Over a number of years TWI has helped member company Arnway Ltd to develop repair procedures for a variety of items of heavy engineering equipment. One instance concerned a 2750t capacity press for extruding aluminium sections owned by High Duty Alloy Extrusions Ltd. Ten years after going into service, leakage was observed through the 150mm wall of the 3m long x 1.2m diameter main hydraulic cylinder. The cause was identified as a fatigue crack initiating at the toe of a T butt weld attaching one of the three column housings to the outside of the cylinder. Closer examination revealed six further cracks.
The steel of the cylinder had a carbon equivalent of 0.4% and, although BS 5235 suggested preheat of 50◦C, it was decided to err on the side of caution because of the very high restraint, and to preheat to 150◦C.
This, combined with the restricted access, obviously made life difficult for the welders. Nevertheless a successful repair was achieved. Subsequent weld toe grinding and post-weld heat treatment meant that the anticipated life of the press was extended by many years.
The economic consequences for High Duty Alloys of this successful operation were significant. Not only was the cost of a replacement press saved, but also the plant was able to resume production rapidly.
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