Cold Insulation Construction in Refrigeration Equipment or Refrigeration Engineering

2025-05-07

In order to save energy, improve equipment efficiency, reduce heat dissipation loss, and prevent surface condensation, in refrigeration equipment or projects, some pipelines or key parts are insulated with thermal insulation materials. The cold insulation structure, from the inside out, generally consists of an anti-rust layer, a cold insulation layer, a moisture-proof layer (or vapor barrier layer), a protective layer, and an anti-corrosion and identification layer. Among them:

Anti-rust Layer
For the outer surfaces of carbon steel and ferritic alloy steel pipelines, equipment and their accessories that need cold insulation, an anti-rust layer should be painted after cleaning. For the outer surfaces of cold-insulated pipelines, equipment and their accessories made of stainless steel, non-ferrous metals and non-metallic materials, there is no need to paint an anti-rust layer after cleaning.
Cold Insulation Layer
The cold insulation layer is the most critical layer that determines the quality of the cold insulation effect. It has structures such as pasting, pouring, spraying, filling and multi-layer composite. The technical performance and thickness of the cold insulation layer materials must comply with the design regulations, and the thickness should be uniform, the joints should be tight, firm and reasonable, the tightness should be appropriate, and the appearance should be intact to ensure good thermal insulation effect. When the thickness of the cold insulation layer is greater than 80mm, it must be constructed in layers.
Moisture-proof Layer
The moisture-proof layer has structures such as pasting, coating and wrapping. It is required that the lap of the moisture-proof layer is appropriate, the thickness is uniform, it is complete and tight, without air holes, bubbles or cracks and other defects. It should have the properties of flame retardancy, water resistance, steam penetration resistance and aging resistance. It is an important layer to ensure the good thermal insulation effect of the cold insulation layer.
Protective Layer
The protective layer has metal and non-metallic structures and is the outer protective layer of the cold insulation structure. It protects the moisture-proof layer and the cold insulation layer from mechanical damage and the erosion and impact of outdoor rain, snow, wind, hail, etc. It is required that the protective layer must be tight, waterproof, moisture-proof, resistant to atmospheric corrosion and light aging, non-combustible or flame-retardant, with low blackness, light specific gravity, no cracking, sufficient mechanical strength, long service life, and can make the appearance of the cold insulation structure neat and beautiful.
Anti-corrosion and Identification Layer
Anti-corrosion paint can be painted on the outer surface of the protective layer according to needs. The outermost layer can use anti-corrosion paint of different colors or make corresponding color marks to identify the type and flow direction of the medium in the pipeline and equipment.
Therefore, the anti-corrosion layer can also serve as an identification layer.
For the thermal insulation materials used as the cold insulation layer, the performance requirements that need to be paid attention to during use are:

The cold insulation layer materials should be closed-cell, water-repellent, non-combustible or flame-retardant materials.
The thermal conductivity of foam plastics and their products at 25°C shall not be greater than 0.044 W/(m·K), and the density shall not be greater than 60 kg/m³; the thermal conductivity of foam glass and its products at 25°C shall not be greater than 0.064 W/(m·K), and the density shall not be greater than 180 kg/m³; the thermal conductivity of foam rubber and plastic products at 0°C shall not be greater than 0.036 W/(m·K), and the density shall not be greater than 95 kg/m³.
The material manufacturer should also provide indicators such as the minimum and maximum service temperature, linear expansion coefficient and shrinkage rate, water absorption rate, and corrosion resistance.
Preferentially select materials with low thermal conductivity, low density, low water absorption and moisture absorption rates, good low-temperature resistance, easy construction, and low cost.
When selecting adhesives, sealants and abrasives used during the construction of the cold insulation layer, pay attention to:
The adhesives, sealants and abrasives should be resistant to low temperatures, easy to cure, insoluble to the cold insulation layer materials, non-corrosive to the metal wall, with strong adhesion and good sealing performance. The abrasive (only for foam glass) should be able to prevent abrasion between the cold insulation layer material and the metal outer wall surface and between the contact surfaces of the cold insulation layer material products under the conditions of temperature change or mechanical vibration.
The service temperature range of the low-temperature adhesive is -196~50°C. Its softening temperature should be greater than 80°C, and the adhesive strength should be greater than 0.05MPa.
The service temperature range of the abrasive is -196~100°C. It has good heat resistance, without flowing or discoloring at 100°C. It has good cold resistance, without falling off or discoloring at -196°C. It has good adhesion, and there is no falling off phenomenon after it is applied to the foam glass and dried.
The adhesives, sealants and abrasives must be compatible with the characteristics of the cold insulation layer materials used. Examples of the matching use of adhesives, sealants and abrasives with the cold insulation layer materials are as follows:
a. For rigid, closed-cell, flame-retardant polyurethane foam plastic products, a two-component polyurethane adhesive or FG low-temperature adhesive should be used, and it can also be used as a sealant;
b. For self-extinguishing expandable polystyrene foam plastic products, a non-solvent adhesive (such as solvent-free phenolic resin adhesive, etc.) should be used, and it can also be used as a sealant;
c. For foam glass, FG low-temperature adhesive and a special wear-resistant sealant should be used.
General requirements for the materials used for the moisture-proof layer:
Good steam penetration resistance, strong moisture-proof and waterproof capabilities, and the water absorption rate shall not be greater than 1%.
Flame-retardant, it can self-extinguish within 1s to 2s after the fire source leaves, and its oxygen index is not less than 30.
Good bonding performance and sealing performance, and its bonding strength at 20°C is not lower than 0.15MPa.
A large safe service temperature range. It has certain temperature resistance, and the softening temperature is not lower than 65°C, without bubbling or flowing in summer. It has certain frost resistance, without cracking or falling off in winter.
Good chemical stability, its volatile matter is not more than 30%, it can resist corrosion, and it shall not dissolve or corrode the cold insulation layer materials and protective layer materials.
It has the stability to remain intact under the conditions of climate change and vibration.
Short drying time, it can be used at room temperature, and the construction is convenient.
Matters needing attention during the construction of the cold insulation structure:

