Polyurethane directly buried insulation pipe is suitable for heat supply system with medium temperature (long-term operation temperature) not higher than 120 ℃ and occasional peak temperature not higher than 140 ℃. The working steel pipe and outer protection pipe are tightly bonded together through insulation layer to form a trinity structure.
1、 Steel pipe
The dimension tolerance and performance of working steel pipe shall comply with GB / t9711 or GB / t8163 or API Spec 5L. The material, nominal diameter and wall thickness shall meet the design requirements. Single steel pipe shall not have girth weld. The surface of working steel pipe shall be pretreated before foaming to remove rust, rolling scale, grease, dust, paint, moisture or other contaminants, The derusting grade of external surface of working steel pipe shall comply with Sa2.5 in GB / T 8923.1.
2、 External protection tube
The inner and outer surface of the outer protection pipe shall be free from grooves that affect its performance, bubbles, cracks, depressions, impurities and uneven color defects by visual inspection; Both ends shall be cut flat and perpendicular to the axis of the outer protection pipe, and the angle error shall not be greater than 2.5 °； The density of outer protective tube should be more than 940kg / M & sup3;, The tensile yield strength at any position shall not be less than 19mpa and the elongation at break shall not be less than 350%
； The longitudinal retraction rate of any pipe section of the external protection pipe shall not be greater than 3%, and the surface of the pipe shall be free from cracks, voids, bubbles and other defects; The wall thickness of external protection pipe shall not be less than the design requirements.
3、 Insulation layer
Polyurethane foam should be free from stains, shrinkage and delamination. Polyurethane foam should be evenly filled with the annular space between the work steel tube and the outer protection pipe. The percentage of the total area of voids and bubbles on any section of insulation layer in the whole section area should not be more than 5%, and the size of a single void in any direction should not exceed 1 / 3 of the actual thickness of insulation layer at the same position. The density of polyurethane foam at any position of the insulation layer should not be less than 60kg/m³ The water absorption of polyurethane foam should not exceed 10%. The obturator rate of polyurethane foam should not be less than 88%. The thickness of the insulation layer shall meet the design requirements, and the surface temperature of the outer pipe shall not be greater than 50 ℃ during operation.
