One of the most important characteristics of GRP is its very high inertness to a wide variety of chemical and physical environments: this is the reason why the early applications as well as a consistent part of those of today are in the chemical industry.
In underground water transportation this corrosion resistance guarantees long - maintenance free - service even in extreme conditions such as domestic sewage systems, where the fermentation of the conveyed fluid produces an acidic environment that corrodes metals and concrete but does not affect at all a GRP pipe or where the high salinity of the soils produces the same effect on the outer part of the pipe wall.
In many cases both conditions are encountered at the same time so it is very expensive to protect from corrosion the traditional materials and there is always the risk that small damages in the lining caused by handling and installation will expose the vulnerable material to localized attack.
This problem does not exist with GRP pipes because it is homogeneously corrosion resistant throughout the wall.
The capacity of GRP pipes to withstand the combined effects of corrosion and mechanical stress are tested according to ASTM standard D 3681.
In this test 18 annular sections of a pipe are subject to different levels of deflection while the most strained part of the sample is in contact with a 19ft solution of sulphuric acid.
The failure of the samples will take place at different times and a regression line can, then, be drawn.
This line shows the reduction of the material properties in its expected working life.

The following graph refers to a 600 mm pipe.
The resin used is isophtalic polyester

The test duration is 10,000 hours and the line can be further extrapolated to 1,000,000 which is equivalent more than 100 years. As shown the residual capacity of the material after 100 years is still almost 50% of the initial value.
Furthermore GRP is more resistant than other polymers such as polyethylene or PVC to the degradation caused by the Ultra Violet radiation and can normally be exposed to the sun rays without any shielding.

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