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• High-turbulent fluid pressures led to an erosion-wear corrosion failure mechanism and anti-abrasive coating can be used to modify the tube surface. • Wet H2S environment and iron oxidation led to tube pitting, leading to stress cracking that can be mitigated using claddings. • Humid environment with high sulfateate compounds and tensile residual stresses caused crack propagation. Excess residual stresses can be reduced by heat treatment. This study examined the premature failure of cupronickel (CuNi10Fe) tubes in a shell-and-tube heat exchanger after five months of service. An investigation to identify the root cause of the tube burst was carried out using macroscopic and microscopic inspection, chemical analysis, and mechanical analysis. The optical microscopy (OM) and scanning electron microscopy (SEM) evaluation revealed crack propagation characterized by pits and inclusions at the tube surface. This was due to the diffusion of hydrogen ions into the material from the hydrogen sulfide (H 2 S) rich geothermal environment. Furthermore, high tensile residual stresses of 172 MPa were recorded in the failed tube, leading to stress cracking in hydrogen-containing material. Additionally, the high sulfide content in corroded water and condensate samples suggests that the leading cause of tube rupture was through hydrogen embrittlement and sulfide stress cracking mechanism in the presence of hydrogen sulfide. Therefore, the use of laser cladding to protect tubes using functionally graded materials is recommended to mitigate degradation in aggressive environments, through careful material selection and additional water treatment to eliminate the contaminants. [ABSTRACT FROM AUTHOR]

The paper focuses on a novel method for enhancing the biofouling resistance of cupronickel (90-10 Cu-Ni) alloy by surface modification involving sand blasting, pickling and coating with silane. After optimizing the experimental parameters for polishing, pickling and sandblasting in order to develop a hydrophobic surface, the surface morphology and the wetting properties of the modified surface were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), confocal laser scanning microscopy (CLSM) and contact angle meter. The enhancement in resistance to bacterial adhesion was demonstrated by adhesion studies on Pseudomonas sp., the major biofilm former in marine environment. The silane based coating on the sand blasted surface of cupronickel alloy brought about two order reduction of bacterial attachment as compared to the control sample. [ABSTRACT FROM AUTHOR]

The solid solution alloys containing short-range order (SRO) structure, such as CuNi alloys, are not well structurally described using conventional quasi-disordered models. Based on the first-principles calculations, the optimal cluster-plus-glue-atom (CPGA) models of six typical solid solution CuNi alloys were demonstrated. These CPGA models are better to be used to describe the microstructure of the six CuNi alloys at the atomic scale from the viewpoint of energy. Our further study shown that the stabilities of CPGA models are highly related to the symmetry of initial CPGA models and the aggregation degree of solute atoms in CPGA models. In the condition of low solute Ni concentration, the stability of CPGA model is mostly determined by the symmetry of initial CPGA model, the CPGA model with high symmetry is more stable. As the concentration of solute Ni increasing, the aggregation degree of solute Ni atoms in CPGA models plays more and more important role. The CPGA model with higher aggregation degree of solute Ni is more stable. The simple selection method of optimal CPGA models, therefore is proposed, and which can be extended to other bielement solid solution AB alloys with positive mixing enthalpy of A-B. Using the selected CPGA models, we found the third additive atoms having negative mixing enthalpy with solvent and solute atoms prefer to reside the central site of characteristic principal cluster (CPC) of CPGA, and thereby enhancing the stability of alloys. Our studies provide a distinctive perspective to select the optimal CPGA models of solid solution alloys containing SRO structure and design alloy using the optimal CPGA model. [ABSTRACT FROM AUTHOR]

The critical exponents around the ferromagnetic–paramagnetic (PM-FM) phase transition and the magnetocaloric effect in the nanocrystalline (NC) Cu 50 Ni 50 powders have been investigated. The alloy powder exhibits a second order magnetic phase transition. For a field change of 1 and 7 T, - Δ S M peak increases from 0.30 to 1.54 J/kg.K, respectively, and the relative cooling power values were found to vary between 43.6 and 271.9 J/kg. The critical behavior has been studied in details by using the modified Arrott plots and critical isotherm plots. The obtained critical exponent values β = 0.505 , γ = 1.062 and δ = 3.037 are close to those predicted from the universal theory of mean-field model. This suggests that the magnetic interactions are long range around the Curie temperature, T C . Low cost magnetocaloric NC CuNi powders are good candidates for magnetic cooling applications. [ABSTRACT FROM AUTHOR]

Advances in flexible optoelectronic devices have led to increasing need for developing high performance, low cost, and flexible transparent conducting electrodes. Copper-based electrodes have been unattainable due to the relatively thermal instability and poor oxidation resistance. Herein, we present oxidation-resistive CuNi nanomesh electrodes that exhibit a low sheet resistance of ∼7.5 Ω/□ and a high optical transmittance of ∼81% at 550 nm. Further, high long-term stability against the effects of oxidation, heat, and chemicals is exhibited by the CuNi nanomesh, in comparison with the behavior of a pure Cu nanomesh sample. [ABSTRACT FROM AUTHOR]

