Detection Of Stress Corrosion Cracking Research Articles

Review of Prediction of Stress Corrosion Cracking in Gas Pipelines Using Machine Learning

Pipeline integrity and safety depend on the detection and prediction of stress corrosion cracking (SCC) and other defects. In oil and gas pipeline systems, a variety of corrosion-monitoring techniques are used. The observed data exhibit characteristics of nonlinearity, multidimensionality, and noise. Hence, data-driven modeling techniques have been widely utilized. To accomplish intelligent corrosion prediction and enhance corrosion control, machine learning (ML)-based approaches have been developed. Some published papers related to SCC have discussed ML techniques and their applications, but none of the works has shown the real ability of ML to detect or predict SCC in energy pipelines, though fewer researchers have tested their models to prove them under controlled environments in laboratories, which is completely different from real work environments in the field. Looking at the current research status, the authors believe that there is a need to explore the best technologies and modeling approaches and to identify clear gaps; a critical review is, therefore, required. The objective of this study is to assess the current status of machine learning’s applications in SCC detection, identify current research gaps, and indicate future directions from a scientific research and application point of view. This review will highlight the limitations and challenges of employing machine learning for SCC prediction and also discuss the importance of incorporating domain knowledge and expert inputs to enhance the accuracy and reliability of predictions. Finally, a framework is proposed to demonstrate the process of the application of ML to condition assessments of energy pipelines.

Simulation of wave propagation in austenitic stainless steel welds with solidification structure predicted by Cellular Automaton method

Austenitic stainless steel is widely used in nuclear power plants (NPPs) and a variety of occurrences of stress corrosion cracking (SCC) near its weld have been reported among NPPs. Ultrasonic testing is a critical technique for the detection and depth sizing of SCCs. However, such welds' anisotropic and heterogeneous properties cause difficulties in ultrasonic testing when ultrasonic waves propagate through welds. Deeply understanding the characteristics of ultrasonic waves with wave propagation simulation is effective to improve the accuracy of ultrasonic testing. To this end, it is necessary to take crystal orientation and grain boundary into account simultaneously in the numerical model. In this study, a model was developed so that the Cellular Automaton (CA) method can simulate the solidification structure from multilayer and multipass welding process, then the solidification structure of a 7-layer and 7-pass weld of austenitic stainless steel was predicted based on welding conditions. Finally, the finite element method was used to compute wave propagation in austenitic stainless steel weld with the solidification structure predicted. Numerical results of wave propagation in austenitic stainless steel weld were compared to those obtained by experiment.

Real-time monitoring of stress corrosion cracking in 304 L stainless steel pipe using acoustic emission

A stress corrosion cracking (SCC) monitoring indicator (MI) based on the acoustic emission (AE) technique is proposed for the real-time detection and monitoring of SCC initiation in 304 L stainless steel (SS) pipes used for the primary circuits of nuclear power plants (NPPs). A device is used to accelerate the initiation of SCC to shorten the experiment timeframe. A non-crack AE signal criterion was established, which was conducted by injecting an etchant and distilled water into 304 L SS pipe specimens as experimental and control groups, respectively. Furthermore, to characterize the AE signal responsible for cracking, the characteristics of the AE signal measured in the section between necking and fracture (where cracks occur and propagate) among the stress curves obtained from the 304 L SS tensile test using AE sensors were investigated. Subsequently, the maximum amplitude, energy, frequency characteristics (range and magnitude), and waveform of the remaining AE signals were investigated after removing some AE signals by applying the non-crack AE signal criterion in the experiment where the SCC penetrated the pipe. These were compared with the maximum amplitude, energy, frequency characteristics, and waveform which were investigated in the tensile test to derive common characteristics for the two sets of crack signals to establish an SCC MI. To evaluate the performance of the developed SCC MI, the SCC monitoring experiment was halted when AE signals corresponding to the SCC MI criteria were measured, to fabricate a pipe wherein non-penetrating SCC was formed. In this manner, by applying the SCC MI to detect SCC in real time, we verified that the SCC MI had excellent SCC detection performance. Furthermore, we performed scanning electron microscopy (SEM) image analyses and SEM-energy dispersive X-ray spectrometry analyses to investigate the causes of SCC propagation.

