ESAB Shield-Bright cored wires pave the way to speedy quality welding
Patent Kft. Is a Hungarian company that successfully survived the country’s political and economic transformation by combining quality traditions with an easy acceptance of new, productive technologies. ESAB is their preferred welding partner, appreciated for its customer orientated practical support. ESAB recently assisted in the implementation of a productive process solution for the welding of stainless steel tanks using Shield-Bright cored wires.
It was clear from the moment Patent Kft. received the order – for the construction of four 1500 cubic metre tanks for Hungary’s largest chemical company that it was the right moment to change to a more economical technology. With assistance and support from ESAB, management embarked on a revolution in welding culture. After two decades of tradition in high quality TIG welding, a company like Patent Kft is steeped in TIG and abandoning it was a massive challenge – as much for the management as for the employees.
ESAB’s stainless steel tank welding solution needed to cover the complete welding process – power sources, consumables, mechanisation and welding procedures. In addition ESAB was asked to provide practical demonstrations and welder training.
The tanks, each with a diameter of 11m and a height of 16m, are made of 304L type austenitic stainless steel in 5, 6, 8, 10 and 12mm thickness. They have 11 rings constructed from 1500 x 6000mm sheets. First the roof is constructed, and lifted, after which the rings are fitted, one by one, from top to bottom to form the shell. The welding of the shell involves 380 m of joints in the PC (2G) position and 100m in PF (3G) position, plus the joints in the roof and bottom plate. The tank welding tasks involved three areas: the bottom, the shell and the roof.
The bottom of the tank is constructed from 5mm thick, 6000 x 1500mm sheets. The sheets are bevelled to 60° butt joints and the root is welded onto 5mm thick stainless steel strips. This bottom plate is welded onto a 12mm thick base ring by means of overlap joints, whereas the first tank rig is joined to the same base ring with two-sided fillet welds. These downhand butt, overlap and fillet welds are suitable for light mechanisation – ESAB’s MIggytrac 2000 welding tractor being a logical choice.
Less obvious was the selection of ESAB’s top-end digital power source, the AristoMig 5000iw with AristoPendant U8 control pendant and AristoFeed 3004w wire feed unit – where a less advanced power source would also have fulfilled the requirements for the complete tank. Patent Kft’s management opted for the AristoMig 5000iw, because its SuperPulse function in the U8 control unit could be applied to other projects. Very thin plate applications – a substantial part of the Patent Kft portfolio which was formerly covered by mechanised TIG can now be welded with the faster MAG process making it possible to combine arc types and fully control the heat input. In this way the company has a ‘work horse’ for heavy welds and, at the same time, a machine for precision welds.
ESAB advised Patent Kft to extensively test 1.2mm Shield-Bright 308L X-tra rutile cored wire for the downhand butt, overlap and fillet welds, convincing them that this consumable best met their high quality and productivity demands. This wire has been specially developed for applications in the PA and PB position, yielding high integrity welds at deposition rates as high as 10kg/h (Ar/2.5% CO2 shielding gas). It allows Patent Kft to weld the butt and fillet welds in the tank bottom in one pass at a travel speed of 50-55 cm/min and a deposition rate of around 10kg/h (butt welds on stainless steel backing strip).
Tibor Patonai, Technical Manager : ‘Previously we welded thicker plates in three runs, using synchronic TIG for the root (two welders welding the same joint simultaneously), and the solid wire MAG process for the filler layers. With ESAB’s Shield-Bright on ceramic backing, we complete joints in one run, even when welding manually. Another advantage is reduced deformation as a result of the high travel speed and low heat input. In addition, we enjoy an extremely low defect rate with hardly any porosity, cold-laps or slag inclusions. The Shield-Bright products became so popular in our workshop that even the proudest TIG welders volunteered to use the wire, in spite of their long time antipathy for the MAG process.’
The tank shell represents the majority of the welding work. During the planning stage, it was divided into two welding areas; the top segments (5 to 5mm, 5 t0 6mm, 6 to 6mm joints) and the lower segments (8 t0 8mm, 8 to 10mm, 10 to 10mm and 10 to 12mm). All involve butt joints in the PC (2G) and PF (3G) positions.
For the top segment, welds in PC position were carried out with solid wire MAG welding with 1.0mm OK Autorod 308LSi welding wire. Welds were performed in one run on FILARC PZ1500/87 ceramic backing with concave groove. Bevelling was not necessary and welds were absolutely free of defects – together bringing substantial time and cost savings. The PF welds were still welded with synchronised TIG, because there was not enough time to train the welders in the use of MAG welding, with ESAB SuperPulse.
For the lower segment in thicker plate, multi-layer welds were performed with 1.2mm Shield-Bright 308L all positional rutile cored wire with fast freezing slag. It was applied in both manual (root runs in PF position) and mechanised welding (filler and cap layers). The root procedure, however, differed for the PC and PF welding positions. Initially, economic root pass welds with Shield-Bright 308L in PC position on ceramic backing at a travel speed of 28cm/min proved unsuccessful, because the necessary heavy tack welds could not be remelted completely. Also big fit-up and root gap variations played a role in insufficient root penetration. This was avoided by welding the root pass in PC position with solid wire on PZ1500/87 backing, but at a lower travel speed of 13-15cm/min. For the filling and cap layers, Shield-Bright 308L yielded high integrity welds at travel speeds of 40 and 60 cm/min, respectively.
In PF position, there were similar conditions for the root pass, but insufficient root penetration was not an issue because of the larger weld pool. The full joint was welded with Shield-Bright 308L. The root pass was done manually on FILARC PZ1500/71 ceramic backing with a rectangular groove. The fit-up tolerances did not allow for mechanisation in the filling and cap layers.
The roof grid was pre-fabricated in the workshop and transported in one piece to the tank construction site. Most of the welding work could be brought in the downhand position to optimise benefit from the high deposition rate of ESAB’s Shield-Bright 308L X-tra. The remaining positional welds were performed with Shield-Bright 308L. After on-site connection of the roof-grid to the tank’s top segment, stiffener beams, cover plates and piping were all welded with the all positional Shield-Bright 308L.
The Patent Kft partnership with ESAB is based on practical, result-orientated advice and support. Prior to the project, this took the form of local demonstrations, the joint evaluation of different solutions, the selection of the most suitable and effective welding technology and the establishment of welding procedures. This co-operation continued into the construction stage, where active support solved occasional problems. The co-operation was the basis for the successful construction of the four 1500 cubic metre tanks within a period of five months – well within the deadline required by the customer.
Mr Tibor Patonai conclude ‘ESAB’s approach is the most sympathetic in the marketplace. They do not press us to apply standard technology, but actively help us to realise the solution that best meets our quality and productivity needs. Their flexible and helpful attitude was key to reaching our targets with this project.’
