Showing papers on "Stress corrosion cracking published in 1995"
TL;DR: In this paper, a review of recent studies on acoustic emission and cracking models, failure processes and frictional sliding processes, mainly based on work carried out in Japan, is presented, where the relation between the distribution of the hypocenters, the occurrence intervals, and the experimentally controlled physical parameters is discussed.
Abstract: This paper reviews recent studies on (1) AE (acoustic emission) and cracking models, (2) failure processes and (3) frictional sliding processes, mainly based on work carried out in Japan Techniques for AE data acquisition and hypocenter location have been greatly improved; one system can record twenty-one channels of waveforms and can locate the AE hypocenter automatically Another system can also record the occurrence time and the maximum amplitude of the AE event without dead time On the basis of these data, we are able to discuss the relation between the distribution of the hypocenters, the occurrence intervals, and the experimentally controlled physical parameters For this purpose, many studies have tried to develop quantitative expression for the statistical characters of these distributions Techniques for evaluating AE source parameters are still being developed; and there has been a great deal of improvement in our knowledge about cracking mode of AE The focal mechanisms have been systematically studied based on the space distributions of the initial motion directions The studies showed that shear type cracking becomes dominant with increasing axial stress These mechanism solutions agree well with the local stress field suggested by the fracture plane Increasing of the failure strength of rocks with increasing stress and strain rates under relatively low confining pressure has been studied experimentally The failure process and the rate dependency of the fracture strength in the low pressure regime are discussed on the basis of a stress corrosion cracking model The failure mechanism under higher confining pressures of up to 3GPa is also examined Some behavior including the variation of AE activity with axial stress differs between low and high confining pressures although the stress-strain relations clearly show brittle deformation in both regimes On the basis of these differences, the researchers proposed that 'high-pressure' brittle deformation was different from ordinarily observed brittle behavior at low pressure, and examined the failure micromechanisms through an optical and an electron microscopes Frictional sliding has also been intensively examined in the past decade Experiments using large samples have demonstrated that the slip propagation process is well described by a slip-weakening model The relations between the dynamic parameters of slip propagation process and the physical parameters of slip surfaces is becoming clearer
128 citations
31 Dec 1995
TL;DR: In this paper, a critical review of the mechanisms of stress corrosion cracking (SCC) is given and, an interpretation of the events occurring during the long ({approx} 15 y) induction times observed in plant is postulated.
Abstract: Alloy 600 is a material commonly used to construct the tubing in the steam generators (SG) of pressurized light water reactors (PWR) and of CANDU heavy water reactors. It is well established which variables and to which extent they influence the crack growth rate (CGR) in Alloy 600 exposed to high temperature (deaerated) water (HTW), especially in very aggressive conditions. There is evidence that the same variables that influence CGR also control the crack induction time. However, there are only a few data on crack induction time and no detailed explanation of the events that lead to the nucleation of a crack on an apparent smooth tube surface. In this paper, a critical review of the mechanisms of stress corrosion cracking (SCC) is given and, an interpretation of the events occurring during the long ({approx} 15 y) induction times observed in plant is postulated.
88 citations
TL;DR: Topical fluoride solutions can cause stress corrosion cracking of commercially pure titanium, and the cold-rolled specimen exposed to the fluoride solution exhibited a brittle fracture, while the unexposed specimen was ductile in nature.
74 citations
TL;DR: In this paper, the chemical and electrical natures of the corrosion deposits, as well as surface morphologies, have been investigated and the influences of both formation temperature and time have been taken into account.
74 citations
15 Jul 1995-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the pitting potential of Al 6061-based metal matrix composites (MMCs) containing carbon fibres, alumina fibres or silicon carbide whiskers (SiC w ) were studied in chloride solutions.
Abstract: Corrosion characteristics of Al 6061-based metal matrix composites (MMCs) containing carbon fibres, alumina fibres or silicon carbide whiskers (SiC w ) and the effects of ageing heat treatment on the stress corrosion cracking resistance of SiC w Al 7075 MMC were studied in chloride solutions. MMCs were prepared by the squeeze casting method in the laboratory. The pitting potentials for Al 6061 and the three Al 6061-based MMCs were similar. The resistance of SiC w Al 6061 MMC to pit initiation is the same as that of the monolithic alloy. Once pits initiate, damage by pitting corrosion would be greater owing to the formation of crevices between the reinforcement and the matrix by the dissolution of the latter in the pits. The cathodic current of the SiC w Al 6061 is slightly larger than that of the matrix alloy, possibly owing to an interfacial layer observed by transmission electron microscopy. Ageing of SiC w Al 7075 MMC at 170 °C for more than 1 h following ageing at 110 °C makes the MMC resistant to stress corrosion cracking in 3.5% NaCl and increases the pitting potential.