The research of platinum metal recovery from compound solutions including process ones with high salt content in non-ferrous and other metals is given. Effective conditions for platinum metal sorption recovery from sulphate cupronickel solutions by nitrating and anodizing methods are stated. The level of platinum family recovery is 95-99%. [ABSTRACT FROM AUTHOR]

The paper describes an experimental study concerning the influence of major environmental parameters (temperature, chloride, carbon dioxide, and oxygen) on the corrosion behavior of 90/10 Cu–Ni alloys widely used for heat-transfer tubes. Electrochemical techniques have been used to investigate the corrosion behavior of 90/10 Cu–Ni alloys in aerated 3.5% NaCl solutions, at temperatures of 25, 50, and 80°C with and without the injection of carbon dioxide. The results have revealed increases in chloride corrosion rates of the 90/10 Cu–Ni alloy with temperature and decreases with CO2presence. Tests performed in aerated chloride–CO2solutions have shown higher corrosion rates relative to those conducted in deaerated chloride solutions saturated with CO2species. The surface morphology of polarized specimens in chloride solutions with and without CO2presence has shown a susceptibility to pitting attack. Pit characteristics have been found to be highly influenced by CO2presence. [ABSTRACT FROM AUTHOR]

This study on the population dynamics of fouling diatoms from a biofouling rich monsoon influenced tropical bay revealed that irrespective of the season and exposure period, the highest diatom abundance and species were encountered on non-toxic (fiberglass > glass) compared to toxic (copper–Cu and cupro-nickel–Cu-Ni) substrata. Though the diatom recruitment on toxic substrata is noticed within 24 h, the multiplication of the settled diatoms was not significant, even with an increase in the exposure period (days to weeks). The diatoms recorded on toxic substrata are the result of fresh recruitment. Results indicated that the potential of Cu and Cu–Ni panels to resist diatom fouling are the same. The dominance of raphid-pennate diatoms ( Navicula , Amphora , Nitzschia and Thalassionema ) throughout the year indicated them as ideal candidates for antifouling studies. The negligible contribution of araphid-pennate diatoms ( Licmophora and Grammatophora ) and the influence of tycho-pelagic/bloom forming diatoms ( Fragillariopsis and Skeletonema ) on fouling community are the other noteworthy observations. Concern with the adverse impact of Cu pollution on the ecosystem this study recommends the incorporation of Cu alloy (Cu–Ni) in the marine structures to combat biofouling as Cu–Ni has a slower leaching rate of the toxic product such as Cu 2 O. [ABSTRACT FROM AUTHOR]

Isothermal compression of BFe10-1-2 cupronickel alloy was carried out on a Gleeble-3800 thermal simulation machine in a wide range of temperatures (1023-1273 K) and strain rates (0.001-10 s-1). Then the experimental stress-strain data from isothermal hot compression tests were used to develop the constitutive equation. The effects of temperature and strain rate on deformation behaviors a represented by Zener-Holloman parameter in an exponent-type equation. The strain-dependent constitutive equation of BFe10-1-2 cupronickel alloy was proposed. Subsequently, the correlation coefficient (R) and the average absolute relative error (AARE) were introduced to verify the validity of developed constitutive equation, and values of R and AARE were 0.988 and 5.663% respectively, which indicated that the strain-dependent constitutive equation can lead a good agreement between the calculated and measured flow stresses in the elevated temperature range for the BFe10-1-2 cupronickel alloy. [ABSTRACT FROM AUTHOR]

The material used to produce one baht coin in the Royal Thai Mint has been changed from cupronickel (75% Cu and 25% Ni) to nickel-electroplated steel, not only for economic reasons but also for the durable properties of the latter. As a result, the higher hardness value of the new material (110 HV30 versus 80 HV10) combined with the high accuracy requirements of the coin detail have reduced the durability and lifetime of coining tools. The number of coins produced by a single coining tool was reduced from approximately 300,000 to only 40,000 coins. However, the tool life can be increased if proper selections of tool material and hard thin film coating technique are made. Two types of tool material were selected: cold working tool steel, 0.97% C and warm working tool steel, 0.5% C. CrN, TiN and TiCN coatings were examined using physical vapour deposition (PVD). It was determined that the type of tool material, the type of coating material, the coating temperature and the coating thickness influenced the lifetime of a coining tool. For the conditions studied, a 3-µm-thick TiN coat on warm working tool steel produced under a coating temperature of 400 °C provided the maximum tool life up to 1.22 million strokes. [ABSTRACT FROM AUTHOR]

