I think Chris or someone else also referred to a USACE experience/paper they
could not then lay their hands on (I think they may have been referring to
http://www.cecer.army.mil/techreports/mar_frep/Mar_FREP.flm.post.pdf -- I had
also seen the VPI paper some time ago)
Randy Conner- ACIPCO
-----Original Message-----
From: PipingDesign@yahoogroups.com
[mailto:PipingDesign@yahoogroups.com]On Behalf Of Geoff Stone DD&D
Australia
Sent: Thursday, February 09, 2006 6:32 PM
To: PipingDesign@yahoogroups.com
Subject: Re: [PipingDesign] GRP
Chris,
Check this paper out.
Geoff
http://scholar.lib.vt.edu/theses/available/etd-72198-94656/unrestricted/thesis.p\ df
Christopher Wright <chrisw@skypoint.com> wrote:
On Feb 9, 2006, at 5:55 PM, Geoff Stone DD&D Australia wrote:
> In short to design in GRP is a specialised subject. If yopu dont have
> the skills stay well away from it. Remeber the salesman has an aim to
> sell product NOT do your job for you. keep this uppermost in your
> mind.
This is a very solid point, with a lot of legs. Plastics in general
are very useful things, but they don't behave like metals. In
particular they can be very sinsitive to environmental factors acids
and ultraviolet light. I had a chance to investigate a failure of an 18
inch fabricated miter joint that let go becasue the fabrication was
faulty. The system (chilled water at about 90 psi) was plagued with
leaks and failed a number of hydro tests as a result. The mitre joint
was made from a single length of pipe sawed at an angle with the pieces
rotated and matcched to form a 90 deg bend. The joint was wrapped
manually with resin-soaked fabric--woven roving, I think, maybe mat.
The interior crotch corner was very problematic because it was
difficult to get the wrap actually to contact the surface. When it
started leaking the assembly crew just wrapped a few more layers and
pumped it up again. The problem was that the wrap hadn't bonded to the
pipe wall, so the added wrap didn't do anything. The ensuing rupture
was quite spectacular. Turns out the money saved by going to FRP had to
be spent on a new system. The owners got very nervous about the FRP
pipe and specified steel. I'm still very nervous about FRP pipe--more
precisely the possible problems with fabricated joints in FRP piping.
I also ran into a problem with a glass fiber wrapped natural gas tank design ed to operate at about 3000 psi. Everyone did lots of really spectacular tests on sample tanks, and convinced themselves that the tanks had a 'safety factor' of 4 based on testing of new construction. Cool as all those tests were they didn't reflect degradation of the glass fiber wrap in service, and there were several bursts at about 3000 psi after the tanks had been run for a while. After a lot more lab work the cause was determined to be 'environmental degradation' of a non-specific sort, possibly battery acid, despite the lack of clear evidence. I have my own suspicions about the cause, and a lot less confidence in the ability of FRP to stand up in service.
Christopher Wright P.E. |"They couldn't hit an elephant at chrisw@skypoint.com | this distance" (last words of Gen.
____________________| John Sedgwick, Spotsylvania 1864)http://www.skypoint.com/~chrisw
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