Preventing vacuum leaks in the Continuous Electron Beam Accelerator Facility cavity pair bellows

Journal Article · Thu Sep 01 04:00:00 EDT 1994 · Journal of Vacuum Science and Technology, A (Vacuum, Surfaces and Films); (United States)

DOI:https://doi.org/10.1116/1.578962· OSTI ID:7082067

Henkel, D P ^[1]; Doolittle, L R ^[2]

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1. Analytical Services and Materials, Inc., Hampton, Virginia 23665 (United States)
2. Continuous Electron Beam Accelerator Facility, Newport News, Virginia 23606 (United States)

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.

• DOE Contract Number: AC05-84ER40150
• OSTI ID: 7082067
• Journal Information: Journal of Vacuum Science and Technology, A (Vacuum, Surfaces and Films); (United States), Journal Name: Journal of Vacuum Science and Technology, A (Vacuum, Surfaces and Films); (United States) Vol. 12:5; ISSN 0734-2101; ISSN JVTAD6
• Country of Publication: United States
• Language: English

Related Subjects

43 PARTICLE ACCELERATORS
430303* -- Particle Accelerators-- Experimental Facilities & Equipment
ACCELERATORS
CAVITY RESONATORS
CEBAF ACCELERATOR
CHEMICAL REACTIONS
CONTAINERS
CORROSION
CRACKS
CREVICE CORROSION
ELECTRONIC EQUIPMENT
EQUIPMENT
INCLUSIONS
JOINTS
LEAKS
LINEAR ACCELERATORS
PRESSURE VESSELS
RESONATORS
WELDED JOINTS