Nishimura, Kawaguchi, Igawa
# 2006 Washington DC
This paper describes test methods for crosslinked polyethylene (PEX) pipes to evaluate long-term performance such as the resistance to chemical degradation due to residual chlorine at high temperature by the formation of crosslinked molecular structure and the addition of suitable antioxidants. As the methods of manufacturing PEX, the silane crosslinking process and the peroxide crosslinking process are used to produce PEX pipes for hot water supply and space and bath heating at Osaka Gas. The Oxidation Induction Test (OIT) and the gear oven test are accelerated tests and useful to evaluate relative thermal stability. However, these tests are not directly correlated to actual life. The immersion test is also useful to clarify the relation between immersion time and time to oxidation in a high concentration of aqueous solution of residual chlorine is obtained. The long-term performance of pipes can be generally evaluated by the stress rupture test. The stress rupture diagram is the most important data to indicate the actual creep strength of PEX pipes. The hoop stress corresponding to a operating pressure of 0.5 MPa even at 90 degrees C is 2 MPa, and the service life under continuous use is 3_104 hr or more, which is almost equivalent to 30 years under intermittent use at the rate of 3 hours a day even when a safety factor of 2 is assumed as the regression line for the experimental data. The stress rupture test by circulating a 3-ppm aqueous solution of chlorine at elevated temperature is a suitable test method to evaluate the actual life of PEX pipes.
Related papers
Author(s) : Hirofumi Kyutoku, Kazuhisa Igawa, Hidekazu Honma, Sakiko Fukunishi, Hiroyuki Nishimura
There are mainly two grades of polyethylene pipes for hot water supply and heating. The excellent molecular structure polyethylene resins having resistance to stress crack growth are used because hot water is flowed for a long time in both polyethylene pipes. Furthermore, various additives are mixed to prevent the...
Author(s) : Takehiro Fujii, Kazuhisa Igawa, Hidekazu Honma, Kazushi Yamada, Hiroyuki Nishimura
The hydrostatic stress rupture test has been conventionally conducted as a good method of the lifetime evaluation. The hot water circulation test which is reflected to the actual operating condition is also useful method. The correlations and differences between the two tests were examined. Compared with the...
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) : Yuichiro Goto, Hiroyuki Nishimura
The damage of PVC pipes caused by the great earthquakes was investigated in Japan by various organizations including public and private institutions. As a result of these investigations it is found that high-impact modified PVC pipes with the long insertion length have the least failures. Moreover it is also reported...
Author(s) : Takehiro Fujii, Hideo Hirabayashi, Kazushi Yamada, Hiroyuki Nishimura
It is important to stabilize the scraped surface of the polyethylene pipe, even if some operator scrape the surface of the polyethylene pipe. In Japan this automatic saddle scraper is widely used for improving workability and plumbing quality The newly developed “Automatic saddle scraper” consists of the casing unit...
Author(s) : Kazuhisa Igawa, Yuji Higuchi, Daisuke Tanemura, Kazushi Yamada, Hiroyuki Nishimura, Sakiko Fukunishi, Kazufumi Kohno, Hidekazu Honma, Hidekazu Sugimori
Recently, as awareness about energy-saving is increasing, high-efficiency energy systems have been developed and introduced. In addition, public and private sectors have simultaneously been implementing various efforts aiming to improve their prevalence rates. These initiatives are represented by the Cogeneration Gas...
Author(s) : Yuji Higuchi, Tomohiro Tanishita, Kazushi Yamada, Hiroyuki Nishimura
Recently, PE resin-back 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 possible to...
Author(s) : Kazuhisa Igawa, Yuji Higuchi, Akio Kamatani, Kazushi Yamada, Hiroyuki Nishimura
The polymer electrolyte fuel cells (PEFC) cogeneration system has been commercialized in Japan. The number of commercialized PEFC residential cogeneration systems have reached 100, 000 in total at the end of last year. The waste heat can be used for hot water supply and central heating. Hot water distribution pipes...