New test method for real-time measurement of SCC initiation of thin disk specimen in high-temperature primary water environment

In this study, a new rupture disk corrosion test (RDCT) method was developed for real-time detection of stress corrosion cracking (SCC) initiation of Alloy 600 in a primary water environment of pressurized water reactors. In the RDCT method, one side of a disk specimen was exposed to a simulated primary water at high temperature and pressure while the other side was maintained at ambient pressure, inducing a dome-shaped deformation and tensile stress on the specimen. When SCC occurs in the primary water environment, it leads to the specimen rupture or water leakage through the specimen, which can be detected in real-time using a pressure gauge. The tensile stress applied to the disk specimen was calculated using a finite element analysis. The tensile stress was calculated to increase as the specimen thickness decreased. The SCC initiation time of the specimen was evaluated by the RDCT method, from which result it was found that the crack initiation time decreased with the decrease of specimen thickness owing to the increase of applied stress. After the SCC initiation test, many cracks were observed on the specimen surface in an intergranular fracture mode, which is a typical characteristic of SCC in the primary water environment.

Assessment and detection of stress corrosion cracking by advanced eddy current array nondestructive testing and material characterization

Oil and natural gas pipelines are under a combination of loading (stresses) due to their pressurized content and some kind of corrosive environmental operational condition including the content materials as well as soil side which is called Stress Corrosion Cracking (SCC). Since the SCC occurs at stresses within the range of typical design stresses, it can cause catastrophic failures without a significant indication in pipeline integrity beforehand. Efficient Nondestructive Inspection (NDI) during the operational life of the structures can prevent such failures by providing accurate information regarding size and characteristics of the SCC flaws. Since majority of SCC defects occur in surface and near surface regions of metallic pipeline, electromagnetic NDI (Eddy Current) is proved to be a promising inspection technique. In this study, Eddy Current Array (ECA) methodology, as a recent advancement and developed version of traditional Eddy Current (EC) NDI technique, was used for assessment of SCC generated in steel samples representing steel pipeline's material in a laboratory setup. ECA as an advanced eddy current NDI uses an array of eddy current coils to provide the scanning image of the inspection area. Prefabricated notches and SCC after a period of load-corrosion application to the samples were detected and characterized. Accuracy and repeatability of the results showed the efficiency of ECA for SCC characterization.

Nonlinearity from stress corrosion cracking as a function of chloride exposure time using the time reversed elastic nonlinearity diagnostic.

The Time Reversed Elastic Nonlinearity Diagnostic (TREND) has a long history of successful nondestructive detection of cracks in solids using nonlinear indicators. Recent research implemented TREND to find stress corrosion cracking (SCC) in the heat-affected zone adjacent to welds in stainless steel. SCC development around welds is likely to occur due to the temperature and chemical exposure of steel canisters housing spent nuclear fuel. The ideal SCC detection technique would quantify the size and extent of the SCC, rather than just locating it, as TREND has been used for in the past. The current paper explores TREND's ability to detect an assumed increase in SCC over time using 13 samples exposed to a magnesium chloride (MgCl2) bath for different lengths of time. The samples are then scanned with TREND and nonlinearity is quantified for each scan point and each sample. The results suggest that TREND can be used to not only locate SCC in the heat-affected zone, but also track an increase in nonlinearity, and thereby an increase in damage, in samples exposed to the MgCl2 solution for a longer duration.

