ESAB has supplied flux-cored wires and welding electrodes to the Forth Crossing Bridge Constructors (FCBC) consortium that designed and built the new Queensferry Crossing road bridge across the Firth of Forth for Transport Scotland. At 1.7 miles long, this is the world’s largest three-tower, cable-stayed bridge. Towering 207m above high tide and requiring 150,000 tonnes of concrete and 35,000 tonnes of steel, the overall scheme has cost approximately £1.35 billion and is Scotland’s biggest transport infrastructure project in a generation. Built to motorway standards, the bridge has two lanes and a hard shoulder running in each direction, with the roadway supported by three composite steel/concrete towers.
To cover all required disciplines for the project, a multinational consortium of four main contractors was required. These were: Hochtief, Germany; Dragados, Spain; Morrison Construction, Scotland; and American Bridge International.
American Bridge was charged with overseeing the production and installation of 121 road sections. This onerous task was coordinated by American Bridge International Senior Engineer, Mr Joshua Ishibashi, who supervised production of the road sections in China, right through to final site assembly at Queensferry.
A particular challenge for the American Bridge engineers was to find a combination of welding processes and consumables that would not only meet the mechanical properties of the steel grades selected, but also the welding environment including weather conditions. After welding trials to establish the ‘best fit’ for the project, Mr Ishibashi and FCBC Welding Engineer Dave Godfrey of Godfrey Welding Engineering settled on four ESAB welding consumables for the task.
Flux-cored welding wire
For most welded joints on the Queensferry Crossing bridge decking, a single flux-cored wire was specified, namely ESAB OK Tubrod 15.14 (T46 2 P C 1 H5). This is a versatile wire that is highly suitable for all-positional welding on the S355 grade structural steel used in this exposed application. The running characteristics of OK Tubrod 15.14 are exceptional in all welding positions. Furthermore, OK Tubrod 15.14 is universally approved to grade 3 by all major authorities. Welding procedures were undertaken in the vertical and horizontal positions, producing excellent results in both. Impact testing at -20degC resulted in values well in excess of those required by the specification. Typical properties for OK Tubrod 15.14 weld metal are shown below.
In some areas where high-tensile S460 grade structural steel was employed, ESAB Filarc PZ6138 (T50 6 1Ni P M H5) was used. This wire, which is commonly specified in the offshore sector, contains 0.9 per cent Ni to ensure reliable Charpy impact properties down to -60°C and good CTOD (crack tip opening displacement) performance to -10°C. Filarc PZ6138 also exhibits a smooth, stable arc with virtually no spatter. Typical properties for Filarc PZ6138 weld metal are shown below.
Manual metal arc
Where exposure to the elements meant that it would be difficult at times to apply the GSFCAW (gas-shielded flux-cored arc welding) process, the MMA (manual metal arc) process was selected. However, on a project where productivity is paramount, it was important that the electrode selected maintained this objective. To this end, ESAB’s basic-coated high-recovery low-hydrogen electrode OK Femax 38.65 (E42 4 B 73 H5) was approved. Used on the S355-grade material, the electrode produced excellent quality welds while maintaining American Bridge’s requirement for high productivity. To maintain their low hydrogen performance, the electrodes were supplied in vacuum packs. Typical properties for OK Femax 38.65 weld metal are shown below.
For other S355 application areas where the GSFCAW process was difficult to apply and all-positional capability was essential, ESAB Ferex 7016 was approved. Ferex 7016 (E 42 5 B 12 H5) is an all-positional, low-hydrogen, thinly-coated, basic electrode that gives excellent Charpy toughness down to -40degC as well as good COD (crack opening displacement) test values. Typical properties for Ferex 7016 weld metal are shown below.
For the S460-grade applications, the basic-coated low-hydrogen electrode Filarc 88S (E8018-G) was procedured. Alloyed with 1 per cent Ni and designed to meet the exacting standards demanded by the oil and gas sector, Filarc 88S has good impact toughness down to -60degC coupled with good CTOD performance at -10degC. Typical properties for Filarc 88S weld metal are shown below.
ESAB was able to ensure the required volumes of welding wire would be available as required by the construction schedule. Thanks to ESAB’s strict quality control procedures, the company could guarantee that the consumables would always be of a consistently high quality. When FCBC awarded the contract to ESAB, it stipulated that the welding wire must be supplied via a local distributor. ESAB therefore shipped large volumes to its distributor IWS (Industrial Welding Supplies), enabling IWS to deliver the welding wire on an almost daily basis from its base at Dunfermline, just three miles from the construction site.
When the welding commenced, the procedures that had been specified by FCBC’s engineers proved to be spot-on. No issues arose relating to the consumables selected, which illustrates the benefits of thorough preparation and demonstrates the consistent quality of ESAB’s welding products.
For more information about ESAB’s welding products, visit www.esab.com.