Installation issues with mixed refrigerant systems
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LNG pipelines and valves are generally welded, so there is no risk of leakage. However, mixed refrigerant systems also have low-temperature pipelines, and their flanges are connected using bolts; therefore, a leak can occur due to the difference between cold and hot temperatures, leading to refrigerant leakage. I’m not sure whether it’s necessary to tighten the bolts cold when installing pipelines and valves
Only the refrigerant pipes at the inlet and outlet of the cold box are connected via valve flanges; the temperature inside the cold box is at normal levels, both the exit and inlet temperatures of the cold box are at normal temperatures, while the exit temperature of the refrigerant compressor is over 100 degrees. Since there is no low temperature below zero, it is not necessary to apply cold tightening
Cold tightening is carried out during the commissioning phase. After the equipment is installed, no insulation is applied to any of the flanged valves; cold tightening is performed several times during commissioning to check for leaks in the valves, and only afterward is insulation applied.