Thermal Stability and Long-Term Strength of Plastics Pipes Required [PEX, PB, PERT]

# 2008 Budapest

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 leakages and failures in actual use. The PEX and PB pipe systems have been evaluated for their high quality. The polyethylene for raised temperature (PERT) pipes has recently been introduced also for central heating and floor heating for residential use as they have a possibility to reduce the pipe cost. There are three modes of failure for plastic pipes, which are ductile failure(I), brittle failure(II), and chemical degradation failure(III) as well known. The amount of remaining antioxidants gradually decreases with time. To prevent brittle failure and chemical degradation failure and to obtain a high stress rupture strength, a high molecular weight resin should be selected for plastic pipes. To delay the occurrence of chemical degradation failure, it is important for antioxidants to be integrated, considering thermal stability and minimizing degradations and to be sufficiently added in a polymer. To maintain long-term resistance of plastic pipes to thermal and chemical degradations due to hot water and residual chlorine at elevated temperature for hot water supply and also for central heating and floor heating, suitable antioxidants are added in general. The Oxidation Induction Time (OIT) test is also a useful test to evaluate relative thermal stability. A value of 100 minutes or more by OIT is required for thermal stability at 210 degrees C in an oxygen atmosphere. The long-term strength of plastic pipes can generally be evaluated by the stress rupture test. A 30-years-or-more service life of the system for central heating should be guaranteed at 90 degrees C under an inner pressure of 0.25 MPa. No failure at 12,000 hrs or more should occur at 110 degrees C by the accelerated stress rupture test specified in ISO1167. The fullnotch tensile creep test at elevated temperature is also useful to evaluate long-term strength as an accelerated test method.

Please note that the whole article content is available on PPCA website onlySource : 2008 Budapest

Related papers


Author(s) : Hirofumi Kyutoku, Kazuhisa Igawa, Hidekazu Honma, Sakiko Fukunishi, Hiroyuki Nishimura 2018 Las-Vegas

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 2016 Berlin

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...

Countermeasures against Deterioration in Non-Cross-Linked Polyethylene Pipes

Author(s) : Kazuhisa Igawa, Yuji Higuchi, Daisuke Tanemura, Kazushi Yamada, Hiroyuki Nishimura, Sakiko Fukunishi, Kazufumi Kohno, Hidekazu Honma, Hidekazu Sugimori 2014 Chicago

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...

Evaluation of Plastic Pipes by Hot Water Circulation, Stress Rupture, and Immersion Tests

Author(s) : Kazuhisa Igawa, Yuji Higuchi, Akio Kamatani, Kazushi Yamada, Hiroyuki Nishimura 2014 Chicago

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...

Evaluation Methods for Crosslinked PE Pipes for Hot Water Supply and Space Heating Systems

Author(s) : 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...

Members of the Association

BOREALISBOROUGEINEOS O&PIRPCKorea Petrochemical IND. Co., LTDLyondellBasellPetroChina Dushanzi Petrochemical CompanyPRIME POLYMERSABICSCG Chemicals & Thai PolyethyleneSinopecTASNEE