GB/T 29047-2021, titled "Prefabricated Directly Buried Insulated Pipes and Fittings-Rigid Polyurethane Foam Insulation with a High-Density Polyethylene Outer Casing," is the most critical national standard for prefabricated directly buried insulated pipes. Published in August 2021 and effective as of March 2022, it replaces the previous version, GB/T 29047-2012.
The new standard defines its scope, covering prefabricated directly buried insulated pipes and fittings designed for continuous operation at temperatures up to 120°C, with occasional peak temperatures reaching up to 130°C. Regarding product structure, the standard specifies the composition-consisting of a high-density polyethylene (HDPE) outer casing, a rigid polyurethane foam insulation layer, and a steel carrier pipe or fitting-as well as the associated requirements, test methods, inspection rules, marking, transportation, and storage protocols.
For the insulation layer, the standard mandates that the density of the polyurethane foam must be at least 60 kg/m³ at any point, the average cell size must not exceed 0.5 mm, and the closed-cell content must be at least 88%. For unaged foam, the thermal conductivity at 50°C must not exceed 0.033 W/(m·K), and the compressive strength must be at least 0.3 MPa.
Regarding the outer casing, the standard requires the use of pipe-grade high-density polyethylene resin (PE80 or higher); the use of recycled or reclaimed materials is strictly prohibited. The outer casing must have a density between 940 and 960 kg/m³, an elongation at break of at least 450%, a yield strength of at least 19 MPa, and a carbon black content of 2.5% ± 0.5%.
For purchasers, understanding these specifications facilitates targeted and effective product acceptance. It is recommended to explicitly stipulate in contracts that products must comply with GB/T 29047-2021 and to require that the manufacturer provide third-party test reports.