Stress Corrosion Cracking Incidents and Repair Technologies on PWR Dissimilar Weld Metal Joints in Japan

2010 ◽  
Author(s):  
Naoki Chigusa ◽  
Shinro Hirano ◽  
Takehiko Sera ◽  
Hitoshi Kaguchi ◽  
Masayuki Mukai ◽  
...  
Keyword(s):  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Power Plants ◽  
Reactor Vessel ◽  
Corrosion Cracking ◽  
Alloy 600 ◽  
Maintenance And Repair ◽  
Head Penetration ◽  
Dissimilar Weld ◽  
Primary Water

Several Japanese PWR power plants have experienced Primary Water Stress Corrosion Cracking (PWSCC) on dissimilar weld joints since 2004. J weld of 3 Reactor Vessel Head Penetration in Ohi unit 3 is one of the PWSCC incidents occurred in 2004 and has been studied by sampling and opening the fracture surface after its repair. Including Ohi unit 3 Reactor Vessel Head Penetration repair, Japanese PWR utilities and MHI have been developing the preventive maintenance and repair technologies applicable to alloy 600 welds and base metal, following PWSCC events on the Bugey-3 and V.C. Summer. This paper describes recent Japanese PWSCC incidents and repair technologies developed in Japan.

Weldability, Thermal Aging and PWSCC Behavior of Nickel Weld Metals Containing 15 to 30% Chromium

2004 ◽  
Author(s):  
J. M. Boursier ◽  
F. Vaillant ◽  
B. Yrieix
Keyword(s):  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Thermal Ageing ◽  
Corrosion Cracking ◽  
Life Assessment ◽  
Alloy 600 ◽  
Head Penetration ◽  
Weld Metals ◽  
Alloy 690 ◽  
Primary Water

In 1991, a vessel head penetration was found leaking at Bugey 3 plant during the hydrotest. Metallurgical investigations confirmed that this problem was again related to primary water stress corrosion cracking of alloy 600. Moreover, the main crack initiated in the base metal of the penetration (alloy 600) has also propagated in the weld metal in alloy 182. More recently, stress corrosion cracking in alloy 182 has been found on welds of U.S. plants. SCC susceptibility of alloy 182 has been evidenced by several laboratories. In France, all original vessel heads using alloy 600 have been or will be replaced with penetrations in alloy 690 (with 30% chromium). With respect to substitution materials, ELECTRICITE´ DE FRANCE has undertaken a large R&D study focusing on the development of new weld metals. The aim of this study was to identify new materials that will be able to weld alloy 690. Weld metals containing 15 to 30% Chromium have been studied. This paper presents an overview of the main results obtained on 19% Cr, 26% Cr and 30% Cr alloys with respect to alloy 182 (15% Cr). Firstly, the weldability of weld metals has been studied focusing on the susceptibility to hot cracking. Secondly, the resistance to thermal ageing has been investigated in order to detect any long term ordering of the solid solution Ni-Cr that could induce embrittlement. Hardness tests, Charpy tests and resistivity measurements did not show any effect of ageing up to 60,000 hours at 360°C. Thirdly, stress corrosion cracking susceptibility in primary water at 360°C has been evaluated during constant load tests, RUB tests, slow strain rate tests. No cracking was observed on material containing more than 26% Cr for both initiation and propagation. Finally, a life assessment was performed for all weld materials with respect to alloy 182.

Mechanical Stress Improvement Process (MSIP) Used to Prevent and Mitigate Primary Water Stress Corrosion Cracking (PWSCC) in Reactor Vessel Piping at V.C. Summer

2003 ◽  
Author(s):  
E. A. Ray ◽  
K. Weir ◽  
C. Rice ◽  
T. Damico
Keyword(s):  
Water Stress ◽  
Stress Corrosion ◽  
Mechanical Stress ◽  
Stress Corrosion Cracking ◽  
Reactor Vessel ◽  
Corrosion Cracking ◽  
The Other ◽  
Water Reactor ◽  
Improvement Process ◽  
Primary Water

