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Research Papers: Nuclear Power

Manufacturing Stress Corrosion-Cracking Tube Specimens for Eddy Current Technique Evaluation

[+] Author and Article Information
Saurin Majumdar

Argonne National Laboratory,
Lemont, IL 60439

Contributed by the Nuclear Division of ASME for Publication in the Journal of Engineering for Gas Turbines and Power. Manuscript received September 17, 2012; final manuscript received September 28, 2012; published online February 21, 2013. Editor: Dilip R. Ballal.

J. Eng. Gas Turbines Power 135(3), 032902 (Feb 21, 2013) (9 pages) Paper No: GTP-12-1362; doi: 10.1115/1.4007872 History: Received September 17, 2012; Revised September 28, 2012

To detect degradation in steam generator (SG) tubes, periodic inspection using nondestructive examination techniques, such as an eddy current testing, is a common practice. Therefore, it is critical to evaluate and validate the reliability of the eddy current technique for ensuring the structural integrity of the SG tubes. The eddy current technique could be evaluated by comparing the data estimated by the eddy current with the destructive examination data of field cracks, which would be both costly and labor intensive. A viable alternative to pulled tube data is to manufacture crack specimens that closely represent actual field cracks in laboratory environments. A crack manufacturing method that can be conducted at room temperature and atmospheric pressure conditions is proposed. The method was applied to manufacture different types of stress corrosion cracking (SCC) specimens: axial outer-diameter (OD) SCC for straight tubes, circumferential ODSCC and primary water SCC (PWSCC) at hydraulic expansion transition regions, and axial PWSCC at the apex and tangential regions of U-bend tubes. To help the growth of SCC into the tube, corrosive chemicals (sodium tetrathionate) and tensile stress were applied. Eddy current and destructive examination data for SCC specimens were compared with the available field crack data to determine whether those SCC specimens are representative. It was determined that the proposed method could manufacture the representative crack specimens.

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Figures

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Fig. 1

Schematic of a straight SCC tube specimen exposed to chemicals

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Fig. 2

Photographs showing a hydraulic expansion transition region covered by lacquer

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Fig. 3

Schematic of a U-bend specimen having axial PWSCC at apex extrados manufacturing procedure

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Fig. 4

+Point maximum amplitudes of axial ODSCC specimens as a function of local or RA max. depth

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Fig. 5

(a) Crack depth profile of an axial ODSCC specimen determined by destructive examination and (b) an isometric plot acquired using +Point probe for the same ODSCC specimen

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Fig. 6

Residual stress distributions near the hydraulic expansion transition region of 19.1 mm (3/4 in.) OD Alloy 600 tubing for (a) axial and (b) hoop directions

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Fig. 7

Eddy current scan of U-bend specimen 890-12; (a) +Point scanning results and isometric plots (b) after and (c) before PWSCC development at U-bend apex

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Fig. 8

(a) Borescope image of the ID surface in 890-12; SEM micrographs showing (b) the circumferential cross-section of the apex extrados region, indicating four SCC sites and (c) higher magnification of one of cracking regions

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Fig. 9

Comparison of ANL axial ODSCC specimens with field axial ODSCC data set in a plot of +Point maximum amplitude versus RA max. depth

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Fig. 10

Comparison of axial ODSCC ANL specimens with field cracks in the plots of (a) burst effective length versus depth, (b) +Point maximum amplitude versus burst effective length, and (c) +Point maximum amplitude versus burst effective depth

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Fig. 11

+Point maximum amplitudes of axial PWSCC U-bend cracks detected in field versus max. depth estimated by +Point

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