The idea of automating a tedious manual welding process may not sound terribly exciting to most ears, but to the folks over at L&T Heavy Engineering the possibility of it must sound like music. Passionate about automation, a crack team of highly skilled engineers assembled from different pockets of the division recently managed to pull off something quite remarkable. It successfully perfected an automated high sagita nozzle welding system that is not only revolutionising the way expensive and resource intensive welding jobs are carried out in HE shops but also making the entire process look cool and futuristic along the way.
For L&T Heavy Engineering which manufactures a variety of custom designed equipment for process industries, Heat Exchangers are something that it makes plenty of. These heat exchangers have nozzles welded to cylindrical shells. Since these equipment work under extremely high-pressures, weld quality is critical and defines the safety of operation as well as determining the service life of the equipment.
Typically, nozzles with low sagita (sagita is the distance between the top most point in an arc and the centre of its base) offers almost flat position for welding and can be mechanized with high deposition Submerged Arc Welding (SAW) process. However, high sagita nozzles, where the angle of sagita is greater than 7.5 degrees, the welding position changes significantly along the profile of nozzle which makes automation a challenge.
Close to 80% of the heat exchangers manufactured at HE shops, the nozzles fall under the high sagita angle category and were welded manually until recently. Lack of automation would mean everything from a greater cycle time to lower productivity, lack of desired welding quality and re-work. Another challenge which plagued the work on the shopfloor was the shortage of experienced and highly skilled welders to complete such jobs. Moreover, safety and comfort were a concern, since the operation was performed by welders seated in a confined space inside the shells which were preheated for welding. In light of all these issues, the need to automate the high sagita nozzle welding jobs had become increasingly urgent.
For the team, the trick was how it can make the position flat and keep it so throughout the profile of nozzle in order to mechanise this process? The team came up with a creative solution; oscillate the shell such that welding location is always in the flat position. Voila!
Solving the problem on paper however was one thing, doing it on the shopfloor quite another. The team designed a manipulator with a rotary positioner which oscillated the shell and a linear slide that moved the welding torch front and back to track the profile of nozzle. A rotary torch axis ensured that the torch is always parallel to the groove.
The beauty of this concept is that the constant surface speed of welding is achieved through the combination of two movements, one is the rotation of the shell and the other is the linear movement of torch. A Programmable Logic Controller (PLC) ensured the constant synchronisation. As for the operator, he can simply sit outside and control the operation using a vision system offering him a look into the welding process.
The team also had to change the Weld Edge Preparation (WEP) from the axial WEP which is parallel to the axis of the nozzle to a radial WEP to keep the weld opening constantly accessible to the SAW torch despite shell oscillation. Further a mechanised gas cutting station for shell cut-out with new WEP was put in place as part of the new process.
When compared with the old, manual way of high sagita nozzle welding process, the quality achieved through the new automated process is considerably better and has resulted in a number of advantages for Heavy Engineering.
What makes the entire process truly unique and praiseworthy is the fact that there is no readymade or off-the-shelf system available in the market and HE’s competitors continues to perform the task manually. All the development for what is highly robust and customised system was done completely in-house, right from concept-to-finish.
The system does not require expert welders and can be performed by anyone after a day’s training. Deskilled operation means resource flexibility and not having to worry about production getting affected on account of unavailability of trained or expert welders.
Since going live, the system has helped HE team weld over 25 nozzles, none of which had to go for any re-work or repair. Typically, in the manual process there was 6-8% repair. There has also been a significant improvement reported in the delivery cycle time which has been cut down by 30% for nozzle welding which in turn has cut down the product/equipment cycle time by 2.5%. In terms of hours saved cost per nozzle, man-hours has come down to 75 hours from the earlier 150 hours during manual process. Besides from a welder deployment standpoint, the same has been halved from two to one welder.
All these benefits post automation have meant that HE saves an estimated Rs. 97 thousand per nozzle and more importantly gets better quality of weld post mechanisation. Ergonomics of the operation has improved with vision system.
For overcoming a challenge that had long hindered shopfloor productivity TD Vaidyalingam and his team members Pravin Koli, Manohar Salvi, Deepak Poojary, Sachin Kadam, Ankit Sharma, Amit Mokashi, Abhijit Nevase, Vishal Chinta, Sumukh Save, Vishvajeet Joshi, and Rahul George have received plenty of praise and recognition from their colleagues at HE not just in Powai but from other locations as well. The team now hopes to spread the word and is helping teams at other HE locations replicate the success.
