What is a Cold-insulated Pipe? Key Points of Cold Insulation Design for Low-temperature Pipes

A cold-insulated pipe is a special piping system equipped with a cold insulation structure on the outer layer of pipes carrying low-temperature media. It prevents external heat from transferring into the pipe and avoids condensation, frost and ice formation on the outer pipe surface. It is widely used in LNG, liquid oxygen, liquid nitrogen, refrigerant, chemical low-temperature medium transportation and central air conditioning systems. Its purpose is opposite to ordinary heat-preserved pipes: heat insulation reduces heat loss from inside the pipe, while cold insulation blocks external heat ingress. Many engineers mix them up during project selection, which leads to insulation failure, excessive energy consumption and equipment damage.

A qualified cold insulation structure consists of multiple layers: pipe base, anti-rust coating, cold insulation layer, vapor barrier layer and outer cladding from inside out. The vapor barrier is the core deciding whether the cold insulation works. Once water vapor from the air penetrates into the insulation layer, it condenses or freezes under low temperature, ruins the insulation performance and causes sharp efficiency drop. In severe cases, the pipe outer wall will be corroded. This is the biggest difference from heat insulation: heat insulation usually does not require a strict vapor barrier, while the vapor barrier for low-temperature cold pipes must be continuous and sealed without cracks or loose overlaps.

Material selection is critical for design. Common cold insulation materials include PIR (polyisocyanurate), rubber-plastic foam and aerogel blanket. PIR features high closed-cell rate, low thermal conductivity and excellent low-temperature resistance, which is the first choice for LNG and cryogenic chemical projects. Rubber-plastic foam is flexible and easy to install, commonly used for central air conditioning refrigerant pipes. Aerogel has ultra-low thermal conductivity and fits compact spaces requiring thin insulation, though its cost is higher. Designers shall select materials based on medium temperature, ambient humidity, fire rating and budget instead of only thermal conductivity.

Cold bridge treatment is an easily overlooked difficulty. Metal components such as pipe supports, flanges, valves and instrument nozzles conduct heat rapidly and form cold bridges, bringing in massive heat and causing local condensation and cold leakage. The standard solution is to install rigid insulation blocks at pipe supports to cut direct metal heat transfer. Flanges and valves adopt detachable insulation boxes for later maintenance. Poor cold bridge treatment causes local dripping and icing even if the insulation thickness meets requirements.

Insulation thickness shall be calculated by thermal formulas according to medium temperature, ambient temperature, relative humidity and allowable cold loss rather than experience. Insufficient thickness brings high cold loss and surface condensation; excessive thickness raises material cost and occupies installation space. Outer cladding options include color steel sheet and aluminum alloy sheet, with watertight and sealed joints to protect the vapor barrier.

Strict construction and acceptance management are required. Cold insulation construction is not suitable in wet and rainy weather. Overlap width of vapor barrier, sealant sealing and cladding fixing must follow standards. After completion, inspect insulation thickness, cold leakage points and vapor barrier integrity. Reasonable design, proper material selection, cold bridge blocking and moisture sealing ensure long-term stable operation, reduce cold loss and avoid costly rework.