Nondestructive inspection of spent nuclear fuel storage canisters using shear horizontal guided waves

Nondestructive inspection (NDI) is an integral part of structural integrity analyses of dry storage casks that house spent nuclear fuel. One significant concern for the structural integrity is stress corrosion cracking in the heat-affected zone of welds in the stainless steel canister that confines the spent fuel. In situ NDI methodology for detection of stress corrosion cracking is investigated, where the inspection uses a delivery robot because of the presence of the harsh environment and geometric constrains inside the cask protecting the canister. Shear horizontal (SH) guided waves that are sensitive to cracks oriented either perpendicular or parallel to the wave vector are used to locate welds and to detect cracks. SH waves are excited and received by electromagnetic acoustic transducers (EMATs) using noncontact ultrasonic transduction and pulse-echo mode. A laboratory-scale canister mock-up is fabricated and inspected using the proposed methodology to evaluate the ability of EMATs to excite and receive SH waves and to locate welds. The EMAT's capability to detect notches from various distances is evaluated on a plate containing 25%-through-thickness surface-breaking notches. Based on the results of the distances at which notch reflections are detectable, NDI coverage for spent nuclear fuel storage canisters is determined.

Stress Generation Accompanying Intergranular Corrosion of X70 Steel

Stress corrosion cracking (SCC) is a primary degradation mode in steel oil and gas pipelines (1). Pre-emptive detection and control of SCC of pipeline steel in high-pH soils is difficult owing to a prolonged incubation stage of precursory intergranular corrosion (IGC). In high-pH environments, pipeline steel exhibits greatest susceptibility to SCC within a narrow potential range between the active dissolution peak potential and the passivation potential, which may suggest an important role for oxide formation (2,3). In the present work, IGC is characterized by electrochemical and microscopic measurements together with in situ stress monitoring. The latter method is well-suited to detect stress generated by internal grain boundary oxidation (4). Low-carbon ferritic steel samples (X70 type) were cut from a pipeline specimen. After polishing, the specimens were mounted in electrochemical cells with the front surface exposed to solution (aqueous 1 M NaHCO3at pH 8.0-8.2) and the back surface utilized for in situ stress monitoring by curvature interferometry. Prior to each constant potential corrosion experiment, the potential was held at -0.978 V vs. Ag/AgCl to cathodically reduce the native oxide layer. Corrosion morphology was examined with scanning electron microscopy (SEM) and profilometry. The internal IGC morphology was exposed at various depths by shallow-angle polishing. Fig. 1 shows the current transients at three potentials between the active current peak potential and the passivation potential. At the two highest potentials, the current density increased to maxima after initial transients associated to passive film formation, and thereafter slowly decayed. Stress measurements at the two highest potentials showed steady compressive stress generation. At -0.575 V, compressive stress increased for about 10 min and then diminished. SEM revealed that localized grain boundary attack initiated during the current rise. During the current decays at -0.521 V and -0.478 V, a micron-thick granular corrosion product accumulated on the steel surface (A in Fig. 2). This external corrosion product is likely an iron oxy-carbonate precipitate (5), with the current decay due to its mass transport resistance. Examination of the internal IGC morphology at these potentials revealed interconnected voids along grain boundaries and a primarily oxide corrosion product coating the attacked steel grains (B-D). At the greatest depths within the IGC layer (D), the oxide completely filled the corroded grain boundaries. In contrast, no oxidation on grain boundaries was detected at -0.575 V. Figs. 1 and 2 demonstrate that the potential dependence of compressive stress follows that of grain boundary oxide formation. This correspondence is evidence that the measured stress is due to steel oxidation along grain boundaries. Compressive stress generation would be localized close to the depth of maximum IGC penetration, where oxide completely fills the grain boundary (D in Fig. 2). The constant rate of stress generation associated with grain boundary oxide formation is permits IGC penetration into steel. We suggest that grain boundary oxide advance may be assisted by tensile stress in the grain boundary ahead of the oxide front, which accompanies compressive oxide stress. Such tensile stress could enhance the driving force for oxygen ion migration to the uncorroded grain boundary, so as to promote self-sustaining oxide penetration (6). ACKNOWLEDGMENT Financial support was provided by U.S. Department of Transportation, Pipeline and Hazardous Materials Safety Administration under Competitive Academic Agreement Program No. DTPH5614HCAP03 and DTPH5614HCAP01. REFERENCES 1. Y. F. Cheng, Stress Corrosion Cracking of Pipelines, Wiley, 2013. 2. R. D. Armstrong and A. C. Coates, Corros. Sci., 16, 423 (1976). 3. R. N. Parkins and S. Zhou, Corros. Sci., 39, 175 (1997). 4. Ö. Ö. Çapraz, P. Shrotriya, K. R. Hebert, J. Electrochem. Soc., 160, D501 (2013). 5. D. H. Davies and G. H. Burstein, Corrosion, 36, 416 (1980). 6. H. Gao, L. Zhang, W. D. Nix, C. V. Thompson, and E. Arzt, Acta Mater., 47, 2865 (1999). Figure 1

