"Tubular structures are steadily gaining popularity; not just for aesthetic reasons, but also as a means of optimizing material usage in terms of weight to strength ratios. Such was the case for a new covering for the famous tennis courts of Wimbledon.
J.N. Rowen Limited, one of the United Kingdom's leading independent structural steel working companies, has recently branched into the design and fabrication of tubular structures requiring high integrity welds. J.N. Rowen Limited has an annual throughput exceeding 20,000 tonnes and have the flexibility to undertake projects from 100 to 10,000 tonnes. J.N. Rowen has a commitment to continuous development and investment in employees, plant, buildings and technology.
After securing the prestigious steel work contract for the new Wimbledon No. 1 Court, J.N. Rowen approached Lincoln Electric (UK) Limited for advice regarding new welding procedures. Lincoln Electric was then able to illustrate the benefits of using the unique inverter based Surface Tension TransferTM process.
The STT process was seen as the next step in their continuing development of welding technology; offering enhanced product quality, greater productivity and increased profitability.
Benefits Indetified by J.N. Rowen Ltd.
Ease of Use
Optimum arc characteristics, were maintained, even with variations in electrode extension. This released the welder from the need to maintain exact lengths and welding gun angles in order to produce a smooth, low spatter, high integrity weld. Full welder training and welder qualifications were completed within one day.
Controlled Arc Energy
The plasma boost caused the arc to broaden; melting a wide surface area, eliminating cold lapping and promoting good fusion, even on heavier gauge materials.
100% CO2 Shielding Gas
Reduction of gas costs. Gas savings in excess of 25% achieved.
Reduction in consumable costs
Low weld repair rate
A result of controlled arc energy
Increase in productivity
Operator friendly process reduce down time and operator fatigue. High travel speeds for root passes and all position welding substantially reduced overall weld times.
Before the STTTM process was introduced to J.N. Rowen Limited, the company looked at various other manufacturers' equipment and processes, such as the Synergic MIG process. These were found not to have the same control and ease of use as the STT process.
Once the STT process was decided upon the next step was to develop a procedure to cover the requirements of the various materials and welding positions that would be encountered on the structure. Working to EN288/3 a Single Vee Butt with an open root in 168mm diameter 50D tube, with a wall thickness of 10.5mm was used. Welds were made in the HL045 (6G) Position.
By setting the peak current and background current independent from the wire feed speed, the required penetration and fusion was obtained. Test pieces were then subjected to full NDT and destructive testing before an actual procedure was written.
From the procedure, all welder qualifications were carried out in a minimal amount of time, to a very high standard.
To fully optimize the STT equipment J.N. Rowen Limited used the process for tack welding on the structure. This eliminated the need to grind back the tack welds as the welders followed up to complete the root runs.
With the ability to weld in all positions with relative ease, the need to rotate and position the structures for welding was eliminated. With over one thousand butts to weld, substantial savings on production times were achieved.
In conclusion, the surface tension transfer power source significantly cut welding costs. The reduction in spatter translated into savings by minimizing or eliminating the labor time to remove spatter. Also additional savings were realized by using 100% CO2 shielding gas, plus savings in time from the ability to produce high integrity welds in any position.
Game, set and match to the STT
Acknowledgements
A special thanks to the Production and Fabrication staff at J.N. Rowen Limited.
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