HDPE Pipe

Features and Benefits of HDPE Pipe

When selecting pipe materials, designers, owners and contactors specify materials that provide reliable, long-term service durability, and cost-effectiveness. Solid wall polyethylene pipes provide a cost-effective solution for a wide range of piping applications including gas, municipal, industrial, marine, mining, electrical and communications duct applications. Polyethylene pipe is also effective for above ground, buried, trench less, floating and marine installations. According to David A. Willoughby, P.O.E., “…one major reason for the growth in the use of the plastic pipe is the cost savings in installations, labor and equipment as compared to traditional piping materials. Add to this the potential for lower maintenance costs and increased service life and plastic pipe is a very competitive product.

Natural gas distribution was among the first applications for medium-density polyethylene (MDPE) pipe. In fact, many of the systems, currently in use, have been in continuous service since 1960 with great success. Today, polyethylene pipe represents over 95% of the pipe installed for natural gas distribution in diameters up to 12” in the U.S. and Canada. PE pipe has been used in potable water applications for almost 50 years and has been continuously gaining approval and growth in municipalities. The production, quality assurance and testing of PE gas pipes, including joints, are carried out according to international AWWA, NSF, and ASTM standards. The fear often expressed in the early days that HDPE would have insufficient resistance to the aromatics contained in natural gas (such as tetrahydrothiophene (THT), concomitant substances and condensates) has not been confirmed, either by laboratory tests, or by practical experience. Other material alternatives do not share PE’s advantages. For instance, there are about 23,000 fractures and corrosion failures of iron mains across the United Kingdom each year. Of these events, the majority are located and dealt with in a safe manner. However, on average, about 600 of these results in the leakage of gas into buildings and annually this results in 3 to 4 major incidents involving fire.

INTRODUCTION OF POLYETHYLENE

Since its discovery in 1933, polyethylene (also known as polythene) has grown to become one of the world’s most widely used and recognized thermoplastic materials . The versatility of this unique plastic material is demonstrated by the diversity of its use. The original Application for polyethylene (PE) was as a substitute for rubber in electrical insulation during World War II. Polyethylene has since become one of the world’s most widely utilized thermoplastics. Today’s modern polyethylene resins are highly engineered for much more rigorous applications such as pressure-rated gas and water pipe, automotive fuel tanks and other demanding applications. Polythene’s use as a piping material was first developed in the mid 1950’s. In North America, its original use was in oil field production where a flexible, tough and lightweight piping product was needed to fulfill all the needs of a rapidly developing oil and gas production industry. The success of polyethylene pipe in these installations quickly led to its use in natural gas distribution where a coil able, corrosion-free piping material could be fusion joined in the field to assure a “leak free” method of transporting natural gas to homes and businesses. Polyethylene’s success in this critical application has not gone without notice and today it is the material of choice for the natural gas distribution industry. Sources now estimate that nearly 95% of all new gas distribution pipe installations in North America that are 12” in diameter or smaller are polyethylene piping .

The performance benefits of polyethylene pipe in these original oil and gas related applications have led to its use in equally demanding piping installations such as potable water distribution, industrial and mining pipe, force mains and other critical applications where a tough, ductile material is needed to assure long-term performance. It is these applications, representative of the expanding use of polyethylene pipe that are the principal subject of this article. In the chapters that follow, we shall examine all aspects of design and use of polyethylene pipe in a broad array of applications. From engineering properties and material science to fluid flown and burial design; from material handling and safety considerations to modern installation practices such as horizontal directional drilling and/or pipe bursting; from potable water lines to industrial slurries, all these things have led to the growing use of polyethylene pipes in the world .

Polyethylene Pipe

The structure and the mechanical properties of a butt weld in a polyethylene pipe were examined and contrasted to non-welded PE pipe. X-ray diffraction, differential scanning calorimeter and Fourier transform infrared spectrometer measurements revealed details of axial amorphous and crystal orientation in the original pipe. Contrary to expectations considering the squeeze, flow nature of butt-welding, formation of randomly oriented crystal structure was determined in the weld region. Tensile and notched impact tests at ambient and sub-ambient temperatures and varying rates of impact showed that welding consistently reduced resistance to failure. Microscopic evaluation of the brittle fracture surfaces revealed the surface morphology of the welded zone to be coarser than the non-welded PE material.

