Stress Corrosion Cracking Conditions Research Articles

Data Mining Applied to the Electrochemical Noise Technique in the Time/Frequency Domain for Stress Corrosion Cracking Recognition

In this paper, time/frequency domain data processing was proposed to analyse the EN signal recorded during stress corrosion cracking on precipitation-hardening martensitic stainless steel in a chloride environment. Continuous Wavelet Transform, albeit with some limitations, showed a suitable support in the discriminatory capacity among transient signals related to the different stress corrosion cracking mechanisms. In particular, the aim is to propose the analysis of electrochemical noise signals under stress corrosion cracking conditions in the time–frequency domain by using the Hilbert–Huang approach. The Hilbert–Huang Transform (performed by the Empirical Mode Decomposition approach) was finally proposed to carry out an identification of the corrosion mechanisms in comparison to conventional data processing methods. By using this approach, a detailed simultaneous decomposition of the original electrochemical noise data in the time and frequency domain was carried out. The method gave useful information about transitions among different corrosion mechanisms, allowing us to (i) identify a specific characteristic response for each corrosion damaging phenomenon induced by stress corrosion cracking, (ii) time each corrosion of the damaging phenomenon, and (iii) provide a topological description of the advancing SCC damaging stages. This characteristic evidences that the Hilbert–Huang Transform is a very powerful technique to potentially recognize and distinguish the different corrosion mechanisms occurring during stress corrosion cracking.

Notch sensitivity and short cracks tolerance in a super 13Cr stainless steel under sulfide stress corrosion cracking conditions

Abstract Notch sensitivity under sulfide stress corrosion cracking (SSC) conditions is quantified in this work, considering its tolerance to short cracks that start at notch tips and become non-propagating after growing for a short while. The considered material is an UNS S41426 super 13Cr5Ni2Mo martensitic stainless steel, frequently used in pipelines to transport aggressive fluids in offshore applications. Tolerance to short SCC cracks depends on the notch size and shape, on the stress gradient ahead of its tip, and on basic material resistances to crack initiation S SSC and growth K ISSC inside the aggressive environment. The proposed notch-sensitivity model can be a powerful and economical alternative design tool to substitute traditional pass/non-pass criteria normally used to choose materials for SSC and similar environmentally assisted cracking (EAC) service conditions. This model is validated by testing the steel into an aqueous solution of 100 g/L of Cl−, pH 4.0, 25 kPa of H2S, and 75 kPa of CO2, at 23 ± 2 °C. After measuring S SSC (461 ± 23 MPa) and K ISSC (36.9 ± 0.6 MPa√m), short crack tolerance predictions are verified on notched specimens loaded under a peak stress at their tips σ max = 0.95⋅S Y >> S SSC, where S Y = 826 MPa is the yield strength of the tested steel.

Сравнительный анализ влияния технологических дефектов на прочность оболочек из сплава Э110 в условиях коррозионного растрескивания под напряжением

The article provides comparative analysis of data on the influence of technological defects on the long-term strength of fuel cladding ∅ 9,1 × 0,65 mm of alloy E110 (Э110) under conditions of stress-corrosion cracking in the environment of iodine, obtained in recent years. The experimental results of stress corrosion cracking of fuel cladding in iodine environment are compared with the test data of fuel cladding made of alloy E110 in the state of delivery, with artificial and technological defects on the inner surface. On the basis of experimental results of stress-corrosion cracking research of irradiation fuel cladding × 9,1 × 0,65 mm E110 of the alloy E110 it is recommended to use the value of the threshold stress as σscc = ∼ 280 MPa at the temperature T = 350 °C in environment of iodine (iodine concentration ∼ 0,2 mg/sm2)

Simulation of Initiation and Development of Corrosion Cracks in Zirconium Fuel Claddings Under Conditions of Stress Corrosion Cracking in Environment of Iodine

