A Contribution to Proof the Component Integrity Taking Into Account the Corrosion-Assisted Crack Growth

2002 ◽  
Author(s):  
Eberhard Roos ◽  
Frank Otremba ◽  
Frank Hu¨ttner
Keyword(s):  
Growth Rate ◽  
Crack Growth Rate ◽  
Data Base ◽  
Crack Growth ◽  
Environmental Conditions ◽  
Power Plants ◽  
Austenitic Steels ◽  
Test Duration ◽  
Low Alloy Steels ◽  
Integrity Assessment

The proof of the component integrity is fundamental for a safe and reliable operation of Nuclear Power Plants (NPP). The concept of the Material Testing Institute (MPA) for integrity assessment is based on fracture mechanic analysis which results in detailed regulations for nondestructive examination. This approach has to account for the main damage mechanisms as fatigue and corrosion. This paper focuses on the influence of corrosion-assisted crack growth which strongly depends on corrosion and environmental conditions (e.g. coolant purity). Up to stress intensity of approximately 60 MPa√m for ferritic low-alloy steels in high-purity water (acc. to specification) under constant load conditions the analysis can be based on a crack extension of max. 70 μm for each load cycle. Related to a test duration of 1000 hours this is equivalent to a formally calculated crack growth rate (CGR) of ≤2 · 10 −8 mm/s. For austenitic stainless steels more complex dependences on material, environmental and mechanical parameters exist. Particularly, for stabilized austenitic steels the crack growth rate data base is relatively weak. Under unfavourable environmental conditions in single cases crack growth rates up 6 mm/a have been measured. Based on experimental results an arithmetic mean value of 0.95 mm/a and a median value of 0.6 mm/a have been determined. A further improvement of data base is desirable.

A Contribution to Proof the Component Integrity Taking Into Account the Corrosion-Assisted Crack Growth

2002 ◽  
Author(s):  
Eberhard Roos ◽  
Frank Otremba ◽  
Frank Hu¨ttner
Keyword(s):  
Growth Rate ◽  
Crack Growth Rate ◽  
Data Base ◽  
Crack Growth ◽  
Environmental Conditions ◽  
Power Plants ◽  
Austenitic Steels ◽  
Test Duration ◽  
Low Alloy Steels ◽  
Integrity Assessment

The proof of the component integrity is fundamental for a safe and reliable operation of Nuclear Power Plants (NPP). The concept of the Material Testing Institute (MPA) for integrity assessment is based on fracture mechanic analysis which results in detailed regulations for nondestructive examination. This approach has to account for the main damage mechanisms as fatigue and corrosion. This paper focuses on the influence of corrosion-assisted crack growth which strongly depends on corrosion and environmental conditions (e.g. coolant purity). Up to stress intensity of approximately 60 MPa√m for ferritic low-alloy steels in high-purity water (acc. to specification) under constant load conditions the analysis can be based on a crack extension of max. 70 µm for each load cycle. Related to a test duration of 1000 hours this is equivalent to a formally calculated crack growth rate (CGR) of = 2 · 10−8 mm/s. For austenitic stainless steels more complex dependences on material, environmental and mechanical parameters exist. Particularly, for stabilized austenitic steels the crack growth rate data base is relatively weak. Under unfavourable environmental conditions in single cases crack growth rates up to 6 mm/a have been measured. Based on experimental results an arithmetic mean value of 0.95 mm/a and a median value of 0.6 mm/a have been determined. A further improvement of data base is desirable.

Fatigue Crack Growth Rate and Fracture Toughness of API5L X65 in Sweet Environments

2013 ◽  
Author(s):  
Michael A. Tognarelli ◽  
Ramgopal Thodla ◽  
Steven Shademan
Keyword(s):  
Fracture Toughness ◽  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Crack Growth Rate ◽  
Environmental Conditions ◽  
Initiation Toughness ◽  
Diffusible Hydrogen