63 citations
TL;DR: In this paper, the authors considered how carbon dioxide (CO2)-containing ground water, which can promote transgranular stress corrosion cracking of pipelines, can be converted to a higher pH, carbonate-bicarbonate (CO32−-HCO3−) solution that promotes intergranular cracking.
Abstract: Consideration was given to how carbon dioxide (CO2)-containing ground water, which can promote transgranular stress corrosion cracking of pipelines, can be converted to a higher pH, carbonate-bicarbonate (CO32−-HCO3−) solution that promotes intergranular cracking of pipelines. The lower pH environment will remain only if the cathodic protection generates insufficient hydroxide ions to convert the free CO2 to HCO3− and/or CO32−. The generation of these ions also requires the transport of anions out of and cations into the solution contained between the pipe surface and its coating.
60 citations
TL;DR: An experimental system was developed to reproduce stress corrosion cracking (SCC) of API X-60 line pipe steels in highly alkaline (pH = 10) carbonate-bicarbonate (1 N sodium carbonate [Na2C...) as mentioned in this paper.
Abstract: An experimental system was developed to reproduce stress corrosion cracking (SCC) of API X-60 line pipe steels in highly alkaline (pH =10) carbonate-bicarbonate (1 N sodium carbonate [Na2C...
51 citations
TL;DR: In this article, the effect of shot peening on stress corrosion cracking of 2205-Duplex stainless steel was studied and shown to be effective in retarding stress corrosion in the material studied.
50 citations
TL;DR: In this article, micro-sampling of the crack tip solution in ASTM A533(B) low-alloy steel (0.013% S) exposed to constant and cyclic loading in 288°C water under various test conditions was used to measure the manganese sulfide concentration directly, while simultaneously monitoring crack length.
Abstract: The importance of the dissolution of manganese sulfide (MnS) inclusions in environmentally assisted cracking (EAC) of pressure vessel steels in high-temperature water is well recognized. However, no direct measurement of the crack tip chemistry that develops during EAC has been performed, and only estimates exist for the dissolution rate of MnS and the resulting sulfur (S) levels in the crack. In the present work, microsampling of the crack tip solution in ASTM A533(B) low-alloy steel (0.013% S) exposed to constant and cyclic loading in 288°C water under various test conditions was used to measure the crack tip S concentration directly, while simultaneously monitoring crack length. A reversing direct current (DC) potential drop method was used to monitor crack length continuously. Ion chromatography (IC) and inductively coupled plasma (ICP) were used to measure the dissolved S species in the microsampled solutions. Most experiments involved varying the corrosion potential by changing the dissolve...
49 citations
TL;DR: In this paper, a correlation between SCC susceptibility and creep strain-rate was investigated at 360 °C on six mill-annealed tubes showing different chemical compositions, mechanical properties and grain sizes.
47 citations
TL;DR: In this paper, it was shown that the cathodic reaction is not restricted to the flanks of the crack or to the crack mouth, but occurs predominantly on the external surfaces, as postulated in the coupled environment fracture model.
31 Dec 1995
TL;DR: In this article, the role of ionic current flow within cracks and near the crack tip is examined in the light of experimental evidence, with emphasis on high temperature "pure" water.
Abstract: Understanding the role of ionic current flow within a crack and near the crack tip is fundamental to modeling of environmentally assisted crack advance. Critical conceptual issues and models related to ionic current flow within cracks, and the associated ``crevice`` chemistry and metal oxidation that results, are presented and examined in the light of experimental evidence. Various advanced techniques have been developed to evaluate the roles of electrochemistry, transport, and crack chemistry in stress corrosion cracking, with emphasis on high temperature ``pure`` water. These include high resolution crack length measurement by dc potential drop performed simultaneously with microsampling, electrochemical microprobe mapping, microinjection of species, and micropolarization of the crack. Conceptual issues addressed include the importance of the corrosion potential vs. oxidant concentration, the absence of oxidants and associated low corrosion potential within cracks, the location and role of macrocell currents associated with potential gradients from differential aeration cells, the localized nature of the microcell currents associated with dissolution at the crack tip, the importance of pH and adsorbed species on repassivation and crack advance, and the role of convection in crack chemistry and crack advance. Correct concepts are shown to be an essential pre-cursor to quantitative modeling.
