Design, Operation and Maintenance of Polyurethane Jacket Pipe System

Overview:

Polyurethane directly buried insulation pipe has become a mature and advanced technology in developed countries. In the past decade or so, China's heating engineering and technical personnel have promoted the development of domestic pipeline network technology to a higher level by studying this advanced technology. Polyurethane direct-buried heat preservation pipe is made of high-functional polyether polyol compound material and multiple methyl polyphenyl polyisocyanates as raw materials and foamed by chemical reaction, because of its simple construction, energy saving and anti-corrosion, light weight, high strength, heat insulation, Soundproof, flame retardant, cold-resistant, anti-corrosion, non-absorbent and other excellent features have significant effects, and are widely used in indoor and outdoor pipelines, central heating pipelines, central air conditioning pipelines, chemical and pharmaceutical industrial pipelines and other thermal insulation and cold insulation projects.

Design, Operation and Maintenance of Polyurethane Jacket Pipe System

Related standards and parameters:

Polyurethane Directly Insulated Pipe Technical Parameters: Axial shear strength: ≥0.12MPa (23±2°C), continuous operating temperature: 140°C Max, peak operating temperature: 150°C Max, service life: ≥30 years (insulation layer and The outer sheath, the service life of the steel pipe is related to the water quality), the net length of the pipe end: 200mm-400mm, the pipe diameter range: DN20-DN1200, the average hole diameter: ≤0.5mm, the closed hole rate ≥88%, density of any position ≥ 60/m3, compressive strength ≥ 0.3MPa (under 10% deformation conditions), water absorption: ≤10% (boiling water at 100°C for 90 minutes), high-density polyethylene outer sheath: density ≥ 950/m3 (20°C), Carbon black content: 2.5%±0.5% (mass percentage), thermal conductivity: 0.43W/(m.°C), thermal expansion coefficient: 18010-6(1°C), fused polyurethane directly buried pipe index: 0.50~0.70g ( MFI 190°C/5kg), Tensile Strength: ≥19MPa, Elongation at Break: ≥350%, Resistance to Environmental Stress Cracking: ≥200h; Implementation of GB/T29047-2012 "High Density Polyethylene External Protector Polyurethane Foam Prefabricated Straight Buried thermal insulation pipe" standard or EN 253 "Integrated prefabricated insulation system for groundwater heat pipe network, made of working steel pipe, polyurethane insulation layer and polyethylene outer casing Into the insulation pipe, the steel pipe can be used: 20# and Q235 steel seamless steel pipe, spiral steel pipe and welded steel pipe, performance indicators in line with national and Ministry of petroleum standards; seamless steel pipe using GB/T8163-2008 standard; spiral steel pipe used SY/T5037-2000, GB/T9711.1-2011, welded steel pipe using GB/T3091-2001. Under normal circumstances, DN20-DN150 using seamless or welded steel pipe, DN200 above the use of spiral steel pipe, can also be used according to the needs of the user requirements of various types of steel pipe. Steel pipe fittings are pushed or pressed. Executive Standard: Steel Butt Weld Pipe Fittings GB/T12459-2005 Steel Butt Weld Pipe Fittings GB/T13401-2005 Steel Bend Pipe SY/T5257-2004; Outer Casing Implementation GB13018-91 "Polyethylene (PE) Pipe Outside Diameter and Wall Thickness limit deviation standard.

structure:

The first layer: Working steel pipes are generally selected from seamless pipes, spiral welded pipes, straight welded pipes, ppr and glass steel pipes according to the design and customer requirements. (Steel pipe surface can be shot blasting process, but also do anti-corrosion)

The second layer: Polyurethane insulation layer is formed by injecting rigid polyurethane foam material into the sandwich layer between the steel pipe and the outer sheath with a low and high pressure foaming machine. (The commonly known as "tube-in-tube foaming process")

The third layer: high-density polyethylene pre-made into the demand side of the wall thickness of the plastic pipe, its role is to protect the polyurethane insulation from mechanical hard material damage, the second is anti-corrosion, waterproof; or the use of fiberglass, which is characterized by light weight , Long life, convenient transportation, low construction costs, no maintenance, low overall cost.

Construction features:

1. Reduce project cost

According to calculations by related departments, double-controlled heating pipes can generally be reduced by 25% of the construction cost (using glass fiber reinforced plastic as a protective layer) and 10% (using high-density polyethylene as a protective layer).

Low heat loss, saving energy

The thermal conductivity coefficient of the polyurethane directly buried heat pipe is: λ=0.013-0.03kcalm·h·oC, which is much lower than other commonly used pipe insulation materials, and the heat preservation effect is improved by 4 to 9 times. In addition, its water absorption is very low, about 0.2kgm2. The reason for low water absorption is that the closed cell ratio of polyurethane foam is as high as about 92%. The low thermal conductivity and low water absorption, coupled with insulation layers and high-density polyethylene or FRP shells with good water-repellent properties, have changed the status of the traditional trench laying heating pipe “wet cotton padded jacket”, which greatly reduced the number of heating pipes. The overall heat loss, thermal network heat loss is 2%, less than the international standard requirements of 10%.

