What type of piping system is not visual inspection required for, when concealed above ceilings?

In sprinkler system installations, the type of piping that does not require visual inspection when concealed above ceilings is typically non-metallic, such as CPVC (Chlorinated Polyvinyl Chloride) piping. This material is used in many residential and some commercial sprinkler systems because it is lightweight, resistant to corrosion, and easier to handle than metal piping.

When CPVC or metal piping is installed in concealed spaces, the inspection requirements differ. Metal piping, such as steel piping, is subject to rigorous inspection protocols since it can corrode and has other concerns regarding structural integrity over time. However, the code allows for certain non-metallic materials like CPVC to bypass extensive inspection requirements due to their stable nature and lower risk of failure in concealed spaces.

In summary, the correct answer indicates that neither CPVC nor metal piping requires visual inspection when concealed above ceilings because it adheres to the guidelines governing the installation of sprinkler systems designed to enhance safety without compromising accessibility for maintenance.