Water supply and drainage - PE pipes and PPR pipes

Water supply and drainage - PE pipes and PPR pipes

1. What are the components of polyethylene pipes and what are their respective functions?

Answer: Polyethylene pipes are made of polyethylene resin as the main raw material, and a certain amount of heat stabilizers, colorants and processing aids are added and made by extrusion molding. Heat stabilizers, also called antioxidants, are used to delay or inhibit high-temperature oxidation of polyethylene during processing; colorants (or light stabilizers) are generally black or blue in polyethylene pipe raw materials, mainly to prevent degradation and serve as warnings; the function of processing aids is to improve the processing performance of polyethylene.

2. What are the advantages of polyethylene pipes over metal pipes?

① Low energy consumption, light weight, recyclable, a new generation of environmentally friendly products, and long service life;

② Reliable and convenient installation (connection), can meet the use requirements of various special occasions, and has low requirements for pipe base;

③ Good flexibility and strong resistance to geological movement;

④ Excellent corrosion resistance.

3. What are the meanings of the currently used polyethylene raw materials PE63, PE80, and PE100? What are the differences in their use?

4. What are the nominal pressure (PN), working pressure, design pressure of the pipe and their relationship?

The nominal pressure refers to the working pressure of the pipe for continuous water delivery at 20℃. If the water temperature is between 25℃-45℃, the working pressure should be corrected according to different temperature drop coefficients.

The working pressure refers to the maximum continuous motion pressure acting on the inner wall of the pipe under normal working conditions of the pipeline, excluding the fluctuating pressure of water.

The design pressure refers to the maximum instantaneous pressure acting on the inner wall of the pipe by the pipeline system. Generally, the sum of the working pressure and the residual water hammer pressure is used.

The relationship between the three: nominal pressure ≥ working pressure

Design pressure = 1.5 × working pressure

The working pressure is calculated by the hydraulic calculation of the pipe network.

5. What is water hammer pressure?

Instantaneous fluctuating pressure generated by sudden changes in the flow rate of water in the pipeline system.

6. What does SDR mean? How does it relate to the nominal pressure (PN)?

SDR is the standard dimension ratio, which is the ratio of the nominal outer diameter to the nominal wall thickness, that is, SDR = dn/en. The larger the SDR, the lower the pressure bearing capacity; conversely, the smaller the SDR, the higher the pressure bearing capacity. The relationship between SDR and PN of PE water supply pipe is as follows:

Nominal pressure (MPa) of polyethylene (PE80) water supply pipe

Nominal pressure (MPa) of polyethylene (PE100) water supply pipe

7. What are the two major methods of PE pipe connection?

There are mainly the following methods for PE pipe connection:

Hot melt connection - including: hot melt butt connection, hot melt socket connection, hot melt saddle connection.

Electrofusion connection - including: electric fusion sleeve connection, electric fusion saddle connection.

8. How is the shrinkage of the pipe end formed?

The shrinkage problem of polyethylene pipe end is inevitable in the production of polyethylene pipe. This is because the production of polyethylene pipe adopts the hollow sizing spray cooling method. During production, the air pressure inside the pipe is mainly used to press the pipe onto the sizing sleeve, and the outside of the pipe is sprayed with cooling water. Therefore, the cooling of the pipe is from the outside to the inside. Due to the circumferential stress of the pipe, when the pipe end is sawed, the stress of the port is released, causing the port to shrink. The degree of shrinkage can be adjusted by process, but it cannot be avoided. Therefore, when measuring the outer diameter of the pipe, it should not be measured at the pipe port, otherwise the measured value cannot reflect the actual situation.

9. Why should an exhaust valve be set in the pipeline? How to set it?

During the operation of the pipeline, the gas in the water will accumulate at the high position of the pipeline and even form air resistance. When the water flow in the pipe fluctuates, the raised part forms an air bag, which will be continuously compressed and expanded. After the gas is compressed, it will generate a large pressure, which is dozens or even hundreds of times greater than the pressure generated by the compression of water. At this time, the pipeline is very easy to rupture, so consider installing an exhaust valve when designing the pipeline.

10. What type of raw materials are used to produce HDPE gas pipes and water pipes?

The raw materials used to produce HDPE gas pipes and water pipes are PE80 and PE100.

11. Classification of polyethylene pipes?

According to the application: outdoor water supply pipe, building water supply pipe, building drainage pipe, buried drainage pipe, gas pipe, electrical conduit, agricultural pipe, industrial pipe, hot water heating, sewage pipe, etc.; According to the material density: high-density polyethylene pipe, medium-density polyethylene pipe, low-density polyethylene pipe; According to the structure: smooth-wall polyethylene pipe, double-wall corrugated pipe, spiral winding pipe, etc.

