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Research Papers: Materials and Fabrication

Comparison of Parent and Butt-Fusion Material Properties of Unimodal High-Density Polyethylene

[+] Author and Article Information
P. Krishnaswamy, D.-J. Shim, S. Kalyanam

Engineering Mechanics
Corporation of Columbus,
Columbus, OH 43221

1Present address: Structural Integrity Associates, Inc., San Jose, CA 95138.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received January 3, 2017; final manuscript received April 28, 2017; published online June 1, 2017. Assoc. Editor: Steve J. Hensel.This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. Approved for public release; distribution is unlimited.

J. Pressure Vessel Technol 139(4), 041413 (Jun 01, 2017) (8 pages) Paper No: PVT-17-1002; doi: 10.1115/1.4036658 History: Received January 03, 2017; Revised April 28, 2017

The U.S. nuclear power industry is seeking U.S. Nuclear Regulatory Commission (USNRC) approval to use high-density polyethylene (HDPE) in safety-related applications. The USNRC had granted approval for the use of HDPE for safety-related service water applications, with limitations, to Catawba (Duke Energy Corp., Catawba, SC) and Callaway (Union Electric Co., Callaway, MO) based on separate relief requests submitted by the licensees. The nuclear industry continues to show increasing interest in utilizing HDPE in safety-related piping systems. In order to evaluate and maintain the structural integrity of HDPE pipes, the material properties and the fracture resistance behavior must be fully characterized. Although there has been extensive work on material property development of HDPE, most of the investigations have been focused on the parent (base) material. Hence, the material property and fracture resistance behavior of the butt-fusion region have not been comprehensively investigated. In this paper, tensile, dynamic mechanical analysis (DMA), and slow crack growth (SCG) tests were performed for unimodal PE 4710 HDPE material. Specimens were machined from both parent piping material and butt-fusion regions. The test results indicate that the tensile and DMA properties show no significant differences between parent and butt-fusion joint materials. However, in terms of SCG resistance, the time to failure for butt-fusion joint material was an order of magnitude lower than that of the parent material.

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Figures

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Fig. 1

Photo of PE 4710 HDPE pipe with butt-fusion joint (12-in nominal outer diameter, DR 11 pipe)

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Fig. 2

Tensile specimen used in this study (type I as per ASTM D638)

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Fig. 3

Layout of tensile and DMA specimens

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Fig. 4

Example of stress–strain curve obtained at 80 °C

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Fig. 5

Photos of specimens after the tensile test: (a) parent-axial-mid (80 °C) and (b) butt-fusion-axial-mid (80 °C)

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Fig. 6

DMA test results for samples from parent and butt-fusion joint materials (circumferential direction)

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Fig. 7

DMA test results for samples from parent and butt-fusion joint materials (axial direction)

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Fig. 8

Specimen dimensions and layout for SCG test specimens

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Fig. 9

SCG test creep frame setup

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Fig. 10

Load-line displacement as a function of time, and post-test photo showing ductile failure in parent materials SCG test specimen, P-1: (a) displacement versus time for specimen P-1 and (b) photo of specimen P-1 at the end of the test showing ductile failure

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Fig. 11

Load-line displacement as a function of time, and post-test photo showing ductile failure in parent material SCG test specimen, P-4: (a) displacement versus time for specimen P-4 and (b) photo of specimen P-4 at the end of the test showing ductile failure

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Fig. 12

Load-line displacement as a function of time, and post-test photo showing SCG failure in specimens P-3 and P-5: (a) displacement versus time for specimens P-3 and P-5 and (b) photo of the fracture surface of specimens, P-3 and P-5

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Fig. 13

Load-line displacement as a function of time, and post-test photo showing SCG failure in butt-fusion joint specimens BP-1, BP-2, and BP-3

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Fig. 14

Photo of butt-fusion joint SCG test specimen BP-1 during and after the test: (a) after 30 h of test time and (b) after 50 h of test time

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Fig. 15

Photos of fracture surfaces of butt-fusion joint SCG test specimens, BP-1, BP-2, and BP-3

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Fig. 16

Load-line displacement as a function of time for all four butt-fusion joint SCG test specimens, BP-1, BP-2, BP-3, and BP-5

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Fig. 17

Photo of fracture surface of butt-fusion joint SCG test specimen, BP-5

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