UNS N06600 Research Articles

Microstructure and Properties of Laser Deposited and Wrought Alloy K-500 (UNS N05500)

Feasibility tests were performed by manufacturing transition joints between Nickel-200 (Ni-200) and Alloy K-500 (K-500) with direct laser deposition. Both sharp and functionally graded interfaces were manufactured with no apparent issues. In addition, Alloy K-500 specimens were manufactured with direct laser deposition to analyze the isothermal hardening response of Alloy K-500. The laser deposited and wrought materials were precipitation hardened at three different temperatures (600 °C, 650 °C, and 700 °C) and various times. A relationship between the hardness and the volume fraction of Ni3(Ti,Al) was developed, and the subsequent analysis showed that the corresponding Johnson-Mehl-Avrami time constants (or n-values) ranged from 1.1 to 1.3 at an aging temperature 600 °C, and decreased to values ranging from 0.6 to 0.66 at an aging temperature of 700 °C. For site saturation and spherical precipitates, the expected n-value is 1.5. This analysis showed that the mechanism for precipitation changed as a function of temperature. The results of the analysis at higher temperatures were rationalized by the possibility of the decay of quenched-in vacancies, precipitation along the grain boundaries, and precipitation along the dislocations. It was, however, difficult to confirm these possibilities with transmission electron microscopy (TEM), since imaging the precipites is difficult at very early aging times. Finally, it was determined that the heat treatment schedule of laser welded or laser clad Alloy K-500 should be similar to that of wrought Alloy K-500.

Localized Corrosion: An Empirical Approach to the Study of Passive Film Breakdown Rates

Electrochemical tests lasting 600 h to 6,000 h, at different potentials, were carried out on Type 316L (UNS S31603), Type 904L (UNS N08904), and nickel alloy 825 (UNS N08895) in sodium chloride (NaCl) solutions. A statistical approach was adopted using samples of 10 to 60 specimens. The pitting or crevice corrosion behavior was reported using cumulative frequency of passive film breakdown vs. time. In this work, we considered the formation of stable occluded cells as the breakdown of passive film. Each corrosion system “passive alloy-environment-geometry-time” was characterized by straight lines (i.e., breakdown rate of passive film, ρb), with a higher slope in the initial stage and a lower slope after some tens/hundreds of hours. The ρb can be used in the design for material selection and industrial maintenance schedules.

Effect of potential formation on the electrochemical behaviour of a highly alloyed austenitic stainless steel in contaminated phosphoric acid at different temperatures

The electrochemical behaviour of the highly alloyed austenitic stainless steel UNS N08031 (Alloy 31) in a contaminated phosphoric acid solution is studied using potentiodynamic curves, EIS and Mott–Shottky. The relative stability of the films formed on Alloy 31 has been studied after a pre-passivated treatment at 0.3, 0.5, 0.8 and 1VAg/AgCl, potentials within the passive domain. The protection of Alloy 31 was provided by the inner oxide film, while the outer film was more defective. The electronic-semiconducting properties of the passive films have been correlated to corrosion resistance. Passivated Alloy 31 at 0.8VAg/AgCl showed lower concentration of charge carriers, which beneficially affects the protecting and electronic properties of the passive oxide film.

Technical Note:Microstructure Effects in the Stress Corrosion Cracking of Alloy 28 Under Sour Conditions

Alloy 28 (UNS N08028), an important candidate material for sour gas well service, was investigated for sensitivity to stress corrosion cracking under a sour environment simulating the down-hole ser...

Systematic study of the corrosion properties of selected high-resistance alloys in natural seawater

Electrochemical measurements were conducted to evaluate localized corrosion on UNS S31603, UNS S31803, UNS S32750, UNS S31254 and UNS N08825 in natural seawater. Critical pitting and crevice temperatures were assessed using a potentiostatic technique and critical potentials for pitting and crevice corrosion initiation and repassivation were identified using potentiodynamic polarization at temperatures from 5 to 40°C. Passivity breakdown always occurred through pitting and crevice growth above a transition temperature. Below this temperature, pitting corrosion was not observed on any of the alloys regardless of the applied potential, but initiation of crevice corrosion occurred after the alloys reached a transpassive potential.

