HDPE pipe is a flexible plastic pipe made of thermoplastic high-density polyethylene widely used for low-temperature fluid and gas transfer. The strong molecular bond of HDPE pipe materials helps it to use for high-pressure pipelines.
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 polyethene (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, 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 into black in color. Other color variants are available but usually not used frequently. Coloured or striped HDPE pipe is usually 90-95% black material, where a colored stripe is provided on 5% of the outside surface.
The physical and mechanical properties of a typical HDPE Pipe is listed below:
Depending on maximum pressure withstanding capability, HDPE Pipes are classified into several pressure grades known as PN grades. They are
Again, based on the types of materials used HDPE pipes are grouped into the following types:
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 PipesAs 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 requests.
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
Various types of mechanical joints can be used for joining HDPE pipes to HDPE or dissimilar pipes. They are
A complete range of HDPE Pipe fittings is available for any purpose. Typical HDPE pipe fittings include:
Factors that can influence the behavior and thus, the design of above ground HDPE piping systems are
A number of variables determine the hydrostatic pressure capacity of HDPE pipes. Those are
Usually, HDPE pipe can withstand short-term hydrostatic water pressures that are considerably higher than the pressure rating, or class. But the duty of the HDPE pipe should always be determined following the pipe’s long-term strength at 20°C to ensure a design life of at least 50 years.
The Barlow’s Formula is also applicable for HDPE piping that is related to the internal pressure, pipe outer diameter, wall thickness, and the circumferential hoop stress and is given by
Here:
The design hoop stresses for HDPE pipe materials are considered as follows as given ISO 4427:
HDPE pipes provide various advantages with respect to other piping materials like
The main disadvantage of HDPE pipes are
The full form of HDPE is High-Density Polyethylene. This hydrocarbon polymer is produced from petroleum by a catalytic process. Famous for its tensile strength in the similar product category, High-Density Poly Ethylene is a kind of thermoplastic.
Both HDPE and PVC are considered plastics. However, they are not the same. HDPE is a thermoplastic made from petroleum and PVC is a durable vinyl polymer. While comparing HDPE and PVC, HDPE due to its flexibility, high strength to density ratio, no corrosion, and chemical stability is a strong choice for low pressure and low-temperature applications.
HDPE or High-density polyethylene pipe is widely used to carry potable water, slurries, wastewater, chemicals, hazardous wastes, and compressed gases. They have been used in various industries like gas, oil, mining, water, and other industries.
Properly designed HDPE piping systems provide a long-lasting performance as compared to other piping systems. As per the estimates of the Plastic Pipe Institute, they are supposed to last 50 to 100 years.
Yes, HDPE is totally safe for carrying drinking water. This is one of the main reasons that in the water industry and desalination plants, high-density polyethylene pipes are widely used. The application of HDPE pipes for potable water applications is certified by NSF. Various disinfectants like chlorine and chloramine are approved for use in HDPE pipes.
PVC is stronger and stiffer as compared to HDPE.