The process models of iodine corrosion cracking of zirconium fuel claddings, used to calculate the durability of the cladding (time for loss of tightness) are considered. A method for determining the corrosion crack propagation rate in claddings made of E110 alloy Ø 9.1 × 0.65 mm and the results of corresponding studies (estimation of corrosion crack propagation rate and stress intensity factor KISCC) are given at a temperature of 380 °C in iodine environment at a concentration of ~ 0.2 mg/cm2. Studies were performed using tubular samples with a fatigue crack. A fatigue crack on the inner surface of cladding made of E110 Ø 9.1 × 0.65 mm alloy is the initiator of a corrosion crack emergence (nucleation). The results of corresponding studies are consistent with data from the literature. The proposed study of the corrosion cracking process of fuel claddings in accordance with the results of fracture mechanics is of practical importance for substantiation of the regulation of reactor operating conditions

Influence of Periodic Removal of the Surface Layer of Metal on the Life of Samples of Low-Alloy Steels in Conditions of Stress Corrosion Cracking

Influence of Periodic Removal of the Surface Layer of Metal on the Life of Samples of Low-Alloy Steels in Conditions of Stress Corrosion Cracking

Stress Corrosion Cracking of Progressively Cold-Drawn Pearlitic Steels: From Tintoretto to Picasso

Progressive cold drawing in eutectoid steels produces a preferential orientation of the pearlitic microstructure in the wire axis or drawing direction. This affects the posterior behaviour of the steels under conditions of stress corrosion cracking (SCC). The experimental results show that cold drawing induces strength anisotropy in the steel, and thus the resistance to SCC is a directional property that depends on the angle in relation to the drawing direction. Therefore, an initial transverse crack changes its propagation direction to approach that of the wire axis, thus producing mixed mode propagation, the deflection angle being an increasing function of the cold drawing degree. This experimental result may be explained by micro-mechanical considerations on the basis of the lamellar microstructure of the steels. A relationship is established between the microstructural angles and the deflection angles of the macroscopic SCC crack, thus providing a materials science type relationship between the microstructure and the macroscopic crack paths with regard to hydrogen assisted cracking (HAC) associated with the cathodic regime and in the matter of localised anodic dissolution (LAD) linked to the anodic regime. Whereas in hot rolled (not cold drawn at all) and slightly drawn steels the phenomenon of SCC develops in mode I, i.e., the SCC crack is a straight line linked with the classical linear perspective painting by Tintoretto, in the case of heavily drawn steels, the SCC deflected crack is a polygonal line associated with the multi-perspective cubist painting by Picasso, these conclusions being valid for both HAC and LAD.

Effects of remedial actions on small piping reliability

This article describes probabilistic calculations that address intergranular stress corrosion cracking of stainless steel piping; a degradation mechanism of major concern to nuclear pressure boundary integrity. The objective is to simulate the cracking of stainless steel piping under intergranular stress corrosion cracking conditions, and to evaluate the structural reliability using remedial actions for intergranular stress corrosion cracking that are limited to benefits of in-service inspections and the induction heating stress improvement process. The results show that an effective in-service inspection requires a suitable combination of flaw detection capability and inspection schedule, and it has been suggested that the residual stresses could be altered to become favorable, thereby improving the reliability piping.

Modeling of SCC initiation and propagation mechanisms in BWR environments

During operation of mainly BWRs’ (Boiling Water Reactors) excursions from recommended water chemistries may provide favorite conditions for stress corrosion cracking (SCC). Maximum levels for chloride and sulfate ion contents for avoiding local corrosion are therefore given in respective water specifications. In a previously published deterministic 288 °C – corrosion model for Nickel as a main alloying element of BWR components it was demonstrated that, as a theoretically worst case, bulk water chloride levels as low as 30 ppb provide local chloride ion accumulation, dissolution of passivating nickel oxide and precipitation of nickel chlorides followed by subsequent local acidification. In an extension of the above model to SCC the following work shows that, in a first step, local anodic path corrosion with subsequent oxide breakdown, chloride salt formation and acidification at 288 °C would establish local cathodic reduction of accumulated hydrogen ions inside the crack tip fluid. In a second step, local hydrogen reduction charges and increasing local crack tip strains from increasing crack lengths at given global stresses are time stepwise calculated and related to experimentally determined crack critical cathodic hydrogen charges and fracture strains taken from small scale SSRT tensile tests pieces. As a result, at local hydrogen equilibrium potentials higher than those of nickel in the crack tip solution, hydrogen ion reduction initiates hydrogen crack propagation that is enhanced with increasing global stresses. In accordance with respective experimental literature data it is shown that decreasing chloride and increasing pH levels of the primary bulk water at 288 °C reduce the total crack propagation rates including anodic path corrosion as well as hydrogen cracking. It is also demonstrated that crack propagation rates can be significantly suppressed by hydrogen water chemistry (HWC) that leads to reduction of bulk surface corrosion potentials. As a conclusion the extended SSC-model for nickel supplies quantitative insight into the frequently controversially discussed high temperature SCC mechanisms of a basic alloying element of BWR components.

