Intergranular Stress Corrosion Research Articles

Failure Analysis of SA-213TP347H High-temperature Reheater of 600 MW Supercritical Boiler

Failure analysis of SA-213TP347H steel tube for high-temperature reheater of 600MW supercritical boiler was studied by means of macroscopic analysis, chemical composition, mechanical properties, microstructure, scanning electron microscopy and energy spectrum analysis. The results show that the chemical composition, hardness and strength of the tube samples meet the limit of ASTM A213/A213M standard. The microstructure of tube-burst sample is austenite, there are some precipitates containing Cr and Nb element at the grain boundaries. The test results for the spare part sample near elbow show that the hardness exceeds the limit of SA-213TP347H steel, there are a lot of slip lines and some non-metallic inclusions containing S in the microstructure. It is concluded that solid solution treatment missing in its manufacturing is the main reasons for the fracture, which makes Cr precipitate on the grain boundary and form the Cr-depleted zone, which is easy to cause intergranular stress corrosion and lead to the tube burst.

Elastic Properties of FeCr20Ni8Xn (X = Mo, Nb, Ta, Ti, V, W and Zr) Austenitic Stainless Steels: A First Principles Study

Austenitic stainless steels suffer from intergranular corrosion and stress corrosion cracking when exposed to elevated temperature (500–800 °C). Under these environments, Cr-carbides and Cr-carbontrides precipitate at the grain boundaries, which results in the formation of Cr-depleted zone. In practice, alloying elements could be added into austenitic stainless steels to modify the precipitation processes. Besides the precipitation processes, the elastic properties of the iron matrix would be influenced. Using the exact muffin-tin orbitals (EMTO) method, the solute effects on the elastic properties of FeCr20Ni8 austenitic stainless steels were studied. Based on the simulated shear modulus (G) and bulk modulus (B), we proposed a design map for FeCr20Ni8 based alloys, aiming to provide a basis for the design of high-performance austenitic stainless steels.

Interactive effect of ant nest corrosion and stress corrosion on the failure of copper tubes

Abstract Premature failure of copper tubes used in air-conditioning units is a serious problem for air conditioning manufacturers and customers. Several failure theories were put forward, such as ant nest corrosion and inter-granular stress corrosion. A new opinion is raised in this article that the interaction of ant nest corrosion and stress corrosion cause the failure of copper tubes. This article analyzes the interactive effect through comparing the morphologies of the failure copper tubes in practical application with the samples which were exposed to the concentration of 1 vol% formic acid vapor in airtight glass vessels for different days. The experiment results show that most of copper failures result from the interactive corrosion due to the morphology of interactive corrosion tunnels is thinner than single ant nest corrosion and the corrosion starting points of interactive corrosion tend to distribute at the bottom of internal groove where the tensile stress was concentrated.

The Effect of Precipitates on Corrosion Resistance of Alloy 28 Tubing in Sour Environments

Alloy 28, an important corrosion-resistant material candidate for use in down-hole tubing in severe corrosive environments, was investigated for the characteristics of its precipitates and their effect on corrosion resistance. The microstructure of the precipitates was observed by optical microscope and scanning election microscopy (SEM), and the type and chemical composition were analyzed by x-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS). It was found that the precipitates in the Alloy 28 were rich in C, Cr, and Mo, mostly σ phase and Cr23C6. The corrosion resistance of Alloy 28 with precipitates was markedly reduced in intergranular corrosion tests and stress corrosion cracking tests. So avoiding precipitates in Alloy 28 by the appropriate heat treatment during manufacture of the tubing is key.

Reversing Sensitization of Naturally Exfoliated 5456-H116 Aluminum Alloys

5456-H116 Al-Mg alloy has been broadly used in the U.S. Navy in order to meet the demand of reducing ship hull weight while considering high specific strength, corrosion resistance, and weldability. A particular concern of these alloy is sensitization, which causes it to be sensitized when highly anodic β phase (Al_3Mg_2) is precipitated at grain boundaries especially in service exceeding 65~200°C, leading to intergranular corrosion (IGC), exfoliation and stress corrosion cracking (SCC). This study investigated the reversal of sensitization of a naturally exfoliated 5456-H116 alloy plate by planned heating treatment with a short exposure to 250°C. The properties of sensitized specimens of 5456-H116 were investigated using microhardness testing, electrochemical measurements, Nitric Acid Mass Loss Testing (NAMLT), optical microscopy, and Scanning Electron Microscopy (SEM). The results reveal that the corrosion resistance of the stabilized specimens approached those of the unsensitized plates, and their mechanical strength was not adversely affected during the recovery process. Therefore, in-service plates can be refurbished by stabilizing heat treatment rather than replacement, potentially reducing maintenance costs.

