Contributed By: Babanna Biradar, PE, CFPS, FSE (TUV) and Vivek Dhingra

ABSTRACT

High-Density Polyethylene (HDPE) pipe offers numerous benefits in fire water applications. They are corrosion-free, have excellent chemical resistance and have superior abrasion-resistant qualities. HDPE pipe has been used extensively infire water applications in geographical areas with low ambient temperatures. In addition to the benefits in performance and life cycle costs, HDPE pipe is easy and safe to install because of its light weight, long pipe lengths and flexibility.

HDPE pipe pressure rating gets de-rated as the temperature increases. Due to high ambient temperature in several geographical areas, HDPE pipe could not be used in fire water applications because of derating in pressure.

This paper describes various properties of HDPE pipe and how it is advantageous to use compared to metallic pipes. It also presents simulations carried out in Pipenet software to justify its use in geographical areas with high ambient temperature with the new higher-pressureclasses available now.

INTRODUCTION

High-Density Polyethylene (HDPE) is a thermoplastic that is manufactured by polymerization of monomer ethylene. It is one of the world’s most widely used and recognized thermoplastic materials.Its use as piping material first occurred in the mid 1950’s. In North America, its original use was in industrial applications, followed by rural water and then oil field production where a flexible, tough and light weight piping product was needed to fulfill the needs of a rapidly developing oil and gas production industry [1].

HDPE pipe is normally joined by heat fusion. Butt, socket, sidewall fusion and electrofusion create a joint that is as strong as the pipe itself and is virtually leak free. This unique joining method produces significant cost reductions compared to other materials. It has excellent corrosion resistance and is virtually inert. It does not need expensive maintenance or cathodic protection. It offers better overall resistance to corrosive acids, bases and salts than most piping materials. In addition, HDPE is unaffected by bacteria, fungi and naturally occurring soils.

HDPE is smoother than steel, cast iron, ductile iron, or concrete. It has less drag and a lower tendency for turbulence at high flow. Its superior chemical resistance and “non-stick” surface combine to almost eliminate scaling and pitting and preserve the excellent hydraulic characteristics throughout the pipe service life. The smooth surface provides a roughness coefficient, also known as C factor, of 150 for Hazen Williams calculations. With non-porous nature of HDPE pipe, the C factor does not change with time. The C factor for other typical pipes materials declines dramatically over time due to corrosion and tuberculation or biological buildup [1].

HDPE pipe is produced in straight lengths above 6 in. diametersand in coils up to 6 in. diameters. Made from materials about one-eighth the density of steel, it is lightweight and does not require the use of heavy lifting equipment for installation. It reduces the need for fittings, is excellent in shifting soils and performs well in earthquake-prone areas. HDPE resists the effects of freezing and allows bending without the need for an excessive number of fittings. Since HDPE is not a brittle material, it can be installed with bends over uneven terrain easily in continuous lengths without additional welds or couplings.Because heat fused HDPE joints are as strong as the pipe itself, it can be joined into long runs conveniently above ground and later buried underground. This significantly reduces the installation time compared to other materials.

HDPE pipe and fittings are inherently tough, resilient and resistant to damage caused by external loads, vibrations, and from pressure surges such as water hammer. HDPE pipe systems can handle repeated surge pressures of 1.5 times the system pressure rating without damage.

APPLICABLE STANDARDS

There are numerous standards and codes by which HDPE pipe and fittings are produced, designed and installed. Some of them are:

ASTM D3350–This specification covers the identification of polyethyleneplastic pipe and fittings materials in accordance with acell classification system[2].

ASTM F412 - This terminology is a compilation of definitions of technical terms used in the plastic piping industry [3].

ASTM F714 – This specification covers polyethylene (PE) pipe made in dimensions based on outside diameters of 90 mm (3.500 in.) and larger [4].

ANSI/AWWA C906–This standard describes outside diameter-controlledpolyethylene (PE) pressure pipe and fittings in diameters ranging from 4 in. through65 in. (100 mm through 1,650 mm) for use primarily in the construction andrehabilitation of water distribution and transmission systems[5].