12. Polyethylene pipe color classification?

PE water supply pipe: GB13663 stipulates that polyethylene for water supply is blue or black with blue stripes;

PE polyethylene gas pipe: GBl5558.1 stipulates that the color of polyethylene pipe for gas is yellow or black with yellow stripes.

13. Comparison between PE80 and PE100?

Under the long-term hydrostatic strength of polyethylene at 20℃, when it is used for 50 years, the hoop stress value of the material being destroyed is 8.0~9.99MPa for PE80 and 1.0~12.49MPa for PE100, which is the basis for the naming and strength design of polyethylene material grades.

The performance differences between the two are:

① Tensile performance: The tensile yield strength of PE100 is 20% higher than that of PE80;

② Impact resistance: The impact resistance of PE100 is higher than that of PE80;

③ Bending performance: The bending modulus of PE100 is 20% higher than that of PE80;

④ Pressure bearing capacity: The pressure bearing capacity of PE100 is higher than that of PE80;

⑤ Resistance to fast and slow crack growth: PE100 is higher than PE80.

14. What is pipe jacking?

It is a trenchless construction method, a pipeline burial construction technology without excavation or less excavation. This is very important for cities with busy traffic, dense population, numerous ground buildings and complex underground pipelines.

15. What is the difference between double-wall corrugated pipe and single-wall corrugated pipe?

Single-wall plastic corrugated pipe refers to a plastic pipe with corrugations on both the inner and outer walls. It has high rigidity, can be bent arbitrarily, and can be rolled in unlimited length.

Double-wall corrugated pipe refers to a plastic pipe with a smooth inner wall and corrugated outer wall. It is formed by a corrugated outer wall and a smooth inner wall extruded at the same time. It adopts a special hollow ring stiffness and good strength and toughness. Under the same strength and stiffness requirements, the use of double-wall corrugated pipe can save 30%-50% of materials compared with ordinary plastic pipes.

16. What kinds of pipes are generally selected for municipal roads?

① Cement pipe; ② PE double-wall corrugated pipe; ③ U-PVC reinforced pipe

17. What is the use of double-wall corrugated pipe?

Double-wall corrugated pipe is mainly used for large-scale water supply, water supply, drainage, sewage, exhaust, subway ventilation, mine ventilation, farmland irrigation, etc. with working pressure below 0.6MPa.

18. What is the reduction factor of working temperature to pipeline working pressure? What is the pressure reduction factor of polyethylene pipe system to temperature?

The ratio of working pressure to working pressure at 20℃ when the pipe is used continuously at working temperature above 20℃.

When the polyethylene pipe system is used continuously at temperature above 20℃, the maximum working pressure (MOP) should be calculated as follows: MOP=PN×f1......(where f1---reduction factor, its data is available in the table below.)

50-year life requirement, pressure reduction factor at temperature below 40℃

19. What is ring stiffness SN? What do SN4 and SN8 represent?

At present, the numerical index of ring stiffness is widely used internationally to indicate the external pressure load resistance of plastic buried drainage pipes. If the ring stiffness of the pipe is too small, the pipe may be deformed too much or suffer from compression buckling instability. On the contrary, if the ring stiffness is too high, it is inevitable to use too large a section moment of inertia, which will result in too much material and high cost.

SN4 and SN8 represent the difference in ring stiffness. SN4 represents ring stiffness ≥4KN/㎡, and SN8 represents ring stiffness ≥8KN/㎡.

20. Are rubber rings with different ring stiffness universal?

They cannot be universal.

21. What are the uses of PE pipes?

PE pipes can be widely used in urban water supply systems, food and chemical transportation systems, ore and mud transportation systems, landscaping pipe networks, replacement cement pipes, cast iron pipes and steel pipes.

22. What is a masterbatch? Why is a masterbatch used in pipes?

A substance that changes the color of plastic when melted at high temperature. The purpose of adding a masterbatch is to make the pipe opaque and prevent ultraviolet rays from causing foreign matter in the pipe.

23. What performance does the hydrostatic test test the pipe?

The hydrostatic test tests the long-term strength performance of the pipe.

24. What is the melt mass flow rate?

Melt mass flow rate refers to the mass of thermoplastics that pass through a standard die every 10 minutes under a certain temperature and load. It is expressed as MFR. Its value is an important technical indicator of the viscosity flow characteristics of thermoplastics in a molten state. It can be used to guide the quality control of raw materials and products, process selection, and molecular parameter research during production, processing, and molding. If the change in the melt mass flow rate before and after material processing exceeds the standard requirements, it means that the material has been significantly degraded during the processing, thereby reducing the performance of the pipe.