Impact of Local Concrete Crack on the Prestressed Steel Stress Corrosion Cracking

The impact of local concrete crack on the prestressed steel stress corrosion sensitivity is studied with the SSRT, SEM and other methods. The result shows that, the local concrete crack will increase the prestressed steel stress corrosion sensitivity. The formation of stress corrosion microcracks on the metal surface below the crevice is based on two mechanisms: one is the pitting corrosion nucleation mechanism caused due to Cl-, and the other is the non-pitting corrosion nucleation mechanism caused due to the film rupture. Once the initial stress corrosion microcrack is formed on the metal surface in the crevice, the interior of microcrack will be in the anodic polarization state due to the effect of the electric field of anodic polarization in the crevice, the metal in the crack will continue to be corroded, and the crack will expand. Moreover, due to the anodic dissolution reaction in the crack, the Fe (OH)3 and Fe2O3 films will be formed on the side wall of the crack, and if the nonmetallic slag inclusions and other defects exist on the side wall of the crack, the origin of secondary crack will be formed here, and the intergranular secondary stress corrosion microcrack will be produced.

Stress corrosion cracking of aluminium alloy 7075(w) under tensile and compressive loading

The effect of compressive loading on stress corrosion cracking of aluminium alloy 7075(W) was studied using specimens containing simulated fastener holes and the results were compared with the behaviour of double cantilever beam specimens with tensile loading. Crack lengths were measured with an eddy current bore probe and confirmed by optical metallography. Intergranular stress corrosion was observed in both tensile and compressive loading. Cracks initiated readily in 3·5%NaCl solution with tensile loading and the alloy was much less susceptible in compression, with cracking being detected only after 14 day exposure to EXCO solution. No cracking was observed in unstressed specimens, even after 56 day continuous exposure to EXCO solution. In both cases, SCC was explained by an active path mechanism due to the galvanic interaction between grain boundary precipitates and adjacent precipitate free zones. Compressive loading produced a positive strain at the crack tip, which ruptured the protective corrosion product film, maintaining the path of preferential corrosion.

Exfoliation Corrosion Mechanism: Interplay between Intergranular Corrosion and Stress Corrosion Cracking during Exfoliation Corrosion of AA7449

It is generally considered that exfoliation corrosion is due to the build-up of corrosion products that create a wedging stress that lifts up the surface grains. However, the exfoliation mechanism is still under discussion: possible operating mechanisms include intergranular corrosion of in plane grain boundaries accelerated by the wedging effect, or crack propagation by a “purely” stress corrosion mechanism. The sensitivity to exfoliation corrosion of AA7449 in relation to the intergranular and stress corrosion cracking sensitivity has been addressed in a program of controlled quenches followed by thermal treatments. Our observations demonstrate that the quench rate has a strong effect on intergranular corrosion and exfoliation corrosion sensitivity and in a lesser extent on stress corrosion cracking. In the first moments of the EXCO test, the initiation of corrosion follows the same trends as those revealed by the ASTM G110 test. We observe intergranular initiation for the slow quench rate (~5°C/s) and pitting initiation for samples quenched between 50 to 500°C/s. On the contrary, the final EXCO corrosion quotations do not seem to correlate with the intergranular resistance but rather with SCC resistance.

Influence of Simulated Outside-Reactor Irradiation on Anticorrosion Property of Austenitic Stainless Steel

The influence of γ-ray irradiation on the properties of inside-reactor stainless steel structures was studied by simulating the working condition of pressurized water reactor (PWR) first circuit and the outside-reactor γ-ray irradiation. The result shows that the simulated outside-reactor irradiation (irradiation dose 4. 4 × 104 Gy) has no influence on anticorrosion properties of solutionized SUS304 austenitic stainless steel, including intergranular corrosion (IC) and stress corrosion cracking (SCC). Anticorrosion properties (IC, SCC) of sensitized SUS304 austenitic stainless steel are reduced by simulated outside-reactor irradiation. The longer the sensitized time is, the more obvious the influence is.

