Corrosion on the inner edge of the seal of the titanium liner of the heater
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I need help. This is a titanium lining for the heater plate, made of TA2 material, and it is used in the heater of an evaporator. The medium used is sodium chloride and calcium chloride, with evaporation taking place at 105°C. Only localized corrosion occurs on the titanium lining; the ends of the heat exchange tubes, etc., are not corroded (see fourth image). Corrosion occurs only inside the sealing ring located near the titanium lining. The sealing material is polytetrafluoroethylene. When it was removed, the black corroded areas in the images showed crystals adhered to them. I’m not sure whether this is crevice corrosion – perhaps electrodes formed as a result of which sodium chloride crystals were attracted and continued to spread inward, causing further corrosion. Let’s take a look and analyze what the reason is; see if this situation has occurred before
Has it been welded? No proper protection was used during welding! !
There is no welding; it’s a single piece of cover plate
For concentration units used with materials containing high levels of salt, we typically supply customers with graphite-based concentration equipment, such as graphite reboilers, graphite evaporators, and graphite condensers.
The 4th image is not clear enough to make a judgment; galling corrosion occurs when both sealing surfaces corrode together.
Could it be polytetrafluoroethylene causing the problem? If fluoride ions are released, wouldn’t that have an impact on titanium?
Crevice corrosion is likely to occur between the flange and the gasket
How are the titanium lining plates connected and fixed to the substrate?
Welding, stress, and chloride ions all promote corrosion mutually; this is the result of their combined effect