Analysis of Environmentally Assisted Cracking in S420 Steel by Using the Theory of Critical Distances

2019 ◽  
Author(s):  
P. González ◽  
S. Cicero ◽  
B. Arroyo ◽  
J. A. Álvarez
Keyword(s):  
Hydrogen Embrittlement ◽  
Cathodic Polarization ◽  
Simulation Analysis ◽  
Low Ph ◽  
Experimental Program ◽  
Aqueous Environment ◽  
Cracking Behavior ◽  
Aggressive Environment ◽  
Environmentally Assisted Cracking ◽  
Finite Elements Simulation

Abstract The behavior of S420 steel under cathodic polarization in low pH aqueous environment is analyzed following the assumptions of the Theory of Critical Distances. This methodology has been successfully applied in fracture and fatigue analysis, but it has not been employed yet under stress corrosion cracking or hydrogen embrittlement conditions. This work focuses on the problem of environmentally assisted cracking by using the Point Method and the Line Method, both of them belonging to the Theory of Critical Distances. Fracture mechanic tests were carried out, using a slow strain rate machine, at two different solicitation rates (6·10−8 m/s and 6·10−9 m/s). The study is based on an experimental program composed of C(T) specimens with notch radii varying from 0 mm up to 2 mm. Cathodic polarization with a 5 mA/cm2 current has been employed and the aqueous aggressive environment was made using the Pressouyre’s method. The study has been completed with finite elements simulation analysis. The results reveal that the Theory of Critical Distances provides accurate predictions of the environmentally assisted cracking behavior of S420 steel in notched conditions.

scholarly journals Environmentally Assisted Cracking Behavior of S420 and X80 Steels Containing U-notches at Two Different Cathodic Polarization Levels: An Approach from the Theory of Critical Distances

Metals ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 570 ◽  
Author(s):  
Pablo González ◽  
Sergio Cicero ◽  
Borja Arroyo ◽  
José Álvarez
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Hydrogen Embrittlement ◽  
Intensity Factor ◽  
Crack Propagation ◽  
Cathodic Polarization ◽  
Cracking Behavior ◽  
Notched Specimens ◽  
Environmentally Assisted Cracking ◽  
X80 Steels

This paper analyzes, using the theory of critical distances, the environmentally assisted cracking behavior of two steels (S420 and API X80) subjected to two different aggressive environments. The propagation threshold for environmentally assisted cracking (i.e., the stress intensity factor above which crack propagation initiates) in cracked and notched specimens (KIEAC and KNIEAC) has been experimentally obtained under different environmental conditions. Cathodic polarization has been employed to generate the aggressive environments, at 1 and 5 mA/cm2, causing hydrogen embrittlement on the steels. The point method and the line method, both belonging to the theory of critical distances, have been applied to verify their capacity to predict the initiation of crack propagation. The results demonstrate the capacity of the theory of critical distances to predict the crack propagation onset under the different combinations of material and aggressive environments.

Environmentally assisted cracking behavior of 18Ni 250 maraging steel welds obtained with and without flux in chloride media

CORROSION ◽  
10.5006/3582 ◽  
2020 ◽  
Author(s):  
Renu Gupta ◽  
Rahul Agrawal ◽  
Poorwa Gore ◽  
Uday Parmar ◽  
VS Raja
Keyword(s):  
Hydrogen Embrittlement ◽  
Maraging Steel ◽  
Chloride Solution ◽  
Electrochemical Corrosion ◽  
Cracking Behavior ◽  
Gas Tungsten Arc ◽  
Environmentally Assisted Cracking ◽  
Steel Welds ◽  
Corrosive Environments

