Preventing vacuum leaks in the Continuous Electron Beam Accelerator Facility cavity pair bellows
作者:
Daniel P. Henkel,
Lawrence R. Doolittle,
期刊:
Journal of Vacuum Science&Technology A: Vacuum, Surfaces, and Films
(AIP Available online 1994)
卷期:
Volume 12,
issue 5
页码: 2896-2902
ISSN:0734-2101
年代: 1994
DOI:10.1116/1.578962
出版商: American Vacuum Society
关键词: CEBAF ACCELERATOR;CAVITY RESONATORS;PRESSURE VESSELS;LEAKS;WELDED JOINTS;CRACKS;INCLUSIONS;CREVICE CORROSION
数据来源: AIP
摘要:
Occasional vacuum leaks have occurred in bellows assemblies of helium pressure vessels at the Continuous Electron Beam Accelerator Facility. The flanged stainless steel bellows assemblies are used to connect the niobium rf cavity pairs to the surrounding liquid helium pressure vessels. An investigation of the source of these leaks has revealed a through‐thickness network of microcracks in the cuff weld zones. The cuff material contained a mixture of soft and very hard elongated intermetallic inclusions that were oriented parallel with the weld fusion line; these inclusions served as crack initiation sites. Surface‐exposed inclusions, in contact with a chlorine residue from a postweld machining process, induced crevice corrosion during a year of storage. Residual stresses in the weld led to a combination of lamellar tearing and stress corrosion cracking. Propagation of the cracks from one inclusion to another resulted in continuous vacuum leakage paths from the primary (2 K) helium circuit to the vacuum insulation space. Additional vacuum leaks were prevented by reconfiguring the weld geometry and avoiding any processing with chlorinated substances.
点击下载:
PDF
(649KB)
返 回