TL;DR: In this article, a corrosion-enhanced plasticity model is proposed to describe the intergranular and transgranular cracking in Alloy 600 and fractographic examinations performed on specimens' fracture surfaces lead to the fact that attention should be paid to a cleavagelike micro-cracking mechanism involving interactions between corrosion and plasticity at the vicinity of grain boundaries.
Abstract: In order to study the mechanisms involved in the stress-corrosion cracking (SCC) of Alloy 600 in primary water, the influence of the relevance of physicochemical and metallurgical parameters was assessed: hydrogen and oxygen overpressures, microstructure, and local chemical com-position. The obtained results show that, even if the dissolution/oxidation seems to be the first and necessary step responsible for crack initiation and if hydrogen effects can also be involved in cracking, neither a dissolution/oxidation model nor a hydrogen model appears sufficient to account for cracking. Moreover, fractographic examinations performed on specimens’ fracture surfaces lead to the fact that attention should be paid to a cleavagelike microcracking mechanism involving interactions between corrosion and plasticity at the vicinity of grain boundaries. A corrosion-enhanced plasticity model is proposed to describe the intergranular and transgranular cracking in Alloy 600.
Patent•
28 Sep 1995TL;DR: In this paper, a method for improving the performance and longevity of coatings of metal deposited from aqueous solutions of inorganic, organic or oraganometallic metal compounds was proposed.
Abstract: A method for improving the performance and longevity of coatings of metal deposited from aqueous solutions of inorganic, organic or oraganometallic metal compounds. The method involves co-deposition of noble metal or corrosion-inhibiting non-noble metal during growth of oxide film on a component made of alloy, e.g., stainless steels and nickel-based alloys. The result is a metal-doped oxide film having a relatively longer life in the reactor operating environment. In particular, incorporation of palladium into the film provides greatly increased catalytic life as compared to palladium coatings which lie on the oxide surface.
TL;DR: In this article, a synergistic effect of hydrogen and stress on a corrosion rate was analyzed with thermodynamics, and it was shown that an interaction of stress and hydrogen could increase the corrosion rate remarkably.
Abstract: A synergistic effect of hydrogen and stress on a corrosion rate was analyzed with thermodynamics. The results showed that an interaction of stress and hydrogen could increase the corrosion rate remarkably. Stress corrosion cracking (SCC) of austenitic stainless steel (ASS) was investigated in boiling chloride solution to confirm the analysis. Hydrogen could be introduced into the specimen and concentrated at the crack tip during SCC in boiling LiCl solution (143°C). The concentrating factor is about 3 which is consistent with calculated results according to stress induced diffusion.
TL;DR: In this article, a critical but non exhaustive review of the aqueous corrosion fatigue mechanisms is proposed with a particular emphasis on the corrosion-deformation interactions, the limits of the classical approaches of corrosion fatigue crack initiation and propagation predictions from the electrochemical point of view are pointed out.
Abstract: A critical but non exhaustive review of the aqueous corrosion fatigue mechanisms is proposed with a particular emphasis on the corrosion-deformation interactions, The limits of the classical approaches of corrosion fatigue crack initiation and propagation predictions from the electrochemical point of view are pointed out. It is shown how the cyclic plastic deformation can locally modify the electrochemical reactions and how corrosion (anodic dissolution and/or hydrogen effects) can change the local plasticity and microfracture. The experimental methods to detect the localized corrosion fatigue damage are detailed. The crack propagation mechanisms near the fatigue threshold are underlined, with a particular attention for the anodic dissolution and hydrogen effects and the interaction between corrosion fatigue and stress corrosion cracking. Finally recent numerical simulations of corrosion fatigue damage and lifetime at mesoscopic scales are proposed and trends for future researches are given.
