Jun’ichi Sakai

Polarization Behavior of High-Alloy OCTG in CO2 Environment as Affected by Chlorides and Sulfides

Abstract Pitting corrosion resistance of 13% Cr steel, duplex stainless steel, and high Ni austenitic stainless alloys for Oil Country Tubular Goods (OCTG) has been examined by electrochemical meas...

Inhibition of hydrogen embrittlement of Ni-Ti superelastic alloy in acid fluoride solution by hydrogen peroxide addition.

Inhibition of the hydrogen embrittlement of Ni-Ti superelastic alloy in an acidulated phosphate fluoride (APF) solution has been attempted by adding various amounts of H(2)O(2). In a 0.2% APF solution, hydrogen absorption is markedly inhibited by adding H(2)O(2), although corrosion is slightly enhanced by increasing the amount of added H(2)O(2). By adding a small amount of H(2)O(2) (0.001 M), in the early stage of immersion, hydrogen embrittlement is inhibited and corrosion is only slightly enhanced. Upon adding H(2)O(2), it appears that the dominant cathodic reactions change from hydrogen evolution to H(2)O(2) reduction reactions, or the surface conditions of the alloy are changed by H(2)O(2) with a high oxidation capability, thereby inhibiting hydrogen absorption. The present study clearly indicates that infinitesimal addition of H(2)O(2) into acid fluoride solutions is effective for the inhibition of the hydrogen embrittlement of the alloy.

Strong interactions between hydrogen in solid solution and stress-induced martensite transformation of Ni–Ti superelastic alloy

Abstract The role of the dynamic interactions between hydrogen in a solid solution and the stress-induced martensite transformation in hydrogen embrittlement has been investigated using trained Ni–Ti superelastic alloy. In a cyclic tensile test in the stress plateau region caused by stress-induced martensite and reverse transformations after hydrogen charging, a further decrease in the critical stress for the martensite transformation is observed. In addition, the number of cycles to fracture for a trained specimen is significantly larger than that for a non-trained specimen. Since most of the charged hydrogen is preferentially trapped in defects induced by training, the hydrogen embrittlement is considerably suppressed as a result of decreasing interactions between the hydrogen and the transformation. The present results indicate that hydrogen in a solid solution more strongly interacts with the stress-induced martensite transformation than hydrogen trapped in defects, thereby further enhancing the hydrogen embrittlement related to phase transformations.

Effect of Relative Humidity on Ammonium Chloride Corrosion in Refineries

Abstract Corrosion behavior and the hygroscopic properties of solid ammonium chloride (NH4Cl) salt were investigated. This study was conducted to determine the root cause of significant corrosion caused by NH4Cl salt deposition in reactor-effluent streams in hydroprocessing units. Corrosion and water absorption tests were performed under various relative humidity (RH) conditions with solid NH4Cl salts using a temperature and humidity control chamber. Eight types of materials commonly used in refineries were examined, including carbon steel (UNS K02702), Type 304 (UNS S30400) stainless steel, duplex (UNS S39274) stainless steel, Grade 2 titanium (UNS R50400), Alloy 400 (UNS N04400), Alloy C-276 (UNS N10276), aluminum brass (UNS C68700), and aluminized carbon steel (hot-dip aluminized UNS K02702). Significant corrosion was observed around 60% RH on all the alloys except Alloy C-276. Carbon steel corroded above 20% RH. Its highest corrosion rate was observed at 60% RH and 80°C. Type 304 stainless steel and d...

First interactions between hydrogen and stress-induced reverse transformation of Ni–Ti superelastic alloy

Abstract The first dynamic interactions between hydrogen and the stress-induced reverse transformation have been investigated by performing an unloading test on a Ni–Ti superelastic alloy subjected to hydrogen charging under a constant applied strain in the elastic deformation region of the martensite phase. Upon unloading the specimen, charged with a small amount of hydrogen, no change in the behaviour of the stress-induced reverse transformation is observed in the stress-strain curve, although the behaviour of the stress-induced martensite transformation changes. With increasing amount of hydrogen charging, the critical stress for the reverse transformation markedly decreases. Eventually, for a larger amount of hydrogen charging, the reverse transformation does not occur, i.e. there is no recovery of the superelastic strain. The residual martensite phase on the side surface of the unloaded specimen is confirmed by X-ray diffraction. Upon training before the unloading test, the properties of the reverse transformation slightly recover after ageing in air at room temperature. The present study indicates that to change the behaviour of the reverse transformation a larger amount of hydrogen than that for the martensite transformation is necessary. In addition, it is likely that a substantial amount of hydrogen in solid solution more strongly suppresses the reverse transformation than hydrogen trapped at defects, thereby stabilising the martensite phase.