Corrosion fatigue and fracture toughness in sour environments of APIX65 5L have typically been studied in relatively severe environments like NACE A and NACE B solutions. There are very limited data in sweet and mildly sour environments that are of interest in various applications. This paper presents fatigue crack growth frequency scans in a range of sweet and mildly sour environments as well as on different microstructures: Parent Pipe, Heat Affected Zone (HAZ) and Weld Center Line (WCL). The fatigue crack growth rate (FCGR) increased with decreasing frequency and reached a plateau value at low frequencies. FCGR in the sweet environments that were investigated did exhibit a frequency dependence (increasing with decreasing frequency) and had plateau FCGR in the range of 10–20× the in-air values. In the mildly sour environments that were investigated, FCGR was found to be about 25 to 30× higher than the in-air values. By comparison, in NACE A environments the FCGR is typically about 50× higher than the in-air values. The FCGRs of parent pipe and HAZ were found to be similar over a range of environments, whereas the WCL FCGR data were consistently lower by about a factor of 2×. The lower FCGR of the WCL is likely due to the lower concentration of diffusible hydrogen in the weld. FCGRs as a function of ΔK (stress integrity factor range) were measured on parent pipe at the plateau frequency. The measured Paris law curves were consistent with the frequency scan data. Rising displacement fracture toughness tests were performed in a range of sweet and sour environments to determine the R-curve behavior. Tests were performed in-situ at a slow K-rate of 0.05Nmm−3/2/s over a range of environmental conditions on parent pipe. The initiation toughness and the slope of the R-curve decreased sharply in the sour environments. The initiation toughness and slopes were largely independent of the notch location as well as environmental conditions. Typical values of initiation toughness were in the range of 90–110N/mm.

Evaluation of Stress Corrosion Crack Growth in Low Alloy Steel Vessel Materials in the BWR Environment

2018 ◽  
Author(s):  
Sampath Ranganath ◽  
Robert G. Carter ◽  
Rajeshwar Pathania ◽  
Stefan Ritter ◽  
Hans-Peter Seifert
Keyword(s):  
Growth Rate ◽  
Crack Growth Rate ◽  
Water Chemistry ◽  
Stress Corrosion ◽  
Crack Growth ◽  
Low Alloy Steels ◽  
Hydrogen Water ◽  
Alloy Steels ◽  
Normal Water ◽  
Reactor Pressure

Low alloy steels (LAS) used in the fabrication of reactor pressure vessel (RPV) and nozzles have been resistant to stress corrosion cracking (SCC) in the Boiling Water Reactor (BWR) environment. The plate material is SA533 Grade B and the nozzle material is SA508 Class 2 for most operating BWRs. While BWR service field experience with the LAS materials has been very good for there have been a limited number of SCC incidents where cracking has been reported especially in Alloy 182 RPV attachment (dissimilar metal) welds. This paper describes the methodology for the assessment of SCC crack growth rate (CGR) of LAS RPV components in the BWR environment. Specifically, it describes the development of CGR disposition lines (also called reference crack growth rate curves) for normal water chemistry (NWC) and hydrogen water chemistry (HWC) in BWR environments. In addition, based on more recent data from tests on the effect of chloride transients in NWC environments are also proposed.

Fractographic Studies of Fatigue Fracture of Metals

1972 ◽  
Vol 30 ◽  
pp. 664-665
Author(s):  
Ryoichi Koterazawa
Keyword(s):  
Growth Rate ◽  
Crack Growth Rate ◽  
Fracture Surface ◽  
Surface Topography ◽  
Crack Growth ◽  
Copper Alloys ◽  
Carbon Steels ◽  
Case Hardening ◽  
Low Alloy Steels ◽  
Lower Growth

1. Correlation between crack growth rate and fracture surface topography.This section describes a part of the result of a co-operative investigation of Subcommittee on Fractography of Japan Society of Mechanical Engineers which is now under way with the aim of correlating microscopic fracture surface topography of different materials to macroscopic parameters. Materials studied are carbon steels, low alloy steels, stainless steels, cast steels, aluminum alloys, titanium alloys, copper alloys, bearing steels, case hardening steels and sintered alloys. Roughly speaking, fairly good correlation was obtained between spacing of fatigue striations and macroscopic crack growth rate with ductile materials in the range of growth rate around 0.03--3 microns/cycle (Fig.1). There was a tendency of striation spacing being larger than macroscopic rate in the range of lower growth rate and smaller in the range of higher growth rate. Above this range, dimples or stretched surfaces were predominant and, below this range, irregular striation-like markings(Fig.2) were main feature of the fracture surface, cleavage-like markings or grain boundary fracture being found occasionally.

