UNS N06600 Research Articles

Predicting Susceptibility to Intergranular Stress Corrosion Cracking of Alloy 690

Abstract Susceptibility to intergranular attack (IGA) and intergranular stress corrosion cracking (IGSCC) of Alloy 690 (UNS N06690) was investigated using chemical etching, double-loop electrochemi...

Review of the Corrosion of Nickel-Based Alloys and Stainless Steels in Strongly Oxidizing Pressurized High-Temperature Solutions at Subcritical and Supercritical Temperatures

Abstract The corrosion phenomena of nickel-based Alloy 625 (UNS N06625), which in the present content is representative of other nickel-based alloys and stainless steels in strongly oxidizing solut...

Inhibitory Effect of Zinc Addition to High-Temperature Hydrogenated Water on Mill-Annealed and Prefilmed Alloy 600

Abstract The effect of zinc addition to pressurized water reactor (PWR) primary water on primary water stress corrosion cracking (PWSCC) susceptibility of mill-annealed Alloy 600 (UNS N06600, 600MA...

High-Resolution Characterization of Intergranular Attack and Stress Corrosion Cracking of Alloy 600 in High-Temperature Primary Water

Abstract Intergranular (IG) attack regions and stress corrosion cracks in Alloy 600 (UNS N06600) U-bend samples tested in 330°C pressurized water reactor water were characterized by analytical tran...

Effect of Galvanic Coupling Between Overpack Materials of High-Level Nuclear Waste Containers

Abstract Effect of environmental parameters and area ratio on the galvanic protection of Alloy 825 (UNS N08825) by A516 Grade 60 steel (UNS K02100) was studied. A simplified model was used to calculate the potential and corrosion current density of the bimetallic couple as a function of the galvanic coupling efficiency. Galvanic corrosion tests were performed to gain confidence in the calculated values. The modeling calculations and laboratory testing indicated that with highly efficient coupling the potential of the galvanic couple could be maintained below the repassivation potential for Alloy 825. As a result, the initiation of localized corrosion on Alloy 825 can be prevented. The formation of oxides, scales, and corrosion product layers between the barriers was shown to reduce the efficiency of the galvanic couple, which may result in conditions leading to the localized corrosion of the inner, corrosion-resistant barrier.

Study of passive film on stainless steels and high grade nickel base alloy using X-ray photoelectron spectroscopy

Abstract In the present study an assessment has been made of the air formed passive film and the passive film existing after a short exposure to a synthetic sea water environment on austenitic (UNS S31603), superaustenitic (UNS S31254 and UNS S32654) and superduplex (UNS S32760) stainless steels and a Ni base alloy (UNS N06625) using X-ray photoelectron spectroscopy. Assessment of their corrosion behaviour has been made through use of electrochemical accelerated tests supported by post-test microscopy. The passive film on the Ni base (low Fe) UNS N06625 alloy is remarkably similar to those formed on the high Cr and Mo stainless steels. It has been demonstrated that the Fe/Cr ratio in the passive film is dependent on alloy composition and on the conditions to which the material has been exposed, and a general correlation between passive film constitution and corrosion resistance is evident.

Effect of Cold Work and Processing Orientation on Stress Corrosion Cracking Behavior of Alloy 600

Abstract Cold work accelerates stress corrosion cracking (SCC) growth rates in Alloy 600 (UNS N06600). However, the variation in crack growth rates generated from cold-worked material has been sign...

Localised effects of macrofouling species on electrochemical corrosion of corrosion resistant alloys

Interactions between macrofouling and corrosion have been studied on two duplex stainless steels (UNS S31803 and UNS S32760), an austenitic stainless steel (UNS S31354), a nickel base alloy (UNS N06625), and a cobalt base alloy (UNS R30006) in long term tests conducted in natural sea water off the west coast of Scotland. After an 18 month exposure period, the specimens were heavily fouled primarily with barnacles and mussels and all the materials exhibited crevice corrosion at the specimen/resin interface, although this was less extensive on the nickel base alloy. Localised corrosion was observed under the base of live barnacles on UNS S31603 stainless steel. Direct current electrochemical anodic polarisation tests undertaken after the 18 month exposure period yielded unusually high currents in the range of potentials between the free corrosion value and the breakdown potential. However, long term exposure and associated macrofouling had little effect on the overall breakdown of general surface passivity as indicated by values of the breakdown potential. The higher currents were associated with the appearance, after the anodic polarisation, of black sulphide corrosion products at the specimen/resin crevices, around barnacles, and around mussel byssus threads.