Passivity degradation of nuclear steam generator tubing alloy induced by Pb contamination at high temperature

Effects of Pb contamination on the passivity of a Ni-based alloy (UNS N06690) in a simulated crevice chemistry of steam generator with near-neutral pH at 300°C are elucidated using electrochemical measurements and surface analysis techniques. The experimental observations reveal that Pb impurity can enter anodic film, which results in substantial changes in the films structure via hindering the dehydration during the passivation and retarding the formation of spinel oxides. The presence of Pb-contamination can also increase hydrogen content in anodic film. Finally, the mechanism of passivity degradation induced by Pb contamination is described on the basis of the experimental data and established theory.

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 performance in severe NH4Cl corrosive environments in refineries. Immersion tests were performed under boiling 20 wt% and 40 wt% NH4Cl solutions. Sixteen materials commonly used in refineries and two new alloys were examined, including carbon steel; aluminized carbon steel; aluminum brass; Types 405, 410, 304L, 316L, and 321 stainless steels (UNS S40500, S41000, S30403, S31603, and S32100); 300-series stainless steel with 6% Mo; two types of super duplex stainless steels; Alloys 800, 625, and C-276 (UNS N08800, N06625, and N10276); Grade 2 and Grade 19 titanium (UNS R50400 and R53530); Alloy A (equivalent to a modified Type 317L [UNS S31703] stainless steel); and a modified Alloy 825 (UNS N06845). Significant corrosion was observed in carbon steel in both solutions. The corrosion rates of carbon steel were as high as 25.4 mm/y and 60.4 mm/y in 20 wt% and 40 wt% NH4Cl solutions, respectively. However, neither general corrosion nor pitting was observed on titanium alloys and alloys with a pitting resistant equivalent number (PREN) of 40 and higher. The maximum pit depth had a close relationship with the PREN. In addition, an electrochemical study was used to investigate the corrosion behavior of carbon steel. The effects of the temperature and NH4Cl concentration were determined from polarization curves and the corrosion potential.

Influence of Microstructure on Pitting Corrosion Resistance of Alloy 904L Superaustenitic Stainless Steel

Alloy 904L (UNS N08904) is a superaustenitc stainless steel with high Cr and Mo additions. The steel also contains high nickel content, which is important to maintain the austenitic structure. Because of its high corrosion resistance, Type 904L alloy is being used in much equipment in chemical and petrochemical plants. Some of this equipment may experience high temperatures in service or during fabrication. The microstructural changes associated with exposures in the range of 650°C to 850°C or as a consequence of melting were analyzed in this paper. The microstructure/corrosion resistance relationships were studied by means of electrochemical pitting corrosion tests and microstructural analysis. Critical pitting temperatures (CPT) of annealed and cast specimens were determined and compared. The results show that the corrosion resistance can vary significantly with fabrication processes and/or service at high temperatures.

Effect of Heat Treatment on Corrosion Behavior of Alloy 690 and Alloy 693 in Simulated Nuclear High-Level Waste Medium

Nickel-based alloys are being considered as candidate materials for the storage of high-level waste generated from the reprocessing of spent nuclear fuel. In the present investigation, Alloy 690 (UNS N06690) and Alloy 693 (UNS N06693) were assessed using the potentiodynamic anodic polarization technique for the corrosion behavior in the solution-annealed and sensitized conditions, in 3 M nitric acid (HNO3) and simulated high-level waste (HLW) at 25°C and 50°C. From the results of the investigation, it was found that the polarization curves for the solution-annealed specimens were characterized by a long passive range and low passivation current density, at 25°C. Increasing solution temperature to 50°C led to a corresponding increase in corrosion potential as well as passivation current density. The solution-annealed specimen showed improved corrosion resistance compared to the sensitized specimen in both media, for both alloys. Double-loop electrochemical potentiokinetic reactivation (DL-EPR) test was carried out for both solution-annealed and sensitized Alloy 690 and Alloy 693 in 0.5 M sulfuric acid (H2SO4) containing 0.0001 M potassium thiocyanate (KSCN), to measure the degree of sensitization (DOS). Microstructural examination was carried out by optical microscopy and scanning electron microscopy (SEM) after electrolytic etching. The results of the present investigation are discussed in the paper.

Alloy 718 for Oilfield Applications

Alloy 718 (UNS N07718) was developed for use in aircraft gas turbine engines, but its unique combination of room-temperature strength and aqueous corrosion resistance made it a candidate for oilfield fasteners, valves, drill tools, and completion equipment. As well environments became more severe, stress corrosion and hydrogen embrittlement failures in production equipment drove the evolution of the composition and microstructure that distinguish today’s oilfield-grade 718 from aerospace grades. This paper reviews the development of the grade and its applications and describes some of its unique characteristics, testing, and manufacturing methods as well as newer alloys designed for high-pressure high-temperature (HPHT) conditions.

