Insulating materials are essential to protect coils during the preheating process when temperatures exceed 200°C over a long period of time.  
Layers of ceramic fiber are also used in heat treatment (PWHT) to prevent heat loss during the heating cycle, as this can last for many hours and reach temperatures above 700°C.

The insulating material is tied above if the heating element is a resistance heaters, or underneath if it is a coil.

 

Insulating materials are:

1. Ceramic fiber cloth

2. Ceramich fiber roll

3. Fiberglass sleeve