April 5 MRB
A Material Review Board (MRB) telecom was held 5 April 2004 at 10:00 am to disposition NCR 00078. In attendance were Jim Martin, Darren Marsh, Jeff Tice, Robert Johnson, Joe Cullinan and Fred Gross (GSFC M&P) by telecom. Fred Gross had previously consulted with Mike Barthelmy (GSFC metallurgist) on this issue for an opinion.
LAT NCR 00078 documented that 7075-T6 aluminum was incorrectly used to fabricate the Tracker sidewall inserts specified in drawings LAT-DS-00094 and DS-00718. The drawings specify the material should be 7075-T76 aluminum. 7075-T6 aluminum is sensitive to stress-corrosion cracking; the T76 heat treat condition provides greater stress corrosion cracking resistance in 7075 and is preferred over T6.
7075-T6 inserts have been epoxy bonded into a total of 122 MCM closeouts and a total of 125 structural closeouts to date; the remaining 7075-T6 inserts are loose and have not yet been bonded into the other Tracker midtray closeouts.
A "use as is" disposition was approved unanimously by the MRB convened this telecom for all affected inserts (bonded and loose). Stress corrosion cracking of the inserts is considered highly unlikely in this environment based on the cleanliness of the inserts, the cleanroom environment in which the inserts will be maintained, the very low level of sustained tensile stress in the inserts, and the high insert redundancy in sidewall design.
The cause of the problem was lack of adherence to the latest released Tracker drawings by Plyform. The problem was found during an audit by INFN of all drawings being used by Plyform. The audit was requested by the LAT Tracker team. This problem revealed a potential for additional nonconformances currently existing with tray production. Additional verification will have to be performed to ensure no other noncompliance is occurring elsewhere in Tracker tray production. The team responsible for this verification and the schedule to implement and complete the verification is to be determined.
Action Items and Responsibilities:
1. LAT QA to update NCR 00078 with disposition and cause/corrective action (Cullinan, ECD 4/5/04)
2. SLAC to formally submit Material Usage Agreement (MUA) to GSFC in accordance with DID 313 to use 7075-T6 aluminum in this specific application (Cullinan/Tice, ECD 4/5/04).
3. Tracker drawings LAT-DS-00094 and LAT-DS-00718 need to be revised to show insert material is 7075-T6, not 7075-T76 (Dave Rich to assign).