TPT September 2011

Arvind Anticor Ltd Fax: +91 79 2584 0958 Email: info@picklingplant.com Website: www.picklingplant.com

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Orbital tube-to-tubesheet welding AXTON Incorporated, located near Vancouver, Canada, has been manufacturing heat exchangers and other industrial equipment since the 1980s. Its list of projects includes the structural engineering and fabrication of the Vancouver 2010 Cauldron for the Vancouver 2010 Olympic Games. Axton was restructured in 2002-2003 and at that time the owners decided to update some of their operations. After careful consideration they purchased a Model 227 orbital welding Power Supply and Model 6 orbital tube-to-tubesheet weld head from Arc Machines Inc in California, USA. Although orbital welding is generally considered to be welding of tube or pipe, orbital welding is defined as “machine or automatic welding in which the arc rotates around a stationary weld joint” and this includes orbital tube-to-tubesheet welding. While the company had some previous experience with orbital welding, they gladly accepted the opportu- nity to refresh their skills by having an AMI factory trainer come to their facility to train their lead welders. Axton is a truly international company that exports a significant amount of their production to countries outside of Canada including Mexico, Africa and others worldwide. Industries served include mining, oil and gas, chemical, acid manufacture, petrochemical, power, transportation and pulp and paper. They are currently fabricating a large stainless steel exchanger for export. The tubesheet on this unit has 990 tubes 1-3/4” (44.45mm) diameter with a wall thickness of 0.084” (2.1mm). The vessel is 50ft (15.24m) long and 140 inches (3.55m) in diameter with tubesheets on both ends. The model 227 weld power supply is microprocessor controlled and stores weld programs, or schedules, consisting of all the programmable weld parameters in the power supply memory. The operator enters the program each time the power supply is turned on. The weld schedule specifies primary and background amperage, travel speed (rotation), pulse times, wire feed speed and other parameters. Thus, if other factors such as tube end preparation, cleanliness, purge flow are constant, there is a very high degree of repeat- ability from weld to weld. The weld head features a chill follower linked mechanically to the torch that is spring loaded to the ID of the tube. This causes the torch to maintain a constant distance from the tube OD even when there is some degree of ovality in the tubes. The chill follower as well as the entire torch block is water cooled, which removes heat from the ID of the tube. This allows the application of additional heat to the weld resulting in better penetration without melting through the tubes. The power supply’s arc gap control (AVC) enables the torch to maintain a constant distance between the tungsten electrode and the weld joint. The welding operator may make small changes in the AVC setting during the day to adjust for changes in ambient tem- perature or humidity. The Model 6 is installed using a separate locating fixture that mounts on the tubesheet. Efficiency is im- proved by having two fixtures so that the welding operator can position the second fixture while the weld head is completing the weld while mounted on the first fixture. When the weld is complete, the operator moves the head from one fixture to the other so there is virtually no downtime between welds.

Орбитальная сварка труб на трубной доске Компания Axton Incorporated, расположенная возле города Ванкувер, Канада, производит теплообменники и другое промышленное оборудование с 1980 года