I work in the Marine industry and bending small bore pipe is very common. US
Navy standards allow 5D bends without question. Any radius less than that has to
go through a qualified procedure and rigid QA inspection. If you utilize 5D
bends, I would not worry about wall thinning and deformation of pipe (piping can
become oval or the inside of the bend can develop ripples). It saves the
material cost of fittings, the welding and fitting of additional joints, and
reduces the number of joints that can fail. It also reduces the possibility of
crevice corrosion and the chance of having a bad fit up of a socket weld fitting
(too deep can cause high stress in the joint once welded). It has been my
experience that piping fabbed in a shop costs 10 times less than piping stick
built on site. Typically this is due to proximity of material and tools in the
shop. We always had welding lines and torches within 20 feet in a shop, but you
may have to search for one in
the field. Material was stored in the shop, where on site there is typically a
material lay down area that is centralized, so no doubt when you get further
away from it, it takes longer to retrieve material.
Hi,
I know that in the pharmaceutical and food processing industries
butt-weld small bore stainless is the norm, to avoid pockets where
bacteria and corrosion can occur. But in petro-chem we've commonly never
worried about this and I've always primarily used carbon steel socket
weld or threaded fittings in small bore. There must be a good reason? I
always thought it was because of fit-for-purpose, i.e. cost effective,
design. Aren't small bore socket weld and threaded pipe and fittings
relatively easy to erect and forgiving in alignment?. Versus the cost of
pipe bends and butt-weld?
Don't get me wrong. I am still holding to the idea that small bore can be done efficiently in the shop. But now I'm enquiring about the cost of socket weld fittings and socket welds versus pipe bends and butt-welds.
Richard B.
Calgary, Canada
-----Original Message-----
From: PipingDesign@ yahoogroups. com [mailto:PipingDesign@ yahoogroups. com]
On Behalf Of Christopher Wright
Sent: May 14, 2008 9:14 PM
To: PipingDesign@ yahoogroups. com
Subject: Re: [PipingDesign] Small Bore Pipe Bending and Shop Fab
On May 14, 2008, at 9:52 PM, Paul Bowers wrote:
> What other considerations should there be for replacing thick wall,
> field socket-welded piping with bends and shop butt-welding?
Corrosion in the crevice formed between the socket ID and the pipe OD.
That's a serious consideration for stainless.
Christopher Wright P.E. |"They couldn't hit an elephant at
chrisw@skypoint. <mailto:chrisw% 40skypoint. com> com | this distance"
(last words of Gen.
____________ ________| John Sedgwick, Spotsylvania 1864)
http://www.skypoint <http://www.skypoint .com/~chrisw> .com/~chrisw
[Non-text portions of this message have been removed]
[Non-text portions of this message have been removed] Received on Fri May 16 11:10:00 2008
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