More safety without welding seams

More safety without welding seams

Keywords: Pressure, Heggemann, Storage

A significant increase in safety for aviation and aerospace is believed to be expected by a new manufacturing process of pressure vessels, which Heggemann Aerospace & Engineering, Germany, has developed; the vessels are made from one piece only, without any welding seams, reportedly giving it a much higher long-term strength. The pressure storage cylinder for the hydraulics in Airbus airplanes have already been produced using this new technique.

Until recently pressure vessels had to be made by welding two halves together. This welding process always bears a risk factor as far as long-term strength and durability is concerned, even if carried out according to the strict aerospace regulations. To eliminate the risk of welding the seam,Heggemann's technicians conceived the idea of manufacturing these vessels from a single piece. This was achieved by a clever combination of techniques.

Such a high pressure vessel in a spherical shape withstands a pressure up to 2,000 bar (Plate 3). As elaborate testing is reportedly no longer necessary, the final product is usually no more expensive than the welded version.

 Plate 3 Seamless spherical pressure vessels

The company have been producing components for the aviation and aerospace industry for more than 30 years. It claims it can deliver complete products including development, machining, welding, heat testment and surface treatment.

For some time now the company has been working on flowforming tubular or cone-shaped parts. This production technology is said to be a little bit like doing pottery. Under high rotation and pressure at certain points the material is workable. Owing to the new technique Heggemann reports that it is now in a position to deliver rotary-symmetrical components from high quality materials. These components are also used as hydraulic cylinders, rocket burners, engine parts, fuel tanks for rockets and satellites, drive shafts, energy and pressure storage, jet tubes and liners.

The seamless pressure vessels can be made from almost all metals: however,the customers prefer high strength, stainless high-grade steel, titanium or aluminium. The material is being cold hardened by flowforming, giving it a higher strength. Using this technique, it is possible to reduce the wall thickness of the components and the weight by up to 30 per cent. Products without welding seams can be made up to 42cm in diameter and 250cm in length.

According to Heggemann the new production method can also be used for the manufacture of composite pressure vessels. In the past, seamless liners in aluminium were used; however, there is now believed to be a preference for components in stainless steel as the aluminium liners often show signs of corrosion after ten or more years in service. The Westphalian technology centre can now supply seamless stainless high-grade steel liners with a wall thickness of 0.3mm. This enables the customers to produce almost maintenance-free composite pressure vessels that will reportedly last 20 years and longer.

Keeping stock of special alloys at their plant at the airport Paderborn/Lippstadt, the aerospace and engineering specialists state that they usually only need a lead time of three to six months for the development of a new product.

Further details are available from Heggemann GmbH. Tel: +49 (0) 2955 7610 14;Fax: +49 (0) 2955 7610 44.