01. Nominal diameter (DN):

The nominal diameter of thermoplastic piping system pipes indicates the size of the inner diameter, outer diameter, or their approximate values.

02. Circumferential bending stiffness / Ring stiffness:

A measure of the pipeline's ability to resist circumferential deformation. It can be determined using testing methods or calculation methods, with the unit being N/m2 or KN/m2.

03. Elastic diameter deformation rate:

The ratio of the vertical elastic deformation value of the pipe diameter under external pressure load to the diameter of the central axis of the pipe wall section before loading, expressed as a percentage and determined by the flattening test.

04. Out-of-roundness:

The difference between the maximum and minimum outer diameters measured at the same cross-sectional point of the pipe.

05. Standard Dimension Ratio (SDR):

The ratio of the nominal outer diameter to the nominal wall thickness of the pipe. SDR = DN / en.

06. Maximum Operating Pressure (MOP):

The maximum effective pressure of fluid allowed for continuous use in a pipeline system, measured in MPa.

07. Declared wall thickness en:

The specified value of the wall thickness of the pipe, measured in millimeters.

08. Overall utilization (design) coefficient C:

A total coefficient greater than 1, which takes into account the usage conditions not reflected in the lower prediction limit and the properties of components such as fittings in the pipeline system.

09. Predicted lower confidence limit of hydrostatic pressure strength (σLPL):

When the confidence level is 97.5%, the lower limit of the predicted value of hydrostatic pressure strength corresponding to temperature T and time t is σLPL=σ(T,T,0.975), with the unit being MPa.

10. Minimum Required Strength (MRS):

The stress value, obtained by rounding down the value of σLPL at 20℃ and a 50-year confidence lower limit to the nearest preferred number according to the R10 or R20 series, is expressed in MPa. When σLPL is less than 10MPa, it is rounded according to the R10 series, and when σLPL is equal to or greater than 10MPa, it is rounded according to the R20 series.

11. Design stress σs:

The allowable stress under specified application conditions is obtained by dividing MRS by the factor C, and then rounded to the next smaller value in the preferred number R20 series, that is, σs=[MRS] / C.

Deviations between the allowable limit values and the specified values are permitted. The difference between the maximum allowable value and the specified value is referred to as the upper deviation, while the difference between the minimum allowable value and the specified value is referred to as the lower deviation.

13. Tolerance:

The allowable deviation of a specified quantity value is expressed as the difference between the maximum and minimum allowable values. It is equal to the difference between the upper and lower deviations.

14. Outer diameter at any point:

The outer diameter measured at any cross-sectional point of the pipe, with the unit being millimeters.

15. Average diameter:

Corresponding to the diameter of the center circle of the tube wall cross-section. The average diameter is equal to the difference between the average outer diameter and the average wall thickness, or the sum of the average inner diameter and the average wall thickness, with the unit being mm.

16, 20℃, 50-year lower confidence limit (σLCL):

A stress value used to evaluate material performance refers to the lower confidence limit of the predicted long-term strength of a pipe made from the material, under an internal water pressure at 20℃ for 50 years, with a confidence level of 97.5%. The unit is MPa.

17. Long-term hydrostatic strength (σLTHS):

It represents the predicted average strength at temperature T and time t (average strength refers to the lower confidence limit of material strength with a confidence level of 50%), with the unit being MPa.

18, 20℃, 50-year long-term strength (σLTHS):

The average or predicted average strength of the pipe material under water pressure at 20℃ for 50 years, expressed in MPa.

19. Environmental stress cracking:

The phenomenon of accelerated stress cracking due to the influence of environmental conditions. The environmental stress cracking resistance of a material is commonly denoted by ESCR.

20. Crosslinking degree:

A physical quantity indicating the degree of crosslinking. When crosslinking occurs between polymer chains, it is expressed as the average number of crosslinking units per polymer molecule. It is also known as crosslinking point density or crosslinking index. It is usually expressed as gel content.

21. Toughness failure:

Damage accompanied by obvious signs of resuscitation and deformation.

22. Brittle failure:

The fractured area shows no obvious damage due to plastic deformation.

23. Penetration failure:

The visible loss occurs when the pressurized fluid inside the tube seeps out through the tube wall, but no obvious cracking damage occurs.

24. Circumferential stress:

The stress induced in the pipe wall by internal pressure, acting along the circumferential direction of the pipe material.

25. Burst pressure:

The maximum pressure before the pipe breaks in the hydrostatic burst test of pipes.

26. Fault temperature:

The maximum temperature that occurs when the pipeline system exceeds its control limit.

