Papers
Plastic Pipes Conference Association # 2018 Las-Vegas
Hiroto Taguchi, Kaori Numata
We elucidated the creep failure behavior of polyamide pipes. We conducted the hydrostatic test and Notched Pipe Test (NPT) at 80 and 90 °C for up to 10000 h for PA pipes whose creep failure behavior has not been fully elucidated yet. In the tests, the change in the failure mode from ductile failure to brittle failure, i.e. SCG, seen in polyethylene pipes, was not observed. Additionally, the PA pipes fractured after more than 6000 h of testing at 90 °C and showed the brittle failure mode, in which the ductile failure originates; subsequently, the cracks propagate in the brittle mode. The observation and analysis of the fractured pipes suggest that hardening by increase in crystallinity could cause the brittle failure. It is assumed that the ductile deformation was inhibited because of the hardening and subsequently the brittle failure occurred.
To reduce installation and maintenance costs, plastic pipes expected to be used more widely under high-pressure conditions. Recently, multilayer polyethylene (PE) pipes and polyamide (PA) pipes have been used at pressures above 1.0 MPa as an alternative for steel pipes in several countries. When plastic pipes are under higher pressure, the evaluation of their creep properties is important. However, only a few studies have been reported regarding the creep failure behavior of high-strength pipes such as polyamide pipes. We performed the hydrostatic test and the notched pipe test (NPT) of PA pipes at 80 °C and 90 °C.
The failure mode of the PA pipes was ductile failure when the pipes was fractured in the entire test time of the hydrostatic test and the NPT at 80 °C and until 4826 h of the tests at 90 °C. The transition of the failure mode from ductile failure to SCG was not observed. Furthermore, NPT method did not shorten the failure time. Hence, we conclude that the PA pipes have extremely high resistance to crack propagation compared with PE pipes.
The PA pipes fractured after more than approximately 6000 h in the tests at 90 °C showed the brittle failure mode. The degradation behavior such as oxidation was not observed in the brittle failure pipes. The fractography showed their failure mode changed from ductile to brittle while proceeding. FT-IR analysis and indentation test suggested that the increase in crystallinity proceeded at 90 °C and it caused hardening. The hardening resulted in inhibiting deformation and the change in failure mode from ductile to brittle.
Related papers
Author(s) : Chris Ampfer, P.E., Harvey Svetlik, P.E.
The current polyethylene (PE) pipe bending limits (longitudinal and circumferential deflection) are based on a circumferential (tangential) strain tolerance limit of approximately 1%. Research in the late 1970’s using constant tensile strain focused on what strain can be imposed on HDPE by bending and not have it...
Author(s) : James F. Mason, Akshay Ponda, Hermann van Laak, Tobias Bauer
The long-term strength of unplasticized polyamide 12 (PA-U12) has been characterized using standard methods for plastic pressure pipe during the qualification process for use in buried piping systems for natural gas delivery operating at low ambient temperatures, usually less than 20 to 30°C at pressures...
Author(s) : Carine Lacroix, Philippe Louvel, Danielle Mark, Dominique Gueugnaut
A test program was carried out on two Polyamide resins, Polyamide 11 (PA11) and Polyamide 12 (PA12), both certified for gas networks. Polyamide’s advantage lies in its implementation, similar to that of polyethylene, and its properties allowing it to operate at up to 18 bar for gas, all other conditions being equal....
Author(s) : Carlos Domínguez, Predrag Micic, Rafael Juan, Nuria Robledo, Rafael A. García-Muñoz
Slow Crack Growth (SCG) resistance is the main property that must be controlled for assessing the long-term performance on polyethylene resins used for pipe application. The latest generation of bimodal and multimodal ethylene-α-olefin copolymers with exceptional balance of mechanical properties and processability...
Author(s) : Chris Ampfer, Gene Palermo, Ernest & Oren Lever
This paper looks at the origin of the 10% allowable scratch depth rule for polyethylene (PE) pressure pipe developed in 1971 and research that has been performed over the years since its inception to determine the validity of this rule. The 10% rule has been used by natural gas pipeline operators since the 1970’s to...
Author(s) : James F. Mason, Akshay Ponda, Hermann van Laak, Buc Slay
The effects of liquid hydrocarbons on long term strength of pipe grade thermoplastic resins is an important consideration when designing pressure pipe for use in the oil and gas industry. There is an extensive body of work going back several decades descri bing these effects for pipe grade polyethylenes, and all...
