New gas for welding cuts danger factor

Scientists at Singapore’s Greengas company say they have produced an alternative fuel to oxyacetylene, one of the most dangerous gases used in welding and flame cutting operations by the offshore, fabrication, construction, and shipbuilding industries. Tests by the Singapore Government’s products and standards board back Greengas’s claim to have developed a low-cost, simple and environmentally […]

Scientists at Singapore’s Greengas company say they have produced an alternative fuel to oxyacetylene, one of the most dangerous gases used in welding and flame cutting operations by the offshore, fabrication, construction, and shipbuilding industries.

Tests by the Singapore Government’s products and standards board back Greengas’s claim to have developed a low-cost, simple and environmentally friendly way to generate a safe, combustible gas on site.

The Ministry of Defence and the offshore and car industries are said to be interested. John Nixon, principal research adviser at Cranfield University’s marine technology centre, expects to be using the gas in comparative studies of cutting performance soon.

‘It has a lot of intriguing possibilities but I cannot talk about that without the hard numbers,’ he says.

Unlike acetylene a hydrocarbon fuel which explodes even at low pressure and forms high levels of poisonous carbon monoxide during burn greengas, produced from water to form a 2:1 mix of hydrogen and oxygen, is stable and non toxic.

It is also cheaper, at £3.12 for six hours’ supply compared to £80 for the same amount of acetylene. As it is extremely light, it will not ignite beyond 75mm, can be delivered up to 45m along a cable and works at up to 30m above the supply unit.

It can be used to cut and weld under water, and the burn temperature adjusts to suit the material through a process called thermo-nuclear reaction.

Using the same pressure around 3.5 bar and flow rate, it is possible to weld aluminium sheet at 660 C or turn tungsten to vapour at 6,000 C. A highly focused greengas flame can drill holes in high-temperature refractory products in seconds and turn brick to glass.

Cranfield’s Nixon says questions about greengas’s performance are raised by the fact that acetylene theoretically has a higher flame temperature than the hydrogen used in greengas, and temperature affects cutting speed.

But greengas’s developers say it can cut up to 25% faster than acetylene, cutting 25mm thick mild steel at 300mm/min. They say a theoretical flame temperature up to 2,900 C is possible, because the flame is formed by implosion not the usual explosion.

The developers use the phrase ‘interactive combustion’ to explain how flame temperature varies according to the material. The flame’s calorific response is governed by the rate of mono-atomic absorption of hydrogen on the surface of the material.

Their main achievement has been to develop a 120kg greengas generator, which produces 1,500 litres of gas per hour. One litre of water makes 1,860 litres of gas.

Sodium hydroxide is used in the electrolysis process, which dissolves water to produce the hydrogen/ oxygen mix. The principle is not new, but the ability to make the gas commercially is seen as a breakthrough.