Nachbehandlung an Schweißnähten - Alte Technik im Vergleich

Post treatment on fillet weld seams - Old technique compared.

The increase of lifetime of welded structures is a permanent challenge for design and stress calculation engineers, but also for the workshop and quality engineers. The inauguration of high strength steels also in structural steel engineering and the need to reduce the weight and therefore the cost requires more and more concentration on weldment details. Fundamental on the increase of lifetime welded structures is to avoid any weak areas, which can fail ahead of lifetime due to initiated cracks.
Particularly fillet welds, which are widely used in all types of structures, are difficult to treat after welding by grinding. Presently in Germany the application of mechanical post weld treatment techniques are discussed and investigated. To compare the quite sophisticated technique UIT with a very simple and cheap workshop tool an own investigation had been carried out. It is shown that even low cost tools appropriate applied can give comparable good effects on extended life time on welded structures. The investigations were carried out with robot welded cruciform joint samples on middle strength mild steel S355.
The UIT treatment techniques give a significant improvement in fatigue strength of fillet welds. This applies not only in the increase of the achieved load cycles, but also in the increase of a possible stress level. The fatigue strength rises from 60 MPa as welded to 145 MPa after UIT treatment. The achievable load cycles can be increased by 10 times.
However with proper application of the quite simple pneumatic needle scaler or slag hammer a similar improvement can be achieved. Even shot peeling improves lifetime up to 5 times.
The effect of these post weld treatment techniques based on three important factors: the improvement of the geometry of the weld toe, the compacting of the metal, thereby a higher strength in the important zone and the neutralization of the welding residual stress by inserting compression stress.