This document applies to welded composite enclosures of cast and wrought aluminium alloy pressurized with dry air, inert gases (e.g. sulphur hexafluoride or nitrogen or a mixture of such gases), used in indoor and outdoor installations of high-voltage switchgear and controlgear with rated voltages above 1 kV, where the gas is used principally for its dielectric and/or arc-quenching properties with rated voltages:-above 1 kV and up to and including 52 kV concerning gas-filled compartments with design pressure higher than 300 kPa relative pressure (gauge);-above 52 kV concerning all gas-filled compartments.The enclosures comprise parts of electrical equipment not necessarily limited to the following examples:-circuit-breakers;-switch-disconnectors;-disconnectors;-earthing switches;-current transformers;-voltage transformers;-surge arrestors;-busbars and connections;-etc.The scope also covers enclosures of pressurized components such as the centre chamber of live tank switchgear, gas-insulated current transformers, etc.