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Ten things you must know about plastic pipes

In the vast and ever-growing field of plumbing, pipe material selection is a critical decision for both seasoned industry professionals and DIY enthusiasts alike. Imagine a scenario where the success of a critical project depends on the durability, cost-effectiveness, and environmental suitability of the piping materials used. This article explains in detail how to quickly identify pipeline standards, uses, pressure conversion, and other issues.

Table of Contents

What plastic pipe is used for water supply?

Commonly used plastic water supply pipes are made of four materials: PVC, CPVC, PPR, and HDPE.

PVC is not suitable for hot water and will deform at 140 degrees Fahrenheit.
CPVC has better high temperature resistance than PVC and can be used for hot and cold water supply.
PPR has excellent heat resistance and leakage resistance, making it very suitable for hot water supply.
HDPE has excellent softness and is not suitable for hot water supply. It is mainly used for municipal water supply main pipes.

What are the standards for plastic water supply pipes?

Common plastic pipe standards include ASTM, ISO, EN DIN, and GB.
ASTM: American Society for Testing and Materials, a non-profit international organization.
ISO: The world’s largest non-governmental standardization agency.
EN: European Standard, a series of technical standards developed by the European Committee for Standardization.
GB: refers to the national standard of the People’s Republic of China.

PVC Standard:

ASTM D1785: This American standard specifies the requirements for polyvinyl chloride (PVC) plastic pipe in Schedules 40, 80, and 120. It covers dimensions, testing, and markings for PVC pipes intended for pressure applications.

ASTM D2241: Standard specification for polyvinyl chloride (PVC) pressure-rated pipe (SDR Series). This covers PVC pipes with specific dimension ratios for various pressure ratings.

ISO 4422: Pipes and fittings made of unplasticized polyvinyl chloride (PVC-U) for water supply. This international standard covers a range of criteria, including dimensions, physical properties, and quality control.

DIN 8061 and DIN 8062: German standards outlining general quality requirements and testing for PVC piping systems for cold water supply and drainage.

EN 1452: European standard for plastic piping systems for water supply – Unplasticized poly(vinyl chloride) (PVC-U). It specifies dimensions, mechanical properties, and performance characteristics.

CPVC Standard:

ASTM F441/F441M: This is the standard specification for chlorinated polyvinyl chloride (CPVC) plastic pipe, schedules 40 and 80. It covers CPVC pipes used in hot and cold water distribution systems, specifying dimensions, pressure ratings, and testing requirements.

ASTM D2846: This standard specifies the requirements for CPVC plastic hot- and cold-water distribution systems. It covers CPVC pipes, tubing, and fittings for potable hot and cold water distribution systems.

NSF/ANSI Standard 61: Drinking Water System Components – Health Effects. This standard evaluates the health effects of materials, components, and products that come into contact with drinking water. CPVC pipes used for water supply must comply with this standard to ensure they do not leach harmful contaminants into the water.

ISO 15877: This series of international standards covers plastic piping systems for hot and cold water installations, made of chlorinated polyvinyl chloride (CPVC). The standards include general requirements, definitions, and test methods for CPVC piping systems.

DIN 8079 and DIN 8080: German standards that outline the general quality requirements and testing for CPVC piping systems for hot water supply and distribution.

PPR Standard:

DIN 8079 and DIN 8080: German standards that outline the general quality requirements and testing for CPVC piping systems for hot water supply and distribution.

DIN 8077: Specifies the general requirements for polypropylene (PP) pipes. It covers dimensions and properties of PP materials for pipes under pressure, including PPR.

DIN 8078: Provides specifications for polypropylene (PP) pipes; quality requirements and testing. This standard complements DIN 8077 by detailing the physical and mechanical properties of PP pipes.

 GB/T 18742.2-201: A Chinese standard that specifies the requirements for polypropylene piping systems for hot and cold water installations. It is similar to the ISO 15874 series and is often used for PPR pipes in China.

HDPE Standard:

ISO 4427: “Plastic piping systems – Polyethylene (PE) pipes and fittings for water supply.” This series of international standards covers the general aspects of polyethylene pipes and fittings for the conveyance of water for human consumption, including raw water prior to treatment and water for general purposes. It specifies characteristics and performance requirements.

ASTM F714: “Standard Specification for Polyethylene (PE) Plastic Pipe (DR-PR) Based on Outside Diameter.” This American standard specifies requirements for HDPE pipes used for the conveyance of fluids, including water.

 GB/T13663.2-2018: A Chinese standard that specifies requirements for HDPE piping systems

What is SDR?

