Weld-on

engineers have been attempting for long to develop a system so that welding could be performed underwater. A newly observed 'dry-tunnel' phenomenon will allow laser welders to carry out deep-water engineering. The new technique would allow them to weld pipelines even below 200 m from the water surface.

A carbon dioxide laser forms a very narrow column ahead of the beam. The laser heats water up to temperatures of nearly 4000c, and instantly vaporises it, forming a penetrating tunnel of superheated steam. Once this millimetre-thick dry corridor is formed, the light beam does not have to pass through water and can weld steel. This is the first time that scientists have investigated the dry-tunnel phenomenon.

At present, engineers employ dry habitats -- water-tight sheds pumped full of oxygen and helium gas for deep-sea repairs. But the technique is very difficult for the divers to work with. At the same time, it is also expensive for them to stay in water for long to perform welding jobs.

In such circumstances, the new laser welding device would prove to be more efficient than the dry-habitats. However, there is a problem with the laser device. The size of the device is equivalent to a small car, which can only weld 6 mm steel. Scientists will have to reduce the size of the laser device to make it more efficient.

SCIENTIFIC DEVELOPMENT Science & Technology