scholarly journals Reflections on Early Stages of Environmentally Assisted Cracking from Corrosion Pits

2021 ◽  
Vol 2 (4) ◽  
pp. 568-581
Author(s):  
Alan Turnbull
Keyword(s):  
Crack Growth ◽  
Grinding Wheel ◽  
Specimen Preparation ◽  
Environmentally Assisted Cracking ◽  
Variable Nature ◽  
Aqueous Chloride ◽  
Fabrication Defects ◽  
Corrosion Pits ◽  
Crack Transition ◽  
Pit Depth

A perspective is presented on the evolution of damage due to environmentally assisted cracking (EAC), from crack precursor development through to long crack growth. The variable nature of crack precursors is highlighted with an observation that uncontrolled chemistry excursions or fabrication defects could eliminate any significant delay associated with that step in the damage evolution process. Specimen preparation by machining and grinding can be critical in determining the apparent susceptibility of the metal to EAC and corrosion, and an example for 316L stainless steel is given to show how physical defects generated by the grinding wheel can become the dominant site for pitting attack relative to MnS inclusions. Corrosion pits are the most commonly observed precursor to cracks in aqueous chloride environments. The loci of sites of crack initiation around a pit are discussed and the inherent challenges in quantifying the growth of cracks smaller than the pit depth described with implications for modelling of the pit-to-crack transition. The remarkably enhanced stress corrosion crack growth rate data for short and small cracks in a 12Cr steam turbine blade in a simulated condensate environment are discussed in the context of crack electrochemistry modelling and the implications for engineering integrity.

The Effect of Microstructure on Pit-to-Crack Transition and Crack Growth in an X-52 Pipeline Steel in Near-Neutral pH Environment

2008 ◽  
Author(s):  
B. Fang ◽  
R. Eadie ◽  
W. Chen ◽  
M. Elboujdaini ◽  
E.-H. Han
Keyword(s):  
Normal Stress ◽  
Pipeline Steel ◽  
Crack Depth ◽  
Width Ratio ◽  
Blunt Crack ◽  
Neutral Ph ◽  
Metallic Inclusions ◽  
Corrosion Pits ◽  
Crack Transition ◽  
Pit Depth

X-52 pipeline steel specimens that had been pitted using a passivation/immersion technique were cyclically loaded in a near-neutral pH solution sparged with 5% CO2/balance N2 gas mixture at a peak normal stress of 109% of the yield strength (YS), a stress ratio, R, of 0.8, and a frequency of 0.0001 Hz. Blunt cracks were seen to have initiated from the corrosion pits. There were many more cracks on the radial transverse (R-T) surface than on the axial transverse (A-T) surface. On the R-T surface, there were a lot of non-metallic inclusions particularly at mid-wall in this steel and these resulted in the nucleation of large pits that were particularly prone to pit-to-blunt-crack transition. At higher peak normal stress, 109% of YS, compared to previous studies at a little lower stresses, there was more rapid crack formation on the R-T surface. In the end, the cracks along the large elongated inclusions penetrated into the steel samples and led to failure. The crack path was transgranular in nature and the fracture surface displayed quasi-cleavage features. Analysis revealed that the pit depth to width ratio for individual pits was a little higher than that for linked pits, however, the ratio of crack depth to crack mouth width was observed to be much larger than the ratio for the linked pits. Strong preferential dissolution was believed to be responsible for the pit nucleation from these non-metallic inclusions, with the plastically deformed regions at the pits acting as the anodic phases.

Crack Growth Rates of Alloy 600 From the Davis-Besse Reactor CRDM Nozzle #3 in PWR Environment

2005 ◽  
Author(s):  
Omesh K. Chopra ◽  
Bogdan Alexandreanu ◽  
William J. Shack
Keyword(s):  
Crack Growth ◽  
Potential Drop ◽  
Compact Tension ◽  
Constant Load ◽  
Alloy 600 ◽  
Pressurized Water ◽  
Control Rod ◽  
Environmentally Assisted Cracking ◽  
Water Reactors ◽  
Nickel Base

Reactor–vessel internal components made of nickel–base alloys are susceptible to environmentally assisted cracking. A better understanding of the causes and mechanisms of this cracking may permit less conservative estimates of damage accumulation and requirements on inspection intervals of pressurized water reactors (PWRs). This paper presents crack growth rate (CGR) results for Alloy 600 removed from nozzle#3 of the Davis–Besse (D-B) control rod drive mechanism (CRDM). The tests were conducted on 1/4-T or 1/2-T compact tension specimens in simulated PWR environment, and crack extensions were determined by DC potential drop measurements. The experimental CGRs under cyclic and constant load are compared with the existing CGR data for Alloy 600 to determine the relative susceptibility of the D-B CRDM nozzle alloy to environmentally enhanced cracking. The CGRs under constant load for the nozzle material are higher than those predicted by the best-fit curve for Alloy 600 at 316 °C. The results also indicate significant enhancement of CGRs under cyclic loading in the PWR environment. Characterization of the material microstructure and tensile properties is described.