Modeling the effects of nuclear environments on crevice corrosion of pure nickel by coupling of phase and polarization behavior

As from long-term operating experience the high purity primary water cycle of light water nuclear reactors may exhibit excursions from the recommended water chemistry leading to potentially favorite conditions for stress corrosion cracking (SCC) which may be initiated and its propagation controlled by local pitting and crevice corrosion. Deterministic modeling of local corrosion including incubation times for crevice corrosion should therefore provide a basis for lifetime predictions of components, which have been subjected to sporadic intermediate water chemistry fluctuations. Based on previous work for room temperature (RT), the chloride-induced crevice corrosion at 288 °C of pure nickel as an important base element in respective high alloyed nuclear materials is modeled by coupling anodic polarization with the precipitation of nickel oxide and nickel chloride calculated from the water–hydrogen–nickel chloride heterogeneous phase equilibrium diagram. The surface corrosion potentials are fixed by bulk levels of hydrogen and oxygen contents as well as pH simulating hydrogen treatment of irradiation subjected cooling water for the reduction of corrosion potentials and mitigation of SCC at operating temperature 288 °C in Boiling Water Reactors (BWRs). Assuming chemical equilibrium conditions during the selected time steps in a relevant component crevice the calculated change of the crevice solution composition is quantitatively shown to initiate crevice corrosion by the breakdown of the passive nickel oxide layer followed by the formation of non-passive nickel chloride and the subsequent acidification of the crevice solution. The effects of corrosion potentials, bulk levels of pH and chlorides, are investigated. As a result, the reduction of corrosion potentials and increase in bulk pH provide significant increases in the passive layer breakdown times and acidification times inside the crevice. Depending on bulk pH and corrosion potentials the reduction of bulk chlorides down to recommended levels in BWRs retards crevice corrosion significantly. For a standard 100,000 h time for crevice acidification to locally less than pH = 0 the respective chloride–pH domain is evaluated. Such diagrams may be related to respective effects on stress corrosion cracking and its mitigation by hydrogen water chemistry (HWC).

Failure analysis of ferritic stainless steel locking ring

A locking ring made of Ferritic stainless steel, fitted in a pressure gauge, failed after the service of seven years. The mode of failure was analyzed by using Scanning Electron Microscope and optical microscope. A finite element model proposed in this work demonstrated the stress distribution in different regions of the locking ring. It was observed that the ring failed in the same region where the maximum stresses were predicted. Furthermore, a detailed study on the mode of failure found that the failure occurred in stress corrosion cracking conditions.

Electrochemical impedance and current fluctuations analysis during slow strain rate test of a UNS S30400 stainless steel in low pH media

This paper is aimed at investigating the electrochemical behavior of austenitic stainless steel UNS S30400 under stress corrosion cracking conditions in acidic solutions at room temperature. Electrochemical impedance spectroscopy and electrochemical current noise measurements were performed at different stress levels during slow strain rate tests at pH 0.00 and 1.00 in order to evaluate the influence of mechanical deformation on the evolution of the electrochemical responses of the interface. Results have shown that, differently to what happens at pH 1.00, the corrosive attack at pH 0.00 is characterized by intensive cracking concomitantly to the progressive spreading out of uniform corrosion on the metallic surface. The coupling of both electrochemical impedance and current noise techniques provided complementary information about the interplay between dissolution and cracking of the stainless steel exposed to electrolytes of different aggressiveness.

Prediction of the remaining lifetime of stainless steels under conditions of stress corrosion cracking

AbstractThe prediction of the lifetime of metal structures and equipment under conditions of stress corrosion is very complicated because of the complexity of this process of degradation. Recently a new method, based on the so‐called corrosion elongation curves, has been found, which can be used to predict the time to failure under these conditions. By upgrading of these curves (and thus obtaining Upgraded Corrosion Elongation Curves – UCEC's) it has been possible to obtain a precise definition of the time needed for the initiation of the corrosion crack, and for its stable growth. It is upon this basis that diagrams for the prediction of remaining lifetime (DPRL's) have been developed. DPRL's can also be used to predict the values of various critical parameters which have to be achieved if a stress corrosion crack is to occur.

