Developing Response Functions for Crack Opening Displacement to Calculate Leak-Rates Through Complex Cracks in Pipes With Weld Overlays

2010 ◽  
Author(s):  
Arindam Chakraborty ◽  
Wasimreza Momin ◽  
Angah Miessi ◽  
Peihua Jing ◽  
Haiyang Qian
Keyword(s):  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Crack Opening ◽  
Corrosion Cracking ◽  
Flaw Size ◽  
Pipe Material ◽  
Response Functions ◽  
Plant Design ◽  
Alloy 690 ◽  
Complex Crack

Leak-Before-Break (LBB) is employed in design of nuclear power reactor piping to eliminate consideration of the dynamic effects of pipe rupture from the plant design basis for the affected piping system. LBB cannot be applied if environmental conditions that could lead to degradation by stress corrosion cracking exists. For Alloy 600/82/182 dissimilar metal welds (DMW) in pressurized water reactor plants, primary water stress corrosion cracking (PWSCC) is found to be active. Application of weld overlay (WOL) of non-susceptible Alloy 690/52/152 material has been shown to mitigate PWSCC growth in DMW. Therefore, LBB can be considered for a DMW with Alloy 690/52/152 overlay. However, WOL sizing design postulates a complex crack which is through wall in the overlay material and part through or full circumferential in the DMW base material. This significantly reduces the critical flaw size and in turn the maximum allowable flaw size for leak rate. The current industry practice conservatively ignores the full circumferential crack in the original pipe material and assumes a through wall crack along the entire pipe thickness. This assumptions leads to significantly reduced leakage due to smaller crack opening. The problem becomes more critical with small diameter pipes. The current work calculates the crack opening displacements (CODs) for a pipe with complex crack. Since it is a function of several geometry and materials parameters, response functions are generated to calculate CODs.

On the role of intergranular nanocavities in long-term stress corrosion cracking of Alloy 690

2021 ◽  
pp. 117453
Author(s):  
Zhao Shen ◽  
Edward Roberts ◽  
Naganand Saravanan ◽  
Phani Karamched ◽  
Takumi Terachi ◽  
...  
Keyword(s):  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Corrosion Cracking ◽  
Alloy 690

Stress Corrosion Cracking in Welds of Reactor Vessel Nozzle at Ohi-3 and of Other Vessel’s Nozzle at Japan’s PWR Plants

2009 ◽  
Author(s):  
Takao Nakamura ◽  
Keiji Taniguchi ◽  
Shinro Hirano ◽  
Narita Marekazu ◽  
Tomonobu Sato
Keyword(s):  
Weld Metal ◽  
Grain Boundaries ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Visual Inspection ◽  
Reactor Vessel ◽  
Corrosion Cracking ◽  
Periodic Inspection ◽  
Depth Direction ◽  
Alloy 690

During the 13th periodic inspection, which started in February 2008, KEPCO’s Ohi unit 3 (1,180MWe PWR) implemented voluntary ECT in addition to the visual inspection of the RV hot and cold leg nozzle welds to confirm the integrity of the concerned section. As a result of inspection, in March 2008, a flaw extending in the depth direction along dendritic grain boundaries of the weld metal was found in the RV A-loop hot leg nozzle. With traces of machining, which could cause residual tensile stresses, it was suspected that SCC initiated and grew at the concerned section. After grinding the section to remove the entire flaw, WJP was applied as the corrective action. Ohi-3 restarted operation on November 2008. It is planned to apply repair welding to the ground out section with alloy 690 during the next periodic inspection [1]. Several Japan’s PWR plants have experienced similar incidents in the nozzle welds. This paper presents the details of repair technologies, which have been developed to address PWSCC found in Ohi-3 RV hot leg nozzle and previous similar incidents in the RV and other vessel’s nozzle welds at Japan’s PWR plants.

Getting to Know Your Bends to Support SCC Management

2020 ◽  
Author(s):  
Chris Wood ◽  
Fernando Merotto ◽  
Brian Kerrigan ◽  
Ramon Loback ◽  
Pedro Gea
Keyword(s):  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Crack Detection ◽  
Axial Stress ◽  
Corrosion Cracking ◽  
Inspection System ◽  
Pipe Material ◽  
Baseline Assessment ◽  
Limited Information ◽  
Metallographic Examination

Abstract Nova Transportadora do Sudeste (NTS) own and operate a gas transmission system in Brazil constructed in 1996. One of the confirmed primary integrity threats to this system is axial stress corrosion cracking. The pipelines vary in diameter, weld type, manufacturer and age. One of the pipelines failed in 2015 due to an axial stress corrosion crack. Since the failure, NTS have executed an intense inspection campaign to detect and size axial cracking within their network. The 2015 failure occurred on a field bend. The inspection campaign and following dig campaign has confirmed that cracking (both axial and circumferential) within field bends is the primary integrity threat. Brazil has a challenging terrain and approximately 40% of joints within the network were subject to cold field bending. The influences of the pipeline geometry within these areas have resulted in localised elevated stresses where the axial stress corrosion cracking colonies are initiating and growing. To date, no cracking (axial or circumferential) has been verified within their straight pipe joints. NTS initially took a conservative baseline assessment approach using API 579 Part 9, due to the limited information regarding the pipe material and complex stress state. In addition to the hoop stress from internal pressure, the baseline assessment also considered weld residual stress and bending stress due to ovalization to determine immediate and future integrity. An intensive dig campaign is underway following a crack detection in-line inspection campaign using electromagnetic acoustic transducer technology. A large number of deep cracks were reported by the in-line inspection system, these were verified to be deep and repaired with a type B sleeve. However, at one site an entire joint was removed for further analysis, to investigate the crack morphology, confirm material properties and refine the predictive failure pressure modelling. This paper outlines how NTS have combined a burst test, mechanical testing, FEA modelling, fractography and metallographic examination to further understand the feature morphology and stresses within these areas and how they have been able to reduce conservatism from their baseline assessment with confidence and adopt a plastic collapse approach to accurately predict failure.

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