10,170 flawless welds
The welding of tubes containing the principal current-carrying busbars in the LHC magnets was one of the main activities of the SMACC project. After a year of preparation and another of intense activity in the tunnel, the last weld was completed on Wednesday 14 May. Over 10,170 welds have been inspected and not a single fault has been found.
Each of the eight sectors of the LHC contains around 210 interconnects between the superconducting magnets. Consolidating these interconnections was the SMACC project’s primary objective.
One of the last jobs before closing the interconnects is the welding of the M lines: each has a 104 mm diameter and a radial clearance of just 45 mm. In total: 10,170 welds carried out in a single year of activities. A true challenge, which was carried out by a team of 30 highly specialised welders, working under the supervision of Said Atieh, a member of the MME Group in the EN Department. “The team consisted of welders, technicians and engineers from various CERN Groups and Member States, but also from Pakistan, with whom we signed a collaboration agreement before the start of the project,” Atieh explains. “The work began in 2012 when the procedures were qualified and a quality plan established, followed by a training programme on mock-ups that were built to simulate the conditions in the tunnel as closely as possible.”
The teams started welding in the LHC tunnel in May 2013. "Thanks to the preparation and the performance of the people involved, we managed to keep up a constant rhythm for the whole 12 months of this campaign without sacrificing quality," says Atieh. "We finished, as planned, on 8 May 2014." But the last two welds were saved for the end-of-activity ceremony on 14 May!
Considering the proximity of the tubes that needed soldering, the materials and the geometry that left no margin for error, the welders used orbital welding machines manufactured by an industrial partner on the basis of an original design produced by CERN. “It was a very special welding technique so the technicians had to be trained for it," Said explains. “The two ends of the tubes are actually welded with no filler metal.”
Once welded, each weld has to be checked one by one. “We kept the quality control process separate from the production throughout the works," says Jean-Michel Dalin, who surpervised quality control throughout the year of works. “In addition to visual checks by the welders themselves, a team of inspectors from an external body carried out a full visual inspection and archived the automatically-recorded orbital videos of each of the welds, while other inspectors regularly audited the welding parameters of each machine.”
As a result of this attention to quality, every one of the 10,170 welds was declared compliant with welding quality standard ISO 5817, Level B, which corresponds to the highest requirement and attests to the absence of structural faults. Bravo!
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| LHC magnets are connected by three tubes: the M lines, which contain the current-carrying busbars and assure the continuity of the helium vessel. | 14 May 2014: the expert team was reunited for the last of the 10,170 welds, which was successfully completed one year after the project began. |