Environmental Effects on Stress Corrosion Cracking Susceptibility of Cr-Mo Steel Tubes in Steam Generators

Steam generator began having severe problems 20 years ago. The main causes were wastage, wear, loose parts, denting. These problems were solved by changing the water chemistry treatment method. Therefore these damage types were replaced by stress corrosion cracking on the inner surface of the tubes and most recently by intergranular attack and stress corrosion cracking on the external surface of the tube. Steam generator has experienced various forms of damage, most involving some kind of corrosion. Some of these problems have been virtually eliminated, others are successfully managed, but a few have not yet been brought under control. This study is to evaluate the environmental effects on the susceptibility to stress corrosion cracking in Cr-Mo alloy under simulated crevice condition. The test is simulated by producing drop, wet and evaporation process. The XRF measurement is performed to investigate the amount and distribution of chromium carbide of grain boundaries. The tests are performed in the alkalic and acidic solution under various strain rates.

Improving the properties of aluminium alloys by retrogression and reageing

AbstractRetrogression and reageing heat treatments offer the potential of improved tensile properties in combination with greatly increased resistance to stress corrosion cracking. The potential of this technique is reviewed with respect to the current application in the European and North American Aerospace Industry. To illustrate the performance increase associated with RRA treatments, the stress corrosion cracking performance of the established aerospace plate and forging alloy 7010 has been evaluated using an alternate immersion constant load tensile type test (ECSS‐Q‐70‐37A) Specimens were cut from a large aerospace rectilinear forging and tested in three different tempers, T652, T7452 and a retrogressed and reaged condition (RRA). In the T652 condition the material has been shown to be highly susceptible to intergranular corrosion and stress corrosion cracking. In the T7452 and RRA conditions 7010 showed much improved resistance to SCC but pitting corrosion resulted in failure of some specimens within the 30day requirement of the test standard.

Inhibitory Effect of Boric Acid on Intergranular Attack and Stress Corrosion Cracking of Mill-Annealed Alloy 600 in High-Temperature Water

Abstract The inhibitory effect of boric acid (H3BO3) on the intergranular attack and stress corrosion cracking (IGA/SCC) propagation of steam generator (SG) tubing was studied under accelerated tes...

Effect of Thermal Exposure on the Corrosion Properties of an Al-Mg-Sc Alloy Sheet

The corrosion behaviour of a scandium containing Al-Mg alloy sheet was investigated performing accelerated corrosion tests. The material was studied in an annealed temper (2h at 350°C) and after additional heat treatments at temperatures ranging from 85 to 150°C for time periods up to 3000h. In the annealed condition, the sheet was resistant against intergranular corrosion and stress corrosion cracking and exhibited a moderate susceptibility to exfoliation corrosion. The corrosion resistance was decreased by thermal exposure at temperatures between 85 and 150°C, as indicated by high mass loss and severe exfoliation corrosion attack observed in the NAMLT test and ASSET test, respectively. When alternately immersed in 3.5% NaCI solution under static loading conditions, the scandium bearing Al-Mg alloy was found to be immune against stress corrosion cracking. For sheet material heat treated in the temperature range from 85 to 150°C, environment-induced failure was observed under the severe loading conditions of the slow strain rate testing technique using an aqueous solution of 3% NaCl + 0.3% H 2 O 2 . The deterioration in corrosion resistance of the Al-Mg-Sc alloy sensitised by thermal exposure was associated with grain boundary precipitation of a magnesium rich phase.

5517851 Method and apparatus for predicting onset of intergranular attack and stress corrosion cracking in tubing subjected to hostile environment

5517851 Method and apparatus for predicting onset of intergranular attack and stress corrosion cracking in tubing subjected to hostile environment

On the relationship between ∑3 n boundaries meeting at a triple junction

Recently, microstructures with the dominance of {Sigma}3{sup n} grain boundaries have attracted considerable attention by researchers. Such microstructures are rather common in different recrystallized materials with relatively low stacking fault energy: f.c.c. metals and alloys, semiconductors with a diamond structure, and intermetallics with an L1{sub o} and L1{sub 2} structures. {Sigma}3{sup n} boundaries are formed mainly by multiple twinning, therefore microstructures consisting entirely of such boundaries are sometimes called ``twin-related``. These microstructures are thought to be of paramount significance for grain boundary engineering, i.e. for developing materials resistant to intergranular degradation such as grain boundary fracture and intergranular stress corrosion. The objective of this note is to clarify some vague matters pertaining to the relation between {Sigma} boundaries meeting at a triple junction.

