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Analytical study on rationalize and reliability improvement of maintenance against stress corrosion cracking in stainless steel welds of lwr primary system

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Abstract

SCC (stress corrosion cracking) may occur in stainless steel welds of the LWR primary systems, which required the welding repair after detecting it over nondestructive inspection (NDI) during the regular inspections. Recently, a new peening method was developed to convert the tensile residual stress of the weld into compressive residual stress, which relieved the SCC issue in the new plant although SCC problems still exist in conventional plant. It was found that fatigue crack and SCC can be rendered harmless by the compressive residual stress over a peening method. This paper proposes a method for increasing the validity and reliability of the weld maintenance for SCC by the following methods. ① Evaluate the depth (ahml) of SCC cracks that can be rendered harmless by peening in advance. ② Detect the cracks of approximately 0.7 ahml or more by NDI. ③ Repair only crack of 0.7 ahml or more by welding. ④ Apply peening to all welds. This paper proposes a method for evaluating ahml, and analyzed the dependence of residual stress and crack aspect ratio (As) via peening. The study showed that it was possible to improve the reliability and rationalize the maintenance for SCC by applying the surface crack nondamaging technology.

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Abbreviations

a :

Crack depth of semielliptical crack in finite plate

a hml :

Maximum harmless SCC crack depth

a NDI(1) :

Minimum detectable crack depth with a = 0.3 mm via nondestructive inspection

a NDI(2) :

Minimum detectable crack depth with a = 0.25 mm via nondestructive inspection

2c :

Crack length of the semielliptical crack

G 0-G 4 :

Shape correction coefficients of the KPr

2l :

Through crack length in an infinite plate

l e :

Equivalent half-crack length

S :

Area of the semielliptical crack

S NDI(1) :

Area of a semielliptical crack with 2c = 0.6 mm and a = 0.3 mm

S NDI(2) :

Area of a semielliptical crack with 2c = 1.4 mm and a = 0.25 mm

d 0 :

Crossing point

t :

Plate thickness

2w :

Plate width

x :

Distance in the depth direction from the surface

As :

Aspect ratio

NDI :

Nondestructive inspection

SCC :

Stress corrosion cracking

σ 1-σ4 :

Coefficients obtained from the fourth-order polynomial

σ 0 :

Compression residual stress at surface

σ m :

Maximum compression residual stress

σ DE :

Design tensile stress

σ u :

Tensile strength

σ y :

Yield stress

K app :

Stress intensity factor due to design tensile stress (σ DE)

K Pr :

Stress intensity factor due to compressive residual stress

\(K_{app}^{Pr}\) :

Sum of Kapp and KPr

K sc :

Threshold SCC stress intensity factor for small cracks

K sc(l) :

Threshold SCC stress intensity factor for large cracks

α A :

Shape correction factor at the deepest crack part (point A)

α C :

Shape correction factor at the surface crack part (point C)

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Acknowledgements

The authors gratefully acknowledge of Ph.D. Kunio Hasegawa of (former) Hitachi, Ltd., and Prof. K. Takahashi of Yokohama National University for his valuable comments.

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Authors and Affiliations

  1. Dept. of Marine Design Convergence Engineering, Pukyong National University, Busan, Korea

    Kyoung-Hee Gu & Ki-Woo Nam

  2. Faculty of Engineering, Yokohama Nat’l Univ., Yokohama, Japan

    Kotoji Ando

  3. Dept. of Materials Science and Engineering, Pukyong National University, Busan, Korea

    Ki-Woo Nam

Authors
  1. Kyoung-Hee Gu
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  2. Kotoji Ando
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  3. Ki-Woo Nam
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Corresponding author

Correspondence to Ki-Woo Nam.

Additional information

Kyung-Hee Gu is a graduate student of Marine Design Convergence Engineering at Pukyong National University, Busan, Korea. She is interested in the fatigue life and the harmless crack of structural material.

Ki-Woo Nam (Ph.D.) is working on Department of Materials Science and Engineering, Pukyong National University, Busan, Korea. His research fields are the crack healing and the harmless crack of structural component.

Kotoji Ando (Ph.D.) is Emeritus Prof. of Yokohama National University in Japan. His research fields are increase fatigue limit, making surface crack harmless, and developing structural ceramics with self-crack-healing ability.

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Gu, KH., Ando, K. & Nam, KW. Analytical study on rationalize and reliability improvement of maintenance against stress corrosion cracking in stainless steel welds of lwr primary system. J Mech Sci Technol 37, 1773–1780 (2023). https://doi.org/10.1007/s12206-023-0317-9

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  • DOI: https://doi.org/10.1007/s12206-023-0317-9

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