Pent study of cross-linked polyethylene pipe resins


Papers # 2016 Berlin

The performance of HDPE resins with regards to slow crack growth has increased dramatically over the past two decades. The most common test method for pipe products is ASTM F1473, Standard test Method for Notch Tensile Test to measure the resistance to Slow Crack Growth of Polyethylene Pipes and Resins (PENT). Results are reported as hours to failure. Failure time has increased from a few hundred hours to over 50,000 hours in some cases. Crosslinked polyethylene (PEX) is known to have very high slow crack growth resistance as a result of crosslinking. Unfortunately the methods used to measure the slow crack growth resistance of PEX are different than those used for standard polyethylene (PE) pipe grades. This study reports PENT data for PEX pipe resins, which allows a more direct comparison of the slow crack growth properties of crosslinked PE pipe grades with standard PE pipe grades.

Crosslinked Polyethylene (PEX) pipe and tube are being used globally for potable water plumbing systems, industrial piping systems, radiant heating systems, etc., successfully. PEX materials are generally believed to have very good slow crack growth properties and some would argue that they are immune to slow crack growth. In general, the three common methods of crosslinking, peroxide, silane grafted, and radiation, are treated equally in the standards with regard to physical and mechanical properties. Most PEX standards include some sort of notched pipe test to demonstrate adequate resistance to crack propagation when a defect (notch) is present. However, there is little slow crack growth data available for PEX materials in a form that can be directly related to other materials. This paper will present PENT data for PEX pipe resins. The methodology used to prepare the samples is critical to successful PENT testing of PEX materials and this will be discussed. The data presented will include multiple temperatures and stresses along with failure mode analysis for each resin.

Related keywords : PENT, PEX, Crosslinked, SCG, Slow Crack Growth.
Please note that the whole article content is available on PPCA website onlySource : 2016 Berlin

Related papers

Accelerated pipe test methods to evaluate PE 100-RC materials - Possibilities for iso standardisation

Author(s) : Thomas R. Kratochvilla, Raimund Eremiasch, Christoph Bruckner 2018 Las-Vegas

In the last years effort has been made to develop and standardise new accelerated test methods to evaluate PE 100-RC materials in short times in form of test bars. The two most important developments, the cracked round bar test (CRB test) and the strain hardening test (SH test) were published as final ISO standards in...

Characterization of post-use polyethylene and polypropylene recyclate blends for pipe applications

Author(s) : Markus Gall, Reinhold W. Lang, Joerg Fischer, Ansgar Niehoff, Steven Schmidt 2018 Las-Vegas

Despite recent efforts in promoting the utilization of recycled polymeric materials for more diverse and more advanced applications, there are still significant knowledge gaps with regards to the applicability of certain recyclate types for specific “re-use” purposes. When it comes to pipe applications, for...

Determination of the slow crack growth resistance of PA12 pipe grades

Author(s) : Mario Messiha, Andreas Frank, Isabelle J. Berger, Jan Heimink, Hermann van Laak, Florian Arbeiter, Gerald Pinter 2018 Las-Vegas

Since the last decade polyamide 12 (PA12) has been successfully introduced as material for SDR 11 gas piping systems up to 18 bar, representing itself as an attractive alternative to steel pipes for high-pressure applications. Practical experience has confirmed that beside the higher strength, PA12 pipe grades also...

Effect of beta-nucleation on aging and crack growth resistance of polypropylene exposed to chlorinated water

Author(s) : Joerg Fischer, Paul J. Freudenthaler, Patrick R. Bradler, Reinhold W. Lang, Susan C. Mantell 2018 Las-Vegas

This research addresses the effect of nucleation on the global aging behavior and the fatigue crack growth (FCG) resistance of commercial alpha- and beta-nucleated polypropylene random copolymer pipe grades (PP-R) when exposed to chlorinated water (5 mg/l free chlorine) at an elevated temperature of 60°C. Comparing...

