While insulated pipes are typically designed for a 30-year service life, some piping networks encounter issues in less than a decade of actual operation. This is not necessarily the fault of the manufacturer alone; the final service life is influenced by multiple stages, ranging from material selection and installation to actual operation.
Raw material quality is the fundamental factor. National standards dictate that polyurethane foam must have a density of at least 60 kg/m³ and a closed-cell content of no less than 88%. To cut costs, some smaller manufacturers reduce foam density to just over 40 kg/m³ or incorporate recycled materials into the outer casing. Insufficient foam density results in poor compressive strength and aging resistance, while recycled materials in the outer casing make it prone to cracking and water seepage after a few years. These defects may not be apparent upon leaving the factory but become evident over time.
The outer casing and the insulation layer together form the pipeline's protective barrier. The outer casing must block groundwater and corrosive substances found in the soil; if the wall thickness is inadequate or joint seals are imperfect, water will seep in. Once the foam absorbs water, insulation performance drops sharply, and the moisture accelerates the electrochemical corrosion of the steel pipe. Excavations of prematurely failed pipelines often reveal waterlogged, softened foam and water stains on the inner surface of the outer casing.
Installation quality is equally critical, particularly at the joints. Joint sealing involves on-site welding of the outer casing and foam injection-processes that lack the controlled conditions of a factory environment. Imperfect sealing creates a vulnerable entry point for water. During trench backfilling, the presence of rocks or a failure to compact the soil in layers can cause cracks in the outer casing; additionally, insufficient constraint can lead to the pipeline buckling or deforming due to thermal expansion. Such installation details are difficult to inspect once the pipe is buried.
Finally, there are operating conditions. The long-term temperature limit for polyurethane foam is approximately 120°C. If the medium temperature consistently exceeds this threshold, the foam ages rapidly-darkening in color, losing strength, and experiencing increased thermal conductivity. In harsh environments-such as areas with high water tables or corrosive soil-the outer casing requires superior crack resistance; otherwise, the service life will be significantly compromised.
A 30-year service life for insulated pipes cannot be guaranteed by meeting a single specification alone. Raw materials, protective structures, construction quality, and operating conditions are all indispensable. Only by paying close attention to these aspects during procurement can the pipeline truly achieve its intended service life.