The initiation of cracks in cladding tubes of Zr-1%Nb alloy under stress corrosion cracking conditions

The initiation of cracks in cladding tubes of Zr-1%Nb alloy under stress corrosion cracking conditions

Mössbauer study of surface films on steels formed in phosphate environments under stress-corrosion cracking conditions

A study on the composition of the surface films and corrosion products of mild and low-alloy (2% Cr) steels in 1M NaH2PO4 under stress-corrosion cracking (SCC) conditions has been carried out using Mossbauer spectroscopy. At potentials in the SCC region the films formed on both steels contain Fe3(PO4)2.4H2O, Fe3(PO4)2.8H2O and FePO4.xH2O. The precipitates in the solution formed under these conditions consist of FePO4.xH2O and iron(III) hydrogen phosphate [most probably Fe(H2PO4)3.2H2O]. An attempt has been made to relate the surface film composition to SCC susceptibility.

Environment and R-ratio effects on fatigue crack propagation transitions in Ti-6A1-4V (ELI)

The multiple-sloped relationship between da/dN and AK in stage II fatigue crack propagation regime in most engineering alloys has been a subject of considerable research efforts. Even though the crack closure is recognized as a crucial factor affecting FCP rates, closure effect on transition behavior is often ignored due to the uncertainties associated with ΔKeff value and the difficulties in measuring closure especially in aqueous environment. The present study therefore focused on the closure-free transition behavior in mill annealed Ti-6A1-4V in moist air and 1% NaCl at a fixed potential of -500 mVSCE as a function ofR ratio. The complex da/dN-ΔK relationship in Ti-6A1-4V remains after closure-correction for eachR ratio and environment, suggesting that closure is not a controlling factor for a transition, while it may complicate transition behavior. After closure-correction, the transition points and slopes are insensitive to R ratio in moist air, suggesting that R ratio effect on transition behavior in moist air is mostly due to crack closure. The 1% NaCl solution further complicates the da/dN-ΔKeff shape in Ti-6A1-4V at R ratios of 0.1 and 0.4 by superimposing cyclic stress corrosion cracking (SCC)-induced transition at intermediate ΔK regime. Varying R ratio in 1% NaCl is complex and appears to modify the cyclic and/or static SCC contribution.

On the influence of ion-induced surface modification on localized corrosion of aluminium

Modern surface modification techniques offer means for changing properties of materials related to physical or chemical reactions at or near the surface. Thus the corrosion behaviour of metals can be affected by applying this method. The influence of Mg and Cr ion implantation and coatings with Zr or Si thin films on the corrosion properties of aluminium and an aluminium alloy was studied. Corrosion measurements were performed under pitting and stress corrosion cracking conditions. The pitting measurements took place in aerated aqueous solution of 2 wt.% NaCl at 25 °C. The resistance against stress corrosion cracking was measured using a method according to ASTM G44, i.e. alternating immersion in an aqueous solution containing 3.5 wt.% NaCl under a constant strain of 100 MPa. The results showed that ion-induced surface modifications can lead to a better corrosion resistance of aluminium. Pitting could be reduced by Cr implantation as well as thin coatings of chromium and zirconium. The initiation of stress corrosion cracking was suppressed for a prolonged period of 890 h with an ion beam mixed Zr coating, in comparison with 39 h for the untreated sample. The results of the corrosion measurements in combination with the other studies lead to the assumption that under the given conditions pitting is not a prerequisite for stress corrosion cracking of the investigated Al alloy.