Effect of Pitting Corrosion on Strength of AISI 410 Stainless Steel Compressor Blades

2014 ◽  
Vol 606 ◽  
pp. 227-231 ◽  
Author(s):  
Mazmir Mat Noh ◽  
Farzin Mozafari ◽  
Muhammad Adil Khattak ◽  
Mohd Nasir Tamin
Keyword(s):  
Stainless Steel ◽  
Pitting Corrosion ◽  
Tensile Specimen ◽  
Maximum Diameter ◽  
Compressor Blades ◽  
Strength Tests ◽  
Corrosion Pits ◽  
Pit Depth ◽  
Geometry Analysis ◽  
Nucleation Phenomenon

In the present paper, effects of pitting corrosion on the strength of members made of AISI 410 Martensitic stainless steel were investigated. Stainless steel compressor blades in power generation industries commonly suffer from pitting corrosion. Pits geometry analysis and strength tests have been conducted. Pits geometry analysis established the maximum pit depth of 0.26 mm along with the maximum diameter of 1 mm. In addition, strength and elongation of the pitted tensile specimen gradually decrease with the increase of the area lost due to pitting corrosion. A damage nucleation phenomenon at the initial load values is also postulated.

Fatigue Crack Growth of LC9 Aluminum Alloy under Flying Loading with Corrosion Damage

2014 ◽  
Vol 488-489 ◽  
pp. 66-69
Author(s):  
Xu Dong Li ◽  
Zeng Jie Cai ◽  
Zhi Tao Mu
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Cracks ◽  
Corrosion Damage ◽  
Growth Behavior ◽  
Transport Aircraft ◽  
Suitable Parameter ◽  
Corrosion Pits

This paper investigates the growth behavior of fatigue cracks initiated at corrosion pits in laboratory coupons of LC9 aluminum alloy subjected to a transport aircraft loading spectrum. Corrosion pits were introduced by exposing the coupons to EXCO solution for a variety of periods to produce corrosion damage varying from mild to severe. In general, the presence of corrosion damage reduced the fatigue lives of components to a severe extent. It was found that the depth of the corrosion pit was a suitable parameter for characterizing the corrosion damage and for predicting the fatigue life of the coupons using commercial fatigue crack growth software

The Corrosion Morphology and Crack Growth Analysis of Aluminum Alloy

2011 ◽  
Vol 80-81 ◽  
pp. 464-468
Author(s):  
Zhi Tao Mu ◽  
Hui Liu ◽  
Zuo Tao Zhu ◽  
Ding Hai Chen
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Crack ◽  
Crack Growth ◽  
Growth Analysis ◽  
Three Dimensional ◽  
Critical Crack ◽  
Corrosion Morphology ◽  
Critical Crack Length ◽  
Corrosion Depth ◽  
Corrosion Pits

The relation between corrosion depth and width with corrosion time is according with the power function. The corrosion pits can be seen as ellipse balls through the examination of QUESTAR three-dimensional optics microscope. Corrosion can decrease the fatigue life of materials and is the main reason of fatigue crack form and grow; through AFGROW analyze we can see that the AFGROW software can simulate crack growth life well and the error is low, the crack growth life and critical crack length are conservative than experiment values.

scholarly journals Modeling of the Onset, Propagation, and Interaction of Multiple Cracks Generated From Corrosion Pits by Using Peridynamics

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Dennj De Meo ◽  
Luigi Russo ◽  
Erkan Oterkus
Keyword(s):  
Structural Damage ◽  
Crack Nucleation ◽  
Numerical Models ◽  
Measurement Techniques ◽  
High Stress ◽  
Numerical Approach ◽  
Multiple Cracks ◽  
Numerical Instabilities ◽  
Corrosion Pits ◽  
Crack Transition