IS 4984 –This Indian Standard lays down requirements for HDPE pipes from 16 mm to 1000 mm of nominal diameter [6].

FM1613 – This standard state approvals criteria for polyethylene pipe and fittings for underground fire service water mains [7].

HDPE piping systems are specified using two important criteria: the ASTM D3350 cell classification and the ASTM F412 thermoplastic piping material designation code. The F412 thermoplastic piping material designation code further defines the performance requirement of the pipe produced from a particular PE compound.

PEXYZZ is the format of the thermoplastic material designation code for PE pipe [8]

Where: PE indicates polyethylene.

X is the characteristic density range for the compound used to make the pipe as defined within ASTM D3350.

Y is the characteristic slow crack growth resistance range for the compound used to make the pipe as defined within ASTM D3350.

ZZ is the long-term hydrostatic stress at 73°F, expressed in hundreds of psi.

The market for PE pipe is characterized by the three common thermoplastics materials designation codes [8].

PE2708 - This piping product is produced from a medium density compound as defined in ASTM D3350 and is widely used in natural gas distribution and some specialty applications.

PE3608 - This piping product is the legacy product resulting from the old PE3408 thermoplastic piping material designation code that was so widely specified and used prior to 2005.

PE4710 - This piping product designation represents the culmination of years of technical research on polymer performance in PE piping and offers the designer or end-user exceptional levels of pipe system performance. PE4710 piping products support a higher long-term hydrostatic stress rating making the pressure rating for a given wall thickness of pipe 25% higher than a comparable PE3608 piping product. These piping products exhibit a significantly higher resistance to slow crack growth.

FIRE WATER SERVICE

Most countries follow the guidelines developed by the National Fire Protection Association (NFPA) for fire protection applications. HDPE piping requirements are foundChapter 10 of NFPA 24 which is titled ‘Underground Piping’ and deals with guidelines for buried piping [9]. HDPE pipe is not allowed for above ground service. NFPA does not list, certify, test or inspect products for compliance to its documents but rather defers to outside organizations for listings and certifications.

FM Approvals, a member of the FM Global Group, offers third party certification to help ensure quality of products and services. Components for fire protection systems are tested to make sure that the products meet performance, safety and quality standards. The FM APPROVED mark is backed by scientific research and testing is an indication that the product conforms to the highest standards.

HDPE pipe pressure rating gets de-rated drastically as the temperature increases as shown in Table 1 for three FM approved pressure classesused in fire water system. The three digits in the pressure class represent the pressure rating of HDPE pipe in psi.

Table 1 - Pressure vs. Temperature - FM Class 2006

Due to high ambient temperature in several geographical areas, HDPE pipe had limitation for use in fire water applications because of derating in pressure as depicted in Table 1.

Pressure Class (PC) is defined as [10]:

σ = allowable long term hydrostatic pressure in psi.

The HDPE material PE4710 was introduced in 2007 to the global market that provided benefits over the traditional HDPE pipe materials that were currently being used. Itoffered higher-pressure ratings and extended slow crack growth resistance, when compared to PE3408 materials.

AWWA revised the design factors/pressure classes of HDPE pipe and fittings manufactured from PE4710 HDPE materials into AWWA C906-2015 after getting satisfied with the performance history and testing results. FM issued a revision to the FM1613 approval standard in February 2017 that includes the increased pressure ratings of PE4710when compared to PE3406/3608 materials. The revised FM1613 approval standard took effect on December 31, 2017. Because of this a new set of Pressure Classes have been created under FM1613, as shown in Table 2 [8].

Table 2 – New FM Classes

Based on above, HDPE pipe manufacturers have come out with pipes of higher pressure ratings. In essence they are the same product and it is really only the change in testing regime that has led to higher pressure ratings.

