Testing welds under heavy test loads

For safety monitoring on welded structures, laboratory samples alone are not enough. Component tests are also important. For this, special equipment for clamping objects is required. The larger the object, the larger this equipment has to be. The BAM Federal Institute for Materials Research and Testing has developed its own medium load test stand producing tensile and pressure forces of up to two mega-Newtons (MN). Two MN are the equivalent of approx. 200 tonnes of test load. BAM now has three weld test stands available for forces of up to 1600 tonnes.

With this new facility, which is unique worldwide, structural steel can be examined in three dimensions during welding. Welding puts a lot of stress on materials. Components may be damaged and their safe operation may no longer be guaranteed if heat input is not carefully guided.

A current BAM project examines heat-resistant structural steels for power plant and petrochemical reactor construction. Heat resistant steels are characterised by their high strength even at high temperatures.

In the new machine, and two similar ones also developed at BAM with 50 and 1600 tonnes of tensile and pressure force respectively, stress and strain distribution in welds under clamped conditions are tested. Simply put, the question is: How do you weld in order to avoid cracks and increase crack resistance?

The new medium load test stand features six independently operating hydraulic cylinders with which component movement can be monitored and changed during welding. Because the swivel arm can be rotated 180 degrees, all welding positions can be achieved.

The machine can be used as a test system for exerting force onto existing samples as well as a measuring system, for example for measuring sample behaviour during welding. "Our goal is to use this system to examine the interactions between materials and study design and stress on components with regard to component safety during manufacturing and operation" says BAM project manager and engineer Thomas Kannengießer.

Contact:
Dr.-Ing. Thomas Kannengießer
Department 9 Component Safety
Email: thomas.kannengiesser@bam.de

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