01 Feb 1995-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, a spray-deposited AlCuMgAg-base alloys for use at ambient and moderately elevated temperatures have been optimized for high strength and high fracture toughness.
Abstract: Chemical composition and heat treatments of spray-deposited AlCuMgAg-base alloys for use at ambient and moderately elevated temperatures have been optimized for high strength and high fracture toughness. This alloy development has led in particular to two new age hardenable aluminium alloys (N213 and N232) with excellent property combinations. Alloy N213 (AlCu5Mg0.4Ag0.4Ti0.4Zr0.15Mn0.2) clearly outperforms commercial 2XXX series alloys such as 2618 in terms of fracture toughness and yield strength at temperatures up to 180 °C. Alloy N232 (AlCu4Mg0.8Ag0.4Zr0.5Mn0.4) shows the highest product of yield strength and fracture toughness ever achieved for aluminium alloys; at 23 °C yield strength and fracture toughness values are RP0.2 = 378 MPa, K IC = 100 MPa m 1 2 (T4 temper), and R P 0.2 = 452 MPa , K IC = 77 MPa m 1 2 (T6 temper). Fatigue strength of this experimentak akkits (T6 temper) is also obviously superior to that of commercial aluminium alloys such as 7475-T7351 and 2219-T8. Alloys N213 and N232 show stress corrosion cracking behaviour comparable with that of commercial 2XXX alloys; plateau crack growth rates around 10−8 m s−1 have been measured. As revealed by transmission electron microscopy studies, the excellent property combinations of the new alloys can be related to microstructural characteristics, such as type, size, density and distribution of the precipitates. Moreover, these studies explain the nature of the microstructure tending towards overaging during extended exposure at temperatures above 150 °C; in particular the harmful impact of higher Mg contents on the microstructural stability at elevated temperatures is evidenced.
TL;DR: In this article, the authors describe the formation of an advancing stress-corrosion front that had formed at the specimen surface and advanced radially inward, resulting in a planar, stress-induced failure in a commercially available, hot isostatically pressed, yttria-fluxed, silicon nitride.
Abstract: Stress-corrosion cracking in a commercially available, hot isostatically pressed (HIPed), yttria-fluxed, silicon nitride was the prevalent mode of failure in specimens creep-ruptured at 1,370 C. High-temperature diffusional processes associated with oxygen were responsible for the creation of an advancing stress-corrosion front that had formed at the specimen surface and advanced radially inward. The volume of material in the wake of the stress-corrosion front possessed a high concentration of lenticular cavities at two-grain boundaries, a high concentration of multigrain junction cavities, and large amorphous ``pockets`` in other multigrain junctions that were abnormally rich in oxygen and yttrium. The combination of tensile stress and the high concentration of cavities in the near-surface volume of the material resulted in microcrack coalescence or the formation of a planar, stress-corrosion crack. The concurrent growth of the stress-corrosion front and crack during the tensile creep-rupture tests ultimately led to stress-induced failure.
TL;DR: In this paper, anodic dissolution-based mechanisms proposed previously for this phenomenon were amended based upon further characterization of the rapid cracking process, based on studies of the relative electrochemical behavior of the microstructural elements in the subgrain boundary region, time-to-failure SCC testing in a simulated crack solution, evolution of crack potential and pH with time, fractographic examination of failed samples, and x-ray diffraction (XRD) of films passivating crack walls.
Abstract: Stress corrosion cracking (SCC) test specimens of Al-Li-Cu alloy that were subjected to fixed-displacement loading and exposed to aerated 3.5 wt% sodium chloride (NaCl) solution for 1 week failed < 24 h after removal into ambient atmospheres. Anodic dissolution-based mechanisms proposed previously for this phenomenon were amended based upon further characterization of the rapid cracking process. Amendments were based on studies of the relative electrochemical behavior of the microstructural elements in the subgrain boundary (SGB) region, time-to-failure SCC testing in a simulated crack solution, evolution of crack potential and pH with time, fractographic examination of failed samples, and x-ray diffraction (XRD) of films passivating crack walls. Results suggested an active path existed along SGB that was composed of the highly reactive T1 (Al2CuLi) precipitate phase and a solute-depleted zone that did not passivate readily when exposed to the crack environment. The matrix phase along crack walls...