Effect of Buffer Capacity on Electrochemical Corrosion Behavior of Alloy 800 in Sulfate Solutions

Abstract Electrochemical corrosion behavior of Alloy 800 (UNS N08800) in sulfate solution was compared in the presence and absence of potassium phosphate monobasic/sodium hydroxide (KH2PO4/NaOH) buffering reagent. Cathodic polarization, cyclic voltammetry, and electrochemical impedance spectroscopy were used to characterize the behavior of hydrogen peroxide (H2O2) reduction in buffered and unbuffered solutions. Open-circuit potential measurements, polarization resistance, electrochemical impedance spectroscopy, and potentiodynamic polarization were utilized to evaluate the corrosion behavior of Alloy 800 as affected by the buffer reagent. Results showed that reduction of H2O2 takes place at higher potentials and with lower charge-transfer resistance in buffered solutions. The Alloy 800 passive layer thickened in the presence of the buffering reagent and showed lower corrosion rate. The overall anodic potentiodynamic behavior was similar in both the buffered and unbuffered solutions. Because of its bufferi...

Passivation behaviour of Alloy 31 (UNS N08031) in polluted phosphoric acid at different temperatures

The influence of temperature (20–80 °C) and chloride concentration (0.06–0.42 wt.% KCl) on the electrochemical behaviour of the UNS N08031 was studied in 40 wt.% polluted phosphoric acid solution. Passivation behaviour was investigated by using potentiostatic tests at different potentials. From the linear regions of the log i vs. log t transients, the parameter n was obtained. The results showed that the applied potential hardly affects on the passivation rate n. However, n values decreased when temperature increased. The values of n demonstrated that the passive film formed on Alloy 31 was compact and highly protective.

Thermogalvanic corrosion of Alloy 31 in different heavy brine LiBr solutions

Thermogalvanic corrosion generated between two electrodes of Alloy 31, a highly-alloyed austenitic stainless steel (UNS N08031), has been investigated imposing different temperature gradients in three deaerated LiBr solutions, under open circuit conditions by using a zero-resistance ammeter (ZRA). Besides EIS spectra were acquired in order to explain the obtained results. On the whole, cold Alloy 31 electrodes were anodic to hot Alloy 31 electrodes, since an increase in temperature favoured the cathodic behaviour of the hot electrode. Thermogalvanic corrosion of Alloy 31 in the LiBr solutions studied was not severe, although it negatively affects the corrosion resistance of the cold anode. The protective properties of the passive film formed on the anode surface were found to improve with thermogalvanic coupling time.

ATI 625HP

Abstract ATI 625HP is a restricted composition of UNS N06625 with exceptional fatigue resistance. This datasheet provides information on composition, physical properties, and tensile properties as well as fracture toughness and fatigue. It also includes information on corrosion resistance as well as forming and joining. Filing Code: Ni-691. Producer or source: Allegheny Ludlum.

Materials and Corrosion 5/2011

Materials and CorrosionVolume 62, Issue 5 Cover PictureFree Access Materials and Corrosion 5/2011 First published: 03 May 2011 https://doi.org/10.1002/maco.201190013AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract Cover: Metallic structure of X1NiCrMoCu32-28-7 (UNS N08031, alloy 31, 1.4562) welded with SG-NiCr23Mo16 (FM 59, 2.4607) after 4 weeks in the vapor phase of nitrating acid (mixture of 66 % HNO3, 34 % H2SO4) at 55 °C. No further treatment of the surface was made. Corrosion behavior was investigated at BAM, the Federal Institute for Materials Research and Testing, in order to extend the BAM-List, where the suitability of materials for transport tanks carrying Dangerous Goods is evaluated. More detailed information can be found in: R. Bäßler. M. Weltschev, H. Alves, M. Langer, Corrosion Resistance of Alloy 31 and 59 in Highly Corrosive Dangerous Goods, Proceedings NACE International Corrosion Conference 2010 San Antonio, paper 10340. Volume62, Issue5May 2011 RelatedInformation

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...