Evaluation and comparison of standard and accelerated slow crack growth determination methodologies: effect of the comonomer type influence

Author(s) : Carlos Domínguez, Álvaro Pérez, Nuria Robledo, Cristina González, Beatriz Paredes, Rafael A. García-Muñoz 2018 Las-Vegas

Last methodologies for fast evaluation of the SCG resistance on polyethylene pipe materials are analyzed in this work and compared with traditional PENT and FNCT tests. Strain Hardening (SH), Crack Round Bar (CRB) and Accelerated Creep Test (ACT) will be good alternatives for evaluating PE100RC resins. Moreover, SH...

Fatigue crack growth testing in chlorinated water at elevated temperatures - Test equipment and test procedure

Author(s) : Joerg Fischer, Patrick R. Bradler, Reinhold W. Lang 2018 Las-Vegas

In the present paper, a novel test system for conducting fatigue crack growth (FCG) experiments under superimposed mechanical-environmental conditions is presented. FCG experiments were performed on a polypropylene (PP) grade and a short-glass fiber reinforced polyamide 66 (PA-GF) grade as model materials. The...

Investigation of the failure behavior of polyethylene electrofusion sockets

Author(s) : Isabelle J. Berger, Andreas Frank, Gerald Pinter, David Nitsche, Dirk Petry 2018 Las-Vegas

Electrofusion (EF) sockets constitute a well-established and practically proven technology for the joining of polyethylene (PE) pressure pipes. As for the pipes, the potential lifetime of such welding connections is beside other properties also depending on the resistance against slow crack growth (SCG). The current...

New crosslinked (PEX) pipes from sustainable resources

Author(s) : Jacob John, Andrew J. Ortquist, Mats Thunwall, Patrik A. Roseen 2018 Las-Vegas

This study investigates production of crosslinked polyethylene (PEX) pipes using a resin obtained from a renewable resource via twin-screw extruder technology. PEX pipes were extruded using petroleum-based and renewable high-density polyethylene (HDPE) for comparison. Testing using relevant ASTM standards on the new...

Preparation and studying of thermoplastic cross-linked polyethylene

Author(s) : Cheng Zhi, Mingyuan Hu, Kaige Duan, Chaoxi Zhou, Dongming Yu 2018 Las-Vegas

The PE properties are obviously improved by crosslinking modified to TPEX, which can approach to that of PEX, while still remaining thermoplastic. It can be processed by the common forming method of thermoplastic; the products can be hot-melted and the scrap can be processed to be reused. The two-layer structure...

Product environmental footprint (PEF) method compared with environmental product declarations (EPDS)

Author(s) : Ludo Debever, Peter Sejersen, Carolin Spirinckx 2018 Las-Vegas

Until today there are various ways of demonstrating the Environmental Performance of products, such as Life Cycle Assessments (LCA), Life Cycle Impact Assessments (LCIA), Environmental Performance Declarations (EPDs). The methods to obtain the result, however, can vary from country to country and can be interpreted...

Sensitivity of strain hardening modulus to molecular structure of polyethylene

Author(s) : Suleyman Deveci, Senthil K. Kaliappan, Joel Fawaz, Umesh Gadgoli 2018 Las-Vegas

A series of non-commercial bimodal high density ethylene-α-olefin copolymers with systematically controlled molecular parameters over a wide range that would result in extremely low and high strain hardening modulus were prepared and tested Strain hardening modulus has been published as a standard test method (ISO...

Slow crack growth resistance of non-virgin polymers

Author(s) : Andreas Frank, Isabelle J. Berger, Mario Messiha, Carl-Gustaf Ek, Norbert Schuler, Jens-Martin Storheil, Erwin Mayrbäurl, Steve Heeley, Frank Krause, Lodewijk Niemöller, Philippe Gabriëls, Yogesh S. Deshmukh, Florian Arbeiter, Thomas Koch, Gerald Pinter 2018 Las-Vegas

In order to improve the circular economy of polymers in terms of sustainability and reduced carbon footprint, the increased use of recyclates has become a topic of major importance. Due to their long design lifetimes, pipe applications represent an excellent opportunity to create added value to non-virgin polymers. In...

