This is one of the most common questions we are asked as experts in the field of Transformer gaskets.
There is a phenomenon known as Creep Relaxation common to all kinds of gaskets. This means that every gasket when subjected to constant pressure will lose some of its original thickness fairly quickly.
It is completely natural for bolts to become loose after some time. Ideally, re-tightening of bolts at ambient temperature should be done around 48 hours to 72 hours after the initial sealing.
This is as per the recommendation of the European Sealing Association, UK, and Fluid sealing Association, USA
So next time you face this issue, do not worry, just follow the process.
If you want to make your transformer 100% leakproof
Click here: https://forms.gle/u64Bw4AEbnMacW7S9