels – Static vacuum insulated vessels – Part 2: Design, fabrication, inspection and testing
EN 13530-2: Cryogenic vessels – Large transportable vacuum insulated vessels – Part 2: Design, fabrication, inspection and testing
ISO 20421-1: Cryogenic vessels – Large transportable vacuum-insulated vessels – Part 1: Design, fabrication, inspection and testing – V > 450 l volume
ISO 21009-1: Cryogenic vessels – Static vacuum-insulated vessels – Part 1: Design, fabrication, inspection and tests
