STORAGE & QUALITY OF CO₂ GAS

CO₂ gas is supplied in cylinders at a  high pressure (140 kg / cm²). When the cylinder is full, nearly 90 % of the volume is filled with CO₂ liquid and balance liquid phases are in equilibrium pressure. Two type of CO₂ cylinders are available viz. Gas type and syphonic type. In gas type cylinders gaseous CO₂ is withdrawn when the cylinder valve is opened. The physical properties of CO₂ are such that if the gas is taken off too fast, the CO₂ gas in the cylinder will freeze as the temperature and pressure within the cylinder drop rapidly. Where CO₂ requirements are in excess of 20 l / min the use of siphon cylinder is recommended. These are fitted with an internal tip tube and CO₂ is withdrawn as liquid which must then be passed through a vapouriser unit with sufficient capacity to suit the rate of draw off required. All CO₂ cylinders must also be fitted with a heater near the gas regulator to avoid freezing around the regulator.

The quality of the CO₂ gas used for welding must conform to BS 4105:1967 or IS 307:1966. As per the above standards the moisture in the CO₂ gas should be less than 10 ppm.