I. Advantages of Polyurethane Foaming

　　Polyurethane foam is a two-component system: Component A is a polyol, and Component B is an isocyanate. During application, the two components are fed into a spray machine, where they are mixed and sprayed out in a fine mist, rapidly foaming, curing, and solidifying within about one minute. This material was only introduced in recent years for use in building thermal insulation and waterproofing. After two to three years of practical application, it has become well understood; it offers numerous advantages and boasts a wide range of applications.

　　1. Excellent thermal insulation performance. With a thermal conductivity of approximately 0.025, it outperforms polystyrene boards and is currently one of the best materials for building thermal insulation.

　　2. Excellent waterproof performance. The foam cells are closed, with a closure rate of 95%, ensuring that rainwater cannot seep through the cell walls.

　　3. On-site spray application creates a seamless, monolithic waterproofing layer—unmatched by any polymer membrane—thereby reducing maintenance requirements.

　　4. Excellent adhesion. It bonds extremely securely to materials such as wood, metal, masonry, and glass, and is resistant to being lifted off by strong winds.

　　5. It is suitable for both new roof construction and the repair of existing roofs, particularly for the renovation of old roofs. There is no need to remove the original waterproofing and insulation layers; simply clean off surface dust, sand, and debris before spraying.

　　6. Construction is simple and fast. More than 200 square meters can be sprayed per worker per day, which helps accelerate project progress.

　　7. The termination detail is simple. When spray-applied polyurethane foam is used for the termination, no special treatment is required, which greatly simplifies the process. In contrast, when using sheet membranes, a groove must be provided at the parapet wall, and the termination should be installed within this groove; if a groove cannot be provided, the termination must be secured with flat steel flashing and then sealed with joint sealant.

　　8. Excellent economic benefits. Separating the insulation layer from the waterproofing layer not only increases construction costs and extends the project schedule, but also makes it impossible to achieve a seamless, integrated result—whereas spray-applied polyurethane foam can be applied in a single operation.

　　9. Excellent aging resistance. According to summaries of field applications and research tests conducted overseas, the service life under aging conditions can reach up to 30 years.

　　 10. Fast curing. After foaming, the material becomes durable, significantly extending its service life.

　　II. Application and Construction of Polyurethane Foaming

　　The insulation layer—polyurethane foam—is applied to the exterior of the steel pipe’s anti-corrosion coating either by on-site spray application or by pre-forming and then installing, offering a simple method with rapid construction efficiency.

　　Low thermal conductivity:

　　Polyurethane foam has the lowest thermal conductivity among insulation materials, thereby minimizing heat loss from the process stream.

　　Waterproof, corrosion-resistant, and aging-resistant:

　　Given that polyurethane foam boasts a closed-cell content of over 92%, its use as the insulation layer for directly buried pipelines not only provides effective thermal insulation but also effectively prevents the penetration of water, moisture, and various other corrosive liquids and gases, thereby inhibiting the growth and proliferation of microorganisms.

　　III. Strong Safety and Applicability

　　 Polyurethane foam exhibits strong adhesion to a wide range of materials; therefore, when used as the insulation layer for directly buried pipelines, there is virtually no need to worry about the adhesion between the insulation and the anti-corrosion coating. The polyurethane insulation layer is suitable for temperatures ranging from +120°C to -196°C, with short-term (on the order of a few dozen hours) exposure up to +190°C. If the customer requires long-term operation at 190°C, we can tailor the formulation using high-temperature-grade polyurethane materials to meet their specific needs.

　　1. For flat roofs with waterproofing and thermal insulation, apply a coat of colored coating as a protective layer on roofs not intended for pedestrian use; on roofs intended for pedestrian use, lay facing tiles on a bed of mortar.

　　2. On tiled pitched roofs, spray expanded polyurethane beneath the batten board; the tiles are grouted onto the batten board, preventing slippage.

　　3. Polyurethane foam insulation for walls offers superior performance. When used in prefabricated wall panels, it can be sprayed between the panel ribs, providing strong adhesion and tight sealing. For hollow masonry units, the foam can be injected directly into the voids to ensure full filling; this is especially effective for cold-storage facility walls. At present, thermal insulation technology is a crucial component of wall renovation, and polyurethane foam has great potential for widespread application.

　　4. External wall insulation and waterproofing in basements are ideal applications for spray-applied polyurethane foam, as it provides both thermal insulation and waterproofing while eliminating the need for additional protective layers—achieving two objectives in one step.

　　IV. Disadvantages of Polyurethane Foam Foaming

　　Despite its numerous advantages, expanded polyurethane is not a panacea; it has inherent limitations and is not suitable for all applications.

　　1. At temperatures below 10°C, the foaming rate decreases. Consequently, its use is markedly constrained by the season.

　　2. Spray-applied polyurethane foam cures and forms rapidly, making it difficult to achieve a perfectly smooth surface; some unevenness is normal. When used for roof waterproofing and thermal insulation, the requirement for surface smoothness can be relaxed; however, poor smoothness in eaves troughs and roof gutters can adversely affect drainage flow rates.

　　3. Therefore, it must also be used in conjunction with other waterproofing materials.