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Research Papers: Materials and Fabrication

Four-Point Fatigue Testing of Pressurized Composite Pipe

[+] Author and Article Information
D. P. Gerrard

 Baker Oil Tools, Houston, TX 77044dave_errard@bakeroiltools.com

R. J. Scavuzzo

Department of Mechanical Engineering, The University of Akron, Akron, OH 44325-3904rscavuzzo@uakron.edu

T. S. Srivatsan

Department of Mechanical Engineering, The University of Akron, Akron, OH 44325-3904tsrivatsan@uakron

T. S. Miner

 National Feed Screw Machining and Welding Engineers, Inc., Massillon, OH 44647tminer@nfm.net

Olagoke Olabisi

Internal Corrosion Engineering, Corporate Engineering Department, Corrpro Companies, Inc., Houston, TX 77040oolabisi@corrpro.com

J. Pressure Vessel Technol 131(3), 031402 (Apr 07, 2009) (17 pages) doi:10.1115/1.3008036 History: Received August 06, 2007; Revised May 12, 2008; Published April 07, 2009

This technical paper presents a comparative study of the fatigue strength of high-pressure composite pipes and high-pressure composite pipes containing joints. The test specimens used in this experimental investigation were exposed to cyclic bending stresses and to cyclic bending stresses in combination with constant or cyclic internal pressures generated by water, brine, and crude oil. The extrinsic influence of elevated temperature on fatigue performance was also examined. A new four-point bending fatigue machine was developed at the University of Akron to accomplish the testing. For each test specimen, two types of failure were distinctly observed. After a number of repeated cycles, the fluid under internal pressure began to gradually leak through the fine microscopic cracks in the matrix. The fine microscopic cracks were oriented in the circumferential direction of the pipe. However, despite the occurrence of “weeping failure” of the pipe, internal pressure could be easily maintained. After about 10–100 times the number of cycles required for “weeping,” the fiber reinforcements of the pipe gradually fractured and the internal pressure could no longer be maintained. The loss of pressure is referred to as “pipe failure.” In these tests, the primary parameter controlling failure was orientation of the fiber reinforcements in the body of the pipe. Those fibers aligned along the pipe axis revealed a substantial improvement in cyclic fatigue resistance. The existence of a joint in the test specimen showed secondary importance while contributing to degradation of the fatigue resistance of the specimen. Both types of failure were found to be dependent on temperature, over the range tested (2266°C, and also dependent on the type of internal liquid used. The specimens tested using crude oil at 66°C as the internal fluid revealed the lowest fatigue resistance.

Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Side view of the four-point fatigue test machine developed for this project

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Figure 2

Measured loads versus deflections (actual data) and linear lines based on the initial stiffness used in Markl calculations for two Manufacturer B specimens

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Figure 3

Load ratio (force, F/(initial force, F0)) as a function of cycles. The reduction of force with cycles approaches a factor of 2.

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Figure 4

Comparisons of Manufacturer A and Manufacturer B pipe weeping failures

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Figure 5

Comparisons of Manufacturer A and Manufacturer B pipe failures

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Figure 6

Manufacturer B weeping failure data for various test conditions (alternating stress versus cycles to failure)

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Figure 7

Manufacturer A weeping failure data for various test conditions (alternating stress versus cycles to failure)

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Figure 8

Initial alternating strain versus cycles to failure for pipe weeping failure data

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Figure 9

Initial alternating strain versus cycles to failure for pipe failure data

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Figure 10

Initial alternating stress versus cycles to both weeping failure and pipe failure for Manufacturer A pipe

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Figure 11

Initial alternating stress versus cycles to both weeping failure and pipe failure for Manufacturer B pipes

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Figure 12

Log of the ratio of cycles to pipe failure to cycles to weeping failure. Most data indicate that pipe failure is from 10 to 100 times the cycles to initiate weeping.

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Figure 13

Comparisons of Manufacturer A and Manufacturer B pipe weeping failures plotted against Markl stresses

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Figure 14

Comparisons of Manufacturer A and Manufacturer B pipe failures plotted against Markl stresses

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Figure 15

Comparisons of Manufacturer A weeping failure data at room temperature and 150°F(66°C) plotted against stresses

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Figure 16

Comparisons of Manufacturer A pipe failure data at room temperature and 150°F(66°C) plotted against stresses

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Figure 17

Comparisons of Manufacturer B weeping failure data at room temperature and 150°F(66°C) plotted against alternating stresses

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Figure 18

Comparisons of Manufacturer B pipe failure data at room temperature and 150°F(66°C) plotted against alternating stresses

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Figure 19

Comparisons of Manufacturer A and Manufacturer B weeping failures at room temperature plotted against alternating stresses

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Figure 20

Comparisons of Manufacturer A and Manufacturer B weeping failures at 150°F(66°C) plotted against alternating stresses

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Figure 21

Comparisons of Manufacturer A and Manufacturer B pipe failures at room temperature plotted against alternating stresses

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Figure 22

Comparisons of Manufacturer A and Manufacturer B pipe failures at 150°F(66°C) plotted against alternating stresses

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Figure 23

Regression analysis of log alternating stress versus log cycles to weeping based on ASTM D 2992

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Figure 24

Regression analysis of log alternating stress versus log cycles to pipe failure based on ASTM D 2992

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Figure 25

A straight pipe without a joint being tested in the test machine (Fig. 1)

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Figure 26

Some of the pipe specimens to be tested

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Figure 27

Failure of a straight pipe without a joint. The pressure stopped the machine, but the failure there was complete ripping of the composite pipe.

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Figure 28

Typical screw-type pipe joint

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Figure 29

Testing of a typical screw-type pipe joint. Water drops on the plastic window are indicative of small cracks through the pipe epoxy matrix while maintaining pressure.

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Figure 30

Thread slip failure of a typical screw-type pipe joint

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