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Research Papers: Materials and Fabrication

Study on the Allowable Temperature for Preventing Over Welding During Thermal Welding of Polyethylene Pipe

[+] Author and Article Information
Jinyang Zheng

Institute of Process Equipment,
Zhejiang University,
Hangzhou 310027, China
e-mail: jyzh@zju.edu.cn

Sijia Zhong

Institute of Process Equipment,
Zhejiang University,
Hangzhou 310027, China
e-mail: zhongsijia@zju.edu.cn

Jianfeng Shi

Institute of Process Equipment,
Zhejiang University,
Hangzhou 310027, China
State Key Laboratory of Chemical Engineering,
Institute of Polymer and
Polymerization Engineering,
Department of Chemical and
Biological Engineering,
Zhejiang University,
Hangzhou 310027, China
e-mail: shijianfeng@zju.edu.cn

Weican Guo

Institute of Process Equipment,
Zhejiang University,
Hangzhou 310027, China
Zhejiang Provincial Special Equipment
Inspection and Research Institute,
Zhejiang University,
Hangzhou 310020, China
e-mail: gwcndt@126.com

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received November 28, 2013; final manuscript received July 17, 2014; published online October 15, 2014. Assoc. Editor: Pierre Mertiny.

J. Pressure Vessel Technol 137(2), 021401 (Oct 15, 2014) (6 pages) Paper No: PVT-13-1200; doi: 10.1115/1.4028053 History: Received November 28, 2013; Revised July 17, 2014

Polyethylene (PE) pipe material may degrade into lower carbon number volatiles quickly during thermal welding when the welding temperature rises up to very high temperature. However, PE may also degrade into lower molecular weight (MW) polymer when subjected to a lower temperature. As a result, determination of the allowable temperature during thermal welding is crucial for guaranteeing the quality of welding joint. In this paper, a typical commercial PE100 material was chosen to conduct thermogravimetic analysis (TGA) and gel permeation chromatography (GPC) tests. The thermal degradation behavior of PE100 was investigated in dynamic and isothermal mode. The composition of the residue after thermal degradation was also analyzed through MW and MW distribution (MWD) measurements. Based on the experimental results, the initial temperature of thermal degradation with volatilization was derived and the thermal degradation process was studied in detail. To limit the degree of thermal degradation within a certain range during thermal welding of PE pipe, the allowable welding temperature for typical commercial PE100 material was determined.

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References

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Figures

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Fig. 1

TG curves of PE100 at different heating rates

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Fig. 2

DTG curves of PE100 at different heating rates

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Fig. 3

Relation between T5% and heating rate in dynamic thermal degradation with volatilization

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Fig. 4

Dependence of T5% on heating rate in dynamic thermal degradation with volatilization

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Fig. 5

TG curves of PE100 in isothermal experiments at different temperatures

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Fig. 6

MWD of PE100 after thermal degradation at different temperatures

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Fig. 7

MWD of the low molecular fraction in PE100 after thermal degradation at different temperatures

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Fig. 8

MWD of the high molecular fraction in PE100 after thermal degradation at different temperatures

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Fig. 9

Change in the peak positions of the two fractions after thermal degradation

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Fig. 10

Change in the relative peak position between the two fractions after thermal degradation

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Fig. 11

Change in Mw as a function of temperature

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Fig. 12

Change in d as a function of temperature

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