How Durable is a Fiberglass (FRP) Flume Anyway?

H Flume with large rocks after a flash flood Time and again the question arises: how durable is a fiberglass flume anyway? To understand the answer, it is important to understand the nature of fiberglass.

Fiberglass (aka glass-reinforced plastic, glass-fiber reinforced plastic, glasfaserverstärkter kunststoff , FRP, GRP, GFRP, GFK) is a composite material made of a polymer (plastic) matrix reinforced with fine glass fibers.

The addition of the glass fibers, in mat, roving, or cloth form, greatly adds to the tensile and compressive strength of the base, unreinforced resin; allowing fiberglass to rival or exceed the comparative strengths of steel.

Two limiting factors in the life span of fiberglass flumes are UV degradation and osmosis. So long as all surfaces of a fiberglass flume have been protected gel coated (with the gel coat specifically selected for the application and provided UV inhibitors), it is much more likely that a fiberglass flume with be removed or abandoned not because the flume itself has developed problems, but that because changes in the process flows mean the flume is over / undersized or a particular monitoring station is no longer needed. In standard sewage applications, fiberglass flumes regularly experience lifespans of 20+ years.

Materials	Specific Gravity	Tensile Strength	Compressive Strength
Polyester resin	1.28	55 MPa	140 MPa
Polyester resin and chopped strand mat laminate - 30% E-glass	1.4	100 MPa	150 MPa
Polyester and woven rovings laminate - 45% E-glass	1.6	250 MPa	150 MPa
Polyester and satin weave cloth laminate - 55% E-glass	1.7	300 MPa	250 MPa
Polyester and continuous rovings laminate - 70% E-glass	1.9	800 MPa	350 MPa

Some flume fabricators are know to skip the exterior gel coat process to save time and money – unfortunately, the chemical and UV barrier that gel coat provides is essential to the longevity of the flume. Remember, if they are cutting corners where you can see it (not gel coating the exterior of the flume), imagine where they are cutting corners and you can’t see it.

Remember, properly fabricated, with materials chosen for the application (and not cost), fiberglass is stronger than sheet metal, light weight, corrosion resistant, low maintenance, will not rust, is non-conductive, radio frequency transparent, has better thermal performance than metal / plastic / wood with heat, cold, or stress.

Rusted Painted Steel Parshall Flume Discharge