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Technical Briefs

Failure Analysis of Type 304 Stainless Steel Tubes in an Energy Production Plant Heat Exchangers

[+] Author and Article Information
M. R. Jahangiri

 Metallurgy Department, Niroo Research Institute, Tehran 14686, Iranmjahangiri@nri.ac.ir

J. Pressure Vessel Technol 133(6), 064503 (Oct 19, 2011) (10 pages) doi:10.1115/1.4003811 History: Received December 17, 2009; Accepted February 20, 2011; Published October 19, 2011; Online October 19, 2011

This work includes results of studies and experiments conducted on heat exchanger (heater) tubes of an energy production unit to determine the causes of their fractures. Experiments indicated that the main mechanism of such tube fractures is the simultaneous presence of relatively high vibrational bending stresses and corrosive agents. It was shown that the role of a vibrational bending stress due to high velocity of input steam is very impressive. The important point in this study was the branching of corrosion fatigue cracks during their growth in presence of NaOH and chloride ions. The use of impingement plates and water chemistry control were the most appropriate methods to prevent such failures.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 4

Stereo microscope images of fractured tubes, (a) low magnification and (b) higher magnification

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Figure 5

(a) Stereo microscope image of small cracks on the external surfaces of tubes and (b) Stereo microscope image of internal surfaces of tubes

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Figure 6

SEM images of fracture surfaces of tubes at (a) low, (b) medium, and (c,d) high magnification

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Figure 7

SEM images of impingement pits and corrosive agents concentration locally on fracture surfaces of tubes at (a) low and (b) high magnification

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Figure 8

Optical microscopic images of microstructre of tubes in (a) nonwelded area and (b) welded area

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Figure 9

Optical microscopic microstructures of cracked tubes, (a) from external surfaces without etching, (b) from external surfaces after etching, (c) from external/internal surfaces simultainously, (d) branching of fatigue corrosion cracks during growth, (e) transgranular nucleation of cracks, (f) transgranular growth of cracks, (g) large branched cracks formed at the external surfaces and growing inward

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Figure 10

Vibration analysis of tubes located in (a) entrance region between tubesheet and second adjacent baffle with unsupported span length equal to 980 mm, (b) entrance region between tubesheet and first adjacent baffle with unsupported span length equal to 630 mm

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Figure 11

Vibration analysis of tubes located in (a) interior regions between two baffles with unsupported span length equal to 350 mm, (b) interior regions between two baffles with unsupported span length equal to 700 mm

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Figure 2

Heat exchanger drawing

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Figure 3

Input position of steam to heat exchangers

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Figure 1

(a) Investigated heat exchanger (b) same heater from other view

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