Dear Gangadharan,
Firstly concerning the name. I am fully aware that this is an
international site and should by now have learned to be more careful with
the terms I use to address the group. The fact is I was not addressing
you personally but the GROUP, who I called a"gang". Like a gang of
workers, or thieves, or thugs. We in the west would take that address in
good humour and see it a s a joke. I was in fact reacting to the reply by
Mr Tony Paulin, and not to your original query. Never the less, the
remark has obviously hit a raw nerve, so please accept my apologies.
As it so happens I have worked with Indians in the past and have more than
a passing interest in Indian English and customs. One of them that has
always fascinated me is that Indians will address a westerner by putting
the address Mr, Mrs or Miss in front of the first name. So one gets Mr
John and Miss Susan etc. In the west the Mr, Miss and Mrs are used only
in front of the last name like Mr Jones, Mrs Jones and Miss Jones. We
never put the Mr, Mrs or Miss in front of the first name which always
stands alone. Also, in some countries, like Germany, the use of the first
name is reserved for very personal friends, and family. In those
countries it is considered an insult to use a persons first name without
their express consent. So, on the subject of names then, if you wish to
address a westerner in a way that makes them feel at home I suggest you
use the first name on its own (like Gordon) or the second with the prefix
like Mr Reddek. If you leave the prefix off the second name it is
generally taken badly in the west because school children and minions are
addressed that way.
I have noticed that Indians tend to have lots of names and they do not in
general seem to mind which one one uses. We in the west have a little
difficulty with that because the way we address people follows fairly
strictly predefined rules.
Now to the technical matters addressed. I successfully generated a fire
storm of replies on this one and will add only the following:
In your discourse you referred to three connecting pipes in different
vector directions. The origin of the in-plane and out-of -plane
terminology seems to be the ANSI pipe specifications and they use the
terminology only for tee's and elbows, so the complications of the third
leg at right angles to the plane are not an issue. The calculations
relate to the Tee and Elbow only.
Regarding friction. When a pipe is cold and at rests on a rack friction
plays no part. As the pipe heats up it expands and so it must slide over
the rack. If one end is attached to an anchor, that anchor will have to
bear the full force of the pipe sliding over the rack, and that force will
occur only while the expansion is taking place, but it will occur. When
the pipe has heated up, the friction force will vanish as you correctly
mention.
Now for the next fire storm:
You mention the coefficient of friction as being 0.3. Have a look in
Marks Mechanical Engineering Handbook and you will find it is greater than
0.7. I have a theory that 0.3 is commonly used because structural
engineers use that value however I consider it to be an inappropriate
figure for pipe stress analysis despite the fact that most of the world
uses it.
Cheers,
Gordon Reddek
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: <a href="/group/PipingDesign/post?postID=EA0V5D6P60ttVFWxTNZYN0XfZo0V-au5lVgfqY1GYLID-C7g8eTpxgymJ_UJbiAQ-d0suYeB8SUKrdhA5CT33n0">gordon.reddek@alcan.com</a>
Gang Cvg <cvg_gang@yahoo.com>
01/07/2004 06:58 PM
Please respond to
<a href="/group/PipingDesign/post?postID=8_oG5uHNze0kK3vJrW2X9USpA9FxhgIr2By9xNkLV9ISFubJgcITzNv13Ak-CAv3a6MZxP6JhBSMQzeuH629m0BIu69VFPw">PipingDesign@yahoogroups.com</a>
To
<a href="/group/PipingDesign/post?postID=8_oG5uHNze0kK3vJrW2X9USpA9FxhgIr2By9xNkLV9ISFubJgcITzNv13Ak-CAv3a6MZxP6JhBSMQzeuH629m0BIu69VFPw">PipingDesign@yahoogroups.com</a>
cc
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.
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[Non-text portions of this message have been removed] Received on Thu Jul 01 22:03:00 2004
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