Quantitative mapping of time-temperature-strain effects on sensitization of type 316 stainless steels

Austenitic stainless steels (SS) are susceptible to the development of sensitization, or grain boundary chromium depletion (GBCD), during thermomechanical (TM) processing and fabrication treatments. Precipitation of chromium-rich M{sub 23}C{sub 6} carbides occurs on grain boundaries during TM treatment, leading to chromium-depletion in the vicinity of the interface. The induction of sensitization has been a recurring cause for intergranular (IG) corrosion and IG stress corrosion cracking (SCC) of primary and secondary power plant components for many years, and is also now being recognized as a potential cause for failure in SS containers used for storage and transport of nuclear and toxic waste materials. Research on sensitization development is, thus, important for understanding phenomena of IG corrosion and IGSCC in SS. Evaluation of thermal and strain cycle effects on carbide precipitation-chromium depletion development in SS also provides a key towards fundamentally understanding mechanisms of precipitate nucleation-growth in materials. While thermal effects on GBCD in SS have been studied for a range of isothermal and continuous cooling heat treatments, research on strain-induced sensitization has only been performed for limited strain and heat treatment schedules. Bain et al observed that straining of Type 304 SS about 50% caused development of accelerated, but less severe,more » sensitization due to precipitation of carbides within transgranular (TG) versus grain boundary regions. Later Tedmon, Vermilyea and Broecker found that TG depletion could also be rapidly desensitized (healed) during heat treatment. Bariant and Ritter observed TG corrosion in heavily deformed Types 304 and 316 SS during (450-800{degrees}C) heat treatment, but considered the onset of sensitization to be enhanced over annealed SS due to absence of previously reported rapid healing.« less

Deformation effects on chromium diffusivity and grain boundary chromium depletion development in type 316 stainless steels

This paper reports on austenitic stainless steels (SS) susceptible to the development of grain boundary chromium depletion (GBCD), or sensitization, during thermomechanical (TM) treatment. The depletion is induced by the precipitation of intergranular (IG) chromium-rich M23C6 carbides during the TM processes. The presence of GBCD produces localized breakdown of the chromium-rich passive oxide film that protects the SS. This renders the SS susceptible to IG corrosion and IG stress corrosion cracking (SCC) in certain aqueous environments. The development of GBCD is dependent on the thermodynamics of carbide precipitation and kinetics of chromium diffusion, both of which may be altered by thermal and strain cycles produced during TM treatment. A thermodynamic and kinetic evaluation of temperature and strain effects on GBCD phenomena can, therefore, be used to understand trends in precipitation-depletion processes occurring in SS during TM treatment. This can be extended further to develop a mechanistic understanding of TM effects on microstructure, microchemistry and property development in materials.

Analysis of Brittle Intergranular Crack Propagation During Stress Corrosion

AbstractCrack growth rates during intergranular stress corrosion, in materials such as Fe in Ca(NO3)2 at +750 mV (SCE), appear to exceed rates which can occur by dissolution and ion transport within the crack. Brittle crack jumps induced by a corrosion or stress corrosion process, and which magnify the dissolution supported crack velocity by a factor of up to 103, could explain this behavior. Hydrogen can induce these very fast crack growth rates, but these rates have been obtained at electrochemical potentials where H reduction is not thermodynamically possible. Other possible mechanisms for this accelerated crack growth include: 1) intergranularcorrosion altered tearing modulus, 2) grain boundary dealloying, or 3) adsorption induced brittle fracture. Examination of each of these mechanisms suggests that intergranular corrosion could reduce the tearing modulus through changes in the crack shape. However, crack opening analysis clearly shows that the crack tip is shielded from the applied stress intensity and that an embrittlement process which reduces the interface toughness is need for brittle intergranular crack jumps to occur. Further research is in progress to identify the source of this embrittlement.

Grain-Boundary Chemistry and Intergranular Stress Corrosion of Iron Alloys in Calcium Nitrate

Abstract Intergranular corrosion and stress-corrosion measurements have been made on Fe alloys in calcium nitrate at 60°C. Tests were conducted on material with grain-boundary chemistries ranging f...

Influence of Grain Boundary Microstructure on the Susceptibility of Alloy 600 to Intergranular Attack and Stress Corrosion Cracking

Abstract The influence of grain boundary microstructure on the susceptibility of thermally treated (TT) Inconel Alloy 600 to intergranular attack (IGA) and stress corrosion cracking (SCC) in 30%NaOH + 10%Na2SO4 at 350 C was investigated. Both mill-annealed (MA) and laboratory solution-annealed alloys were aged at 700 C to establish the effect of initial processing on the material's response to thermal treatment. Treatments of 1 h or more at 700 C greatly improved the SCC resistance of solution-annealed material but did not improve the performance of MA material containing a high density of intragranular carbides. The poor behavior of this material after thermal treatment was associated with the formation of small M23C6 carbides growing at a high angle to the boundaries and the development of these into cellular colonies. This is attributed to the use of a MA temperature that was too low to take into solution sufficient carbon for the development of semicontinuous grain boundary carbides during the subsequ...