During the October 2000 refueling outage at the V.C. Summer Nuclear Station, a leak was discovered in one of the three reactor vessel hot leg nozzle to pipe weld connections. The root cause of this leak was determined to be extensive weld repairs causing high tensile stresses throughout the pipe weld; leading to primary water stress corrosion cracking (PWSCC) of the Alloy 82/182 (Inconel). This nozzle was repaired and V.C. Summer began investigating other mitigative or repair techniques on the other nozzles. During the next refueling outage V.C. Summer took mitigative actions by applying the patented Mechanical Stress Improvement Process (MSIP) to the other hot legs. MSIP contracts the pipe on one side of the weldment, placing the inner region of the weld into compression. This is an effective means to prevent and mitigate PWSCC. Analyses were performed to determine the redistribution of residual stresses, amount of strain in the region of application, reactor coolant piping loads and stresses, and effect on equipment supports. In May 2002, using a newly designed 34-inch clamp, MSIP was successfully applied to the two hot-leg nozzle weldments. The pre- and post-MSIP NDE results were highly favorable. MSIP has been used extensively on piping in boiling water reactor (BWR) plants to successfully prevent and mitigate SCC. This includes Reactor Vessel nozzle piping over 30-inch diameter with 2.3-inch wall thickness similar in both size and materials to piping in pressurized water reactor (PWR) plants such as V.C. Summer. The application of MSIP at V.C. Summer was successfully completed and showed the process to be predictable with no significant changes in the overall operation of the plant. The pre- and post-nondestructive examination of the reactor vessel nozzle weldment showed no detrimental effects on the weldment due to the MSIP.

Stress Corrosion Cracking Behavior of Alloy 182 Weld in Pressurized Water Reactor Primary Water Environment at 325ºC

CORROSION ◽  
2011 ◽  
Vol 67 (8) ◽  
pp. 085004-1-085004-9 ◽  
Author(s):  
L.I.L. Lima ◽  
M.M.A.M. Schvartzman ◽  
C.A. Figueiredo ◽  
A.Q. Bracarense
Keyword(s):  
Stress Corrosion ◽  
Oxide Layer ◽  
Stress Corrosion Cracking ◽  
Power Plants ◽  
Corrosion Cracking ◽  
Pressurized Water Reactor ◽  
Pressurized Water ◽  
Cracking Behavior ◽  
Water Reactor ◽  
Primary Water

Abstract The weld used to connect two different metals is known as a dissimilar metal weld (DMW). In nuclear power plants, this weld is used to join stainless steel to low-alloy steel components in the nuclear pressurized water reactor (PWR). The most common weld metal is Alloy 182 (UNS W86182). Originally selected for its high corrosion resistance, it exhibited, after a long operation period, susceptibility to stress corrosion cracking (SCC) in PWR. The goal of this work was to study the electrochemical corrosion behavior and SCC susceptibility of Alloy 182 weld in PWR primary water containing 25 cm3 and 50 cm3 H2/kg H2O at standard temperature and pressure (STP). For this purpose, slow strain rate tensile (SSRT) tests and potentiodynamic polarization measurements were carried out. Scanning electron microscopy (SEM) with energy-dispersive spectrometry (EDS) was used to evaluate fracture morphology and determine the oxide layer chemical composition and morphology. The results indicated that at 325°C Alloy 182 weld is more susceptible to SCC at 25 cm3 (STP) H2/kg H2O and the increase of dissolved hydrogen decreased the crystal size of the oxide layer.

Evaluation and Repair of Primary Water Stress Corrosion Cracking in Alloy 600/182 Control Rod Drive Mechanism Nozzles

2002 ◽  
Author(s):  
Charles R. Frye ◽  
Melvin L. Arey ◽  
Michael R. Robinson ◽  
David E. Whitaker
Keyword(s):  
Water Stress ◽  
Boric Acid ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Base Material ◽  
Corrosion Cracking ◽  
Alloy 600 ◽  
Control Rod ◽  
Drive Mechanism ◽  
Primary Water

In February 2001, a routine visual inspection of the reactor vessel head of Oconee Nuclear Station Unit 3 identified boric acid crystals at nine of sixty-nine locations where control rod drive mechanism housings (CRDM nozzles) penetrate the head. The boric acid deposits resulted from primary coolant leaking from cracks in the nozzle attachment weld and from through-thickness cracks in the nozzle wall. A general overview of the inspection and repair process is presented and results of the metallurgical analysis are discussed in more detail. The analysis confirmed that primary water stress corrosion cracking (PWSCC) is the mechanism of failure of both the Alloy 182 weld filler material and the alloy 600 wrought base material.

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