How to extend the life of the bimetallic thermometer

In workpiece chrome electroplating cell, using titanium pipe as the protection of the bimetallic thermometer, using 3 h under 120% of the working temperature electrolyte corrosion of the bimetallic strip, the pointer thermometer, and because he didn't know temperature to the workpiece surface heat treatment of chromium plating. Titanium is a kind of not easy corrosion and electrochemical precious metals, the reasons for this phenomenon is the purity of titanium was not enough. But on the market to buy the high purity titanium for protecting tube of bimetallic temperature object difficult, and expensive. In order to solve the above problems, can consider in titanium protection tube coat a corrosion resistant and not easily electrolytic protection tube. Protecting tube can be used the following materials: 1, pure iron or mild steel. 2, the plastic pipe.