When constructing the cold insulation layer, the joints of the same layer should be staggered, and the upper and lower layers should cover the joints. The joints should be filled, tightened, leveled, bonded firmly, sealed with adhesives and sealants, and the joint width shall not be greater than 2mm.
The metal fixing parts of the cold insulation structure shall not penetrate the cold insulation layer.
Rigid heat insulation pads should be used at the supports, hangers and brackets of the cold insulation structure, or rigid wooden pads treated with moisture-proof and moth-proof measures should be used for support.
When using polyurethane foam plastic for on-site pouring or spraying as the cold insulation layer, before the formal pouring or spraying, a trial pouring or spraying must be carried out in advance according to various technical requirements.
After the filling of the cold insulation layer in the cold insulation box is completed, the joint openings must be sealed, and an air leakage test shall be carried out.
The reserved expansion joints should comply with the following regulations:
a.
The positions of the expansion joints of each layer of the double-layer or multi-layer cold insulation layer must be staggered, and the staggering distance should not be greater than 100mm.
b. An expansion joint can be reserved on the cold insulation layer of the long straight pipe sections at both ends of the elbow. When the distance between the two elbows is very small, the expansion joint on the cold insulation layer of the straight pipe section can be determined according to the medium temperature to reserve only one or not to reserve.
c. An expansion joint should be reserved at a distance of 100mm to 150mm from the connection of the head on the cylinder cold insulation layer of the horizontal equipment.
d. For vertical equipment and vertical pipelines, an expansion joint with a width of 25 mm should be reserved below the support ring of the cold insulation layer.
e. The spherical container should reserve expansion joints as specified in the design.
f. The expansion joints of the cold insulation layer should be tightly filled with soft foam plastic strips, or squeezed and scraped with a foaming adhesive. The outside should be pasted and sealed with a 50 mm wide non-drying adhesive tape. The expansion joint must be insulated again.
In one of the following situations, an appropriate expansion gap should be left on the other side in the direction of expansion movement:
a. Packing compensators and corrugated compensators;
b. When the height of the sliding support is less than the thickness of the cold insulation layer;
c. Between the cold insulation structure and fixed components such as walls, beams, railings, platforms, supports, and the holes through which the pipelines pass.
Matters needing attention during the construction of the moisture-proof layer:

The outdoor construction of the moisture-proof layer should avoid being carried out in rain and snow.
The outer surface of the coating-type moisture-proof layer should be flat, uniform and tight, and its thickness should reach the design specification.
For the wrapped moisture-proof layer, the lap width of the wrapping material joints should not be less than 50mm, and the lap joints must be firmly bonded. The longitudinal joint position of the horizontal equipment and horizontal pipeline should be lapped on both sides, and the joint opening should face downward. The circumferential joint of the vertical equipment and vertical pipeline should be "upper lap lower". The pasting method can be spiral winding or flat laying.
Matters needing attention during the construction of the protective layer:
The metal protective layer should be made of galvanized thin steel plates with a thickness of 0.3mm to 0.8mm, or rust-proof thin aluminum plates with a thickness of 0.5mm to 1mm to form a protective shell. The metal protective layer of large equipment should be assembled into a shell with corrugated or grooved metal protective shell plates. The structure and fastening form of the metal protective shell must meet the requirements of the expansion joints and expansion gaps of the cold insulation layer. The joints of the metal protective shell should be lapped or locked. When fastening the metal protective shell, it is strictly prohibited to pierce the moisture-proof layer.
Flame-retardant non-metallic anti-corrosion materials can be used as the protective layer in an acid-base environment.