Taking polyethylene (PE) pipe to new heights ... and new diameters!

Author(s) : Norbert Jansen, Albert Lueghamer 2018 Las-Vegas

Demand for polyethylene (PE) pipe continues to grow on a global basis. The performance properties of this tough, durable piping material are widely recognized by the engineering and design community on a worldwide scale and the range of applications expands. The evolutionary trend in PE piping systems has been very...

The influence of molecular design variables of bimodal HDPE on the slow crack growth resistance measured by accelerated methods

Author(s) : Cliff Mure, Siddharth Athreya, Dane Chang, Rujul Mehta 2018 Las-Vegas

New generations of PE100 and PE4710 pressure pipe materials exhibit a superior balance of mechanical properties. The slow crack growth performance of these materials measured by traditional tests such as PENT and FNCT can exceed one year. Accelerated test methods, including strain hardening modulus, accelerated FNCT,...

Corrugated polyethylene pipe used in mining applications, their compliance with specifications and anticipated design life

Author(s) : Jim Goddard, Mario Paredes 2016 Berlin

Samples of polyethylene pipe supplied to mining projects throughout the Americas were selected and tested for compliance with existing ASTM specifications. Estimated service life of these pipe products in mining applications are made based on the laboratory tests required in the ASTM specifications. Anticipated...

Determining the residual quality of PE pipes using the strain hardening test

Author(s) : Ernst van der Stok, Frans Scholten 2016 Berlin

Samples machined directly from pipe show that orientation has a large influence on the strain hardening modulus. No effects arising as a result of residual stresses were found. Samples machined in the axial direction from a hydrostatic pressurised pipe showed no effect as a result of this mechanical degradation. For...

Evaluating strain hardening (SH) and cracked round bar (CRB) test methods with respect to molecular structure of materials and correlation to notched pipe test (NPT)

Author(s) : Suleyman Deveci, Dongyu Fang 2016 Berlin

Latest developments in polyethylene production (hexene co-monomer and bi-modality) have increased the material’s Slow Crack Growth (SCG) properties, which is a time dependent brittle type failure under low stress levels and one of the most important long term properties of pipe grade polyethylene materials. Despite...

Fatigue crack growth resistance of polypropylene in chlorinated water at different temperatures

Author(s) : Joerg Fischer, Patrick R. Bradler, Reinhold W. Lang, Gernot M. Wallner 2016 Berlin

The present paper aims to study the crack growth resistance of a black-pigmented polypropylene pipe grade when exposed to elevated temperatures and various environmental media (air, deionized water, ionized water with a specific chloride content, and chlorinated water) under the simultaneous application of cyclic...

Flexible plastic solution for district heating pipes

Author(s) : Dr. Anton Vasilenko 2016 Berlin

In today’s world a lot of energy is wasted. More than 50 % of the energy is lost on its way to the customer. The fundamental idea of modern district heating is to recycle heat that otherwise would be lost and to use renewable sources to heat homes. In other words: a market place for green heat that reduces...

Lifetime prediction of PE100 and PE100-rc pipes based on slow crack growth resistance

Author(s) : Andreas Frank, Isabelle J. Berger, Florian Arbeiter, Pavel Hutař, Gerald Pinter 2016 Berlin

Due to the high slow crack growth resistance of modern polyethylene pipe grades a reliable lifetime assessment of pipes with focus on stage II failure has become challenging. The current paper presents a scientific approach for a fracture mechanics lifetime prediction based on Cyclic Cracked Round Bar (CRB) Tests....

Members of the Association

BOREALISBOROUGEFormosa Plastics CorporationINEOS O&PIRPCKazanorgsintez PJSCKorea Petrochemical IND. Co., LTD (KPIC)LyondellBasellPetroChina Dushanzi Petrochemical CompanyPRIME POLYMERSABICSCG Chemicals & Thai PolyethyleneSinopecTASNEE