Experiments were conducted on the condensing heat transfer of eleven horizontal tubes with refrigerant R134a at saturated temperature of 40 °C (1.01 MPa). The tube materials are titanium, cupronickel (B10 and B30), stainless steel and copper, among whom the former four materials are of low thermal conductivity. The enhanced tubes include integral-fin and three dimensional geometries. The results indicate that the heat transfer coefficients of the enhanced copper tube are about 1.6-2.1 times of low thermal conductivity tubes with the same enhanced geometries. Compared with plain tube the mean enhanced ratio of tubes made from titanium, B10, B30 and stainless steel are 8.48, 8.31, 8.22 and 7.52, respectively. The reason why low thermal conductivity affects the condensation heat transfer of enhanced structure is discussed in detail. [ABSTRACT FROM AUTHOR]

Abstract: Cupronickel was used as the electrode material to fabricate microstructures on polycrystalline diamond by electrical discharge machining (EDM). The electrodes were shaped into tiny rotary wheels driven by the flow of EDM fluid. Results showed that material removal rate was improved by a factor of five compared to conventional electrode materials. Raman spectroscopy and energy dispersive X-ray spectroscopy indicated that graphitization of diamond and diffusion-based chemical reactions between nickel and diamond dominated the EDM process. Effects of electrode rotation rate and discharge energy on the EDM characteristics were clarified. High form accuracy (∼0.5μm/1mm) and low surface roughness (∼0.1μm Ra) were obtained. [Copyright &y& Elsevier]

Abstract: The effects of room-temperature deformation on mechanical properties, the microstructure and texture evolution of continuous columnar-grained BFe10-1-1 cupronickel alloy tubes during room-temperature rolling and drawing were investigated. The results showed that continuous columnar grains were gradually thinned down into fiber microstructure, and the degree of working-hardening of the BFe10-1-1 alloy was increased continually with the increase of room-temperature reduction during rolling and drawing. After the rolling deformation degree of 82.8%, the ultimate tensile strength (UTS) of the BFe10-1-1 cupronickel alloy tubes increased to 418.7MPa from 212.0MPa of the as-cast state, and the elongation (El) of 8.5% was still obtained. The as-rolled BFe10-1-1 cupronickel alloy tubes were further drawn to the deformation degree of 99.0%, and the ultimate tensile strength (UTS) increased to 603.7MPa and the elongation (El) reduced to 2.2%. The excellent room-temperature extensibility of the continuous columnar-grained BFe10-1-1 cupronickel alloy tubes is significantly beneficial from the relative high volume fraction of the <100> texture as well as low angle boundary. [Copyright &y& Elsevier]

Abstract: Corrosion of the metal oxide surface of cupronickel (CuNi) alloys is a problem in applications such as household water pipes, industrial pipelines, and marine vessels. On other substrates, thin films have been used as barriers to corrosion. Here, the formation of self-assembled monolayers (SAMs) on the CuNi metal oxide surface has been investigated. Stable, well-ordered SAMs of octadecylphosphonic acid (ODPA) and 16-phosphonohexadecanoic acid (COOH-PA) were formed on the metal oxide surface of CuNi foils (55% Cu/45% Ni) using a solution deposition method. The ODPA modified surfaces could be used to provide a non-reactive barrier that inhibits corrosion of the CuNi metal oxide surface. Meanwhile, COOH-PA films could be used for further surface reactions such as surface initiated polymerization, in which polymer coatings are grown directly from a well-ordered film. Film-modified surfaces were characterized using diffuse reflectance infrared Fourier transform spectroscopy, contact angle analysis, and matrix assisted laser desorption ionization time of flight mass spectrometry. The ability of the films to inhibit corrosion by limiting oxidation of the CuNi surface was assessed using cyclic voltammetry. [Copyright &y& Elsevier]

Abstract: Corrosion inhibition of Cu–30Ni alloy in aerated 0.5M H2SO4 solution by cysteine, an amino acid, has been investigated. Potentiodynamic polarization and impedance spectroscopy (EIS) at open circuit potential were performed. Corrosion current density was also determined from colorimetric experiments. Voltammetric curves showed that cysteine addition to 0.5M H2SO4 affects largely the cathodic process; shifting the corrosion potential to more negative values and decreasing significantly the corrosion current density. The inhibiting efficiency reaches a value of 91% at an inhibitor concentration of 10−3 M. Impedance data reveal the adsorption of the inhibitor and the surface relaxation process due to nickel. Polarization resistance deduced from impedance measurements or voltammetric experiments are in a good agreement. [Copyright &y& Elsevier]

