________________________________

From: Hutch Neilson 
Sent: Tuesday, July 10, 2007 10:36 PM
To: Michael R. Kalish; Wayne T. Reiersen; Rodney D. Templon; James H. Chrzanowski; Phil Heitzenroeder; Irving J. Zatz; Thomas G. Brown
Cc: James L. Anderson
Subject: Summary of TF#2 recovery meeting of July 10

 

Summary of engineering review of TF#2 recovery plan,  July 10, 2007

 

One of the wedge castings separated from TF#2 as it was being removed from the mold at Everson Tesla. Mike Kalish summarized what happened, the recovery plan for TF#2, and mitigation plan to avoid recurrence on future coils.

 

A brief summary is as follows.

 

What happened

The bands that hold the wedges to the coil were displaced ("bunched up") as the cover was being installed on the mold. The bands were cut but ETI decided, without informing PPPL, to continue with the VPI.  Their intention was to secure the bands afterward with a wet wrap process. 

 

When the cover was lifted, the wedge came up with it and pulled away from the coil.

 

TF#2 recovery

After cleanup of the area, the wedge was pressed back down to within 0.020 in. of the coil in the free condition. With clamping the gap closes to 0.010 in. Mike says there is very little yielding of the wedge, and the wedge can be secured to the coil with the bands.  Tolerances, which are determined by a final machining operation after assembly, can be met.

 

To repair, ETI will lift up the wedge by enough (about 0.060 in.) to inject epoxy to fill the gaps between the coil and wedge. The attendees recommended using a room temperature cure epoxy rated for cryogenic service (CTD-540?). There was also a chit recommending that a 0.005 in. thk. sheet of glass be inserted between the wedge and coil to reduce the risk of resin-rich areas subject to cracking  and falling out during operation.  The bands will be epoxy-soaked and installed in a "wet wrap" process.

 

Future

Measures will be taken to reduce the risk of the wedge being pulled off when the cover is being removed:  Pre-wrap the wedge area in mylar.  Carefully adjust the number of layers of glass to avoid bunching of the bands.  Install jack screws on the top cover to push the coil out. (A similar feature exists on the bottom cover, and worked well.)

 

Quality and Schedule

Concerns about quality and adherence to procedure have begun to surface recently on this contract, this problem being an example.  Others were use of a banned conductive O-ring material on the mold, and a failed hi-pot at cryogenic temperatures. 

 

Poor schedule performance has been a chronic problem.

 

It was decided that a PPPL delegation representing management, engineering, QA, and procurement should visit ETI soon for a contract review with an emphasis on quality and schedule issues.  Action: Kalish to arrange.

 

Design

In the course of looking at the pictures a potential design problem, unrelated to the issue at hand, was recognized.  The wedges are intended to support the central solenoid. However, due to the lack of shear strength in the bond between the wedges and the coil, it is not clear if they can provide that support. Wayne will follow up with the appropriate engineers.

 

 

This meeting was declared a peer review. Several chits were generated. Official records will be documented accordingly and the chits will be resolved by Mike.

 

 

 

Please bring any errors or issues to my attention.

 

Summary by:

Hutch Neilson