| Although there are many living waste water used as circulating cooling water in thermal power plant, the paper-making water directly reused in the circulating cooling water system is without precedent. The papermaking waste water is planned to be used as circulating cooling water in a new heating supply unit of600MW. As the papermaking waste water quality is relatively complex, corrosion on metal pipe is not well understood. This paper is carried out a concentrated study on corrosion resistance performance in papermaking waste water of several common metals used as condensation pipe in order to provide test data for selection of new power plant condenser tube material.Based on the power industry standard "Guideline for the selection of condenser tube materials in power plant",5kinds of metal materials widely used in engineering were selected as the testing materials, which were aluminum brass (HA177-2), Navy brass (HSn70-1AB), copper (BFe30-1-1), stainless steel (TP317) and stainless steel (254SMo). The respective application scopes of selected metal materials were determined through static test and dynamic simulation test.The test was divided into two parts--static test and dynamic simulation test using cooling water. The purpose of static test was to determine the corrosion resistance performance of5kinds of materials selected in papermaking waste water through qualitative study. Two kinds with the best corrosion-resistant materials among the5materials were used in dynamic simulation test. The dynamic simulation test gave the quantitative description on the corrosion resistance parameters of each material.Static test was carried on a ZAHNER Zennium Electrochemical work station, which included:polarization curve and impedance. Base on this test, microscope method and salt spray test were attached to support the conclusion. Original papermaking waste water that had been disposed according to the national standards for discharge was used as test solution in electrochemical test. In order to simulate the working corrosion environment accurately, a series of experiments were carried out with0%,2%,4%,6%mass fraction of NaCl added respectively in the solution. The test results shows that the corrosion resistance of aluminum brass (HA177-2), Navy brass (HSn70-1AB), and copper (BFe30-1-1) are worse than the stainless steel (TP317) and stainless steel (254SMo).Aimed at the new power plant circulating cooling water system operation conditions and design parameters, a circulating cooling water test system was designed and built up to simulate corrosion environment of the condenser in power plant which will use cooling water. This system was proved not only to be a very good simulator of power plant corrosion process, but also achieve the requirements and objectives for design.Based on the corrosion process of test materials, the dynamic simulation test was carried in a period of15days for each material. Stainless steel (TP317) and stainless steel (254SMo) were tested and compared. It can be found in the test results that in the condition without any inhibitor and the control circulating ratio equal to3,254SMo stainless steel corrosion resistance is most close to the requirements of condenser metal tube that the rate of corrosion was less than0.005mm/a. Meanwhile, that the annual corrosion rate of TP317is more than3times of254SMo can be found in the test results.Based on the static test and dynamic simulation test results, it can be concluded that prior selected metal for the new power plant condenser is stainless steel254SMo, and the latter is stainless steel TP317. If stainless steel TP317was used as the tube metal, inhibitor must be added in the cooling water. The results that corrosion resistance of aluminum brass(HA177-2), Navy brass (HSn70-lAB), and copper (BFe30-1-1) in papermaking waste water is poor is also proved that these metals is not suitable for using in the new power plant. |
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