Influence Of Reynolds Number On The Corrosion Behaviour Of Titanium And Microplasma Arc Welded Titanium In Polluted Phosphoric Acid Solutions

摘要

Introduction The most important procedure to obtain phosphoric acid is the wet process, which consists of the addition of sulphuric acid to the phosphate rock. This method generates severe corrosion problems given that the phosphate rock may contain several impurities, such as chlorides (CI) in presence of sulphuric acid (H_2SO_4) traces. In fact, sulphuric acid is the most common impurity in the wet process acid since it is necessary in a certain excess. Additionally, chlorides attack generates pitting corrosion, being the action of chlorides intensified by the presence of sulphuric acid. Besides this, the effect of the hydrodynamic conditions together with the high temperatures reached during this process could aggravate corrosion problems. Titanium and titanium alloys, as well as their welded forms, are widely used in the industrial field, because they make possible to build light pipelines. However, welding introduces metallurgical changes and residual stresses in materials, diminishing their corrosion resistance. Objective and Experimental The main objective of this work is to study the effect of Reynolds number (Re) on the corrosion behaviour of titanium and microplasma arc welded titanium in polluted phosphoric acid at 60 °C. Different Re were evaluated: 1456, 3166 and 5066. To this end, a flow circuit was designed to evaluate corrosion under hydrodynamic conditions. As Table 1 shows, phosphoric acid was polluted with sulphuric acid and chlorides. Results Results show that the highest corrosion rates are obtained for the welded titanium under all the evaluated Reynolds numbers. Furthermore, the general effect of Reynolds number is to decrease both corrosion and passivation current densities.