25. Why are there fish eyes on the outer surface of the pipe? How to eliminate it?

Possible reasons: The temperature of the machine head is too high and the cooling is insufficient.

Elimination method: Reduce the temperature of the machine head and increase the amount of cooling water

26. Why are there stripes on the inner wall? How to eliminate it?

Possible reasons: The temperature of the core rod is too low.

Elimination method: Increase the temperature of the core rod.

27. Why are there bubbles and pits on the inner wall? How to eliminate it?

Possible reasons: The material is damp.

Elimination method: Pre-dry the raw materials.

28. Why is the wall thickness of the pipe uneven? How to eliminate it?

Possible reasons: The center of the mouth mold and the core mold is not aligned.

Elimination method: Ask a specialist to check or redesign.

29. Why is the pipe bent or elliptical? How to eliminate it?

Possible reasons: ① The mouth mold and the core mold are not concentric; ② The temperature around the machine head is uneven, and the material is uneven; ③ The supply of cooling water is uneven; ④ The gap between the rubber conveyor belt of the traction machine is small and the clamp is too tight.

Troubleshooting method: ① Adjust the gap between the die and the core die to make them concentric; ② Adjust the heating temperature to be uniform; ③ Adjust the cooling water volume and flow direction appropriately; ④ Adjust the gap between the conveyor belts.

30. Why is the tube partially thin and transparent? How to eliminate it?

Possible reasons: ① The temperature of the machine head is too high; ② The water supply of the cooling shaping ring is small.

Troubleshooting method: ① Appropriately reduce the temperature of the machine head; ② Appropriately increase the water supply.

31. Why are there threads or bamboo joints on the inner wall? How to eliminate it?

Possible reasons: ① The temperature of the machine head is uneven or the local temperature is too high; ② The compressed air pressure is too low.

Troubleshooting method: ① Appropriately adjust the temperature of the machine head to make it uniform; ② Appropriately increase the compressed air.

32. Why is it broken or cannot be pulled out? How to eliminate it?

Possible reasons: ① Unreasonable design of the machine head; ② Too much or too little water supply of the cooling shaping ring; ③ Too much compressed air supply.

Elimination method: ①Finish the machine head; ②Control the water supply of the cooling shaping ring; ③Reduce the supply of compressed air.

33. Why is the surface of the pipe rough? How to eliminate it?

Possible reasons: ①The material contains too much water; ②The material temperature is low; ③The die is not clean; ④The extrusion speed is too fast.

Elimination method: ①Raise the temperature of the dryer to dry the material; ②Adjust the process temperature; ③Clean the die; ④Adjust the extrusion speed.

34. Why are there bright spots on the surface of the pipe? How to eliminate it?

Possible reasons: ①The die temperature is too high; ②Insufficient cooling.

Elimination method: ①Lower the die temperature; ②Increase cooling.

35. Why is the surface of the pipe uneven? How to eliminate it?

Possible reasons: ①Pulsation of material flow; ②Unstable traction speed.

Elimination method: ①Adjust the extrusion speed; ②Repair the traction speed control system.

36. Why is the pipe not round? How to eliminate it?

Possible reasons: ① Low vacuum; ② Extrusion speed is too fast; ③ Insufficient traction cooling; ④ Too high water level in cooling water tank.

Elimination method: ① Adjust vacuum; ② Adjust extrusion and traction speed; ③ Adjust cooling water volume and temperature; ④ Lower cooling water tank water level.

37. What is the reason for impurities in pipes? How to eliminate it?

Possible reasons: ① Damaged filter; ② Degradation of plastic; ③ Poor quality filler or coloring masterbatch.

Elimination method: ① Replace the filter; ② Adjust process temperature; ③ Replace filler or coloring masterbatch.

38. What is the reason for pipe bending? How to eliminate it?

Possible reasons: ① Uneven pipe wall thickness; ② Uneven pipe cooling; ③ Insufficient pipe cooling.

Elimination method: ① Adjust pipe wall thickness; ② Adjust cooling water nozzle; ③ Adjust cooling water volume and temperature or reduce extrusion speed.

39. What is the reason for the compounding chain? How to eliminate it?

Possible reasons: ① The die shaping length is not enough; ② The melt temperature is too low; ③ The die head structure is unreasonable.

