1. In this paper, the corrosion of brass and cupronickel condenser tubes produced by a copper alloy factory in Shizuishan power plant is summarized. The corrosion causes of brass and cupronickel condenser tubes are studied, on this basis, suggestions for improvement are put forward. 2. The brass tube is HSN70-1B, which is produced by medium frequency induction melting-horizontal continuous casting-reverse extrusion-drawing-annealing-process, and tested by composition, tensile mechanical properties and ammonia fumigation before leaving the factory, the composition and tensile mechanical properties of the alloy are shown in tables 1 and 2 respectively. The composition and mechanical properties meet the requirements of GB/t 8890-1998.

BFe-30-1-1, the production process is the same as that of brass tube. The composition, tensile mechanical properties and ammonia fumigation test are carried out before leaving the factory. The composition and tensile mechanical properties of the alloy are shown in tables 3 and 4 respectively, the composition and performance meet the requirements of GB/t 8890-1998.

3.6 corrosion observation of inner surface of brass tube: After being used for half a year, there is a thin deposit on inner surface of Brass Tube, the adhesion strength of deposit is not high, and there is no corrosion after uncovering deposit. The inner wall of the copper tube coated after 3 months and used for 1 year has a thick and dense deposit, but the adhesion strength is low. Corrosion products were deposited on the inner wall of the new tube after coating for 1.5 years, which may be due to the formation of a better anti-corrosion film. 3.7 analysis of corrosion reason of brass tube inner wall 1) sediment can be formed on the inner wall of brass tube by deposition of mud and sand, adhesion of microorganism and formation of scale in circulating cooling water. The quality of circulating cooling water, bactericidal treatment, anti-scaling treatment, circulating water velocity, cleaning condition and the disuse of condenser are all the factors that affect the formation of sediment. Because of the uneven distribution of sediment on the inner wall of Copper Tube, the difference of oxygen supply and the difference of medium concentration in different parts, the micro-battery effect is formed, which leads to local corrosion. . .

4.6 corrosion observation of inner surface of Cupronickel Tube. ● after being used for half a year without coating, there is a thin layer of deposit on the inner surface of Cupronickel Tube, however, there are some stripes at an angle of about 45 ° with the direction of pulling and pulling. The inner wall of the copper tube which has been coated for one and a half years has a relatively thick non-uniform and loose deposit layer, and the adhesion strength is low, no deposit layer was found on the inner wall of the copper tube after half a year of operation and 2 years of service, but there were obvious pitting pits and a few bulge corrosion products

The deposit (such as mud, sand, silt, calcium scale, etc.) will affect the diffusion of the initial corrosion copper(I) chloride and inhibit its hydrolysis, cU2 + : CUCL → CU2 + + CL-+ E can be oxidized to CU2 + : CuCl, and the newly formed copper ions can react with the base copper to produce CU2 + + Cu →2Cu + , thus forming Autocatalysis and accelerating the corrosion of copper. In the pitting pits, Cu, CuCl and Cu2O coexist, resulting in a Ph of 2.5 ~ 4.0. Therefore, under autocatalytic and acidic conditions, pitting will intensify and eventually penetrate the metal pipe wall.

5. Some suggestions 1) from the aspect of material quality, the following measures are suggested: Further improvement of drawing process, improvement of inner surface finish of copper pipe, study of annealing process-relationship between elimination of internal stress and inner surface corrosion resistance of pipe, further improvement of inner surface corrosion resistance of pipe. 2) from the analysis of composition and phase of corrosion products of used copper tubes, it can be seen that cooling water contains a lot of CA, MG, CL, s plasma, CA, Mg etc are the main components of scaling layer, Cl, s ion is the main cause of dezincification corrosion and pitting corrosion. Therefore, it is suggested that power plant users strengthen the quality control of circulating water, including purification water quality, descaling treatment and strict control of Cl, s ion content. 3) comparing the effect of different coating methods on the corrosion resistance of the inner wall of the tube, it can be seen that the corrosion resistance of the coated copper tube is better than that of the coated copper tube after a period of time. Therefore, it is suggested that power plant users should carry out coating treatment before the operation of the new tubes. 

Source: Copper Alloy Casting

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