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ABSTRACT The corrosion behavior of copper-brazed joints with a ternary filler metal, Cu-P-Ag (74.75% Cu, 7.25% P, 18% Ag) in the form of wire for brazing, was studied in 400 g/L, 700 g/L, 850 g/L, and commercial lithium bromide (LiBr) solution (850 g/L LiBr solution with 4.3 g/L lithium chromate [Li2CrO4] as inhibitor and 0.08 g/L lithium hydroxide [LiOH] as pH control) at 25°C. Corrosion resistance was studied on three different geometrical types of electrodes designed to study copper-brazed joints. Type 1 or filler metal (FM) was tested to study the influence of the alloying elements on the copper corrosion resistance. Type 2 or melted filler metal (MFM) was used to study the thermal effect on the filler metal corrosion behavior. Type 3 Cu//(CuP-Ag) or brazed copper was configured to study the brazing method, the melting process on copper, and the galvanic effect on copper-brazed joints. Corrosion resistance was estimated from the polarization curves. Metallographic examination was carried out to characterize the microstructure of the samples. The results showed that Li2CrO4 improved corrosion resistance of brazed joints with inhibiting efficiencies up to 95%. In the commercial solution, the alloying elements in copper improved corrosion resistance; however, the melting process shifted open-circuit potential (EOCP), critical potential (Ec), and corrosion potential (Ecorr) toward more negative values. Galvanic studies showed that copper behaved as the anode when coupled to the simulated copper-brazed joint, Type 3 configuration; however, it behaved like the cathode with the melted filler metal in the most concentrated solutions. Aqueous solutions containing high concentrations of lithium bromide (LiBr) are used as the most effective absorbent in absorption heating and refrigerating systems that use natural gas or steam as energy sources1-5 because of their favorable thermophysical properties, high heat of hydration, high solubility of solid phases, good thermal stability, and appropriate viscosity.6 However, it can cause serious corrosion problems of structural materials in a heat absorption plant.7 The high electrical conductivity of copper is matched by its excellent thermal conductivity, which makes copper the first choice for the manufacturing of heat exchangers. Comparing copper, aluminum, and steel, copper is by far the best conductor of heat. In addition, copper and copper alloys present good mechanical properties and corrosion resistance in such environments. Copper tubes and fittings are easily joined metallurgically by soldering or brazing. Brazed joints with filler metals that melt above 450°C and capillary fittings are used for refrigeration piping where high joint strength is required or where service temperatures can be as high as 177°C.8 Copper-phosphorus brazing alloys (BCuP),9 often with silver added as a third element, are used extensively for joining copper, especially in refrigeration and air-conditioning copper piping and electrical con-
ABSTRACT A new method has been developed for online visualization of corrosion processes. The system allows surface images of the tested electrode to be captured simultaneously with the recorded electrochemical signal caused by corrosion processes without disturbing the electrochemical system. The experimental device consists of an electrochemical system with a horizontal electrochemical cell coupled to optical equipment. The horizontal position of the electrodes tested permitted the direct observation of surface modifications with time and of the experimental conditions by means of a triocular microscope stereoscope assembled to an image acquisition system. The new methodology was applied in the study of zinc corrosion and galvanic behavior when coupled to copper in lithium bromide (LiBr) media. Zinc exfoliation was observed in potentiodynamic tests. Zero-resistance ammetry was the electrochemical technique used to evaluate the galvanic corrosion in the Cu/Zn pair. The online visualization of the electrodes allowed the measurement of the corroded area of zinc and the study of how it grows with time. Hydrogen evolution was produced on the localized cathodic sites of the zinc surface when the Cu/Zn pair was immersed during 24 h at room temperature in the LiBr solution. This hydrogen generation was accelerated by the effect of temperature when the The interpretation of electrochemical data could be ambiguous in some circumstances because of the diversity of corrosion processes. As a result of complex physical and chemical phenomena, a number of different corrosion morphologies can be observed, which can be further subdivided into numerous corrosion types. Most corrosion analysis methods rely either on mechanical or electrochemical measurements, or on various chemical analyses. However, it is generally recognized by experts that the visual observation of corroded surfaces is an essential stage in the identification of corrosion causes.1 Image analysis is a relevant tool to characterize corrosion processes qualitatively and quantitatively. Pit growth kinetics has been studied for stainless steels using image analysis.2-4 Direct correlation between the individual effects on the surface of the specimen and the observed fluctuations of potential and current was established for AISI C1008 (UNS G10080)(1) carbon steel.5 Attempts have been made to automatically characterize corrosion (pit formation and cracking) based on visual images,6-8 specifically using texture analysis.
- Materials > Chemicals (0.94)
- Materials > Metals & Mining > Steel (0.54)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
ABSTRACT Lithium bromide (LiBr) heavy brines are used in absorption refrigeration and heating systems and are one of the most widely used absorbents.1 Although LiBr possesses favorable thermophysical properties, it can cause serious corrosion problems on metallic components of cooling systems and heat exchangers at absorption plants. These problems are more serious if electrical contacts are established between different metallic elements. Galvanic corrosion can accelerate the corrosion processes inside the heat pumps with the subsequent hydrogen generation, which causes a pressure increase and the loss of heating-refrigerating efficiency and the damage of the main metallic components of the absorption systems. Galvanic corrosion is particularly important in the applications of zinc and its alloys. In most situations, unlike many other metals, galvanic corrosion of zinc is desirable because it is required for protecting another metal. Most galvanic corrosion studies of zinc are related to galvanized steel.2-8 It has been documented for zinc-aluminium alloys,9-10 stainless steels (SS),11 copper,12 and iron.13 Copper has been the topic of some investigations coupled to steel,14-15 SS,16 titanium,13 and different copper alloys.16-17 Literature related to galvanic corrosion in LiBr is scarce; only one research work has been found that studied the behavior of Tungum (brass alloyed with nickel) at 140°C and different types of copper alloys, titanium, silver, and tin.16 With respect to corrosion of uncoupled materials in LiBr, there are documents about molybdate inhibition effect on carbon steel (CS) corrosion,18 the variation of pitting potential in SS with molybdenum,19 the corrosion of CS by mixtures of LiBr and calcium chloride (CaCl2),20 the corrosion of CS21-22 and titanium in aqueous LiBr solutions,22 the study of galvanized steel corrosion,23
- Materials > Metals & Mining > Steel (0.68)
- Materials > Metals & Mining > Zinc (0.54)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)