Dear Mr Gangadharan,
I'm sorry I'm not clear even when the pipe is not moving (i.e. in steady state)
why is the frictional force not acting? If the friction was not there the pipe
would have moved further. Because an object is not in motion doesn't mean that
it is not under force.
I would be glad to have your comments on this.
Regards
Sudipto
-----Original Message-----
From: Gang Cvg [mailto:cvg_gang@yahoo.com]
Sent: 01 July 2004 14:29
To: PipingDesign@yahoogroups.com
Subject: Re: [PipingDesign] Moment calculation
Dear Reddek,
Please do not address me as Gang. It happens to be
just an abbreviation in my E-mail id. My name is
Gangadharan. If you feel it is too difficult, you may
cut it short to Ganga. (Ganga is the name of a river
in India.) It might be easier for you to handle it.
Let us come to the subject! It is a tricky situation:
Imagine a three-element piping configuration, with say
10 m pipe towards North, then 10 m pipe towards East
and the next 10 m upwards. I call the plane
constituted by the first two as H-plane. The other on
is V-plane. Now, the 10 m East-West segment is common
to H-plane as well as V-plane.
If we consider the effect of "out-of-plane vector"
from the H-plane on it; the same vector is "in-plane"
for it in the V-plane. It has got its own "in-plane
vector" due to the V-plane as well.
Now the next question: Can these vectors be added
together? If yes, is the addition algebraic or
vectorial? We resolve all the forces and reactions
into X, Y and Z components. It is from this
standpoint, the possibility of algebraic addition
comes into the picture. This is my curiosity. Can
anyone give a convincing explanation to the concept of
the forces and reactions with reference to the stress
analysis softwares?
The effect of combined reactions in a complex pipe run
cannot probably be broken down into simplified sectors
of pipes where we consider the forces act in the most
simplistic way, resolvable by elementary rules of
"Strength of Materials". What the FEM does is
precisely this. The results could be taken as the
solutions, which justify the many observed phenomena.
And to that extent, we have to be content also. The
"real" values still remain elusive. We work within the
limits "safely" due to the built-in safety margins
attributed and accumulated over various successive
steps. This avoids catastrophic failures, within the
expected plant lives. Luckily, there are not many
accidents due to pipe failures! We have to be "happy"
about this, and hope for the (still) better. If one
takes a set procedure of checks of the checklist, in
the context of HOT and CRITICALl lines, the outcome
generally turns out to be SAFE.
There is another fallacy in the stress analysis
programmes. That is regarding the friction factor.
Friction, as we all know, is associated with motion.
The pipe (the support point) does move from cold to
hot condition, DURING THE WARMING UP period. Once it
attains the HOT / OPERATING condition it is STATIONARY
or otherwise known as STEADY STATE. Friction no more
comes to the scene. Most of the stress analyses are
evaluated at the HOT / OPERATING condition. Then the
question comes; what is the role of friction factor,
0.3 for steel to steel and 0.1 for steel to PTFE?
Probably, it brings down the number of iterations of
the loop and comes to a FASTER solution. Also it might
result in more acceptable and palatable values of
forces and reactions. Can anyone throw some more light
on this matter?
Regards.
Gangadharan.
- Gordon.Reddek@Alcan.com wrote:
> Gang,
>
> And yet another way of seeing it:
>
> Imagine the Elbow or Tee with straight pipe attached
> to each leg lying on
> a flat table. The table is the plane we are talking
> about. If the
> moment on a leg tends to bend the leg so that it
> lifts off the table or
> presses into the table, then the leg is bending out
> of the plant and the
> moment is known as an out-of-plane moment. If the
> moment on a leg causes
> the leg to bend so that it remains flat on the
> table, then the leg is
> remaining in the plane and the moment is called an
> in-plane moment.
>
> Now for the trick questions?
> When the moment is a torsion which tends to rotate
> the whole tee or elbow,
> is it in-plane or out-of-plane, and does it matter?
> Can you have in-plane and out-of-plane forces?
>
> Lets hold a feeding frenzy on this one.
>
> Cheers,
>
> Gordon
>
>
>
>
> Gordon Reddek
> Specialist Mechanical Engineer
> Alcan Engineering, Level 3, 443 Queen St, Brisbane,
> Qld 4001, Australia.
> Tel: +61 7 3328 6424
> Fax: +61 7 3328 6990
> Email: gordon.reddek@alcan.com
>
>
>
>
> "Tony Paulin" <tony@paulin.com>
> 30/06/2004 03:32 PM
> Please respond to
> PipingDesign@yahoogroups.com
>
>
> To
> <PipingDesign@yahoogroups.com>
> cc
>
> Subject
> Re: [PipingDesign] Moment calculation
>
>
>
>
>
>
> The concept of in-plane and out-plane, once
> understood, is simple, but
> during the process of understanding can be
> complicated, additionally,
> there
> is often confusion when interpreting pipe stress
> program results.
>
> Rahul wrote, "The concept of inplane is the moment
> in the plane in which
> the
> piping is." While this is conceptually correct, the
> direction the
> in-plane
> moment vector points is normal to the plane of the
> piping. For example, an
> inplane moment for an elbow or tee defined
> geometrically, completely in
> the
> X-Y plane, points in the Z direction, or in a
> direction that is
> "out-of-the-plane" of the geometry. Out-of-plane
> moments for a 90 degree
> elbow running in the X and Y directions are in the X
> direction for the Y
> leg, and in the Y direction for the X leg.
> Out-of-plane moments for a 90
> degree branch connection whose header is in the X
> direction and whose
> branch
> is in the Y direction are in the X direction for the
> branch, ann in the Y
> direction for the run. If the branch is a lateral
> then there are several
> possible interpretations for the out-of-plane
> direction, while the
> in-plane
> moment direction is clear.
>
> Regards,
> A.Paulin
>
> ----- Original Message -----
> From: "Gang Cvg" <cvg_gang@yahoo.com>
> To: <PipingDesign@yahoogroups.com>
> Sent: Wednesday, June 30, 2004 12:13 AM
> Subject: Re: [PipingDesign] Moment calculation
>
>
> > Yes, I agree with Rahul. The classical book under
> > reference is "Kellog". Good luck!
> > Regards.
> > C. V. Gangadharan.
> > --- Rahul Kulkarni <rdk77@yahoo.com> wrote:
> > > Hi
> > > The concept of inplane is the moment in the
> plane in
> > > which the piping is. and Out of plane is
> > > perpendicular to that.
> > > It is like the bending moment is resolved in to
> > > these two components.
> > > The methods you are reading are bases on bisic
> SOM.
> > > But the methods now a days are used are based on
> > > single dim. FEA. Caser II is the software best
> for
> > > the application.
> > > Calog (i hope the spell is correct) is the best
> > > book. One of the topic towads the end of the
> book
> > > explains the method in short.
> > > Rahul
> > >
> > >
> > >
> > > RAHUL DEEPAK KULKARNI
> > > GHARKUL 36 MANISHANAGAR
> > > PANDHARPUR
> > > PIN 413304
> > > RDK77@YAHOO.COM
> > >
> > > ---------------------------------
> > > Do you Yahoo!?
> > > Yahoo! Mail is new and improved - Check it out!
> > >
> > > [Non-text portions of this message have been
> > > removed]
> > >
> > >
> >
> >
> >
> >
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Received on Thu Jul 01 05:25:00 2004