After-effects induced by interactions between hydrogen and the martensite transformation in Ni–Ti superelastic alloy

Abstract The effects of dynamic interactions between hydrogen and a stress-induced martensite transformation on the recovery of deteriorated tensile properties by ageing in air at room temperature have been investigated for a Ni–Ti superelastic alloy. A specimen is subjected to single stress-induced martensite and reverse transformations immediately after hydrogen charging. Upon tensile testing, brittle fracture occurs in the latter half of the elastic deformation region of the martensite phase after the stress-induced martensite transformation. Upon ageing before the tensile test, fracture occurs during the stress-induced martensite transformation. In addition, the nano- and micro-morphologies of the brittle outer part of the fracture surface of the specimen are changed by ageing. Thus, the tensile properties markedly deteriorate, rather than recover, by ageing. The present results clearly indicate that dynamic interactions between hydrogen and the stress-induced martensite transformation have serious after-effects on hydrogen embrittlement of Ni–Ti superelastic alloy.

Corrosion of Carbon Steel and Alloys in Concentrated Ammonium Chloride Solutions

Corrosion resistance and the behavior of carbon steel and alloys in high concentration ammonium chloride (NH4Cl) solutions were investigated. This study was conducted to better understand material ...

Critical Contents of Nickel and Chromium Required for SCC Resistance of High Alloy Oil Country Tubular Goods

Abstract Based on the laboratory SCC test results of 10 to 37% Cr, 25 to 45% Ni, 3% Mo, bal. Fe alloys, it is shown that the beneficial effect of increased Ni content on SCC resistance is retained only when the Cr content is appropriate. Good SCC resistance is obtained when the stability of austenite is above a critical value; therefore, the content of ferrite formers, e.g., Cr and Mo, should not exceed a certain limit determined by the content of austenite formers, e.g., Ni. The critical stability of austenite depends on the annealing temperature, a higher temperature requiring a higher stability of austenite.

Hydrogen Absorption Behavior of Titanium Alloys by Cathodic Polarization

Titanium and Ti-5mass%Ta alloy has been utilized in nuclear fuel reprocessing plant material because of its superior corrosion resistance in nitric acid solutions. However, Ti alloy have been known to high susceptibility of hydrogen embrittlement. To evaluate properties of hydrogen absorption and hydrogen embrittlement of Ti alloys, cathodic polarization tests and slow strain rate tests (SSRT) under cathodic polarization were carried out. Results show titanium hydrides covered on the surface of metals and hydrides thickness were within 10μm. But hydride did not observed at inner part of metals. Ti and Ti-5%Ta did not show hydrogen embrittlement by SSRT under cathodic charging. These results suggested that Ti and Ti-5%Ta could absorb hydrogen. But hydrogen did not penetrate inner portion of the metals more than 10μm in depth because titanium hydrides act as barrier of hydrogen diffusion. It is considered that retardation of hydrogen diffusion hindered hydrogen embrittlement of Ti and Ti-5%Ta alloys.Copyright

Development of technical module of erosion-corrosion in boiler water for carbon steel

RBM (Risk Based Maintenance) that is a promising technique for the maintenance of aged industrial plants. The risk here is defined as likelihood by multiplication of consequence. Likelihood is decided by means of a technical module of each damage mechanism. In each technical module, there are some damage sensitivity prediction models for several environments. Technical module is needed to determine likelihood of failure, but currently, available technical module to evaluate likelihood is limited mainly for refinery and petrochemical plants. This study is targeting to construct exhaustive technical modules. As the first step, the technical module of erosion-corrosion that is strongly required from many industries is developed. In this paper, a new corrosion rate prediction model of erosion-corrosion is proposed based on published data and the modification is done using originally collected actual plant data. Finally, it is demonstrated that the new model is adequate to predict remaining life of the plant that is damaged by erosion corrosion.