Author(s) : Mario Messiha, Britta Gerets, Jan Heimink, Andreas Frank, Florian Arbeiter, Gerald Pinter
A majority of field failure of viscoelastic plastic pipes can be attributed to slow crack growth (SCG) and has become crucial in terms of characterization of newly developed materials – particularly, if they are designed for pressurized pipe applications. In this study, investigations in terms of SCG resistances...
Author(s) : M. Eckes & Dr. B. Baudrit, Dr. M. Troughton & D. Wylie, H. van Laak & J. Fritz
Unplasticized polyamide 12 (PA-U12) is increasingly being used in pipe applications, especially in the gas sector. However, the material behavior in the usual quality tests for pipe welds has not yet been thoroughly investigated. For this reason, two research institutes, worked in cooperation with a manufacturer of...
Author(s) : Justin Brandt, Mike Griffin, Tony Cuvo
As plastic pipe gains share in new markets and applications, additional joining methods add further value, enabling continued growth for plastic pipes. To date, definitions of a “fit-for-purpose” mechanical joint for High Density Polyethylene (HDPE) pressure piping systems can vary significantly. As such, mechanical...
Author(s) : Mark Boerakker, Rudy Deblieck, a Harm Caelers, Arno Wilbers, Tine Boonen a DSM, Britta Gerets, Mirko Wenzel
Components made of plastic are facing ever-increasing demands with respect to their production, use and durability. This also holds for gas and drinking water pressure pipes made of high-density polyethylene (PE-HD), where service lifetimes of up to 50 years and in some cases even 100 years are required. One of the...
Author(s) : Hermann van Laak, Jan Heimink, Mario Messiha, Andreas Frank, Christoph Bruckner, Thomas Kratochvilla
For high pressure pipes above maximum operation pressure of 10 bar, this paper emphasizes PA-U12 as the easy to install alternative to steel. It underlines the superb performance of PA-U12 pipes for alternative installation techniques without need for a separate mechanical protection. An unplasticized polyamide 12...
Author(s) : Mario Messiha, Andreas Frank, Isabelle J. Berger, Jan Heimink, Hermann van Laak, Florian Arbeiter, Gerald Pinter
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 ...
Author(s) : Joerg Fischer, Patrick R. Bradler, Reinhold W. Lang
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...
Author(s) : Cheng Zhi, Mingyuan Hu, Kaige Duan, Chaoxi Zhou, Dongming Yu
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...
Author(s) : Yuji Higuchi, Rei Hyuga, Kazushi Yamada, Hiroyuki Nishimura
Recently, thermoplastic-based composite pipes have been developed in order to satisfy the higher requirements for gas and water distribution. Although the stress rupture test is now the major test method used to evaluate the long-term performance of these pipes, developing a new, convenient test method making it...
Author(s) : Hiroto Taguchi, Hideto Kurokawa, Kaori Numata
This study pursued a quantitative evaluation of “the resistance to third party attacks”, whether pipes are destroyed or not, of two polyethylene pipes (PE80 and PE100) and two polyamide12 (PA) pipes. Two types of tests that simulate the impact from actual digging machine (attack simulation test) and four types of the...
Author(s) : Rieky Steenbakkers, Linda Havermans, Patrick Voets, Jonathan Rabiei, Rudy Deblieck
The resistance to Slow Crack Growth of HDPE is related to the strain hardening modulus as determined from a tensile test at 80 °C. Correlatio ns between traditional methods (e.g. Full Notched Creep Test, Notched Pipe Test) and other accelerated tests (e.g. fatigue testing) show that the same failure mechanism is...
Author(s) : Ernst van der Stok, Jeroen Weller, Frans Scholten
This paper describes falling-weight tests as a first step towards determining the effect of residual stresses on the fracture behaviour of old PVC-U gas pipes at impact. Results showed that the level of surrounding pipe support, the quality of the material and the diameter of the striker had a major effect on the...
Author(s) : J. Weller, R.J.M. Hermkens, E.J.W. van der Stok
To prevent an enormous surge in the replacement costs of the Dutch PVC gas distribution grid a so-called Exit Assessment programme was started in 2004. This programme determines the actual quality of old excavated PVC-U and PVC-Hi pipes using a tensile-impact test at temperatures varying from -25°C to +47,5°C,...
Author(s) : Edward Ingham, Mike Shepherd
Exova has previously demonstrated that under normal operating conditions PE 100 pipes would be expected to have a lifetime of over 200 years, but in the UK concerns have been reported about relatively high failure rates within the water utilities of fusion joints, particularly for large diameter pipes. For some time,...
Members of the Association
