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Research Papers: Materials and Fabrication

CFRP Reinforcement and Repair of Steel Pipe Elbows Subjected to Severe Cyclic Loading

[+] Author and Article Information
Ioannis Skarakis, Nicholas G. Tsouvalis

School of Naval Architecture and
Marine Engineering,
National Technical University of Athens,
Athens 15780, Greece

Giannoula Chatzopoulou, Aglaia E. Pournara

Department of Mechanical Engineering,
University of Thessaly,
Volos 383 34, Greece

Spyros A. Karamanos

Department of Mechanical Engineering,
University of Thessaly,
Volos 383 34, Greece;
School of Engineering,
Institute of Infrastructure and Environment,
The University of Edinburgh,
Edinburgh EH9 3FG, UK

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received March 9, 2017; final manuscript received June 29, 2017; published online August 2, 2017. Assoc. Editor: David L. Rudland.

J. Pressure Vessel Technol 139(5), 051403 (Aug 02, 2017) (14 pages) Paper No: PVT-17-1045; doi: 10.1115/1.4037198 History: Received March 09, 2017; Revised June 29, 2017

In order to ensure safe operation and structural integrity of pipelines and piping systems subjected to extreme loading conditions, it is often necessary to strengthen critical pipe components. One method to strengthen pipe components is the use of composite materials. The present study is aimed at investigating the mechanical response of pipe elbows, wrapped with carbon fiber-reinforced plastic (CFRP) material, and subjected to severe cyclic loading that leads to low-cycle fatigue (LCF). In the first part of the paper, a set of LCF experiments on reinforced and nonreinforced pipe bend specimens are described focusing on the effects of CFRP reinforcement on the number of cycles to failure. The experimental work is supported by finite element analysis presented in the second part of the paper, in an attempt to elucidate the failure mechanism. For describing the material nonlinearities of the steel pipe, an efficient cyclic-plasticity material model is employed, capable of describing both the initial yield plateau of the stress–strain curve and the Bauschinger effect characterizing reverse plastic loading conditions. The results from the numerical models are compared with the experimental data, showing an overall good comparison. Furthermore, a parametric numerical analysis is conducted to examine the effect of internal pressure on the structural behavior of nonreinforced and reinforced elbows, subjected to severe cyclic loading.

Copyright © 2017 by ASME
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References

Figures

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Fig. 1

Steel elbow specimens

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Fig. 2

Implementation of the CFRP patch on the pipe elbow

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Fig. 3

Experimental setup for (a) nonreinforced elbow, (b) reinforced pipe elbow and (c) LVDT and strain gauge locations

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Fig. 4

(a) Crack configuration at crown area in nonreinforced pipe elbow specimens and (b) loss of containment because of through-thickness crack development in nonreinforced specimen 5

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Fig. 5

(a) Crack failure of CFRP-reinforced specimen at the elbow intrados and (b) loss of containment in reinforced pipe elbow specimen

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Fig. 6

Fatigue crack at the vicinity of girth weld between the elbow and the pipe, in reinforced pipe elbow-specimen no. 6

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Fig. 7

De-bonding of the CFRP from the pipe elbow surface

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Fig. 8

Force (kN) versus displacement (mm) for ΔL equal to ±20 mm, ±25 mm, and ±30 mm; experimental results

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Fig. 10

Hoop strains evolution for different displacement ranges

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Fig. 11

Repair of cracked nonreinforced specimens, with CFRP/GFRP wrapping

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Fig. 12

Burst and loss of containment in CFRP-repaired specimens due to burst (specimen 4)

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Fig. 13

Model of a reinforced pipe elbow with CFRP patch

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Fig. 14

(a) Finite element model of reinforced pipe elbow with the CFRP patch and (b) partition of CFRP patch in eight sectors

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Fig. 15

Location of strip specimens extracted from the elbows

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Fig. 16

Stress–strain curve from monotonic tests of P235 elbow material

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Fig. 17

Stress–strain curve of cyclic tests of P235 steel elbows material; strain ranges are: (1) ±0.8%, (2) ±1.0%, and (3) ±1.2%

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Fig. 18

Force (kN) versus displacement (mm) for ΔL equal to ±20 mm, ±25 mm, and ±30 mm; nonreinforced elbow specimens

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Fig. 19

Force (kN) versus displacement (mm) for ΔL equal to ±20 mm, ±25 mm, and ±30 mm; reinforced elbow specimens

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Fig. 20

Hoop strain evolution for ΔL equal to ±20 mm; nonreinforced elbow specimens

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Fig. 21

Hoop strain evolution for ΔL equal ±25 mm; nonreinforced elbow specimens

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Fig. 22

Hoop strain evolution for ΔL equal ±30 mm; nonreinforced elbow specimens

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Fig. 23

Hoop strain evolution for ΔL equal to ±30 mm; nonreinforced and reinforced elbows

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Fig. 24

Evolution of ovalization in nonreinforced and reinforced elbows for ΔL equal to ±30 mm

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Fig. 25

Axial strain evolution in nonreinforced and reinforced elbows for ΔL equal to ±30 mm

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Fig. 26

Distribution of strains in nonreinforced elbows for ΔL equal to ±30 mm: (a) hoop strains, (b) axial strains, and (c) equivalent plastic strains

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Fig. 27

Distribution of strains in reinforced elbows for ΔL equal to ±30 mm: (a) hoop strains, (b) axial strains, and (c) equivalent plastic strains

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Fig. 28

Force (kN) versus displacement (mm) for ΔL equal to ±25 mm for different levels of internal pressure; nonreinforced elbow specimen

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Fig. 29

Hoop strain evolution for ΔL equal to ±25 mm for different levels of internal pressure as a percent (%) of yield pressure; nonreinforced elbow specimen

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Fig. 30

Force (kN) versus displacement (mm) for ΔL = ±25 mm for different levels of internal pressure; reinforced elbow specimen

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Fig. 31

Hoop strain evolution for ΔL equal to ±25 mm for different levels of internal pressure; reinforced elbow specimens

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Fig. 32

Axial strain evolution for ΔL equal to ±25 mm for different levels of internal pressure; reinforced elbow specimens

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