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esass13 (Civil/Environmental)
8 Nov 05 11:13
Does anyone know what the limit should be for holding PVC pipe on a supply yard that is exposed to sunlight?  At what timeframe is the PVC no longer usable?  How much effect does UV have on PCV pipe's strength, etc.?  Is there a way to tell based on the amount the pipe has faded, even though this is subjective?  Any info is appreciated

Thanks
Zambo (Civil/Environmental)
8 Nov 05 11:25
I think you take a sample and send it off to the manufacturer. In the meantime you could also assemble a few lengths and carry out a hydro test.
Helpful Member!  Ussuri (Civil/Environmental)
8 Nov 05 11:49
I did a Google Scholar search (http://scholar.google.com/) for "UV degradation of PVC Pipe" and came up with 605 hits.

I have worked on projects for water companies where they have been very jumpy about it.  In particular, that we designed to ensure no PVC saw sunlight, anywhere.  Where we had a pop up above ground we used ductile iron.

The 'Pipeline Materials Selection Manual' might also be a good place to look as well.
stanier (Mechanical)
8 Nov 05 18:52
Australian standards have reduced the time from 24 to 12 months. Then the material should be covered.

In any event the damage may stil be done.

The last people I would have test it is the manufacturer. Use independent laboratories.

kenvlach (Materials)
8 Nov 05 21:20
Never use any faded PVC.
No way to tell how brittle – it depends upon pigments and raw material used in manufacture.

Brittle PVC can explosively shatter when pressurized –> flying shrapnel.

For exposed use, use a compatible paint.  In hot locations, e.g., flat rooftop, I have used CPVC (also painted).
bimr (Civil/Environmental)
9 Nov 05 10:38
Taken From the "Handbook of PVC Pipe" by the Uni-Bell PVC Pipe Association.

When exposure in excess of two years to direct sunlight is anticipated, PVC pipe should be covered with an opaque material while permitting adequate air circulation above and around the pipe.

PVC pipe can suffer surface discoloration when exposed to UV radiation from sunlight. The resulting reaction occurs only on the exposed surface of the pipe and to extremely shallow depths of .001 to .003 inch. The effect does not continue when exposure to sunlight is ended.

A two-year study was done by Uni-Bell. The study found that exposure to UV radiation results in a change in the pipe's surface color and a reduction in impact strength. Other properties such as tensile strength  (pressure rating) and modulus of elasticity (pipe stiffness) are not adversely affected.

The most common method used to protect aboveground PVC pipe from the sun is painting.

See "The Effects of Ultraviolet Aging on PVC Pipe," Uni-Bell's UNI-TR-5.

kenvlach (Materials)
12 Nov 05 11:27
Additional documentation for bimr's and my posts above, plus for UV sterilizers, which could be considered accelerated sunlight UV testers.  From Harrington Plastics Engineering Handbook for Industrial Plastic Piping Systems, page 71.  Lots of useful info. Free download  from  http://www.harringtonplastics.com/


“SUNLIGHT WEATHERING AND PAINTING
Plastic pipe and fittings have varying resistance to weathering.  PVC, CPVC, and Polypropylene undergo surface oxidation and embrittlement by exposure to sunlight over a period of several years.  The surface oxidation is evident by a change in pipe color from gray to white.  Oxidized piping does not lose any of its pressure capability.  It does, however, become much more susceptible to impact damage.
PVDF is unaffected by sunlight but is translucent when unpigmented.

PVC and CPVC pipe and fittings can be easily protected from ultraviolet oxidation by painting with a heavily pigmented, exterior water base latex paint.  The color of the paint is of no particular importance, as the pigment acts as an ultraviolet screen and prevents sunlight damage.  White or some other light color is recommended as it helps reduce pipe temperature.  The latex paint must be thickly applied as an opaque coating on the pipe and fittings that have been cleaned well and very lightly sanded.

Polypropylene and PVDF pipe and fittings are very difficult to paint properly and should be protected by insulation.”


“ULTRA-VIOLET LIGHT STERILIZATION
UV sterilizers for killing bacteria in deionized water are becoming common.  The intense light generated will stress crack PVC, CPVC, polypropylene, and PVDF piping over time that is directly connected to the sterilizer.  PVDF goes through a cross-linking of H-F causing a discoloration of the fitting and pipe material, and joint stress cracking.”

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