Troubleshooting methods: ① Lengthen the die shaping length; ② Increase the process temperature; ③ Choose a die head with a reasonable structure.

40. What is the approximate drying temperature of the material?

The drying temperature is about 80℃.

41. What do the blue and red lines on the PPR pipe represent?

The blue line PPR is a cold water pipe; the red line PPR is a hot water pipe.

42. What is the purpose of PPR pipe?

PPR pipe can be used for domestic water, pure water, hot water supply, and floor radiant heating system pipes.

43. What is the difference between PPR pipes and metal pipes?

For thermoplastic materials, they have more outstanding creep properties than metals under the continuous action of force, and have the characteristics of significant twisting fluids.

44. How to indicate the specifications of PPR pipes?

The specifications of PPR pipes are expressed by pipe series S, nominal outer diameter dn, and nominal wall thickness en.

45. What is pipe series S? What is the calculation method?

The pipe series corresponds to the wall thickness of the pipe.

Calculation method: S = design stress of the pipe / design pressure of the pipe, or S = (dn-en) / 2en

46. What are the types of pipe series S?

There are S5, S4, S3.2, S2.5, S2.

47. How to choose pipe series S?

The larger the S, the thinner the corresponding pipe wall, so the selected S must be less than or equal to the calculated S to ensure the safety and service life of use.

48. Storage of special materials for PPR pipes?

In a dry, ventilated, clean warehouse with good fire-fighting facilities, it should be stored away from heat sources and prevent direct sunlight. It is strictly forbidden to stack in the open air.

49. Why does PP-R pipe not breed bacteria and scale?

PP-R pipe material is random copolymer polypropylene, which is a low-polarity saturated aliphatic hydrocarbon long-chain polymer. Its product PPR pipe has a low surface tension, so water cannot infiltrate the pipe wall, even at a high temperature, water cannot infiltrate the surface of the pipe. PP-R material itself is extremely difficult to serve as a nutrient for bacteria, so it is difficult for bacteria to attach and grow on the surface of the pipe, and it is difficult for calcium and magnesium ions in the water to accumulate and scale on the pipe wall.

50. PP-R pipe material is modified polypropylene, why is it non-toxic and odorless?

PP-R pipe special material is a small amount of ethylene and propylene, which is randomly polymerized by gas phase copolymerization. It is a chemical modification, which is different from the general physical modification of adding other additives. Its molecular long chain is composed of only C and H elements, does not contain any toxic elements, and does not release harmful substances. After full combustion, it only produces carbon dioxide and water, and the waste can be recycled. Therefore, PP-R pipes are non-toxic and odorless, and are green building materials.

51. The difference between pipe diameters such as D, DN, De, and Φ

DN refers to the nominal diameter of the pipe.

Note: This is neither the outer diameter nor the inner diameter, but the average of the outer diameter and the inner diameter, called the average inner diameter.

For example: DN200~Φ219×6 De refers to the outer diameter of the pipe. Generally, De is used for marking, and it needs to be marked in the form of outer diameter x wall thickness.

De25=Φ25X3.0 (outer diameter x wall thickness)

D generally refers to the inner diameter.

Φ represents the diameter of a circle or pipe (usually refers to the outer diameter). The expression of the pipe diameter should comply with the following regulations: For pipes such as water-gas transmission steel pipes (galvanized or non-galvanized), cast iron pipes, etc., the pipe diameter should be expressed in nominal diameter DN; for pipes such as seamless steel pipes, welded steel pipes (straight seams or spiral seams), copper pipes, stainless steel pipes, etc., the pipe diameter should be expressed in outer diameter × wall thickness; for pipes such as reinforced concrete (or concrete) pipes, clay pipes, acid-resistant ceramic pipes, and tile pipes, the pipe diameter should be expressed in inner diameter d;

For plastic pipes, the pipe diameter should be expressed according to the product standard method, and De is generally used for marking;

d -- nominal diameter of concrete pipe

De mainly refers to the outer diameter of the pipe. The outer diameter of PPR, PE pipes, and polypropylene pipes, which are generally marked with De, need to be marked in the form of outer diameter × wall thickness.

D generally refers to the inner diameter.

Φ-- Nominal diameter of seamless steel pipe, its specification is, such as ф100:108 X 4

Φ also represents the diameter of a circle: Φ plus the letter representing the circle. Such as ΦO, ΦA, followed by =. For example, ΦO=3 cm.

DN refers to the nominal diameter of the pipe d-- Nominal diameter of concrete pipe De mainly refers to the outer diameter of the pipe Φ-- Nominal diameter of seamless steel pipe