PIPENET SIMULATION

In one of the recent Refinery project in South-East Asia, HDPE pipe has been proposed in place of originally envisaged cement lined carbon steel. A simulation in Pipenet software [11] has been carried out to justify the use of HDPE pipe. With maximum ambient temperature of 37oC, the design temperature for underground main has been considered to be37oC and design pressure is considered to be17 barg based on fire water pump shut-off pressure. FM approved HDPE pipe class 335 has been used for the simulation with dimensions per Table 3 [2].

Table 3 – Pipe Dimensions – FM Class 335 (DR 7)

Table 4 - Pressure vs. Temperature - FM Class 335 (DR 7)

With derating shown in Table 4, FM Class 335 can be used for this project as it meets the design pressure and temperature requirements. Earlier FM Class 267 could not be used as it did not meet the design pressure requirement as shown in Table 1. Hence with the introduction of new pressure classes, HDPE pipe has been justified for use in this project and has replaced earlier cement lined carbon steel pipe.

New installations in geographical areas with high ambient temperatures should evaluate the use of HDPE pipe in fire water underground service and take the advantage of various benefits of HDPE pipe.

CONCLUSION

HDPE pipe has been used in a wide variety of industrial markets over the years. With a wide array of industrial applications, the best way to identify whether HDPE should be used for your plant is to find out what it cannot do.It cannot meet pressures greater than 25 barg at ambient temperatures or constanttemperature greater than 60oC. HDPE pipe is an exceptional piping product well suited for wide range of applications. Tough, resilient HDPE piping is widely used in municipal water and sewer applications, natural gas distribution, industrial process piping, fire water loops, mining/slurry handling systems, etc. With the change in testing regimes and availability of higher-pressure ratings, HDPE pipe can now be used in underground fire water systems in geographical areas with high ambient temperature.

NOMENCLATURE

ANSI                      American National Standards Institute

ASTM                    American Society for Testing and Materials

AWWA                  American Water Works Association

DR                          Dimension Ratio

FM                          Factory Mutual

HDPE                     High-Density Polyethylene

in.                            Inch

IS                            Indian Standards

mm                         Millimeter

NFPA                     National Fire Protection Association

PC                           Pressure Class

PE                           Polyethylene

psi                           Pound per Square Inch

REFERENCES

[1]Handbook of Polyethylene (PE) Pipe, Second Edition, Published by Plastics Pipe Institute, Inc. (www.plasticpipe.org)

[2] ASTM D3350-14 – Standard Specification for Polyethylene Plastic Pipe and Fittings Materials (www.astm.org)

[3] ASTM F412-17a –Standard Terminology Relating to Plastic Piping Systems (www.astm.org)

[4] ASTM F714-13 – Standard Specification for Polyethylene (PE) Plastic Pipe (DR-PR) Based on Outside Diameter(www.astm.org)

[5] ANSI/AWWA C906-15 – Polyethylene (PE) Pressure Pipe and Fittings, 4 in. Through 65 in. (100 mm Through 1,650 mm) for Waterworks (www.awwa.org)

[6] IS 4984-2016 – Polyethylene Pipes for Water Supply – Specification (Fifth Revision) (www.standardsbis.in)

[7] FM 1613 – Approval Standard for Polyethylene (PE) Pipe & Fittings for Underground Fire Protection Service, Feb 2017 (www.fmapprovals.com)

[8]ISCO Product Catalogue – North American Q1 2018 (www.isco-pipe.com)

[9] NFPA 24 –Standard for Installation of Private Fire Service Mains and Their Appurtenances, 2016 Edition (www.nfpa.org)

[10] Technical Note PP 841-TN – Pressure Capability of HDPE PE4710 and PVC Pipe (www.performancepipe.com)

[11] Pipenet Vision (Software), Spray/Sprinkler Module, Version 1.6 by Sunrise Systems Limited (www.sunrise-sys.com)                

Babanna Biradar, PE, CFPS, FSE (TUV)

Vivek Dhingra

Bechtel India Pvt Ltd

Knowledge Park, 244 245, Udyog Vihar Phase IV, Gurgaon 122011, Haryana, India