Electrochemical Noise for Detection of Stress Corrosion Cracking of Low Carbon Steel Exposed to Synthetic Soil Solution

Summary of the mechanical properties obtained from SSRT of X52 steel. Environment YS (MPa) RS (MPa) UTS (MPa) E (GPa) Strain (%) EL (mm) TF (h) RA(%) PE (%) Air 368 243 450 245 19.1 4.85 52.31 78.95 17NS4 pH 5 330 212 422 259 15.7 3.99 45.28 72.72 15NS4 pH 8 463 273 545 279 15.5 3.94 45.24 67.90 14NS4 pH 10 372 153 462 209 15.6 3.95 45.44 68.16 15 Table 4. SCC index obtained from mechanical properties of SSRT. Environment RA (%) RAR TF (h) TFR PE (%) PER ELR (mm) ELR Strain (%) SR Air 78.95 - 52.31 - 17 - 4.85 - 19.1 -NS4 pH 5 72.72 0.92 45.28 0.87 15 0.88 3.99 0.82 15.7 0.82NS4 pH 8 67.90 0.86 45.24 0.86 14 0.82 3.94 0.81 15.5 0.81NS4 pH 10 68.16 0.86 45.44 0.87 15 0.88 3.95 0.81 15.6 0.82 was not observed. However, a decreases in YS, UTS, EL and deformation was observed, which can be attributed to diffusion of hydrogen atoms into the steel generating hydrogen embrittlement. 3.4 Surface fracture analysis Figure 5 shows the SEM images of the fracture surfaces of the X52 pipeline steel after carried out the SSRT in air and in the synthetic soil solution (NS4 solution). Measurements of final diameter of fracture were carried out in order to calculate the reduction area (RA). The SSRT of the X52 steel in air presented a ductile fracture, and it is characterized by extensive plastic (permanent) deformation of the material (figure 5a). One mechanism of ductile fracture is known as microvoid coalescence

Probability of detection model for the non-destructive inspection of steam generator tubes of PWRs

This study proposes a probability of detection (POD) model to discuss the capability of non-destructive testing methods for the detection of stress corrosion cracks appearing in the steam generator tubes of pressurized water reactors. Three-dimensional finite element simulations were conducted to evaluate eddy current signals due to stress corrosion cracks. The simulations consider an absolute type pancake probe and model a stress corrosion crack as a region with a certain electrical conductivity inside to account for eddy currents flowing across a flaw. The probabilistic nature of a non-destructive test is simulated by varying the electrical conductivity of the modelled stress corrosion cracking. A two-dimensional POD model, which provides the POD as a function of the depth and length of a flaw, is presented together with a conventional POD model characterizing a flaw using a single parameter. The effect of the number of the samples on the PODs is also discussed.

Detection of SCC on 304 stainless steel in neutral thiosulfate solutions using electrochemical noise based on chaos theory

PurposeThis paper aims to investigate the stress corrosion cracking (SCC) process of sensitized 304 stainless steel during the slow strain rate test by using the electrochemical noise (EN) technique.Design/methodology/approachEN data are interpreted based on chaos and wavelet analyses, and correlation dimension and wavelet energy distribution are used as indicators for SCC process identification.FindingsExperimental results reveal that the corrosion potential abruptly decreases from 180 to 100 mV at 6,300 s and the current increases from 10 to 100 nA accordingly, which is attributed to passive film breakdown and crack initiation. Chaos and wavelet analyses results reveal that, as crack initiates, the correlation dimensions increase from 1.2 to 1.9, and the corresponding distribution frequencies of maximum relative wavelet energy change from high frequency to low frequency.Originality/valueSCC is monitored in lab, and crack initiation and propagation are identified by chaos and wavelet analyses. This work lays the foundation for SCC detection in field using EN.

