Plastic does not corrode
Externally towards the environment, in terms of humid environments and outdoor applications plastic show no corrosion. Also internally, the extra smooth surface of plastic pipes prevents any encrustation (calcium) build-up.
The consequences are that the internal surface roughness of 0.007mm for plastic is valid for the minimum 25 year life-span of the plastic pipe system. No need to take corrosion into account for pressure drop calculations as is standard practice for metal pipes.
Resistance to Condensation - No External Corrosion
External corrosion of metallic pipe systems often occurs on post-insulated pipe systems where the insulation and outer jacket do not create a vapour seal. Under these circumstances humidity fomr the external environment can ingress into the insulation and for condensation on the internal carrier pipe. These leads to the insulation losing its insulating properties (as water conducts energy far better than a gas) and also to corrosion (oxidation) of the internal metallic carrier pipe.
Pipe Roughness Values (mm)
CIBSE, the UK chartered engineering association, publishes pipe roughness values for various key metal pipes, showing the degradation to be expected on the internal surface of pipes ofer time.
Plastic Pipes : Smooth internal bore
Plastic pipes have a internal roughness factor of 0.007mm - far better than most metals. This value ca be sued over the complete life-span of the plant and pipe system.