Abstract: Pin-hole leakage was observed in a number of 90/10 cupronickel evaporator tubes of a chilling plant which was in service for about 6years. Chilled water is cooled from 12°C to 7°C which flows inside the evaporator tubes, while the OD side has LiBr environment. The failure investigation of the failed tubes revealed greenish/blackish uniform deposits together with some spots where localized thick deposits on the ID surfaces were present. Underdeposit corrosion beneath these thick deposits was the primary reason for failure of the tubes. Intergranular corrosion was also observed underneath the thick deposits. The ID surface of the failed tubes confirmed the presence of wide variety of deposits, e.g. carbonates, silicates, phosphates, and sulphur-bearing compounds. The stagnant conditions under the thick deposits alter the chemistry inside the crevices thus formed. The altered chemistry conditions caused rapid corrosion (and intergranular attack) on the cupronickel tubes. Remedial measures that may be undertaken to prevent future occurrence of the problem are addressed. [Copyright &y& Elsevier]

Abstract: The failure of 90/10 cupronickel heat exchanger tubes in hydrogen coolers were seen after few years in use. The tubes had river water flowing at a velocity of 2.5m/s. The shell side was exposed to hydrogen at a pressure of 3.5kg/cm2. The inlet and outlet temperature of the cooling water of the cooler are 37°C and 47°C, respectively. The failures were pin hole type with a thick layer of muck deposit on the inner side of the tube. The metallographic studies carried out for the tube showed a well annealed microstructure. The region near the pit showed attack along the grain boundaries with dislodging of the grains. The electron probe micro analysis (EPMA) studies revealed the denickelification near the pits. The energy dispersive spectroscopy (EDS) analysis of the pit showed the presence of copper chloride and also the variation in the copper and nickel concentration with respect to the unaffected regions of the tube. Microbial presence was detected in the water as well as the muck deposits in the tubes. The pin hole failure of the tube was a result of the combined action of the chloride as well as the deposits in the tube which gave a conducive environment for the microbial activity to flourish which has caused the propagation of the pit through intergranular corrosion. [Copyright &y& Elsevier]

Abstract: Failure analysis of cupronickel condenser tubes of a crude distillation unit of a petrochemical refinery has been conducted. Condenser tubes carrying sea water were found to undergo premature failure which was preceded by extensive overall thinning, formation of shallow channels, pits, etc., and greyish-black internal deposits in one of the units. In the other unit, the failure of tubes was noticed without any significant overall thinning and in the presence of adherent, hard and black-brown deposits. The studies indicated that the increased velocity of sea water as well as the deficiency of iron in the alloy had resulted in failure in one case whereas relatively low velocity of water associated with deposition of sludge and bio-fouling were the causes of failure in the other case. The failure of tubes could be controlled by maintaining the water velocity within a specified range, flushing the tubes with clean water, use of anti fouling paints, selecting a more appropriate composition of the cupronickel alloy, through control of sea water sulphur level, etc. [Copyright &y& Elsevier]

Abstract: On the basis of high temperature ductility tests in single-phase cupronickel CuNi25 sample has been found a relation between microstructure, grain size and effect of ductility minimum temperature (DMT). Metallographic tests confirmed literature studies that cracks nucleate at points of two or three grain joints and cross-cut of twined grain with border of the grains. The non-homogeneous character of chemical composition concentrating in areas of grain joints and cracks at high temperature has been investigated by linear and point Cu and Ni analysis (EDS). This analysis shows that local areas of non-equilibrium formation concentrate at this places. This fact can be accepted as one of the reasons of non-homogeneous deformation, cracking and its location at DMT. Experimental results were compared with two-dimensional finite element method (FEM) simulation results of proposed hypothesis of non-uniform deformation. [Copyright &y& Elsevier]

• A heat-exchanger (cupronickel tubes, mild steel baffles) showed leakage in a tube. • Thinning of the tube had occurred from the OD side only at baffle locations. • Loose debris of magnetite and adherent CuO detected on the tube OD surface. • Deformation of tube at baffles, reflected by deformed grains and hardness increase. • Failure of the tube was concluded to be caused by fretting corrosion. The present paper describes a failure investigation of a tube that had shown leakage in a shell and tube type heat-exchanger with 70/30 cupronickel tubes and mild steel baffles (13 nos.). Corrosion damage or thinning of the failed tube was found to have occurred from the outer surface at all the baffle locations. Further examination of the failed tube was done using an optical microscope, a scanning electron microscope equipped with energy dispersive spectroscopy, Raman spectroscopy and an instrumented microhardness indentation machine for hardness measurement. Based on the results, it was concluded that the failure and the loss in wall-thickness of the tube at locations where it was in contact with the mild steel baffles were caused by fretting corrosion. The focus of this investigation is to bring out the metallurgical changes and the surface conditions (including changes in microstructure and microhardness, mode of corrosion attack and type of oxides/corrosion products) of the tube material undergoing fretting corrosion at micro level. Recommendations to avoid such a failure are also suggested. [ABSTRACT FROM AUTHOR]