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Research Papers: Design and Analysis

Limit Load Determination and Material Characterization of Cracked Polyethylene Miter Pipe Bends1

[+] Author and Article Information
Tarek M. A. A. EL-Bagory

Assistant Professor
Mechanical and Industrial Engineering
Department, College of Engineering,
Majmaah University, KSA,
P.O. Box 66, Majmaah,
Riyadh 11952, Saudi Arabia
on sabbatical leave from Helwan University,
Department Mechanical Design,
Faculty of Engineering, El-Mataria,
Helwan University,
Cairo, El-Mataria 11724, Egypt
e-mail: telbagory@yahoo.com

Maher Y. A. Younan

Associate Dean
School of Sciences and Engineering,
The American University in Cairo AUC,
Cairo 11835, Egypt
e-mail: myounan@aucegypt.edu

Hossam E. M. Sallam

Professor
Department of Civil Engineering,
Faculty of Engineering,
Jazan University, KSA,
P.O. Box 706,
Jazan 82822-6694, Saudi Arabia
on sabbatical leave from Zagazig University,
Department of Materials Engineering,
Faculty of Engineering, Zagazig University,
Zagazig 44519, Egypt
e-mail: hem_sallam@yahoo.com

Lotfi A. Abdel-Latif

Professor
Department of Mechanical Design,
Faculty of Engineering, El-Mataria,
Helwan University,
Cairo, El-Mataria 11724, Egypt

Participated in the Proceedings of the ASME 2011 Pressure Vessels and Piping Division/K-PVP Conference PVP2011 July 11–21, 2011, Baltimore, MD, Paper Number: PVP 2011-57587 “in recognition for being a Finalist in the Student paper competition.”

Mechanical Design Department, Faculty of Engineering, Mataria, Helwan University-Cairo/Egypt

Pipes and Plastic Products Company (PPP) in the 10th of Ramadan City, Egypt.

2Participated in the Euro-Mediterranean Innovation Marketplace Jan. 26–28, 2010, Cairo, Egypt, “Ranked as the first among all the applicants of the contest” for the invention “Testing Station for Natural Gas Piping Systems.”

3Participated in the International Exhibition of Inventions of Geneva Apr. 6–10, 2011, Geneva Palexpo, Switzerland, “Ranked as the Gold Medal among all the applicants of the contest” for the invention “Testing Station for Natural Gas Piping Systems.”

4Deceased.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received September 28, 2012; final manuscript received October 11, 2013; published online April 16, 2014. Assoc. Editor: Pierre Mertiny.

J. Pressure Vessel Technol 136(4), 041203 (Apr 16, 2014) (11 pages) Paper No: PVT-12-1159; doi: 10.1115/1.4026330 History: Received September 28, 2012; Revised October 11, 2013

The quality of Natural Gas Piping Systems (NGPS), must be ensured against manufacturing defects. The main purpose of the present paper is to investigate the effect of loading mode and load angle (30 deg, 45 deg, and 60 deg) on the limit load of miter pipe bends (MPB), under different crack depths a/W = 0–0.4 at a crosshead speed 500 mm/min. The geometry of cracked and uncracked multi-miter pipe bends are pipe bend angle, α = 90 deg, pipe bend factor, h = 0.844, standard dimension ratio, SDR = 11, and three junctions, m = 3. The material of the investigated pipe is a high-density polyethylene (HDPE), which is commonly used in NGPS. The welds at the miter pipe junction are produced by butt-fusion welding. For all loading modes the limit load is obtained by the tangent intersection (TI) method from the load–deflection curves produced by the specially designed and constructed testing machine at the laboratory5. Tensile tests are conducted on specimens longitudinally extruded from the pipe with thickness, T = 10, 30 mm, at different crosshead speeds (5–500 mm/min), and different gauge lengths (G = 20, 25, and 50 mm) to determine the mechanical properties of welded and unwelded specimens. The fracture toughness is determined on the basis of elastic plastic fracture mechanics (EPFM). Curved three-point bend specimens (CTPB), are used. All specimens are provided with artificial precrack at the crack tip, a/W = 0.5. The effect of specimen thickness variation (B = 10, 15, 22.5, 30, 37.5, and 45 mm) for welded and unwelded specimens is studied at room temperature (Ta = 23 °C) and at different crosshead speeds, VC.H, ranging from 5 to 500 mm/min. The study reveals that increasing the crack depth leads to a decrease in the stiffness and limit load of MPB for both in-plane, and out-of-plane bending moment. In case of combined load (out-of-plane and in-plane opening; mode), higher load angles lead to an increase in the limit load. The highest limit load value occurs at a loading angle, ϕ = 60 deg. In case of combined load (out-of-plane and in-plane closing; mode), the limit load decreases with increasing load angles. At a load angle ϕ = 30 deg, the higher limit load value occurred in both cases. For combined load opening case, higher values of limit load are obtained. The crosshead speed has a significant effect on the mechanical behavior of both welded and unwelded specimens. The fracture toughness, JIC, is greater for unwelded than welded specimen.

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Figures

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Fig. 1

Tensile test specimen for thick 30 and 10 mm

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Fig. 2

Configuration of (a) ring cut into five 72 deg sector and (b) CTPB specimen

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Fig. 3

Schematic illustrations of (a) miter pipe bend with attached straight pipe, and (b) loading mode and combined loading (−Fy + Fz, +Fy − Fz)

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Fig. 4

Crack geometry and razor blade configurations

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Fig. 5

Collapse load construction by TI method [18]

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Fig. 6

Engineering stress–strain diagram for unwelded specimen, type I

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Fig. 7

Engineering stress–strain diagram for welded specimen, type I

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Fig. 8

Yield strength as a function of crosshead speed for welded and unwelded specimen configurations, types I, II, and III

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Fig. 9

Apparent modulus of elasticity as a function of crosshead speed for welded and unwelded specimen configurations, types I, II, and III

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Fig. 10

Percentage of strain as a function of crosshead speed for welded and unwelded specimen configurations, types I, II, and III

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Fig. 11

Fracture resistance as a function of crack growth for unwelded CTPB specimen at B/W = 0.3, and VC.H = 5 mm/min

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Fig. 12

Plastic zone on the fracture surface of CTPB specimen used to measure the crack extensions, a1a5

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Fig. 13

Fracture toughness as a function of crosshead speed at different specimen thicknesses for unwelded CTPB specimen with a/W = 0.5

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Fig. 14

Fracture toughness as a function of specimen thickness for unwelded CTPB specimen (VC.H = 5, 100, 500 mm/min, and with a/W = 0.5)

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Fig. 15

Fracture toughness ratio between welded, and unwelded specimen at different crosshead speeds

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Fig. 16

Fracture toughness ratio between welded, and unwelded specimen at different specimen thicknesses

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Fig. 17

Load–deflection curves at load line (δ0), and different a/W for in-plane close, and open loading

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Fig. 18

Variation of collapse load with crack width ratio for in-plane open and close

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Fig. 19

Load–deflection curves at load line (δ0) for out of plane loading (+Fz) at different crack depth

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Fig. 20

Trend of Variation in collapse load with crack width ratio, a/W for out-of-plane loading (−Fz)

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Fig. 21

Load–deflection curves at the load line (δ0) for combined load closing (−Fy + Fz) at different ϕ and a/W = 0

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Fig. 22

Load–deflection curves at the load line (δ0) for combined load opening (+Fy − Fz) at different ϕ and a/W = 0

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Fig. 23

Variation of collapse load with loading angle for combined load opening and closing modes

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