Prediction of the Crack Growth Rate Under Creep and Neutron Irradiation for Austenitic Stainless Steels in Initial, Aged and Irradiated Conditions

2013 ◽  
Author(s):  
Andrey Buchatsky ◽  
Boris Margolin ◽  
Alexander Gulenko ◽  
Alexander Kashtanov
Keyword(s):  
Growth Rate ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Base Metal ◽  
Neutron Irradiation ◽  
Austenitic Stainless Steels ◽  
Thermal Ageing ◽  
Austenitic Steels ◽  
Experimental Investigations ◽  
Initial Condition

This work is aimed at investigating the crack growth rate in austenitic steels under creep and neutron irradiation for a material in initial and aged conditions. The crack growth rate under creep is studied for 18Cr-9Ni steel and its welds. This steel and its welds are the base structural materials for manufacturing BN-600 fast reactor components. Experimental investigations of crack growth rate have been performed for the base metal, weld metal and heat-affected zone which were subjected to thermal ageing during operation. It is shown that the fastest crack growth rate is observed for specimens from the base metal. The crack growth rates are compared for the base metal in initial and aged conditions. The initial condition of metal is modeled by annealing thermally aged metal taken from the components after its operation. The investigations show that the crack growth rate for the initial condition is faster than for the aged condition. A method for predicting the crack growth rate under creep and irradiation has been developed on the basis of a physical-and-mechanical intergranular fracture model proposed before [1]. The crack growth rate for the material in initial condition is used as input data to calculate this rate under creep and irradiation according to the developed method.

Fatigue Crack Growth in Low Alloy Steels Under Tension-Compression Loading in Air

2018 ◽  
Author(s):  
Kisaburo Azuma ◽  
Yasuhiro Yamazaki
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Growth Curves ◽  
Low Alloy Steels ◽  
Alloy Steels ◽  
Crack Growth Rates

Low alloy steels are extensively used in pressure boundary components of nuclear power plants. The structural integrity of the components made of low alloy steels can be evaluated by the procedure of flaw evaluation provided by Section XI of the ASME Boiler and Pressure Vessel Code. According to the Code, the range of stress intensity factor ΔK can be used to determine the fatigue crack growth rates of the material. However, it has been reported that crack closure behavior also strongly influence the fatigue crack growth rate under strong compressive load cycles. This paper discusses the relation between ΔK and the fatigue crack growth rate for cracks in low alloy steels exposed to air. Compressive-tensile cyclic loadings were applied to center-notched plates to obtain the fatigue crack growth curves. The test data demonstrated that effective SIF range ΔKeff more accurately described the crack growth property due to plasticity induced crack closure. Comparing the test results with the reference crack growth curves in the ASME Code Section XI, it may seem that the crack growth prediction based on the Code underestimates the crack growth rates for compressive-tensile cyclic loadings under high stress level.

Hydrogen Embrittlement of Low Alloy Steels Under Cathodic Polarization

CORROSION ◽  
10.5006/3240 ◽  
2020 ◽  
Vol 76 (3) ◽  
pp. 299-311 ◽  
Author(s):  
Ramgopal Thodla ◽  
Narasi Sridhar ◽  
Herman Amaya ◽  
Behrang Fahimi ◽  
Christopher Taylor
Keyword(s):  
Growth Rate ◽  
Stress Intensity ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Water Adsorption ◽  
Cathodic Polarization ◽  
Low Alloy Steels ◽  
Applied Potential ◽  
Alloy Steels ◽  
Rate Limiting

Hydrogen embrittlement of low alloys steels at three different strength levels (745 Mega Pascals [MPa], 904 MPa, and 1,166 MPa) were evaluated under cathodic polarization. Crack growth rate measurements were performed under constant stress intensity (K) conditions, as a function of applied K values as well as applied potential to characterize the behavior of the three different steels. At −1,050 mVSCE saturated calomel electrode (SCE), the threshold stress intensity (Kth) value increased from 44 MPa√m to 60 MPa√m as the yield strength decreased from 1,166 MPa to 745 MPa. The crack growth rate at 66 MPa√m and −1,050 mVSCE decreased from 3 × 10−5 mm/s to 4 × 10−8 mm/s as the yield strength decreased from 1,166 MPa to 745 MPa. For the 1,166 MPa steel at low values of K, the crack growth rate decreased by two orders of magnitude as the potential decreased from −1,000 mVSCE to −950 mVSCE. At higher values of K, the effect of potential on the crack growth rate was not as significant. The 745 MPa steel in general exhibited slow crack growth rate values (2 to 4 × 10−8 mm/s) over the range of K values and applied potentials in which it was evaluated. Water adsorption on fresh metal surfaces in the estimated crack tip chemistry was modeled using density functional theory. The variation in crack growth rate with applied potential at low and intermediate values of K correlated with the fractional coverage of water adsorption on the fresh metal surface. It is proposed that the water reduction reaction and the subsequent generation of hydrogen are the rate limiting steps in the slow subcritical crack growth rate processes for low alloy steels under the conditions evaluated. For the higher values of K, where the crack growth rate showed a weak dependence on applied potential, water reduction, and generation of hydrogen are likely not the rate limiting steps.

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