I am looking for opinions concerning the following :
A sheathed thermocouple, 1 mm dia, SS or Inconel sheath, passing through a bore (~1.02 mm) in a small SS plate.
The thermocouple is brazed in the bore by induction in vacuum, BNi-7.
The plate is part of a pressure vessel, volume of several liters, water, 120 bar, 300 Celsius.
What are the applicable documents and rules have I to consider for testing and qualification of such a seal?
I can perform Helium leak test, hydraulic test, metallography.
Any mechanical test suggested?
Thanks in advance
C. Truta
The only document I can think of is something I am unfortunately not familiar with, but I will risk commenting anyway. The Boiler and Pressure Vessel code has requirements for qualification of brazers and braze procedures, but I doubt it tells you which specific tests must be done on a special joint. For mechanical integrity, a pull test might be sufficient to show the TC sheath will fail before the brazed joint, but since the sheath is being pushed out by the pressure, a pull test may not be relevant, so a pressurized proof test would be good. You probably want to pressurize to some overpressure, such as 1.5 times the max operating pressure. The Code may specify what is needed. For leaks, testing with air may be sufficient. Helium may be overkill unless leakage is critical, such as with fuels or refrigerants. Will the completed vessel undergo a proof pressure and leak test? If so, the brazed joint integrity may be sufficiently proven as part of the vessel testing.