Gas tungsten arc welding is extensively employed in the fabrication of 18Ni 250 maraging steel motor casings. In this work, the role of flux addition on the environmentally assisted cracking (EAC) and electrochemical corrosion behaviors of these welds in their peak aged condition is presented. Studies were carried out in order to bring out the potential influence of long-term exposure of maraging steel welds to neutral 0.1 M NaCl (mildly corrosive) and acidified 0.1 M NaCl (a relatively more corrosive) environments to understand the EAC behavior of the welds. The study showed that both the fluxed and un-fluxed weld metals suffered 21-23% loss in ductility in neutral 0.1 M NaCl solution from that of obtained in air. The EAC of the welds in the neutral chloride solution was due to anodic dissolution, while in the acidified chloride solution it was found to be predominantly due to hydrogen embrittlement. The effect of flux in refining the weld microstructure was reflected in, (a) preventing intergranular mode of hydrogen embrittlement of the un-fluxed welds and transforming the mode to transgranular cracking, (b) lowering a wide scatter in electrochemical corrosion rate and (c) reducing the selective attack in the inter-dendritic regions of the un-fluxed welds. Such a transition from intergranular to transgranular cracking might affect long-term service behavior of the welds to corrosion and EAC, though it is not reflected in the short-term tests.

Application of the Incremental Step Loading Technique to Small Punch Tests in Hydrogen Embrittlement

2019 ◽  
Author(s):  
B. Arroyo ◽  
P. González ◽  
L. Andrea ◽  
J. A. Álvarez ◽  
R. Lacalle
Keyword(s):  
Hydrogen Embrittlement ◽  
Cathodic Polarization ◽  
Experimental Program ◽  
Small Punch Test ◽  
Test Technique ◽  
Small Punch ◽  
Punch Test ◽  
Medium Strength ◽  
Step Loading ◽  
Incremental Step

Abstract In this work, the incremental step loading technique to measure hydrogen embrittlement threshold in steels from ASTM F1624 standard is applied to the Small Punch test technique. For the experimental program, a medium strength steel is employed, simulating the hydrogen embrittlement environment by a cathodic polarization of 5 mA/cm2 in an acid electrolyte mainly consisting of 1N H2SO4 in H2O. Regular standard tests on cylindrical tensile specimens were carried out under the same environment following the ASTM F1624 standard, observing the same trends in both cases, which validates the methodology proposed. In order to adapt the aforementioned standard to small punch testing, the duration of the loading steps had to be modified, proposing much shorter ones according to the Small Punch specimen dimensions and the punch rate taking place in these scenarios, which is pointed in bibliography. This proposal allows to obtain a threshold load by using at least 3 specimens in a total time of around a week.

Effects of Cathodic Protection on Cracking of High-Strength Pipeline Steels

2010 ◽  
Author(s):  
M. Elboujdaini ◽  
R. W. Revie ◽  
M. Attard
Keyword(s):  
Hydrogen Embrittlement ◽  
Cathodic Protection ◽  
Cathodic Polarization ◽  
Water Solution ◽  
Reference Electrode ◽  
High Strength ◽  
Point Of View ◽  
Pipeline Steels ◽  
Different Levels ◽  
Reduction Index

A comparison was made between four strength levels of pipeline steels (X-70, X80, X-100 and the X-120) from the point of view of their susceptibility to hydrogen embrittlement under cathodic protection. The main aim was to determine whether the development of higher strength materials led to greater susceptibility to hydrogen embrittlement. This was achieved by straining at 2×10−6 s−1 after cathodic charging in a simulated dilute groundwater solution (NS4) containing 5% CO2/95% N2 (pH approximately 6.7). The results showed quantitatively the loss of ductility after charging, and the loss of ductility increases with strength level of the steel. All four steels exhibited a loss of ductility at overprotected charging potential and an increasing amount of brittleness on the fracture surface. Ductility in solution was measured under four different levels of cathodic protection, ranging from no cathodic protection to 500 mV of overprotection with respect to the usually accepted criterion of −850 mV vs. Cu/CuSO4 reference electrode. Experiments were carried out by straining during cathodic polarization in a simulated dilute ground water solution (NS-4 solution). Strain rates used were 2×10−6 s−1. After failure, the fracture surfaces were characterized by examination using scanning electron microscopy (SEM). Under cathodic protection, all four steels showed loss of ductility and features of brittle fracture. The loss of ductility under cathodic polarization was larger the greater the strength of the steel and the more active (i.e., more negative) the applied potential. The Ductility Reduction Index (DRI) was defined to quantify the reduction in ductility.

