Explain about the main advantages and disadvantages of FRP composites?

What are the specific strength and specific stiffness? Why are they (specific
strength and specific stiffness) defined. and also what are the advantages and disadvantages of FRP composites?

By way of answers, you can find a lot of discussion at places like this:

http://www.pipingdesign.com/archive/0803/15212.html

There aren’t any specific strength and stiffness, because it varies by resin, amount and means of glass spinning, end finishing, quality of manufacture, etc.