Why thermo wells are used? What materials are used in thermo wells?

In numerous applications, it is neither desirable nor practical to expose a temperature sensor directly to a material. Wells are therefore used to protect against damage corresion, arosion, aborsion and high pressure processes. A thermo well is also useful in protecting a sensor from physical damage during handling and normal operations.Materials used in thermo wells:

1. Stainless steel
2. Inconel
3. Monel
4. Alloy Steel
5. Hastelloy