Detection and characterization of stainless steel SCC by the analysis of crack related acoustic emission

In the paper the results of the acoustic emission (AE) based detection and characterization of stress-corrosion cracking (SCC) in stainless steel are presented. As supportive methods for AE interpretation, electrochemical noise, specimen elongation measurements, and digital imaging of the specimen surface were used. Based on the defined qualitative and quantitative time and power spectra characteristics of the AE bursts, a manual and an automatic procedure for the detection of crack related AE bursts were introduced. The results of the analysis of the crack related AE bursts indicate that the AE method is capable of detecting large scale cracks, where, apart from intergranular crack propagation, also some small ductile fractures occur. The sizes of the corresponding ductile fracture areas can be estimated based on a relative comparison of the energies of the detected AE bursts. It has also been shown that AE burst time and power spectra features can be successfully used for the automatic detection of SCC.

Research on High Resolution Stress Corrosion Crack Detection Based on Remote Field Eddy Current Non-Destructive Testing

Although remote field eddy current had achieved successive application in pipes and tubes non-destructive testing, the poor ability and sensitivity to axial crack such as stress corrosion crack prevented its further application. A novel high resolution remote field eddy current detection method which can be suitable for axial crack especially stress corrosion crack detection was proposed and verified by simulation and experiment. First of all, conventional detection ability of remote field eddy current for crack in different directions was researched with detail. Aside from this, applicability of orthogonal magnetic filed in remote field eddy current was analyzed and simulated by finite element method, and appropriate configuration using to generating orthogonal magnetic fields for tubular structure was discussed and verified. Thirdly, design of detection system including key parameters selection and detection coil mode were researched. At last, proposed high resolution detection system were verified experimentally using various type defects, such as parallel axial crack and real stress corrosion crack. From the above research, conclusions were drawn as followed: the detection ability and sensitivity of proposed remote field eddy current detection system could be improved significantly compared with conventional system, especially for axial crack which was not easily to detect, and real stress corrosion crack could be detected and evaluated successively.

Acoustic detection of stress-corrosion cracking of nitrogen austenitic steels

Structural changes and resistance to the stress-corrosion cracking of the nitrogen-bearing austenitic steels 04Kh20N6G11M2AFB and 09Kh20N6G11M2AFB (with 0.04 and 0.09 wt % C, respectively) after different treatments, including thermomechanical action, quenching from 1200°C, and aging at 700°C for 2 and 10 h, have been studied. It has been shown that aging at 700°C of the air-melted austenitic steel 09Kh20N6G11M2AFB leads to a decrease in the strength of samples with an induced crack upon the cantilever bending in air and in a 3.5% aqueous solution of NaCl as compared to the strength of the steel 04Kh20N6G11M2AFB-EShP with a smaller carbon content after high-temperature mechanical treatment or quenching from 1200°C. The smallest resistance to stress-corrosion cracking is observed in the samples of 09Kh20N6G11M2AFB steel after 10 h of aging, which is accompanied by the most intense acoustic emission and by brittle intergranular fracture. This is explained by the high rate of the anodic dissolution of the metal near chromium-depleted grain boundaries due to the formation of continuous chains of grain-boundary chromium-containing precipitates of carbides and nitrides.

The Features of 304 Nitrogen Controlled Stainless Steel during Slow Strain Rate Test by Electrochemical Noise

An investigation was carried out on the features of electrochemical noises of 304 nitrogen controlled stainless steel (304NGSS) in solution 4mol/LNaCl +0.01mol/LNa2S2O3under slow strain rate testing (SSRT) conditions. Electrochemical voltage and current noise were measured simultaneously in the Zero Resistance Ammeter (ZRA) mode. After experiment, there are several cracks on the edge of pit on the specimen. In order to characterize the stress corrosion cracking (SCC) processes of 304NGSS, time analysis of data alongwith the spectral estimation using FFT method, the results show SCC processes consisted of breakdown of the oxide film, the formation of pitting, crack initiation and crack propagation. According to the varieties of spectrums in time and frequency, the different state can be distinguished. The work in this paper will contribute to the research of indicator for real-time detection of SCC in plant.

