Types and Design of HDPE Pipes (With PDF) – What Is Piping

 

Types and Design of HDPE Pipes (With PDF) – What Is Piping

HDPE pipe is a flexible plastic pipe made of thermoplastic high-density polyethylene widely used for low-temperature fluid and gas transfer. In recent times, HDPE pipes got their extensive uses for carrying potable water, hazardous wastes, various gases, slurry, firewater, stormwater, etc. The strong molecular bond of HDPE pipe materials helps it to use for high-pressure pipelines. Polyethylene pipes have a long and distinguished service history for gas, oil, mining, water, and other industries. Due to its low weight and high corrosion resistance, the HDPE pipe industry is growing tremendously. In the year 1953, Karl Ziegler and Erhard Holzkamp discovered high-density polyethylene (HDPE). HDPE pipes can work satisfactorily in a wide temperature range of -2200 F to +1800 F. However, the use of HDPE Pipes is not suggested when the fluid temperature exceeds 1220 F (500 C).

 

 

 

 

 

 

HDPE pipes are made by the polymerization of ethylene, a by-product of oil. Various additives (stabilizers, fillers, plasticizers, softeners, lubricants, colorants, flame retardants, blowing agents, crosslinking agents, ultraviolet degradable additives, etc.) are added to produce the final HDPE pipe and components. HDPE pipe lengths are made by heating the HDPE resin. It is then extruded through a die, which determines the diameter of the pipeline. The Pipe wall thickness is determined by a combination of the die size, the speed of the screw, and the speed of the haul-off tractor. Usually, 3-5% carbon black is added to HDPE to make it UV resistant, which turns HDPE pipes black in color. Other color variants are available but usually not used frequently. Colored or striped HDPE pipe is usually 90-95% black material, where a colored stripe is provided on 5% of the outside surface.

Properties of HDPE Pipes

The physical and mechanical properties of a typical HDPE Pipe are listed below:

 

Governing Codes: ISO 1183, ISO 4427, AS/ NZS 4130, BS EN 12201, EN 12056, AWWA C901, AWWA C906, etc

Available size range: DN 16 to 1600 (However, other customized sizes can be manufactured)

The density of HDPE Pipe: 930-970 kg/m3

 

Typical Mechanical Properties of HDPE Pipe are given in Table 1 below. However, these values vary from one manufacturer to another. So, must be consulted with the manufacturer.

Mechanical PropertiesHDPE PropertiesYield Strength18-26 MpaElongation10%Elastic Modulus900 MpaHardness61 Rockwell (Shore)Poisson’s Ratio0.45Linear Coefficient of thermal expansion0.17 mm/m-0CBrittleness temperature<-700CTable 1: Mechanical Properties of HDPE Pipe

 

Types of HDPE Pipes

Depending on maximum pressure withstanding capability, HDPE Pipes are classified into several pressure grades known as PN grades. They are

PN 2.5 – max pressure 2.5 bar

PN 4 – max pressure 4 bar

PN 6 – max pressure 6 bar

PN 10 – max pressure 10 bar

PN 16 – max pressure 16 bar

PN 20 – max pressure 20 bar

PN 25 – max pressure 25 bar

 

Again, based on the types of materials used HDPE pipes are grouped into the following types:

PE 63 – medium pressure piping systems

PE 80 – gas pipe for natural gas distribution network with pressure rate up to 4 bars or drinking water pipe with pressure rate up to 16 bar – sewers, outfall pipes, industrial pipes

 

PE 100 – high demands piping applications

The numbers following PE indicate the minimum required strength in Bar at 200 C for 50 years life span corresponding to ISO-4427. The rated working pressure of HDPE pipes is determined at 200 C. For higher temperatures, a derating factor (Table 2 Below) is used to determine the maximum pressure to which the HDPE Pipe can be subjected.

 

Fluid Temperature (0C)Temperature Derating factor0-201>20-250.9>25-300.8>30-350.7>35-400.6>40-450.5>45-500.4Table 2: Temperature Derating Factor for HDPE Pipes

Length of HDPE Pipes

As HDPE Pipe manufacturing is a continuous process, pipes of any length can be manufactured. However, due to transportation requirements and ease of handling at the site, the HDPE pipe length is limited and normally produced in standard lengths of 6, 10, 12, 15, 24, and 30 meters. HDPE Pipe lengths of 50 and 100 meters can be produced on request.

 

Joining HDPE Pipes

HDPE Pipes and fittings are joined to each other by Welding or by mechanical fittings. There are two types of welding methods used to join HDPE pipes. They are

 

Electrofusion Welding: Electrofusion is a simple and quick method to permanently join individual pipes and HDPE fittings or prefabricated sections in tight places. This method is suitable for on-site joints.

Butt Welding: Butt-welding homogenously joins HDPE pipes and fittings into prefabricated sections using heat and pressure without using additional connection fittings.

 

Various types of mechanical joints can be used for joining HDPE pipes to HDPE or dissimilar pipes. They are

Plug-in joint

Snap joint

 

Screw-thread joint

Flanged joint

Contraction sleeve

 

Sleeve coupling

Metal coupling

Rubber collar joint

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