How can one distinguish between glass fiber pipe types with sand inclusion and those without sand inclusion based on their appearance?

It can only be distinguished from the cross-section.

Fiberglass reinforced plastic sand-filled pipes actually consist of a fiberglass reinforced plastic pipe with an additional sand-filled layer added in the middle, and the purpose of this is to increase the stiffness of the pipe. When designing pipes, it is determined whether sand filling is necessary based on factors such as the pressure and stiffness to which they will be subjected. If the thickness of the pipe is sufficient to meet both the pressure and stiffness requirements, then generally no sand filling is needed. If the thickness of the pipe meets the pressure requirements but not the stiffness requirements, sand embedding is used to increase the thickness in order to meet the stiffness criteria (of course, it is also possible to simply increase the thickness without using sand to meet these requirements, but this would result in very high costs). Compared to ordinary fiberglass pipes, sand-embedded fiberglass pipes have an additional sand layer; this layer can be considered as a replacement for glass fibers using quartz sand. Compared to glass fiber reinforced pipes, sand-filled pipes of the same thickness are cheaper, but have lower strength ； Glass fiber pipes are the opposite. I found this by searching on Baidu; as for whether it can be fitted, it depends on the specifications or by looking at the cross-section