Re: GRP

That USACE report was quite a good read.

It shows the pig ignorance often exhibited when dealing with GRP. GRP has many different formulations and comparing GRP to steel is a bit like comparing fish to beefsteak.

A fairer comparison would be to compare GRP to metal pipe.

GRP is a good material; they make planes out of it.

Unfortunately it is a difficult material to design, select, specify and fabricate.

The majority of failure can be attributed to faulty design or fabrication.

I still use GRP for large ducting as it is cost effective in corrosive environments at moderate temeratures and stresses can be kept to conservativew levels.

But to use it for a condensate return system is asking for trouble even using a vinyl ester resin. With a polyester, you dont stand a chance.
I use a bit of GRP pipe for handling hot fluosilicic acid solutions but much prefer to use a straight plastic (PP in this instance) pipe as soon as conditions permit.

Fatigue is a big issue with composites and it is seldom dealt with in the level of detail required (apart from aircraft - I hope).

Because GRP is nowhere near as well understood as, say, steels or thermoplastics, it is a good idea to be very wary of it in situations where generous design/safety factors are not appropriate.

Its a great material, but there arent that many people around who know how to use it to its full advantage. Salesmen will probably disagree unless they are flogging metallics or thermoplastics.

Cheers

Steve

• In PipingDesign@yahoogroups.com, "Conner, Randy" <RConner@...> wrote:
  >
  > 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.pdf
  >
  > Christopher Wright <chrisw@...> 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@... | this distance" (last words of Gen.
  > ____________________| John Sedgwick, Spotsylvania 1864)
  > http://www.skypoint.com/~chrisw
  >
  >
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