136 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1057 



Tlie initial closure operatiuiis consisted of brazing into each end of 

 the repeater housing a Kovar-to-glass seal. These seals are equipped 

 with small diameter nickel tubulations which were used to flush and 

 pressurize the repeaters with nitrogen. After these operations had been 

 performed, one of the tubulations was pinch welded, overb razed and 

 coiled down into the seal cavity. The repeater was then placed in a pres- 

 sure cylinder with the open tubulation extending through and sealed to 

 the test cylinder. A mass spectrometer was then attached to the tubula- 

 tion and the test cylinder pressurized with helium at 10,000 psi. At the 

 conclusion of this test the repeater was removed from the test cylinder 

 and, after breaking the desiccator diaphragm, the remaining open tubu- 

 lation was pinchwelded and overbrazed. At this point, it became neces- 

 sary to determine whether the final pinchweld and overbrazing would 

 leak under pressure. 



Since there was no longer any means of access to the inside of the 

 repeater, all testing had to be done from the outside. This was accom- 

 plished by filling the glass seal with a solution of radioisotope cesium 

 134, which was retained by a fixture. The repeater was then placed in a 

 test cylinder and hydraulic pressure applied, which was transmitted to 

 the radioisotope in the fixture. After 60 hours under pressure, the re- 

 peater was removed from the cylinder and the seal drained and washed. 

 An examination was then made Avith a Geiger counter to determine if 

 any of the isotope had entered the final weld. 



The washing procedure, after application of the isotope solution, in- 

 volved some sixty operations with precise timing. In the case of the re- 

 peater at the rubber seal stage where both ends were tested, it was 

 desirable that these operations be performed concurrently. This was 

 accomplished by recording the entire process on magnetic tape which, 

 when played back, furnished detailed instructions and exact timing. 



RAW MATERIAL INSPECTION 



As might be expected, raw materials used in the project were very 

 carefully examined and nothing left to chance. Every individual bar, 

 rod, sheet, tube, bottle or can of materials was given a serial number and 

 a sample taken from each and similarly identified. Each sample was 

 then given a complete chemical and physical analysis before each corre- 

 sponding piece of material was certified and released for processing. In 

 many cases, the cost of inspection far exceeded the cost of the material. 

 However, the discrepancies revealed and the assurance provided, more 

 than justify the expense. 



Detailed records of all raw material inspection were compiled and 

 furnished to the responsible raw material engineer who examined them, 