The Influence of Crack Length on SCC Crack Growth Behavior of High-Strength Steel under Dynamic Loading Conditions

The influences of crack length on stress corrosion cracking (SCC) crack growth of a 523K tempered high·strength steel, SCM435H (ΔB=1 770 MPa) immersed in 3.5 % NaCl solution were investigated under dynamic loading conditions : static SCC under a sustained load, dynamic SCC under a sustained load with high frequency vibratory stresses superimposed, and cyclic SCC under 10w frequency variation. Threshold values of static and dynamic SCC of short crack, whose crack length from notch root, l, ranged from 1.52 mm to 2.81 mm, were smaller than those of long crack (l= 6.86-9.78 mm). Dissolution of fracture surface was more prevalent in short crack than in long crack, and a decrease in threshold values of short crack is considered to be caused by increased hydrogen uptake at the crack tip associated with accelerated dissolution of fracture surfaces compared to long crack. Crack growth rates of short crack (1l6.5 mm) at the plateau region were also accelerated compared to those of long crack (l>6.5 mm). Static SCC crack growth rates of long crack were accelerated and the threshold value was lowered by deaeration of the solution. However, the deaeration had no influence on crack growth rates of static SCC of short crack. In the case of cyclic SCC at R=0.1, no influence of crack length (1>1.18 mm) on crack growth rates was observed. But at R =0.5, crack growth rates of short crack were accelerated compared to those of long crack.

The influence of crack length on SCC crack growth behavior of high-strength steel under dynamic loading conditions.

The influences of crack length on stress corrosion cracking (SCC) crack growth of a 523K tempered high·strength steel, SCM435H (ΔB=1 770 MPa) immersed in 3.5 % NaCl solution were investigated under dynamic loading conditions : static SCC under a sustained load, dynamic SCC under a sustained load with high frequency vibratory stresses superimposed, and cyclic SCC under 10w frequency variation. Threshold values of static and dynamic SCC of short crack, whose crack length from notch root, l, ranged from 1.52 mm to 2.81 mm, were smaller than those of long crack (l= 6.86-9.78 mm). Dissolution of fracture surface was more prevalent in short crack than in long crack, and a decrease in threshold values of short crack is considered to be caused by increased hydrogen uptake at the crack tip associated with accelerated dissolution of fracture surfaces compared to long crack. Crack growth rates of short crack (1l6.5 mm) at the plateau region were also accelerated compared to those of long crack (l>6.5 mm). Static SCC crack growth rates of long crack were accelerated and the threshold value was lowered by deaeration of the solution. However, the deaeration had no influence on crack growth rates of static SCC of short crack. In the case of cyclic SCC at R=0.1, no influence of crack length (1>1.18 mm) on crack growth rates was observed. But at R =0.5, crack growth rates of short crack were accelerated compared to those of long crack.

The influences of small vibratory stresses and anisotropy of grains on SCC strength in aluminum alloys.

The influences of small vibratory stresses and the loading axis against grain flow directions on the initiation behavior of stress corrosion cracking (SCC) were investigated in high-strength aluminum alloys sensitive to active path corrosion type SCC. Irrespective of loading direction, the strength of dynamic SCC under a sustained load with small superimposed vibratory stresses (≧59MPa) was considerably lower than that of static SCC under a sustained load, σscc. The static SCC resistance in the TT orientation, where the loading axis is normal to the rolling direction, was superior to that in the LL orientation, where the loading axis is parallel to the rolling direction. Under dynamic loading, on the contrary, the strength in the LL orientation was higher than that in the TT orientation. Static SCC cracks under a sustained load were initiated at grain boundaries, whereas dynamic SCC cracks were initiated at grain boundaries, hydrogen-induced {111} plain cleavages, and transgranular sites associated with corrosion fatigue.

The influences of small vibratory stresses and anisotropy of grains on SCC strength in aluminum alloys.

The influences of small vibratory stresses and the loading axis against grain flow directions on the initiation behavior of stress corrosion cracking (SCC) have been investigated on high-strength aluminum alloys sensitive to active path corrosion type SCC. Irrespective of loading directions, the strength of dynamic SCC under a sustained load with small vibratory stresses (>59 MPa) super-imposed was considerably lower than that of static SCC under a sustained load, σSCC. The static SCC resistance in the TT orientation, where the loading axis is normal to the rolling direction, was superior to that in the LL orientation, where the loading axis is parallel to the rolling direction. Under dynamic loading, on the contrary, the strength in the LL orientation was higher than that in the TT orientation. Static SCC cracks were initiated at intergranular cracks, whereas the initiation sites of dynamic SCC were intergranular cracks, hydrogen-induced {111} plain cleavage fracture, and transgranular cracks associated with corrosion fatigue.