ISO tank IMO7 repair

[chinleong]

I'm checking a 5000usg LN2 cryogenic tank. I found out that annular space(vacuum break) will blow out air when i were pressurize inner tank, but there is no leak or crack of inner vessel. Can anyone explain why would this happen?

 

[iainuts]

Generally the pipes break.

 

[chinleong]

TY for your reply but we checked all pipes and connection with helium and all is still good.
We done by pressurize annular space with helium+N2. Then purge some N2 to inner vessel for bring out helium detect purpose. That is no signal show on leak detector machine.