SDR (Standard Dimension Ratio) is a method used to rate pressure in piping systems, including those made of PVC, CPVC, HDPE, and other plastic materials. SDR is a ratio of the pipe’s outside diameter to its wall thickness, providing a standardized indicator of the pipe’s strength and pressure capacity. The formula to calculate SDR is:

SDR=Outside Diameter➗Wall Thickness

What is SDR rating pressure?

Each SDR value correlates to a specific maximum pressure rating at a standard temperature (usually 20°C or 68°F). These ratings are defined in various standards and specifications for different materials and applications. For example:

The lower the SDR number, the thicker the pipe wall and the higher the pressure rating it can withstand.

  • SDR 11: Often used for high-pressure applications, where the pipe needs to withstand substantial forces.
  • SDR 17: More suited for moderate pressure applications, offering a balance between strength and material efficiency.
  • SDR 26 or higher: Typically used for low-pressure or gravity-flow conditions, where the forces exerted on the pipe are minimal.
SDR Value Pressure Rating (bar) Pressure Rating (psi) Pressure Rating (MPa) PN Equivalent
SDR 6 25 363 2.5 PN25
SDR 7.4 20 290 2 PN20
SDR 9 16 232 1.6 PN16
SDR 11 12.5 181 1.25 PN12.5
SDR 17 8 116 0.8 PN8
SDR 21 6.3 91 0.63 PN6.3
SDR 26 5 73 0.5 PN5
SDR 33 4 58 0.4 PN4
SDR 41 3.2 46 0.32 PN3.2

What does the DN on the pipe mean?

DN: refers to the nominal diameter, also known as the average outer diameter, which is neither the outer diameter nor the inner diameter of the pipe, but the average of the outer diameter and the inner diameter.
DN is a standardized diameter series for pipes and accessories. The use of nominal diameters is conducive to the standardization of parts, and also facilitates design, manufacturing, repair and management, and reduces manufacturing costs. For pipes, DN is a representation of a certain size that is smaller than the outer diameter and larger than the inner diameter. Corresponding to a certain nominal diameter of the pipe, its outer diameter is a certain value, and its inner diameter changes with the wall thickness. Its correspondence with imperial units is as follows:

Φ: refers to the outer diameter of the pipe, that is, the outer edge diameter of the pipe including the pipe wall thickness.
De: refers to the outer diameter of the pipe. The outer diameter of PPR, PE pipe and polypropylene pipe is generally marked by De, which is often marked in the form of outer diameter x wall thickness.

En is the nominal wall thickness

Such as: De110×En6.6.

Inch DN Nominal outer diameter (mm)
1/2" 15 Φ20
3/4“ 20 Φ25
1“ 25 Φ32
1-1/4“ Φ40 32
1-1/2“ 40 Φ50
2“ 50 Φ63
2-1/2“ 63 Φ75
3“ 80 Φ90
4“ 100 Φ110
5“ 125 Φ140
6“ 150 Φ160

What are the 4 most common pressure units in piping systems?

Pressure is a physical quantity that defines the force exerted per unit area. The four common pressure units in pipeline systems are: Bar, Pa, PSI, Kg/cm².

  1. PSI (Pounds per Square Inch):

    • Preferred in: The United States and, to a lesser extent, Canada. PSI is widely used in various industries including automotive, industrial, and scientific fields within the U.S. due to the country’s continued use of the Imperial measurement system.
  2. MPa (Megapascals):

    • Preferred in: Countries that use the metric system or have adopted the International System of Units (SI) for scientific and engineering purposes. This includes most countries in Europe, Asia, and parts of the Commonwealth. MPa is often used in high precision engineering, materials science, and in the fields where extremely high or low pressures are discussed.
  3. Bar:

    • Preferred in: Europe and other parts of the world for general engineering and automotive industries. The Bar is not an SI unit but is accepted for use with the SI. It is commonly used because its value is conveniently close to atmospheric pressure (1 Bar ≈ 0.987 atm).
  4. Kg/cm² (Kilograms per Square Centimeter):

    • Although you mentioned “Bra,” it seems like there might have been a confusion with “Bar.” However, kg/cm² is another unit worth mentioning. It is commonly used in parts of Asia for certain applications, like hydraulic pressure, due to its direct correlation with the force exerted by gravity on a given area.

What does PN mean in pipe?

The “PN” stands for “Pression Nominal” in French, which translates to “Nominal Pressure” in English.PN represents the nominal pressure of the pipeline.

For example, PN16: PN16 usually indicates a nominal pressure of 16 bar (bar), which is equivalent to 1.6 megapascal (MPa).

The PN rating system is used to categorize the pressure capabilities of piping components, helping ensure that all parts of a piping system are compatible with the pressure levels they will be subjected to during operation.

How do you convert between pressures?

