CERN Accelerating science

Article
Report number	LHC-PROJECT-Report-1072 ; CERN-LHC-PROJECT-Report-1072
Title	Leak-Tight Welding Experience from the Industrial Assembly of the LHC Cryostats at CERN
Author(s)	Bourcey, N ; Campos, P ; Chiggiato, P ; Limon, P ; Mongelluzzo, A ; Musso, G ; Poncet, A ; Parma, V
Affiliation	(CERN) ; (Fermilab, Batavia, IL, USA) ; (Serco, Saint-Genis-Pouilly, France)
Publication	2008
Imprint	Dec 2007
Number of pages	9
In:	AIP Conf. Proc. 985 (2008) 325-332
In:	Conference on Cryogenic Engineering and Cryogenic Materials, Chattanooga, TN, USA, 16 - 20 Jul 2007
DOI	10.1063/1.2908564
Subject category	Accelerators and Storage Rings
Accelerator/Facility, Experiment	CERN LHC
Abstract	The assembly of the approximately 1700 LHC main ring cryostats at CERN involved extensive welding of cryogenic lines and vacuum vessels. More than 6 km of welding requiring leak tightness to a rate better than 1.10-9 mbar.l.s-1 on stainless steel and aluminium piping and envelopes was made, essentially by manual welding but also making use of orbital welding machines. In order to fulfil the safety regulations related to pressure vessels and to comply with the leak-tightness requirements of the vacuum systems of the machine, welds were executed according to high qualification standards and following a severe quality assurance plan. Leak detection by He mass spectrometry was extensively used. Neon leak detection was used successfully to locate leaks in the presence of helium backgrounds. This paper presents the quality assurance strategy adopted for welds and leak detection. It presents the statistics of non-conformities on welds and leaks detected throughout the entire production and the advances in the use of alternative leak detection methods in an industrial environment.

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