Effects of Lead Oxide Addition on the Electrochemical Properties of Alloy 600 in Aqueous 1 M Sodium Hydroxide Solution

Abstract Effects of lead oxide (PbO) addition on the electrochemical properties of alloy 600 (UNS N06600) have been studied in aqueous 1 M sodium hydroxide (NaOH) solution at room temperature using...

Effect of Heat Treatment on Caustic Stress Corrosion Cracking Behavior of Alloy 600

Abstract Constant elongation rate tests (CERT) were conducted to evaluate the effect of heat treatment on intergranular stress corrosion cracking (IGSCC) susceptibility of alloy 600 (UNS N06600) in 140°C and 50% caustic solution at −900 mV vs saturated calomel electrode (SCE). Results showed: — Heat treatment at low temperature for a long time (600°C for 260 h) led to a material that was not susceptible to caustic intergranular (IG) cracking. Increase in heat treatment temperature enhanced IG cracking susceptibility. Caustic IGSCC susceptibility was at maximum near the carbon solubility limit. However, when the heat treatment temperature was higher than the carbon solubility limit, a significant decrease in crack growth rate was observed. — Grain boundaries acted as a preferential crack path when grain boundary carbon segregation was likely. Thermodynamic considerations suggested that severe caustic IGSCC susceptibility near the carbon solubility limit could be explained in terms of carbon segregation at ...

Effects of Silicon and Titanium on the Corrosion of Low-Alloy Steels in a Simulated Coal Gasification Environment at 600°C

Abstract Results of corrosion tests carried out on a series of Fe-12% Cr alloys in coal gasification environments at 600°C were studied. Effects of Si and Ti on corrosion resistance were assessed using data obtained from a commercial 12% Cr alloy, type 410 (UNS S41000), three specially cast “model” 12% Cr alloys containing 2.7% Si with Ti levels of 0%, 0.4% and 0.7%, respectively, and a higher alloy (type 28 [UNS N08028]) heat exchanger steel. Corrosion tests were carried out using a simulated dry-feed entrained slagging gasifier gas. The gas (64% carbon monoxide [CO], 3.8% carbon dioxide [CO2], 0.8% hydrogen sulfide [H2S], and balance H2 [in vol%]) was premixed and passed over the test pieces at a rate high enough to prevent thermodynamic equilibrium achievement. Results showed that Si had a strongly beneficial influence on corrosion resistance. Ti, depending upon the amount added, exerted a positive or negative influence on corrosion resistance and reduced problems associated with workability. The kinet...

Passive Dissolution and Localized Corrosion of Alloy 22 High-Level Waste Container Weldments

Localized corrosion of high level nuclear waste containers is considered an important factor that will have a strong influence on the overall performance of the proposed repository at Yucca Mountain, NV. The present candidate container material, Alloy 22 [UNS N06022 (57Ni-22Cr-13.5Mo-3W-3Fe)], is highly resistant to localized corrosion. Assessing the performance of the HLW containers also requires an evaluation of localized corrosion resistance and determination of the passive corrosion rate of Alloy 22 weldments. The localized corrosion resistance of welded Alloy 22 specimens was evaluated by measuring the repassivation potential in chloride containing solutions whereas potentiostatic tests were used to determine the passive corrosion rate of the welded material. The results for the welded material are compared to those for the base metal.

Effect of Silicon Compounds on Stress Corrosion Cracking of Alloy 600 in Caustic Solutions

Abstract Silicon compounds are abundant in both steam generator tube deposits removed from operating plants and in the hide-out return analyses performed during plant operation. Despite their abundance, the effect of these compounds on the susceptibility to intergranular attack (IGA) and stress corrosion cracking (SCC) of alloy 600 (UNS N06600) has not been established clearly in laboratory tests or under operating conditions. The present work studied the effect of different compounds of silicon, such as silica (SiO2) and sodium metasilicate (Na2SiO3), on the susceptibility to IGA/SCC of alloy 600 in caustic solutions, with and without impurities. Experimental work included measurement of potentiodynamic polarization curves and development of stress corrosion tests with potentiostatic control at 315°C. Results of both tests indicated an inhibiting effect of silicon compounds on stress corrosion of mill-annealed (MA) alloy 600. Polarization curves in solutions with silicon compounds showed a wider range of...

