Copper containers up to a diameter of 6 m and a length of 14 m can be welded by pro-beam electron beam welding machines. Not only copper to copper welding of longitudinal and transverse seams are possible but also the joining of copper to stainless steel for flange connections.
pro-beam manufactured important parts for a spectacular project for INFN (Instituto Nazionale di Fisica nucleare). The laboratory, located near a ten-kilometre motorway tunnel in the interior of the Gran Sasso massif in Central Italy, is where physicists are studying neutrinos, massless particles which can travel right through the earth with the speed of light. The entire Massif, used as a shield as a first giant filter against unwanted radiation, is used in association with other technical facilities for the detection of neutrinos. The neutrinos, generated 720 km away by the CERN laboratory, are directed at Gran Sasso. At the end of the "filter" is a cryostat consisting of six interleaved copper containers working close to the absolute temperature zero point of minus 273 °C. Radiation-free lead from thousand-year old Roman galleys, protected from radiation on the seabed between copper cauldrons, provides further shielding material for the experiments.
In order to remain radiation-free and usable for the experiment, the material used for the six copper containers had to be stored for a long time in the interior of the mountain before processing. In addition, the requirement that the material should not leave the protection of the interior of the mountain for more than 3 months was a challenge for all the production participants. Welding in high vacuum with an electron beam was found to be the only suitable welding method to safely prevent contamination by welding or burning of welding electrodes.
It was also a requirement that a stainless steel flange had to be welded to the outer container, of course also without filler material.
The advantages of electron beam welding for this project were as follows:
- perfect welding to keep below the permissible leakage rate to less than 10-11 mbarl/s
- copper/copper and copper/stainless steel welding without filler material
- fast production turnaround at pro-beam to be able to adhere to 3-month rule "from the mountain / back to the mountain"
- avoiding contamination of any kind by electron beam welding in high vacuum without welding consumables
Your contact for contracting welding
Mr. Thomas Gaeb
Phone: +49 (0) 89 - / 899 233 67