Polyethylene (PE) pipes have been produced in Australia and New Zealand since the mid 1950s, initially in small diameters for industrial and agricultural applications. The first Australian Standard was released in 1962 and Iplex Pipelines (then Hardie Iplex) commenced production in the early seventies. Usage has grown rapidly with over 40,000 tones of PE pipes being produced annually in Australasia. Polyethylene has become one of the most widely used of all plastic polymers.

Terms frequently used to describe this material when used for engineering applications are high density (HDPE), medium density (MDPE) and most recently high performance (HPPE) polyethylene. Others such as low density (LDPE) and linear low density (LLDPE) are sometimes used for irrigation pipelines.

The Type 50 PE of AS1159, which was in common use until 1994, is an HDPE with a long-term design stress of 5.0 MPa. However, with the introduction of new Standards, terminology relating to density alone is no longer recommended. AS/NZS4130 and AS/NZS 4131 recognized this, allow for three specific classifications by material strengths, and sub classifications by performance at elevated temperatures. The higher strength PE 80 and PE100 compounds are sometimes referred to as second and third generation materials. They were introduced into general service in the late seventies and early nineties respectively.

POLI plex polyethylene is an integrated family of PE pipes produced by Iplex , based on PE 80B, PE 80C and PE100 materials. These are manufactured to AS/NZS 4130 from polyethylene complying with AS/NZS 4131. Diameters range from DN 16 to DN 1000 with pressure ratings of up to 2.0 MP a. Pipes up to DN 110 can be supplied in coils lengths of up to 300 meters in some diameters. Larger diameters are typically 12 m long although 15 m and longer are occasionally manufactured by arrangement. Note that the nominal diameter of PE pipes refers to the outside diameter in accordance with international practice.

Iplex THERMAPIPE is a white co-extruded PE developed by Iplex, designed for above ground pipelines in hot climates to significantly reduce the heating effect due to exposure to solar radiation, which occurs with the normal black pigmented PE. This allows the use of lower class pipes to give reduced purchase and operating costs.

 

POLI plex PE pipes may be joined economically using thermal butt welding equipment. However, diameters of up to DN 110 are more commonly joined using the Iplex Metric compression couplings. These provide an easy system for making joints quickly which can be undone and reused when altering the system layout. An alternative form of welding PE is the electro fusion system where heating elements are embedded in PE sockets. These sockets form part of a coupling or other fitting and require an electrical input to produce a welded joint. For pipes, which are, constantly being uncoupled and moved, shouldered ends can be provided to suit proprietary metal clamps. For bends and tees a range of both injection molded and fabricated fittings

I am obliged to express my thanks

All praises to the almighty Allah, who induced the man with intelligence, knowledge, sight to observe and mind to think. Peace and blessing of Allah be upon the Holy Prophet, Hazrat Muhammad ( ) who exhorted his followers to seek for

Knowledge from cradle to grave.

I feel great pleasure in expressing my sincere gratitude and profoundest thanks to my project advisor Professor Sajid Hussain Shah, Department of Mechanical, Preston University, for his kind guidance, constant help, invaluable suggestions and unforgettable cooperation throughout my project work. I am very much obliged to Mr. Jahanzeb Ahmed, Mr. Muhammad Hafeez, Mr. Muhammad Ali and Madam Zenat Shahrazi, , for providing facilities to complete this work, and all other teachers of the Department for their help and encouragement.

I am obliged to express my thanks to Professor Dr.Muhammad Tahir Hussain, University of Textile Engineering Faisalabad. He has been sympathetic, amiable and very kind to me. He is always a source of aspiration for me.

I am thankful to my friends Ahmad Nadeem and Abdul Rehman for their cooperation and encouragement.

I express my feelings of gratitude to all the members of non-teaching staff of the Department for their constant help.

My special thanks are due to my parents, brothers, sisters, and wife for their full support, encouragement, and sincere prayers for my success.

(MUHAMMAD ABDUL RAUF)