Intergranular Attack and Stress Corrosion Cracking Propagation Behavior of Alloy 600 in High-Temperature Caustic Solution

Abstract The effect of stress intensity factors (K) at the intergranular attack and stress corrosion crack (IGA/SCC) tips on the IGA/SCC propagation behavior of steam generator (SG) tubing was studied under accelerated test conditions. Values of K at the IGA/SCC crack tips were calculated using the statically indeterminate model. Based upon analysis of those factors, the double-cantilever beam (DCB) and SG model boiler tests were carried out to evaluate the effect of stress intensity on IGA/SCC crack propagation. K at the crack tips increased with increasing crack length. For a long crack, K decreased with an increasing numbers of cracks. However, for a short crack, K decreased slightly with an increasing number of cracks. DCB test results showed the IGA/SCC crack velocity of alloy 600 (UNS N06600) increased gradually with increasing K in the range from 15 MPa√m to ∼ 60 MPa√m. This is the range relevant to IGA/SCC crack tips of typical SG tubes under operating conditions of pressurized-water reactors. Met...

Corrosion Fatigue Crack Growth Rate in Sensitized Alloy 600 in Thiosulfate Solution at Room Temperature

Abstract Corrosion fatigue crack growth (FCG) behavior of alloy 600 (UNS N06600) sensitized at 1,100°C/0.5 h + 700°C/5 h in 0.1 M sodium thiosulfate (Na2S2O3) solution at room temperature under app...

Control of Alkaline Stress Corrosion Cracking in Pressurized-Water Reactor Steam Generator Tubing

Abstract Outer-diameter stress corrosion cracking (ODSCC) of alloy 600 (UNS N06600) tubings in steam generators of the Kori-1 pressurized-water reactor (PWR) caused an unscheduled outage in 1994. Failure analysis and remedy development studies were undertaken to avoid a recurrence. Destructive examination of a removed tube indicated axial intergranular cracks developed at the top of sludge caused by a boiling crevice geometry. A high ODSCC propagation rate was attributed to high local pH and increased corrosion potential resulting from oxidized copper presumably formed during the maintenance outage and plant heatup. Remedial measures included: (1) crevice neutralization by crevice flushing with boric acid (H3BO3) and molar ratio control using ammonium chloride (NH4Cl), (2) corrosion potential reduction by hydrazine (H2NNH2) soaking and suppression of oxygen below 20 ppb to avoid copper oxide formation, (3) titanium dioxide (TiO2) inhibitor soaking, and (4) temperature reduction of 5°C. Since application o...

Effects of Temperature and Thiosulfate on Chloride Pitting of Austenitic Stainless Steels

Abstract Potentiodynamic polarization curves were measured for types 304 (UNS S30400), 316L (UNS S31603), and 904L (UNS N08904) stainless steels (SS) in 1 M sodium chloride (NaCl) solutions with va...

Effects of the Valence of Sulfur on Passivation of Alloys 600, 690, and 800 at 25°C and 95°C

Abstract Effects of the valence of sulfur, as sulfur oxyanions and sulfide (S2− or HS−), on passivation of alloys 600, 690, and 800 (UNS N06600, N06690, and N08800) in various heat treatments were ...

Influence of Product Type on Stress Corrosion Cracking of Alloy 600

Abstract Stress corrosion cracking (SCC) initiation tests were carried out on alloy 600 (UNS N06600) in primary water at 325°C and 360°C and in steam with hydrogen at 400°C to gain some insight int...

Electrochemical, Galvanic, and Mechanical Responses of Grade 2 Titanium in 6% Sodium Chloride Solution

Abstract The electrochemical, galvanic, and mechanical responses of grade 2 titanium in 6% sodium chloride (NaCl) solution at different temperatures were investigated. The initial corrosion potential and cathodic reaction rate increased with decreasing pH and increasing temperature. The initial corrosion potential changed when titanium was coupled with other metals. Naval brass and alloy 600 (UNS N06600) anodically polarized titanium, while zinc and aluminum caused titanium to become a cathode. HY80 steel (UNS K31820), type 316 stainless steel ([SS] UNS S31600), and Monel K500 (UNS N05500, a copper-nickel alloy), polarized titanium anodically or cathodically depending upon temperature and pH. Hydrides formed on the titanium surface at potentials < ∼ −600 mVSCE to −700 mVSCE. Zinc at all temperatures and HY80 at high temperatures caused hydride formation in titanium when coupled galvanically with titanium. Mechanical tests showed an ≈ 10% decrease in ductility under prior and dynamic hydrogen charging cond...