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RESEARCH PAPERS

Urea Reactor Integrity Evaluation Based on Failure Analysis

[+] Author and Article Information
Mingda Song1

School of Mechanical Engineering, Shandong University, 73 Jingshi Road, Jinan 250061, Shandong Province, People’s Republic of China; Shandong Special Equipment Inspection & Research Academy, 9 Shanda Road, Jinan, 250013, Shandong Province, People’s Republic of Chinasmdaazyf@163.com

Weiqiang Wang, Yuliang Cui

School of Mechanical Engineering, Shandong University, 73 Jingshi Road, Jinan 250061, Shandong Province, People’s Republic of China

Yafan Zhao

School of Materials Science and Engineering, Shandong University, 73 Jingshi Road, Jinan 250061, Shandong Province, People’s Republic of China

1

Corresponding author.

J. Pressure Vessel Technol 129(4), 744-753 (Feb 24, 2007) (10 pages) doi:10.1115/1.2767368 History: Received August 10, 2006; Revised February 24, 2007

Multilayered pressure vessels tend to induce stress corrosion cracking (SCC) in the heavy weld. This conclusion is based on the recent ruptured urea reactor failure analysis. Finite element simulation proved that multilayered urea reactors have yielded zones at the heavy weld where the SCC crack initiated. Acoustic emission (AE) examination conducted for two in-service urea reactors revealed AE event clusters at the heavy weld and subsequent phased array reexamination confirmed the existence of propagating defects in the heavy weld. The results also showed that AE evaluation and phased array reexamination are sound combination methods to evaluate the integrity of multilayered urea reactors. Besides, they are superior to γ-ray inspection because of the uncertain propagation direction of SCC cracks.

Copyright © 2007 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Largest upper part of the urea reactor

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Figure 2

Fracture of the largest upper part

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Figure 3

Intermediate part of the urea reactor

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Figure 4

Bottom part of the urea reactor

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Figure 5

Schematic of the urea reactor

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Figure 6

Heavy weld structure

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Figure 7

Weep hole structure

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Figure 8

Fracture of ejected part (C-3)

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Figure 9

Schematic of the fracture

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Figure 10

Cross section of circumferential weld (C-4)

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Figure 11

Stress corrosion cracks

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Figure 12

Widmanstattens where the cracks initiated

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Figure 13

Intergranular cracks in the layers

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Figure 14

Elastic equivalent stress contour of heavy weld

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Figure 15

Von Mises stress distribution through heavy weld

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Figure 16

Elastic-plastic equivalent stress contour of heavy weld

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Figure 17

Sensor arrangements for the coverage of a reactor

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Figure 18

Phased array scanning area of the heavy weld

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Figure 19

AE event locations of the developed surface of a 12yr reactor during loading stage

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Figure 20

AE event locations of the developed surface of a 14yr reactor during loading stage

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Figure 21

Parts without AE source

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Figure 22

Layer mismatch of AE source A

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Figure 23

Latent defects of AE source A

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Figure 24

Layer mismatch of AE source B

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Figure 25

Latent defects of AE source B

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Figure 26

Clearance propagation of AE source C

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Figure 27

Phased array reexamination of AE source D

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Figure 28

Pulse echo reexamination of AE source D

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Figure 29

γ-ray film at AE source cluster A

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Figure 30

Schematic of γ-ray examination

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