Behavior of Self Compacted Concrete Ferrocement Beams

2021 ◽  
pp. 1-14
Author(s):  
Abeer M. Erfan ◽  
Tamer H. K. Elafandy ◽  
Mahmoud M. Mahran ◽  
Mohamed Said
Keyword(s):  
Energy Absorption ◽  
Low Cost ◽  
Steel Wire ◽  
Construction Material ◽  
Point Load ◽  
Wire Mesh ◽  
Experimental Program ◽  
Cracking Behavior ◽  
Group B ◽  
Wire Meshes

Many researchers have been conducted on the ferrocement as a low cost construction material and a flexible structural system. This experimental investigation on the behavior of ferrocement beams after exposed to different type of ferrocement and different of ferrocement layer are presented in this paper. The experimental program consisted of seven simply supported beams tested up to failure under four-point load. The dimensions of 150mm×250mm×2000mm. Each beam was reinforced using steel 2 f 12 in top and 2 f10 in bottom and the stirrups was 10 f 10/m. In addition to six of them contains ferrocement different steel wire meshes and different of ferrocement layer. The test specimens are divided in three groups and the results of each one compared with the control specimen. The first group (A) which used the welded wire mesh. The second group (B) which used the expanded wire mesh. But the third group (C) which reinforced using woven wire mesh. The mid span deflection, cracks, reinforcement and concrete strains of the tested beams were recorded and compared. The performance of the test beams in terms of ultimate flexure load cracking behavior and energy absorption were investigated. The experimental results emphasized that high ultimate loads, better crack resistance control, high ductility, and good energy absorption properties could be achieved by using the proposed ferrocement beams. The cracks propagation decreased and its number and width decreased by using woven, expanded and welded wire mesh especially in specimens with two layers of wire mesh. Theoretical calculation was carried out to compare the oplained results with the theoretical ones, which show good agreement.

scholarly journals Effect of Steel Fibers on the Hysteretic Performance of Concrete Beams with Steel Reinforcement—Tests and Analysis

Materials ◽  
2020 ◽  
Vol 13 (13) ◽  
pp. 2923 ◽  
Author(s):  
Violetta K. Kytinou ◽  
Constantin E. Chalioris ◽  
Chris G. Karayannis ◽  
Anaxagoras Elenas
Keyword(s):  
Reinforced Concrete ◽  
Steel Reinforcement ◽  
Steel Fibers ◽  
Experimental Program ◽  
Engineering Practice ◽  
Cracking Behavior ◽  
Tension Softening ◽  
Proposed Model ◽  
Hysteretic Performance ◽  
Cracking Performance

The use of fibers as mass reinforcement to delay cracking and to improve the strength and the post-cracking performance of reinforced concrete (RC) beams has been well documented. However, issues of common engineering practice about the beneficial effect of steel fibers to the seismic resistance of RC structural members in active earthquake zones have not yet been fully clarified. This study presents an experimental and a numerical approach to the aforementioned question. The hysteretic response of slender and deep steel fiber-reinforced concrete (SFRC) beams reinforced with steel reinforcement is investigated through tests of eleven beams subjected to reversal cyclic loading and numerical analysis using 3D finite element (FE) modeling. The experimental program includes flexural and shear-critical SFRC beams with different ratios of steel reinforcing bars (0.55% and 1.0%), closed stirrups (from 0 to 0.5%), and fibers with content from 0.5 to 3% per volume. The developed nonlinear FE numerical simulation considers well-established relationships for the compression and tensional behavior of SFRC that are based on test results. Specifically, a smeared crack model is proposed for the post-cracking behavior of SFRC under tension, which employs the fracture characteristics of the composite material using stress versus crack width curves with tension softening. Axial tension tests of prismatic SFRC specimens are also included in this study to support the experimental project and to verify the proposed model. Comparing the numerical results with the experimental ones it is revealed that the proposed model is efficient and accurately captures the crucial aspects of the response, such as the SFRC tension softening effect, the load versus deformation cyclic envelope and the influence of the fibers on the overall hysteretic performance. The findings of this study also reveal that SFRC beams showed enhanced cyclic behavior in terms of residual stiffness, load-bearing capacity, deformation, energy dissipation ability and cracking performance, maintaining their integrity through the imposed reversal cyclic tests.

