It is common to have a reservoir of perlite at the top if the tank above the interstitial space between the tank shells. This should normally drop down to replace compacted fill. Your situation may involve contaminated perlite or unusual compaction for some reason, then again it may be normal condensation if the level inside the tank is static and the outside dew point is appropriate.

IFRs (Petroleum) thank you for reply: [img ]

The level in the tank is not static, and the condensation is more important when we have tanker loading, last time we observe frost on the external wall, you can see it in the picture attached,
is it possible to add perlite without decommissioning of the Tank?

Have you done a vapor test of LNG at the sealed joint in the captioned picture that seems to be a source of LNG leakage?

we didn't do any test, we have a temperature sensors between the inner and outer tank for detecting leakage, the temperature still stable on all sensors.

There should not be cold spots like this. Something is amis. there should be excess perlite above the inter-tank space. Is it possible that there is a construction bracket bridging the gap? Grab the original construction drawings to see your tank's particular details.

if you need other information please dont hesitate, I need to know if we can add perlite and the tank in operation?

Do you have any gas detectors in the voids?

Can you take off the filling tube cap nearest your freezing point and gas test and then if OK lower in a boroscope to see what's happening.

Then if all you need is more perlite pour some more in.

That clamp / bolt at the top looks like a suspect area to me.

a full page of that third page would be nice and attach it also as a file. Adding as a photo is good, but the files size gfoes down and you can't zoom into different sections

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

possibly perlite void is formed around that place. You can insert a camera thu perlite fill nozzle to verify. How long have this tank operated? If it is less than a year from construction, perlite void is a high possibility due to inadequate perlite vibration.