3. Anti-corrosion, good insulation performance, long service life

Because the insulation layer of the polyurethane directly buried insulation pipe is tightly bonded to the outer surface of the steel pipe, which insulates the infiltration of air and water, it can play a good anti-corrosion effect. At the same time, its foaming pores are closed and the water absorption is small. The high-density polyethylene shell and glass fiber reinforced plastic shell have good anti-corrosion, insulation and mechanical properties. Therefore, the outer skin of the working steel pipe is hardly affected by the outside air and water. As long as the internal water quality of the pipeline is well handled, according to the introduction of foreign materials, the service life of the polyurethane burial heat insulation pipe can be more than 50 years, which is 3 to 4 times longer than the traditional trench laying and overhead laying.

4. Less land occupation, quick construction, favorable environment protection

Polyurethane burial pipe insulation does not need to build huge trenches. It is only necessary to bury the insulation pipe in the ground, thus greatly reducing the project's land occupation, reducing earthwork excavation volume by more than 50%, and reducing civil engineering masonry and concrete volume by 90%. At the same time, the polyurethane direct burial heat preservation pipe processing and the on-site trenching are carried out in parallel. Only the on-site joints can shorten the construction period by more than 50%.

5. Alarm system can be set to automatically detect leaks in the pipe network, accurately indicate the fault location and automatically alarm

The polyurethane burial thermal insulation pipe is equipped with a leakage alarm line. Once a leak occurs in a certain place of the pipeline, the transmission line through the alarm line can show the exact position of the water leakage and the leakage of the thermal insulation pipe and the degree of leakage. In order to inform the infiltration personnel to quickly handle the leaked pipe section, to ensure the safe operation of the heating pipe network.

Storage method:

1. The heat pipe shall not be exposed to the sun, rain and soaking, and it shall be covered with a tarpaulin when stored in the open air. Keep away from the heat source and the fire source.

2. Drainage ditch should be dug in the site, and there should be no water in the site.

3. Stacking site should be set pipe support, the outer protective pipe should be higher than the ground 150mm.

4. The height of the insulation pipe should not exceed 2 meters.

5. The ground should be smooth and free of gravel and other hard impurities.

Precautions and instructions:

1. It must be understood that the direct burial of heating pipes can be divided into two ways: make up for direct burial and no compensation for direct burial. During the design and construction, the working principles, characteristics, and places of application of the two methods are indeed mastered so that they can be reasonably selected in design and safe, reliable, and economical in construction.

2. After entering the site, conduct serious inspections. Before the construction, it is necessary to conduct research on the manufacturers of the prefabricated direct-buried thermal insulation pipes. Reject the use of unqualified insulation.

3. In the construction of polyurethane direct buried insulation pipe, welding is a key task to ensure the quality of the project and must be given enough attention.

4. The construction quality of various wells directly affects the quality of the project and the service life of the pipeline, fixing the bracket. If the well is not well-water proofed, the parts will be damaged by flooding. Therefore, serious construction should be carried out to ensure construction quality.

5. Under pressure conditions, it is necessary to stress the pressure of the polyurethane directly buried heat pipe. First, the water is drained to clean the air, and then it is divided into two steps: there is no leakage during the pressure regulation within 10 minutes. Strength test: raise the pressure in the pipeline to 1.5 times the working pressure; use a 1kg hammer to inspect the welds one by one around the weld; tightness test: when the pressure in the tube is reduced to working pressure, 30 minutes Leakage and pressure drop of not more than 0.2 atmospheres are acceptable; the pressure test records should be made according to the specifications.

6. Because the polyurethane direct buried thermal insulation pipe is buried in the ground, most of the project is a concealed project. If the acceptance is not serious, the completion data will not be detailed, which will affect the future use.

7. Welding between pipe and pipe (Fiberglass connection process and pressure test standard are set separately), after installation, make joints fully cured (48 hours) before putting the pipe into the ditch, so as to avoid unsatisfactory joint processing Put in the bottom of the ditch, water soaking the joints of the pipe and reduce the waterproof, anti-corrosion, heat preservation effect.

8. Polyurethane directly buried insulation pipe on site joint insulation must be qualified after the pressure test before conducting joint insulation construction on site. This item is specific to the construction of polyurethane burial insulation pipes, and the construction quality will directly affect the service life. The insulation layer has two methods of on-site foam construction and insulation tile construction. No matter which method is used for construction, there can be no defects such as annular space, cracking, delamination, etc. There are many kinds of maintenance layers (such as high-density polyethylene and fiberglass). Protective layer) but must ensure the integrity of the joint, tightness, waterproof.

9. The depth of burying must ensure that the truck with a load of 10 tons is safely passed. To minimize the heat loss, it should be laid below the ice line. Different areas should be dealt with specifically according to the different conditions in the area.

10. The size of trench excavation shall ensure that there is a 200-250 interval between the pipes and between the pipe and the trench wall for site installation and joint treatment. The trench bottom shall be compacted with bricks and soil, if necessary, bedding with fine sand.

11. When the direct-buried pipe passes through the road, the laying depth is not changed, but the form of the pipe ditch is not filled with complex soil, and the reinforced concrete plate or the concrete casing pipe is covered on the pipe ditch.

12. During the process of installing the heat pipe, it can be installed side by side while doing joint processing. It can also be installed after the pressure test is completed.

(1) In order to ensure joints waterproof, anti-corrosion, insulation effect, it is necessary to ensure the conditions of the joint site.

(2) On-site temperature of joints shall be maintained at 10°C or higher during operation, and shall not be lower than 5°C at the minimum. Therefore, it is not appropriate to do joint processing in winter, and it is not suitable to do joint treatment in rainy days, and the bottom of the trench is not wet and the water must not be jointed. .