1. Crevice corrosion: Titanium rod manufacturers pointed out that crevice corrosion is a local corrosion phenomenon that occurs in close gaps, which can be caused by structures (such as flange connection surface or gasket surface, tube and tube sheet expansion joint, and The connecting surface of bolts or rivets, etc.) can also be caused by scaling or deposits under the covering surface. In the early days, it was believed that titanium did not undergo crevice corrosion at all in seawater and salt spray. Later, in high-temperature chloride medium (such as seawater heat exchanger), wet chlorine gas (such as wet chlorine gas tube condenser), oxidant corrosion inhibition hydrochloric acid solution In media such as formic acid and oxalic acid solutions, crevice corrosion damage of equipment has occurred successively.
Crevice corrosion of titanium rods is related to many factors such as ambient temperature, chloride type and concentration, pH value, and the size and geometry of the crevice. In addition, the crevices composed of titanium and polytetrafluoroethylene, titanium and asbestos and other non-metals are more sensitive to crevice corrosion than those composed of titanium and titanium.
2. Pitting corrosion: Pitting corrosion is a form of corrosion peculiar to passivated metals. Compared with stainless steel or aluminum alloy, the pitting corrosion resistance of titanium is very good. Due to the increasing application of titanium in high-temperature concentrated chloride solutions, the number of pitting corrosion cases of titanium equipment has gradually increased.
The titanium anode basket in electrolytic zinc, the titanium coil heated in zinc chloride solution, and the titanium ball valve of 72% calcium chloride solution at 175℃ have all experienced pitting damage. Generally speaking, pitting corrosion of titanium is more difficult than crevice corrosion, which usually occurs in the form of pitting corrosion on the crevice surface.
3. Galvanic corrosion: Galvanic corrosion is a phenomenon in which dissimilar metals contact (including electrical contact) in the electrolyte solution. Due to the difference in the steady-state potential of the metal, one metal accelerates the corrosion of another metal (ie, anode dissolution). The oxide film is very stable, and it is always in the cathode state. Galvanic corrosion will not accelerate the anode dissolution of titanium.
However, titanium rod manufacturers believe that it is necessary to pay attention to the hydrogen absorption of titanium in the cathode state and ultimately lead to hydrogen embrittlement, and it is necessary to prevent the accelerated corrosion of coupling metals (such as aluminum, copper, zinc, etc.). The size of the galvanic corrosion of the metal depends on the difference of the galvanic sequence of the coupled metal in the medium.
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