27. Structural wall tube:

The general term for composite pipe wall structures composed of multiple layers of materials, as well as for pipe materials with special-shaped pipe wall structures such as open ribbed, closed ribbed (hollow), etc.

28. Special-shaped wall tube:

A general term for tubular materials with smooth inner walls and outer walls consisting of spiral, ring-shaped, or corrugated ribbed tube structures.

29. Double-wall corrugated pipe:

The inner wall is smooth and flat, while the outer wall features trapezoidal or curved corrugated ribs. The space between the corrugations of the inner and outer walls constitutes a hollow, irregular-shaped tubular wall material.

30. Annular ribbed tube:

Special-shaped pipe material with a smooth and flat inner wall and an outer wall featuring annular reinforcing ribs.

31. Spiral ribbed tube:

The inner wall of the tube is smooth and flat, while the outer wall features spiral reinforcement ribs. It is a specially shaped tube wall material made through a spiral winding process.

32. Flat-walled tube:

Homogeneous pipe material with smooth inner and outer walls.

33. Mechanical connection fittings:

Pipe fittings that achieve connection through mechanical connection methods (such as threaded connection, crimping connection, etc.).

34. Resilient sealing pipe fittings:

Pipe fittings that utilize elastic sealing rings to achieve sealed connections typically cannot transmit axial loads.

35. Solvent-cemented pipe fittings:

Pipe fittings that are connected using solvent-based adhesives.

36. Electrofusion fittings:

A pipe fitting with an electric heating element preset on the connecting surface (below).

37. Hot-melt butt fittings:

A pipe fitting with ports of the same size as the pipes to be connected, which achieves connection through hot melt butt welding.

38. Hot-melt socket fittings:

Heat the inner surface of the pipe fitting socket and the outer surface of the pipe or valve insertion end using a heating tool, then insert and weld them together, thus achieving a connected pipe fitting.

Classification of pipe materials

Non-metallic pipe materials

Non-metallic pipe materials encompass a diverse array of common plastic pipes (including rigid PVC pipes for water supply, ABS engineering plastic pipes, PP-R engineering plastic pipes, etc.), composite pipes (aluminum-plastic composite pipes, steel-plastic composite pipes, etc.), concrete pipes, rubber pipes, fiberglass pipes, and more.

1. Plastic pipes

Concept: Plastic pipes are generally made from synthetic resin, also known as polyester, with the addition of stabilizers, lubricants, plasticizers, etc. They are extruded and processed in a pipe-making machine using a "plasticizing" method.

Advantages: lightweight, corrosion-resistant, aesthetically pleasing appearance, odorless, easy to process, convenient for construction, etc.

Disadvantages: Low strength and poor heat resistance.

Purpose: Primarily used for piping, drainage, exhaust, and sewage sanitary pipes in tap water supply systems for housing construction, underground drainage systems, rainwater pipes, as well as conduits for wire installation and other supporting purposes.

Classification: Based on different pipe materials: Plastic pipes used in construction mainly include polyvinyl chloride (PVC) pipes, chlorinated polyvinyl chloride (CPVC) pipes, polyethylene (PE) pipes, cross-linked polyethylene (XLPE) pipes, etc.

1. Unplasticized polyvinyl chloride pipe (PVC-U)

Purpose: For water supply (non-potable water), drainage pipes, and rainwater pipes.

Advantages: corrosion resistance, smooth inner wall, less scaling, good hydraulic conditions, lightweight and easy to install, less prone to aging, low thermal conductivity, hard texture, low price, easy to bond, flame retardant.

Disadvantages: not resistant to impact, poor durability, high technical requirements for joint bonding, and long curing time.

Connection methods: Socket bonding, plastic welding, flange connection with dedicated fittings, threaded connection.

2. Chlorinated polyvinyl chloride pipe (PVC-C)

Purpose: It is commonly used as a hot water pipe, waste liquid pipe, and sewage pipe abroad, while domestically, it is mainly used as a sheathing pipe for power cables.

Advantages: Best temperature resistance, good anti-aging performance, and excellent flame retardancy.

Disadvantage: High price.

Connection methods: Socket bonding, plastic welding, flange connection with special fittings, threaded connection.

3. Polyethylene pipe (PE)

Purpose: HDPE and MDPE pipes are widely used as urban gas pipelines and urban water supply pipelines abroad. Currently, HDPE and MDPE pipes in China are mainly used as urban gas pipelines, with a small amount used as urban water supply pipelines, while LDPE pipes are largely used as agricultural irrigation and drainage pipelines.

Classification: Based on their different densities, they are categorized into high-density polyethylene (HDPE) pipes, medium-density polyethylene (MDPE) pipes, and low-density polyethylene (LDPE) pipes.