To convert between PSI, Bar, MPa, kg/cm², and PN, you can use the following standard conversion factors. These conversions are based on the relationships between pressure units:

1 Bar = 14.5038 PSI
1 Bar = 0.1 MPa
1 Bar = 1.01972 kg/cm²
PN ratings are in Bar (i.e., PN 16 means the component can withstand up to 16 Bar).
From PSI to Others:
To Bar: Divide the PSI value by 14.5038.
To MPa: Divide the PSI value by 145.038.
To kg/cm²: Divide the PSI value by 14.2233.
From Bar to Others:
To PSI: Multiply the Bar value by 14.5038.
To MPa: Multiply the Bar value by 0.1.
To kg/cm²: Multiply the Bar value by 1.01972.
From MPa to Others:
To PSI: Multiply the MPa value by 145.038.
To Bar: Multiply the MPa value by 10.
To kg/cm²: Multiply the MPa value by 10.1972.
From kg/cm² to Others:
To PSI: Multiply the kg/cm² value by 14.2233.
To Bar: Multiply the kg/cm² value by 0.980665.
To MPa: Multiply the kg/cm² value by 0.0980665.
PN to Other Units:
Since PN ratings are essentially in Bar, you can directly apply the conversions above to translate a PN rating into PSI, MPa, or kg/cm².
Here are some examples:

PN 16 to PSI: PN 16 means 16 Bar, so 16 Bar * 14.5038 = 232.0608 PSI.
PN 16 to MPa: 16 Bar * 0.1 = 1.6 MPa.
PN 16 to kg/cm²: 16 Bar * 1.01972 = 16.31552 kg/cm².
These conversion factors enable you to switch between different units of pressure as needed, facilitating calculations and ensuring compatibility across systems that use different units of measurement.

How do you read Plastic Pipe markings?

Manufacturers typically mark pipes with a series of numbers and letters that provide information about pipe material, diameter, wall thickness and pressure rating, usage, and standards. as the picture shows:

PVC drain pipe

Figure 1 Pipes are marked with pipe materials, sizes, standards, uses, and pressure levels.

Figure 2 The pipes are marked with information such as size, material, use, pressure level, etc.

Material name:
PVC, CPVC, HDPE, PPR, etc.: Types of plastic materials from which pipes are made.
Nominal diameter:
Expressed as “DN” followed by a number (e.g., DN20) or sometimes simply as a numerical value (e.g., 20mm), it represents the approximate inside diameter of the pipe.
SDR or PN rating:
SDR (Standard Dimension Ratio): A number indicating the ratio of a pipe’s outer diameter to its wall thickness. The lower the SDR, the thicker the wall and the higher the pressure-bearing capacity.
PN (Nominal Pressure): followed by a number (e.g. PN16) indicating the maximum pressure in bar that the pipe can withstand at 20°C (68°F). The higher the PN number, the higher the pressure the pipeline can withstand.
Pipe markup example:
“PVC PN16 DN20”: This mark indicates PVC pipes with a nominal pressure rating of 16 bar and a nominal diameter of 20 mm.
“HDPE SDR11”: This represents HDPE pipe with a standard size ratio of 11, indicating a certain wall thickness relative to its diameter that is designed for a specific pressure capacity.
Additional tags
ASTM, ISO, EN, DIN, etc.: These abbreviations refer to the specific standards that pipes adhere to and provide further insight into their design specifications and applications.

How to measure Pipe and fitting sizes

We measure the outer diameter of pipes and the inner diameter of pipe fittings. Because the pipe must be pressed inside the pipe fitting.
As shown below,

Measuring pipes

Measuring pipes

Measuring Fittingss

Measuring Fittingss

The technical terms “pipe size” and “fitting size” often cause confusion, but they refer to specific aspects of duct system components. Here’s a breakdown of the differences:

Pipe size
Diameter: Pipe size is primarily determined by its diameter, which can be divided into two main types:
Nominal Diameter (DN): This is a standardized number and is not the actual measured diameter of the pipe.
Outside Diameter (OD): Especially important for piping and systems where accurate assembly is critical, OD is the actual outside diameter of the pipe.
Wall Thickness: Expressed in the United States by a pipe gauge (e.g., SCH 40, SCH 80) or internationally by a Standard Dimension Ratio (SDR), which expresses wall thickness relative to the pipe diameter. This directly affects the pressure rating of the pipeline.
Accessory size
Compatibility with pipe sizes: Fittings are designed to join pipes of specific sizes and must match the nominal diameter of the pipe they are intended to be used with.
The size of the fitting indicates the inner diameter of the fitting, which is the biggest difference from the pipe.

     I am the author of this article and the CEO and Marketing Director of SWDPLASTIC with 15 years of experience in the valve and pipeline industry. If you have any questions, you can contact me anytime.

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