Author(s) : Toshiki SHIMURA, Shinobu KAWAGUCHI Kazumi NAKAYAMA, Tomoko WATANABE, Yoshito OHTAKE
To clarify the appropriate acceleration test method and the evaluation index for it, a series of acceleration tests was conducted on commercial poly-propylene (PP) pipe for outside use. Various tests and analyses were carried out on degraded PP pipes and these results were compared with PP pipe that had actually been...
Author(s) : Nishimura Hiroyuki
The effect of antioxidants of polyethylene of raised temperature resistance (PE-RT) pipes for a long lifetime for hot water supply and for space heating was evaluated in this paper. Some polyethylene specimens mixed with different amount of antioxidants such as hindered phenol and hindered amine were prepared by...
Author(s) : Yuji Higuchi, Masaaki Ishikawa, Toshiaki Furuno, Eiji Okamura, Masahiro Mutoh, Hiroyuki Nishimura, Asami Nakai, Hiroyuki Hamada
Pipe materials that are resistant to damage by thirty-party works were investigated with attention to materials already used for other purposes. Pipes for underwater cables, water service and agricultural use, both multiple-layer and single-layer types, were selected for the test. Protective materials were also...
Author(s) : Shinobu Kawaguchi
In order to evaluate the deformability of the whole polyethylene (PE) piping system for city-gas supply, tensile tests were conducted at the various tensile-velocities and environmental temperatures for the test specimens. They consist of commercial PE pipes and a socket-type of an electro-fusion (EF) fitting having...
Author(s) : Kazuhisa Igawa
Plastic pipes such as PEX and PB pipes have been widely used for water and hot water supply, and for central heating for residential use in Japan. The qualities of PEX and PB pipes and joints have been maintained at high levels as products and as jointing techniques for 20 years or more in Japan. There are few...
Author(s) : Nishimura, Kawaguchi
The required performance of polyethylene pipes for gas distribution is firstly described. As an evaluation method for slow crack growth, the relation between crack growth length and time under test was obtained to investigate the stress crack resistance of polyethylene pipes for gas distribution after conducting...
Author(s) : Nishimura, Inoue, Inoue, Tani, Higuchi
Electrofusion (EF) joints have been widely used as easy-to-fuse and high-quality joints for joining polyethylene (PE) pipes. When we introduced EF joints 150 mm or more in diameter, an electrofusion simulation program was concurrently developed to reduce time for design and experimental works. It was verified that the...
Author(s) : Yoshida, Kitaoka, Nishimura
Because dirt ( sand, mud, etc. ) on the fusion interface causes a decrease in the strength of fusion joints, it is necessary to scrape and clean the pipe surface before fusion jointing. We have determined the degree of dirt that causes a decrease in the strength of fusion joints by experiments on peeling off at the...
Author(s) : Nishimura, Macba, Ishikawa, Ueda
In the Great Hanshin-Awaji Earthquake, dthough leak and cracking occurred mainly in joints of small-diameter steel pipes with screwed joints, no damage occurred to polyethylene pipes. To secure aseis~uicresistance of gas pipeline, polyethylene pipes are expected to come into wider use i n the future. To deternune the...
Author(s) : Higuchi, Nishimura, Tamamura, Harada
To estimate the long-term performance of polyethylene pipe, molecular structure of polyethylene resin were analyzed and the long-term performance test were done. By linking the molecular structure of the resin to the results of long-term performance tests such as tensile creep tests and tensile fatigue tests, it...
Author(s) : Kitao, Hiarse, Nishimura, Inouge, Ishikawa, Otani, Miyasa, Kato
In this paper, the behavior of rapid crack propagation in gaspressurized polyethylene pipes was analyzed using the method in which two characteristic curves, i.e., the crack velocity and the gas decompression velocity, were compared. The crack velocity of 216mm outer diameter SDR13.5 medium density polyethylene...
Author(s) : Nishimura, Suyama, Inoue, Higuchi
This paper describes an evaluatio~i metl~od for elearofusion joint strer~gtl~ and a basic co~~cept for determination of suitable fusion jointing col~ditio~~s. Firstly, the concept for estimating electrofusion joint strength is indicated. As an experimental result, it was found that the optimum fusion range lay...
Members of the Association
