Application of TA10 titanium alloy in ammonium chloride evaporator
February 22, 2022
Industrial pure titanium has strong corrosion resistance in room temperature ammonium chloride solution, but there is a gap corrosion tendency in high temperature and high concentration of ammonium chloride solution. A pure titanium ammonium chloride evaporator in a chemical plant in China was severely corroded after 8Mo, and had to be scrapped. This is a φ 1000mm×5000mm large evaporator, ammonium chloride concentration 15%-20%, temperature 110℃-120℃, pH (4.0-6.0), the final product is ammonium chloride crystal. The evaporator tube plate, tube bundle and shell are made of TA2 industrial pure titanium, and its impurity content is not greater than (%) : Fe0.30, C0.10, K0.05, H0.015, O0.25, other impurities 0.1 and 0.4 respectively. Less than 8Mo operation of the equipment, serious corrosion occurred at the edge of tubesheet at the lower end of the middle heating chamber, and at the weld joints of the pipe and tubesheet. The whole inside of the upper part of the lower vertebral body is corrodes, with local penetration. The corrosion pit is 6mm deep and 80mm-100mm wide. Industrial pure titanium is not suitable for use, because serious gap corrosion will occur in high concentration and high temperature NH4Cl solution.
Analysis of the test
Qiu Honglin et al. conducted metallographic and scanning electron microscopy analysis on the corrosion. Metallographic analysis of the corrosion site found no abnormal changes in the structure, nor did the presence of hydride produced by gap corrosion, which was still equiaxed structure.
The corrosion site was analyzed by PSEM-500X scanning electron microscopy. The surface was honeycomb, but no cracks were found. Elemental energy spectrum analysis showed that the corrosion site contained a large amount of Cl, consisting of 58.207%Ti, 34.205%Cl, 4.631%Fe, 2.441%Ca, 1.259%Si, and 0.254%K. The corroded part contains 0.020%h, which is higher than that of the uncorroded part (150-200) PPM. Obviously, the titanium in the corroded part has obvious hydrogen absorption phenomenon; The corrosion site is uneven, honeycomb, serious corrosion, corrosion product composition: 58.207%Ti, 34.205%Cl and other elements, corrosion products contain a large number of Cl ions, showing a typical gap corrosion characteristics. The tube plate is corroded at the lower end of the heating chamber, and there is accumulation at the corroded part.
