TPT July 2018

I NDUS T RY

Welding consumables selected for Queensferry Crossing

also exhibits a smooth, stable arc with virtually no spatter. 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. 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 is said to have produced excellent quality welds while maintaining American Bridge’s requirement for high productivity. To maintain their low hydrogen performance, the electrodes were sup- plied in vacuum packs. 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 Charpy toughness down to -40°C as well as good COD (crack opening displacement) test values. For the S460 grade applications, the basic-coated, low-hydrogen electrode Filarc 88S (E8018-G) was used. Alloyed with 1% Ni and designed to meet the exacting standards demanded by the oil and gas sector, Filarc 88S has good impact toughness down to -60°C coupled with good CTOD performance at -10°C. ESAB was able to ensure the required volumes of welding wire would be available as required by the construction schedule. 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.

The new three-tower, cable-stayed Queensferry Crossing road bridge

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 suit 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. 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 versatile wire is suitable for all-positional welding on the S355 grade structural steel used in this exposed application. OK Tubrod 15.14 is universally approved to grade 3 by all major authorities. Welding procedures were undertaken in the vertical and horizontal positions. Impact testing at -20°C resulted in values well in excess of those required by the specification. 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

ESAB, a specialist in welding and cutting technologies, has supplied flux- cored wires and welding electrodes to the Forth Crossing Bridge Constructors (FCBC) consortium, which designed and built the new Queensferry Crossing road bridge across the Firth of Forth for Transport Scotland. At 1.7 miles long, it 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 £1.35bn and is Scotland’s largest 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: Hochtief, Germany; Dragados, Spain; Morrison Construction, UK; and American Bridge International, USA. American Bridge was charged with overseeing the production and installation of 121 road sections. This task was coordinated by American Bridge International senior engineer Joshua Ishibashi, who supervised production of the road sections in China, through to final site assembly at Queensferry. A particular challenge for the American Bridge engineers

ESAB Group (UK) Ltd – UK Email: info@esab.co.uk Website: www.esab.co.uk

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JULY 2018