Effect of Creep Relaxation on the Delayed Hydride Cracking Behavior of Irradiated Zirconium 2.5%Wt Niobium Pressure Tube Material

2006 ◽  
Author(s):  
Heather Chaput ◽  
Brian W. Leitch ◽  
Don R. Metzger
Keyword(s):  
High Stress ◽  
Local Stress ◽  
Operating Conditions ◽  
Experimental Results ◽  
Pressure Tube ◽  
Experimental Program ◽  
Tube Material ◽  
Cracking Behavior ◽  
Delayed Hydride Cracking ◽  
Hydride Cracking

Surface scratches and flaws encountered in CANDU nuclear pressure tubes must be evaluated to ensure that a cracking mechanism, called delayed hydride cracking (DHC), is not initiated. The stress concentration due to a flaw can cause diffusion of hydrogen and precipitation of zirconium hydride at the flaw tip. The presence of a hydride results in reduced fracture resistance in a local region where high stress prevails. In many cases, flaws exist for an extended period of time before the hydrogen content in the base material is sufficient to form a hydride. In this situation high stress creep can significantly relax the local stress at the flaw tip. The assessment of flaws on the basis of local stress distribution not considering creep is expected to be overly conservative, and may result in unnecessary remedial action in reactor operation and maintenance procedures. An experimental program has been developed to isolate and quantify the effect of creep on DHC in irradiated Zr-2.5%Nb pressure tube material. As part of this program, the thermal and load histories relevant to reactor operating conditions have been considered, and initial experimental results indicate that the action of creep increases the threshold load for crack initiation. Finite element analysis of creep relaxation around a hydride also supports the experimental results, and a fracture initiation model is applied to the experimental conditions in order to establish an analytical trend for the effect of creep. The quantitative effect predicted by the model is in reasonable agreement with the experimental results, and an improved, less conservative assessment procedure that accounts for creep is deemed to be practical.

Derivatization and Cleanup Improvements in Determination of Residues of Glyphosate and Aminomethylphosphonic Acid in Blueberries

1982 ◽  
Vol 65 (1) ◽  
pp. 35-39 ◽  
Author(s):  
Richard A Guinivan ◽  
Neal P Thompson ◽  
Willis B Wheeler
Keyword(s):  
Handling Time ◽  
Low Ph ◽  
Electron Capture Detection ◽  
Aqueous Environment ◽  
Sample Handling ◽  
Aminomethylphosphonic Acid ◽  
Gel Permeation ◽  
Cation Exchange Column ◽  
Derivatives Of

Abstract A new method based on development of the 2-chloroethyl N-heptafluorobutyryl derivatives of glyphosate and its major metabolite aminomethylphosphonic acid is reported for fortified blueberry samples. The concentrated aqueous extract is chromatographed on a gel permeation column in a low pH eluant. Under these conditions, sugar is eliminated by permeation and pigments are strongly adsorbed. Additional sugar is eliminated with a small cation exchange column and then the sample is easily dried and derivatized. The derivatized compounds are extracted from an aqueous environment with hexane and analyzed by gas chromatography with electron capture detection. This procedure requires significantly less sample handling time and provides greater sensitivity for glyphosate than the commonly used procedure recommended by EPA.

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