Characteristics: HDPE pipes exhibit high strength and rigidity; MDPE pipes, besides possessing the pressure resistance of HDPE pipes, also demonstrate excellent flexibility and creep resistance; LDPE pipes exhibit good flexibility, elongation, and impact resistance, particularly in terms of chemical stability and high-frequency insulation resistance.

Connection methods: electrothermal welding, hot melt butt joint, flange, threaded screw thread, etc.

4. Cross-linked polyethylene pipe (PE-X)

Purpose: Primarily used for indoor cold and hot water supply in buildings and radiant floor heating. Cross-linked polyethylene (PEX) pipes are generally categorized into three types: a, b, and c. PE-Xa pipes are used for cold and hot water pipelines, oil pipelines, fuel tanks, chemical pipelines, etc.; PE-Xb pipes are used for floor heating pipes (with toxic properties phased out of the market); and PE-Xc pipes are currently the most environmentally friendly floor heating pipes.

Advantages: Excellent temperature resistance, good creep resistance, good memory performance, easy to correct.

Disadvantages: It can only be connected using metal parts and cannot be recycled for reuse.

Connection methods: ferrule type with dedicated metal connectors, clamp type connection, and threaded connection.

5. Heat-resistant polyethylene pipe (PE-RT)

Purpose: Ideal for indoor cold and hot water piping, especially for hot water systems. It is also an excellent choice for radiant heating applications.

Advantages: Excellent temperature resistance, suitable for use at -70℃ to 90℃; superior thermal insulation performance, with a low thermal conductivity; long service life, ensuring safe use for over 50 years; chemical corrosion resistance; good shape memory recovery performance; vibration resistance and impact resistance; excellent hydraulic characteristics.

Disadvantages: Not recyclable; limited overhead span of the pipeline, requiring multiple support installations; due to complex factors such as cross-operation during construction, PE-RT pipes are prone to punctures, and the reserved pipe ends are easily flattened, leading to frequent repairs and rework.

Connection methods: There are three major types: hot melt connectors, electrofusion connectors, and mechanical connectors.

6. Type III polypropylene pipe (PP-R)

Purpose: Primarily used for domestic cold and hot water supply, as well as radiant floor heating.

Advantages: Good temperature resistance, recyclable and reusable, green and environmentally friendly product, good hygienic performance, suitable for pure water transportation.

Disadvantages: Under the same pressure and medium temperature conditions, the pipe wall is thick and flammable.

Connection methods: There are mainly electric hot melting, hot melting butt joint, as well as flange connection and threaded connection using special fittings.

7. Polybutylene pipe (PB)

Purpose: Primarily used in tap water, hot water, and heating and cooling pipes.

Advantages: Excellent temperature resistance, good tensile and compressive strength, impact resistance, low creep, high flexibility, the thinnest pipe wall under the same pressure and medium temperature conditions, and it is a green product.

Disadvantages: Dependent on imports, high price, flammable.

Connection methods: There are mainly electric hot melting, hot melting butt joint, and also rubber ring sealing butt joint can be adopted.

8. ABS engineering plastic pipe (ABS)

Purpose: It is commonly used as a sanitary ware downpipe, gas pipeline, and highly corrosive industrial pipeline abroad. In China, it is generally used for indoor cold and hot water pipes, dosing pipelines for water treatment, and industrial pipelines with corrosive effects.

Advantages: High strength, impact resistance, capable of being threaded directly, good hygienic performance, suitable for pure water transmission.

Disadvantages: Long bonding and curing time, flammable.

Connection methods: There are mainly socket connections, as well as flange connections using specialized fittings, and threaded connections.

II. Composite pipes

Concept: It is based on metal pipes, with inner and outer welding of non-metallic materials such as polyethylene and cross-linked polyethylene, exhibiting characteristics of both metal and non-metallic pipes.

Advantages: light weight, smooth inner wall, low resistance, good corrosion resistance.

Disadvantages: It is prone to damage when subjected to external impact, and repairing such damage inevitably leads to waste.

Purpose: Water supply and drainage pipeline.

Classification: aluminum-plastic composite pipe, steel-plastic composite pipe, copper-plastic composite pipe, plastic-coated composite pipe, steel-framed PE pipe, etc.

1. Aluminum-plastic composite pipe

Purpose: For use as domestic cold and hot water pipes. The composite pipe, with inner and outer plastic layers made of cross-linked polyethylene, is suitable for use as a hot water pipe, with a working temperature up to 90℃.

Structure: Its basic composition should be five layers, namely, from the inside out, plastic, hot melt adhesive, aluminum alloy, hot melt adhesive, and plastic.