Influence of reference electrode distance and hydrogen content on electrochemical potential noise during SCC in high purity, high temperature water

The potential and limits of the electrochemical noise (EN) measurement technique for the detection of stress corrosion cracking (SCC) initiation in austenitic stainless steels under simulated boiling water reactor (BWR) conditions was investigated at PSI within a small feasibility study. Because of the limited throwing power in low conductive, high purity water, it seems obvious that the distance between EN electrode and the specimen (or cracking location) plays an important role on the detectability of SCC initiation by the EN technique. This effect was evaluated by performing constant extension rate tensile tests in a simulated BWR environment (high purity water, T = 288°C, p = 9 MPa, O2 content = 2 ppm) with simultaneous potential noise measurements versus multiple reference electrodes. These experiments confirmed that for the detection of SCC initiation by EN measurements the electrode distance is a limiting factor for the application in low conductivity electrolytes. The detection sensitivity decreases with increasing distance between the specimen surface and the reference (or counter) electrode. Furthermore, it was evaluated that the basic/background noise level is very low in highly reducing environment.

光ファイバAE計測システムを用いたCBB試験中に発生する応力腐食割れの検出

光ファイバAE計測システムを用いて，従来は困難であった高温・高圧環境下におけるCBB試験中のSCC発生，進展モニタリングを行う手法を開発した．CBB治具と一体型となった光ファイバセンサホルダに光ファイバを巻き付けることで高感度でAE信号を検出することができた．低合金鋼と炭素鋼の溶接継手から採取した試験片に対して180℃，1.0 MPaの環境下で28日間（2.4 Ms）のCBB試験を行った結果，試験中に発生したAE信号は約11万カウントであった．波形の相関およびガイド波の特徴を用いたAE分類によって試験器からのノイズを除去した結果，96カウントがSCCによって発生したAE信号であると推定された．AE発生タイミングから，SCCは試験開始後約1.2 Msから発生，進展したと推定された．

OS0707 応力腐食割れの検出におけるSPACEの有効性

OS0707 応力腐食割れの検出におけるSPACEの有効性

Nondestructive Evaluation of SCC on the Surface of Ni-Base Alloy by Microwaves

To detect stress corrosion cracking (SCC) and evaluate its depth on the surface of Ni-base alloys, a microwave microscope was employed. An open-ended coaxial line sensor was used to increase the spatial resolution. The working frequency was 110 GHz and the standoff distance between the sensor and the sample was 60 μm. The shape of SCC was obtained by microwave imaging. By measuring the amplitude of reflection coefficient, detection of SCC was achieved. To evaluate SCC depth, the attenuation constant of microwave in the crack was decided by comparing the measured microwave signal with the depth of a reference SCC obtained by destructive testing. Finally, the distribution of the depth of another SCC was evaluated by the proposed equation with the obtained attenuation constant.

C208 マイクロ波によるNi基合金溶接部表面の応力腐食割れの非破壊評価(亀裂の検査・モニタリング技術-(2),OS5 保全・設備診断技術),動力エネルギーシステム部門20周年,次の20年への新展開)

To detect stress corrosion cracking (SCC) and evaluate its depth on the surface of Ni-base alloys, a microwave microscope was employed. An open-ended coaxial line sensor was used to increase the spatial resolution. The working frequency was 110GHz and the standoff distance between the sensor and the sample was 60μm. The shape of SCC was obtained by microwave imaging. By measuring the amplitude of reflection coefficient, detection of SCC was achieved and V-shaped and W-shaped characteristic signal was obtained. The distribution of SCC depth along the crack length was evaluated using the measured amplitude of reflection coefficient.