Materials and Corrosion 4/2011

Materials and CorrosionVolume 62, Issue 4 Cover PictureFree Access Materials and Corrosion 4/2011 First published: 05 April 2011 https://doi.org/10.1002/maco.201190010AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Abstract Cover: Metallic structure of X1NiCrMoCu32-28-7 (UNS N08031, alloy 31, 1.4562) welded with SG-NiCr23Mo16 (FM 59, 2.4607) after 4 weeks in the vapor phase of nitrating acid (mixture of 66 % HNO3, 34 % H2SO4) at 55 °C. No further treatment of the surface was made. Corrosion behavior was investigated at BAM, the Federal Institute for Materials Research and Testing, in order to extend the BAM-List, where the suitability of materials for transport tanks carrying Dangerous Goods is evaluated. More detailed information can be found in: R. Bäßler. M. Weltschev, H. Alves, M. Langer, Corrosion Resistance of Alloy 31 and 59 in Highly Corrosive Dangerous Goods, Proceedings NACE International Corrosion Conference 2010 San Antonio, paper 10340. Volume62, Issue4April 2011 RelatedInformation

Crevice corrosion testing methods for measuring repassivation potential of alloy 22

Alloy 22 (UNS N06022) belongs to the Ni–Cr–Mo family, and it is highly resistant to general and localised corrosion; however, it may suffer crevice corrosion in aggressive environmental conditions. The susceptibility to crevice corrosion is measured by the value of the repassivation potential. The objective of this work is to compare different electrochemical methods for determining the repassivation potential of alloy 22; these include cyclic potentiodynamic polarisation, Tsujikawa–Hisamatsu electrochemical, potentiodynamic–potentiostatic–potentiodynamic and potentiodynamic–galvanostatic–potentiodynamic methods. The potentiodynamic–galvanostatic–potentiodynamic technique was found to be the most conservative laboratory technique, which gave the lowest repassivation potential in a relatively short testing time. The polytetrafluoroethylene (PTFE)-wrapped ceramic crevice formers formed more severe crevices, leading to higher repassivation potentials than the solid PTFE crevice formers. Torque values higher than 2 N m were needed for obtaining reliable repassivation potentials. Surface roughness did not affect significantly the repassivation potential.

Corrosion Resistance and Galvanic Coupling of UNS N08031 Base Metal, Heat-Affected Zone, and Weld Metal in Phosphoric Acid at Different Temperatures

Abstract Open-circuit potential tests and potentiodynamic anodic polarization curves have been carried out to obtain information about the electrochemical behavior of a highly alloyed austenitic stainless steel (UNS N08031) used as base metal (BM), heat-affected zone (HAZ) region, and weld metal (WM). The weld was performed using the gas tungsten arc welding technique (GTAW) with a nickel-based alloy (UNS N06059) as filler metal. The galvanic corrosion generated by the electrical contact between the base metal, the HAZ, and the weld metal was estimated from the polarization diagrams according to the mixed potential theory. The objective of the present work was to study the effect of the solution temperature on the corrosion resistance of the studied materials. These materials were tested in 5.5 M phosphoric acid (H3PO4) solution at 25°C, 40°C, 60°C, and 80°C. Results demonstrated that materials passivated spontaneously in the studied solution and their corrosion resistance decreased with temperature.

Dependence of Stress Corrosion Cracking of Alloy 690 on Temperature, Cold Work, and Carbide Precipitation—Role of Diffusion of Vacancies at Crack Tips

Abstract The growth rate of stress corrosion cracking (SCC) was measured for cold-worked, thermally treated Alloy 690 (UNS N06690, CW TT 690) and cold-worked, solution-treated Alloy 690 (CW ST 690) in hydrogenated pressurized water reactor (PWR) primary water under static load condition. Three important patterns were observed. First, intergranular stress corrosion cracking (IGSCC) was observed in CW TT 690 in PWR primary water in the range between 320°C and 360°C; this rate of SCC growth was slower than in CW mill-annealed Alloy 600 (UNS N06600, CW MA 600). No significant IGSCC was observed in CW ST 690 after 5,109 h in hydrogenated PWR primary water at 360°C. This is opposite of the behavior reported in the literature for high-temperature caustic solutions. Second, to assess the role of creep, rates of creep crack growth were measured in air, argon, and hydrogen gas environments using 20% CW TT 690 and 20% CW MA 600 in the range between 360°C and 460°C; intergranular creep cracking (IG creep cracking) wa...