Tanks, accessories and mainly GRP pipes. carried as internal surface finish with mirror finish and perfectly circular section, because these matrices are molded on in one piece.

Because corrosive properties and that they are not attacked by microorganisms is difficult to adhere on its surface fouling, pipes do not increase their roughness and inner section does not decrease, even in long periods. With great economy foregoing is achieved in the choice of flow area, with respect to traditional materials, which becomes very important in large diameter pipes. The absolute roughness, can be estimated by 30 a.

As approximate values ​​of roughness coefficients can be more usual to use the following: