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: