Jannie Bronkhorst, product manager for welding and automation equipment at ESAB South Africa, talks about the ESAB Railtrac B42V tractor system – selected by South Africa’s tank farm service provider Trotech for the construction of a new state-of-the-art tank terminal in KwaZulu-Natal:
ESAB has secured an order for the supply and support of mechanised equipment, welding machines and consumables for the construction of a new tank terminal in KZN. “The new terminal is currently under construction using an ESAB solution: our ESAB Railtrac B42V welding tractor along with welding power sources, wire feeders and ESAB consumables,” says Bronkhorst.
Trotech is a recognised South African tank manufacturer with the full suite of engineering, design, quality control and inspection capabilities – and a local construction company that can build tanks that conform to the global API standards. The project involves the construction of 18 large multipurpose and chemical tanks, each 16m in diameter and 22m high.
Mechanisation for improved quality and reduced costs
These large tanks, according to Bronkhorst, were previously fabricated on site using traditional manual welding techniques and a ‘bottom up’ technique. The bottom section of the tank wall, called the first strake, was manually tack-welded to form a cylinder and then the vertical and horizontal seams welded, all using shielded metal arc welding (SMAW)/stick welding electrodes. Then the next strake would be added, tacked and welded, from the bottom up, followed by subsequent strakes. Once the required height was achieved, walkways, a reinforcing ring and the roof would be added.
Tanks for the project will also be manufactured on site, but Trotech has selected a far more modern, safe and cost-efficient construction technique. “At the start of the contract negotiations, we invited Trotech to our new ESAB facility located at Tunney Ridge Business Park in Johannesburg, where we set mock-up plates for the vertical and horizontal seams with different plate thicknesses. ESAB demonstrated how the use of the mechanised Railtrac system together with the fluxed cored wire successfully produced sound quality weld seams,” explains Bronkhorst.
Railtrac, he continues, is a mechanised bug-and-band type welding tractor system. “A magnetised track is aligned to the weld seam. The tractor, carrying and manipulating a welding torch, gets attached to the rack; a torch suitable for flux-cored arc welding (FCAW) is then clamped into a holding bracket and aligned. The Railtrac system is then able to manipulate the torch in terms of travel speeds; weaving speeds and widths, hold times and positions on either side of the weld preparation.
“During the demonstration, ESAB produced quality sound welds, which at the end of the day is going to save tremendous amounts of time and costs due to the high quality and consistency that comes with mechanisation,” Bronkhorst says.
Further highlighting the productivity advantages of mechanisation using ESAB’s Railtrac system, he points out that there is a lot less stopping and starting, resulting in fewer arc starts and arc stops compared to the SMAW process, in turn reducing repair rates. The welding speed is also faster, which reduces the heat input into the plate, so distortion on the tank also reduces. “FCAW delivers better and more consistent weld metal quality than the SMAW process can,” he says, adding, that these advantages “sealed the deal”.
Railtrac itself also offers flexibility and practical control: “Welders have a pendant enabling them to keep the weld on the seam, increase or decrease the speed and to accommodate on-site variations. This is why we call it mechanised welding and not automated welding. The process offers a good compromise between the flexibility offered by a manual welder and a key problem with fully automated systems – that they cannot deal with fit-up variations,” Bronkhorst points out.
Trotech purchased 32 mechanised Railtrac B42V units from ESAB, complete with Fabricator EM 500i power sources and Fabricator Feed 364 wire feeders. In addition, the manual tack welding is being done using ESAB’s OK 55 7018-1 low hydrogen welding electrode, while the vertical and horizontal seams are being welded with OK Tubrod 15.15 E71T-1 H4R flux-cored welding wire, which is designed specifically for out-of-position welding. “This wire has a fast freezing designed to supporting weld metal when welding out of position joints,” Bronkhorst adds.
Emphasising the simplicity of the system, he says: “Welders still need to line up and tack the joints for each strake. Then they position and align the Railtrac magnetised track along the next weld seam. Once lined up, they attach the tractor, align the torch and start the welding process. The operator then monitors the system welding, making occasional adjustments where necessary.”
He continues: “Because we are using a flux-cored wire, we can use a standard CV (constant voltage) process, which enables us to use a wide welding parameter set depending upon the position and the plate thickness.”
Jack-up tank construction
To further raise safety and productivity in the project, Trotech chose to use the alternative ‘jack-up’ method of construction. “This technique is sometimes called the ‘top-down’ method, because the top and thinnest strake section is welded first, while still at ground level, and the bottom, thickest section comes last,” Bronkhorst explains.
“A temporary support structure is first created around the tank’s foundations and floor. The strake for the top section is assembled and tacked together at ground level. The vertical seams between the plates of this strake are then welded using the Railtrac system and the flux-cored welding process. The horizontal seams are then also completed to make a cylindrical section. Then the whole ring and roof are jacked up to allow another ring of strakes to be inserted below, tacked into place and welded in the same way. Because all the welding takes place much closer to ground level and inside the temporary support structure, safety issues are easier to manage, wind becomes less of a problem, and quality improves.”
To increase import capacity, more tank farms will be required; the investment cost of these is significantly less than that required to upgrade refineries to meet the new standards – which bodes well for investments in modern tank farm fabrication equipment and techniques.
“Using the ESAB Railtrac B42V mechanised solution, we at ESAB have developed a total welding solution for the mechanised manufacture of tanks, with component parts that can be configured to maximise productivity and minimise complications in harsh environments,” Bronkhorst concludes.
ESAB’s Railtrac B42V welding tractor key features include:
• 42 Vac powered from the power source or battery driven with standard Makita®18 V system.
• Possible to programme a specific welding length with auto return to start position.
• Stepper motors for drive and weaving functions have extremely high precision, and a wide speed range is available in a single unit.
• Remote is programmable for weave patterns and travel speed and is capable of controlling voltage and wire feed speed in up to five standard programmes.
• Unit can be programmed to run directly from the controls on the Railtrac machine if the remote control is lost, damaged or not preferred.
