In our previous post on inert gas leaks, we discussed two different methods for locating inert gas leaks: thin film (soap bubble) leak testing and vacuum leak testing.
Once you have identified and corrected all of the inert gas leaks, it is important to note that the entire inert gas system has been potentially exposed to atmospheric conditions and ancillary water vapor. Now, in order to get it back online, we must remove air from the inert gas system and validate that all of the repairs made were successful.
If you utilized thin film leak testing to identify leaks, the pressure is still in the inert gas system. However, if you made any repairs afterward or utilized vacuum leak testing to identify leaks, this means the inert gas system was breached and needs to be purged. As a result, you need to follow a few key steps to bring it back online:
- If you isolated the liquid system, which is normally outside, you must reopen the outside valve to allow pressure back into the backfill reservoir tank.
- Bring the backfill reservoir tank up to 75 psi.
- Thin film leak test all of the repairs made.
- If any leaks are discovered in the inert gas system, then you need to bring the pressure in the backfill reservoir tank back down to zero and fix them again. If there are no leaks, then you need to go back and close the outside service valve again.
Remember, there is no such thing as a small leak, which is why it is paramount that the tolerance of leaks in your backfill system equals zero. This is because, as soon as gas starts flowing into the furnace, any “harmless” pressure leaks on the backfill system of the furnace, the partial pressure system, the argon/nitrogen tank, the evaporator, the lines to, before and after it, etc. will aspirate air into the furnace.
Once you have verified that there are no leaks in the inert gas system, you need to bring the pressure down to zero and begin final charging of the inert gas system. It is during final charging of the inert gas system that a large number of people make a very common mistake when it comes to air in their system, which often results in lost production.
In our next post in the series, Finding Leaks in Your Vacuum Furnace – Part VIII, we will discuss how to avoid this common mistake, as well as examine two different methods for properly accomplishing final charging of the system.