Alkaline washing of titanium materials can allow bismuth to catch fire, especially the alkaline washing of titanium sheets is more likely to catch fire. The cause and mechanism of fire in alkaline washing of titanium are still under discussion. The chemical activity of titanium in lye. When it is washed in molten lye containing oxidant, the overall lye temperature is too high or the local temperature is too high, which will cause the original flash of titanium burning.
Due to the potential difference between titanium and steel tools (alkaline washing frame) in the molten alkali solution, there is a galvanic effect. When titanium and steel are in contact, a galvanic current is formed, and the smaller the contact point, the greater the current. Excessive current density at the contact causes local overheating, so that the titanium alloy often starts to burn from the contact point of the two metals.
In order to prevent and reduce the fire during alkaline washing of titanium pipes, the following measures can be taken:
(1) Choose reasonable alkaline lotion composition. The test indicated that (85%-95%)NaOH+(15%~5%)NaN03 alkaline lotion has better effect.
(2) Strictly control the temperature of the lye. For alkaline washing in the lye of the above composition, the temperature should be strictly controlled, whether it is the whole or part, it should be strictly controlled within the range of 480-520T.
(3) Use high temperature resistant coatings or high temperature resistant insulating gaskets to insulate the alkaline washing frame. If the stainless steel alkaline washing frame is used, ceramic strips or ceramic sheets can be used to separate the titanium material from the steel frame, so as to avoid fire.
During the alkaline washing process, the lye is constantly taken away by the workpiece or evaporates, so it is necessary to replenish the lye. When replenishing lye, it is necessary to analyze the composition of NaOH and NaN03 regularly, and make adjustments in time to keep the composition of lye relatively stable.
During alkaline washing, insoluble oxide scale slag precipitates on the bottom of the tank, which affects the good thermal conductivity of the tank body, and the gap caused by the precipitation makes the steel tank prone to electrochemical corrosion, which greatly shortens its service life. Therefore, the sediment must be cleaned up in time. It is a common method to collect slag at the bottom of a movable trough. When the sediment needs to be eliminated, only the bottom of the movable trough needs to be lifted away.