Patent•
17 Feb 1995
TL;DR: In this paper, the authors proposed a method for mitigating crack growth on the surface of stainless steel or other metal components in a water-cooled nuclear reactor by injecting a noble metal, e.g., palladium, into the water of the reactor in the form of a solution or suspension.
Abstract: A method for mitigating crack growth on the surface of stainless steel or other metal components in a water-cooled nuclear reactor. A compound containing a noble metal, e.g., palladium, is injected into the water of the reactor in the form of a solution or suspension. This compound has the property that it decomposes under reactor thermal conditions to release ions/atoms of the noble metal which incorporate in or deposit on the interior surfaces of the crack. The compound may be organic, organometallic (e.g., palladium acetylacetonate) or inorganic in nature. The palladium deposited inside a crack should exhibit catalytic behavior even if the bulk surface palladium is depleted under high fluid flow conditions. As a result, the electrochemical potential inside the crack is decreased to a level below the critical potential to protect against intergranular stress corrosion cracking.
TL;DR: In this article, controlled-purity Ni-x% Cr-9% Fe-y% C alloys at 360°C were tested for intergranular (IG) cracking and time-dependent deformation in high-puri...
Abstract: Mechanical testing of controlled-purity Ni-x% Cr-9% Fe-y% C alloys at 360°C revealed an environmental enhancement in intergranular (IG) cracking and time-dependent deformation in high-puri...
TL;DR: The susceptibility of alloy 600 (UNS N06600) to stress corrosion cracking (SCC) in hydrogenated high-temperature water was studied as a function of the degree of cold work (CW) of the allo...
Abstract: The susceptibility of alloy 600 (UNS N06600) to stress corrosion cracking (SCC) in hydrogenated high-temperature water was studied as a function of the degree of cold work (CW) of the allo...
15 Jul 1995-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the authors investigated the necessary conditions for SCC in Zr, and the preventive method against SCC by alloying were investigated, and they showed that Zr-15%Ti alloy is immune to SCC under applied potential conditions in hot HNO 3 ; this alloy forms a stable passive film composed of ZrO 2 and TiO 2.
Abstract: Since zirconium (Zr) has superior corrosion resistance to concentrated nitric acid (HNO 3 ) at elevated temperature, it has been successfully used as a material for chemical plants to produce HNO 3 or spent nuclear fuel reprocessing plants. However, the occurrence of stress corrosion cracking (SCC) has recently been reported in hot nitric acid conditions. The necessary conditions for SCC in Zr, and the preventive method against SCC by alloying were investigated. The slow strain rate technique test, electrochemical measurements, strain electrode tests, and analysis of corrosion products were carried out in this work. SCC does not occur in Zr in boiling HNO 3 at concentrations less than 70%, whereas SCC is initiated in 6–94% HNO 3 when a potential is applied above the critical potential for SCC. A new invention of Zr-15%Ti alloy is immune to SCC under applied potential conditions in hot HNO 3 ; this alloy forms a stable passive film composed of ZrO 2 and TiO 2 .
TL;DR: In this article, the mechanisms for stress corrosion cracking (SCC) induced by chlorides are surveyed and the cause for the high SCC resistance of duplex stainless steels has been discussed and evaluated.
Abstract: Stress corrosion cracking (SCC) induced by chlorides frequently causes problems in applications where standard austenitic stainless steels are being used. Often this problem can be solved by the use of duplex stainless steels.
In this report the mechanisms for SCC have been surveyed, and the cause for the high SCC resistance of duplex stainless steels has been discussed and evaluation of test methods for SCC and how duplex stainless steels respond to them, as well as practical experience of duplex stainless steels. The study shows that no single mechanism can be attributed to the good resistance to SCC of duplex stainless steels. Probably a synergistic effect of electrochemical and/or mechanical effects is responsible for the good performance.
Test methods for SCC often give relatively good correspondence with real applications, but ranking is often doubtful, and comparisons of different material types should be made with caution. Numerous cases with SCC on standard austenitic stainless steels have been solved by the use of duplex stainless steels.
TL;DR: In this article, a probabilistic model for crack propagation through a grain boundary (GB) network is proposed, where the process of crack advance across GB segments is modeled by a Markov chain.
