Inquiry concerning CPVC pipe for outdoor use 3

[dinghy]

thread378-215896
Gentlemen, I read your thread with great interest. I am involved in boat-building and wish to explore using CPVC schedule 80 pipe to replace stainless steel for some structural components on a boat in a hi-use outdoor marine setting. Many inflatable boats are made of PVC and have PVC fittings all over them for handles, stand-offs, etc... They are mostly useless in 4-5 years due to UV degradation.

I wish to custom bend, possibly weld lengths of sched 80 11/2" pipe into grab rails in sections as long as 4 feet. Out of the box, the application works, as CPVC -80 is strong and stiff, but I am concerned about maintaining strength and integrity over a time span of 5-10 years. Grab rail standards in the marine environment is a serious affair.

Can you suggest durable UV protective coatings that don't scrape off, or other means that I might employ to make the pipe useable??

 

[MikeHalloran]

When it breaks, who you gonna call?

Who's your lawyer gonna call?

Yes, I know CPVC is great stuff, but the plastic piping industry has had some, ahem, hiccups, over the years, with class action suits and such about other, initially promising, materials.

You're proposing a new use for a relatively new product, and expecting long term performance in an application for which the product has not been specifically tested. Do not expect a CPVC producer to become a willing codefendant.

For some illumination, go to blazemaster.com, a site owned by Lubrizol that sells CPVC for use in fire sprinklers, and also goes to some trouble to explain that environmental stress cracking is already a known problem.

Search the site (search box in u/r corner) for the word 'incompatible'. The page that you will find lists, among other things, SikaFlex sealant and WD40 as specifically _not_ approved for contact with CPVC. Both are likely to be found on boats.

Environmental stress cracking in plastics doesn't work the same way as it does in metals; the environmental stress and the physical stress can be separated in time and still cause a failure, and the environmental stress exposure may be very brief and still cause failure.

The best/ worst/ easiest example of ESC in plastics is polycarbonate. Make a coupon, bend it, twist it, beat on it, you can't break it. Dip a similar coupon in any of dozens of solvents, wipe it off immediately, wash it if you like, try to bend it, and it snaps like glass. CPVC may not be that dramatic... or it may be.

My suggestion: Stick to stainless steel; you got trouble enough.



Mike Halloran
Pembroke Pines, FL, USA

 

[rconner]

fyi

http://cr4.globalspec.com/thread/37780

 

[dinghy]

Thank you for your helpful comments on PVC issues from general useage. It seems that my product will most likely be made of formed schedule 80 conduit, and installed on inflatable boats, already covered with PVC glue-on items which are always under load. Shear, torque and pull occurs at all times on most of these items. Oar locks, lifting rings, securing straps, hand grips & seat brackets. In fact, many of the inflatables themselves are made out of PVC cloth. That said, a stainless version will be offered for those willing to pay the shocking price.
Dinghy

 

[cheute79]

Mike covered the answer very well. I would add something from my past experience. I did a fair amount of work in the desert southwest of the US (southern AZ, SE corner of CA). PVC and CPVC are often run for water and other services for their convenience and relative ease of repair, but then, if the line is to be in use for a year or more, it is wrapped in fiberglass or it is insulated with preformed fiberglass and caulked. The reason is strictly for UV control. Any PVC in the tropical or subtropical sun ought to be covered with something or it will give a false sense of security and that leads to injury.

 

[patprimmer]

To expand on Mikes comments.

I have promoted plastics materials into new applications for most of my life. I would run away from this as fast as I could yelling don't do it don't do it.

Regards
Pat
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