In spite of insulation on tank, it will see some heat transfer into the tank, which will result in vaporization of LNG. This gas is called boil of gas (BOG). This gas can be re-liquefied by compressing and sending it to BOG condenser where LNG will come in contact with compressed gas and re-liquefy it. This is common process to maintain LNG in liquid state both onshore and on LNG tankers during transportation. Cases where BOG rate is too high gas will be flared.