Tanks for carrying and storing bitumen would be insulated, probably with the dreaded asbestos, and the visible external skin is only thin sheet metal. The tanks normally had internal steam coils to heat the bitumen keeping it fluid and the external parts of these pipes were lagged with asbestos tape wound on like a bandage, or a thicker type that had its own metal cover. The HSE regs; for handling bitumen are quite extensive!
Mick