A few months back this happened to me and I reported it as a bug but it is still around so have fun.
When you bring a gas up above the liquidation temperature of an insulation tile instead of it melting it just flakes off 5kg worth of igneous rock. This very quickly breaks off large amounts of rock pieces from the insulation but doesn't damage the insulation at all. It also cools down the gas.
I had made insulation tiles out of sedimentary rock since I didn't have any other use for it. What else does sedimentary rock have? A lower than normal melting point. This meant that it wasn't all that hard for the steam or whatever to get to that temperature.
Appears that after enough time the tile does disappear. The mass of the tile is not updated in the properties tab.
You can do this with Granite as well. Which means you only need to bring the temp above ~700c to do this.