High stress regions around corrosion pits can lead to crack nucleation and propagation. In fact, in many engineering applications, corrosion pits act as precursor to cracking, but prediction of structural damage has been hindered by lack of understanding of the process by which a crack develops from a pit and limitations in visualization and measurement techniques. An experimental approach able to accurately quantify the stress and strain field around corrosion pits is still lacking. In this regard, numerical modeling can be helpful. Several numerical models, usually based on finite element method (FEM), are available for predicting the evolution of long cracks. However, the methodology for dealing with the nucleation of damage is less well developed, and, often, numerical instabilities arise during the simulation of crack propagation. Moreover, the popular assumption that the crack has the same depth as the pit at the point of transition and by implication initiates at the pit base has no intrinsic foundation. A numerical approach is required to model nucleation and propagation of cracks without being affected by any numerical instability and without assuming crack initiation from the base of the pit. This is achieved in the present study, where peridynamics (PD) theory is used in order to overcome the major shortcomings of the currently available numerical approaches. Pit-to-crack transition phenomenon is modeled, and nonconventional and more effective numerical frameworks that can be helpful in failure analysis and in the design of new fracture-resistant and corrosion-resistant materials are presented.

scholarly journals IMAGING OF CORROSION PITS ON METALLIC PIPES USING A LASER SCANNER

2011 ◽  
Author(s):  
Homayoun Najjaran
Keyword(s):  
Laser Scanning ◽  
Laser Scanner ◽  
Scanning Speed ◽  
Displacement Sensor ◽  
Statistical Characteristics ◽  
Measuring Instruments ◽  
Scanning System ◽  
Laser Measurements ◽  
Corrosion Pits ◽  
Pit Depth

This paper describes the hardware and software of a laser scanning system that is used to produce 3D images of external surfaces of pipes. The images are produced in the form of 3D raster images with a resolution of up to 0.1×0.1 mm and an accuracy of 3-10 microns, depending on the desired scanning speed, to portray the corrosion pits on the pipes. The main application of the scanner is to establish patterns for calibrating nondestructive testing techniques (e.g., Remote Field Eddy Current (RFEC) and ultrasound testing that are commonly used to measure the remaining wall thickness of ductile and cast iron pipes), and also identifying the statistical characteristics of the measuring instruments utilized in those methods. The images may also be useful to scrutinize corrosion and failure mechanisms, especially when estimates of average or maximum pit depth are insufficient. The scanning system consists of a 2-DOF robot that can move a laser displacement sensor along a pipe and an instrumented rig that rotates the pipe about its axis. Rotating the pipe and moving the rangefinder along the pipe’s axis, the scanning system acquires laser measurements into a host computer to produce the image. The paper also presents the images and statistical analysis of corrosion pits of pipe samples exhumed and sandblasted for scanning.

scholarly journals Effect of Material Heterogeneity on Environmentally Assisted Cracking Growth Rate of Alloy 600 for Safe-End Welded Joints

Materials ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 6186
Author(s):  
Kuan Zhao ◽  
Shuai Wang ◽  
He Xue ◽  
Zheng Wang
Keyword(s):  
Growth Rate ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Welded Joints ◽  
Welding Process ◽  
Growth Behavior ◽  
Crack Growth Behavior ◽  
Alloy 600 ◽  
Material Heterogeneity ◽  
Environmentally Assisted Cracking

Environmentally assisted cracking (EAC) is essential in predicting light water reactors’ structural integrity and service life. Alloy 600 (equivalent to Inconel 600) has excellent corrosion resistance and is often used as a welding material in welded joints, but material properties of the alloy are heterogeneous in the welded zone due to the complex welding process. To investigate the EAC crack growth behavior of Alloy 600 for safe-end welded joints, the method taken in this paper concerns the probability prediction of the EAC crack growth rate. It considers the material heterogeneity, combining the film slip-dissolution/oxidation model, and the elastic-plastic finite element method. The strain rate at the crack tip is a unique factor to describe the mechanical state. Still, it is challenging to accurately predict it because of the complicated and heterogeneous material microstructure. In this study, the effects of material heterogeneity on the EAC crack growth behavior are statistically analyzed. The results show that the material heterogeneity of Alloy 600 can not be ignored because it affects the prediction accuracy of the crack growth rate. The randomness of yield strength has the most influence on the EAC growth rate, while Poisson’s ratio has the smallest.

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