Final answer:
Pipe thread protectors are not used in installations because they can cause corrosion by trapping moisture and debris, and they may become difficult to remove if cemented or welded in place.
Step-by-step explanation:
The question pertains to pipe thread protectors and their relevance in pipe installations. The reason pipe thread protectors should not be used in installations is that they can cause corrosion. While designed to protect threads during handling and transport, when protectors are left on during the installation, they can trap moisture and debris, leading to corrosion that compromises the integrity of the pipe connection. Furthermore, protectors may also inadvertently get cemented or welded into place during installation, making future disassembly for maintenance or modification challenging.