TL;DR: In this article, the effect of applied potential on the stress corrosion cracking (SCC) behavior of sensitized type 316 stainless steel (SS) in high temperature water containing 5 ppm chloride over the temperature range from 100 to 300 °C has been investigated using the slow strain rate test (SSRT) technique.
Journal Article•
TL;DR: In this article, the sampling and analysis of corrosion products to describe corrosion scenarios that occur under shielding disbondments are reviewed, both as input to risk assessment models and as part of current research into stress corrosion cracking on pipelines.
Abstract: The NOVA Gas Transmission pipeline system is protected by both cathodic protection (CP) and external coating. Pipelines suffer the threat of external corrosion where protective coatings fail and create shielding disbondments. The sampling and analysis of corrosion products to describe corrosion scenarios that occur under shielding disbondments are reviewed. Understanding this environment is of interest both as input to risk assessment models and as part of current research into stress corrosion cracking on pipelines.
TL;DR: In this paper, the electrochemical and stress corrosion cracking behavior of grade 550 pipeline steel with coating disbandments was studied in a range of bicarbonate solutions using a potentiodynamic polarization technique and slow strain rate test.
Abstract: The electrochemical and stress corrosion cracking behavior of Grade 550 (X-80) pipeline steel with coating disbandments was studied in a range of bicarbonate solutions using a potentiodynamic polarization technique and slow strain rate test. The shape of the polarization curves were found to vary with bicarbonate concentration. Increase in bicarbonate concentration results in a wider passive region and a more noble breakdown potential. Low concentrations of chloride ion in bicarbonate greatly affect the polarization characteristics and can cause the elimination of passivity in specific solutions. Tensile specimens were pulled at constant strain rate {dot {epsilon}} = 10{sup {minus}6}/sec. under potential control ranging from {minus}350 mV to {minus}900 mV (SCE) in NS-4 solution (dilute bicarbonate solution with chloride ion). Fracture surface of the specimens were examined under scanning electron microscopy. Overall fracture is ductile dimple, however, transgranular stress corrosion cracking has been found in the edge of specimen for the sample with potential controlled at {minus}800 mV, {minus}750 mV and {minus}650 mV (SCE).
TL;DR: In this paper, the authors studied the stress corrosion cracking behavior of four austenitic Fe-32% Mn-9% Al alloys containing ≈ 1 wt% carbon and showed that they are susceptible to hydrogen embrittlement in 3.5% NaCl solution at large cathodic applied potentials.
Abstract: The stress corrosion cracking (SCC) behavior of four austenitic Fe-32% Mn-9% Al alloys containing ≈ 1 wt% carbon was studied. All of the four alloys were susceptible to SCC in room temperature and 160°C NaCl solution. SCC was enhanced by applying an anodic potential. The crack path was transgranular, and cleavage-like regions were observed on the fracture surface. The corrosion-assisted microcleavage model proposed for the transgranular SCC behavior of face-centered cubic (fcc) materials very likely was the operating SCC mechanism of the austenitic Fe-Mn-Al alloys. Adding 1.23% Mo or 1.27% Si to the austenitic Fe-32% Mn-9% Al alloys did not change the SCC mechanism and crack paths. Adding 1.27% Si made the alloys more susceptible to SCC, but no such effect was observed with the addition of 1.23% Mo. All four alloys studied were susceptible to hydrogen embrittlement (HE) in 3.5% NaCl solution at large cathodic applied potentials, and the crack paths were intergranular. The addition of Mo, Cr, or S...
Patent•
06 Apr 1995
TL;DR: In this article, a corrosion monitoring apparatus and method for determining the corrosive effects of a chemical environment, having an environmental pressure, on a vessel containing the chemical environment is presented, where a probe is exposed to the environment and is made of a material substantially similar to that of which the vessel is made.
Abstract: A corrosion monitoring apparatus and method for determining the corrosive effects of a chemical environment, having an environmental pressure, on a vessel containing the chemical environment. A probe is exposed to the environment and is made of a material substantially similar to that of which the vessel is made. The probe has a sealed internal chamber which contains a pressurized fluid which is monitored. A pressure transducer is in communication with the sealed internal chamber of the first probe for translating any pressure change within the chamber into a (preferably electrical) signal which is indicated by an electrical meter or similar device. Stress corrosion cracking of the probe causes fluid leakage and, therefore, a pressure change.