Hello,

I want to know about the details of what b31.3 explains about including bourdon pressure in stress calculations. I searched for it & not able to find much details about it. Anybody can please help in this matter.

B31.3 doesn't discuss Bourdon Pressure Effects, this is why you didn't find it.

Do we need to consider in our calculation Bourdon pressure effect? Bcoz sometimes it creates more loads in caesar for high pressure & big diameter pipes. Especially for lines connected to compressor & turbine we used to consider bourdon effect. What basis the calculations r done in caesar? Any experts here to comment about including bourdon effect in our calculations

Hello hman,

Do we need to consider in our calculation Bourdon pressure effect?

Yes.

The responsible engineer is required by B31.3 to address ALL LOADINGS. Perhaps you should research the subject of Bourdon effect more.

Why should Bourdon effect be included in structural analyses that are required to assure compliance with ASME B31.3?

Because.....sometimes it creates more loads in caesar for high pressure & big diameter pipes. Especially for lines connected to compressor & turbine we used to consider bourdon effect.

With all due respect sir might I ask that you read the Wikipedia site:

http://en.wikipedia.org/wiki/Netiquette

.....and especially:

The rules of netiquette are slightly different for newsgroups, web forums and IRC (Internet Relay Chat). For example, on Usenet it is conventional to write in standard English and not use abbreviations such as "u" for "you" or "ne1" for "anyone". These abbreviations are only slightly more likely to be tolerated on web forums, but are almost universal on IRC where, since discussion is real-time, they serve the practical purpose of speeding the flow of conversation. Many IRC users look down on this form of conversation, though. Issues such as the level of tolerance for off-topic discussion or spoilers may also vary from one newsgroup, forum, or channel to another.

Thank you, sir and best regards, John

Read these two posts:

http://www.coade.com/cgi-local/ultimatebb.cgi?ubb=get_topic;f=1;t=000440#000000

http://www.coade.com/cgi-local/ultimatebb.cgi?ubb=get_topic;f=1;t=001151#000000

Thank you very much Mr.Richard.

Mr. Richard Ay,


Sir, do you have any literatures or recommended reading materials for me to understand "Bourdon effects" more? (Except for old posts here)

hoping,
rommel

Dark,

Unfortunately "no". This stuff is impossible to find.

......but Rich,

Just get the reference from your copy of the Mare Island Mec-21 Manual. You still have your copy don't you???

Regards, John

1) Yes we've still got that Manual - I'm not exactly sure where it is, but it is here someplace.

2) Was the Mare Island implementation correct? Nope - and we've corrected and tweaked what we have in CAESAR II a number of times.

3) The best reference I can point anyone to is: HARVEY, "THEORY AND DESIGN OF PRESSURE VESSELS", P. 61, which is what we've got in CAESAR II now.

4) The subject of Bourdon Pressure Effects in Piping Systems is a real ugly can of worms (and needless to say I'm no expert here). There needs to be a whole lot of research done here, with specific guidelines and rules developed for different (piping) conditions.

Yep,

It is an interesting subject. But I am not sure how useful the research would be to "real world" piping systems. I did a rather exhaustive literature search on the subject when we took over the contract for maintaining MEC-21 and MEL-40 (Circa 1973) and I came up empty.

From a practical standpoint, it would be comforting just to know the diameters and associated wall thicknesses at which the effect "kicks-in" (for any given pressure). I "know" the stiffening effect of internal pressure provides more meaningful effects but the Bourdon effect is still "one of the loadings".

Well, it is close enough to 5:00 PM now so I will give some attention to getting to TGI Fridays where I can consider the Bourbon effect (three fingers over ice please) on older piping engineers.

JB

Sir Richard Ay,

When i analyzed same piping system, with a different options offered by CAESAR II (1.translation only & 2.translation and rotation considered), i noticed that loads on restraints changes, i would like to know the difference or basis of CAESAR in making calculations for each options? (specifically, the engineers approach)

anyone?

Hello Dark,

I think this question is "off topic" from hman's original question (as were the previous comments). Sometimes it is better to ask a new question by starting a new thread.

Am I correct in interpreting your question to mean:

You have modeled a piping system in Caesar II and you have included restraints at various locations and you have modeled the restraints (first) as translational only. Then (second) with no other changes to the model you have moodified some of the restraints by adding rotational restraint with the translational restraint and made another run, From this you have noted that the calculated loadings at the restraints change significantly when rotational restraint is added. You are asking for an explanation for the differences in calculated loadings at the restraints. Is this your question?

Regards, John.

Sir John Breen,

I'm sorry for being "off topic".



Yes, Sir john, that is indeed my question.


The world is full of wonderful people.

Hello Dark,

Please imagine for example an short "L" shaped piping system lying on a horizontal plane. If you have a vertical "Y" restraint on one leg and also a vertical "Y" restraint on the other leg, and you run a weight only analysis. A weight force will be calculated for each of the restraints. If you add a rotational restraint to one of the two "Y" restraints and you restrain the rotation about the pipes axial centerline at that point and run the weight only analysis again you will see less weight transferred to the restraint on the other leg. This is because by using the rotational restraint (restaining rotations will result in a moment reaction) the moment reaction reduces the vertical weight being transferred to the "Y" restraint located "around the corner".

Regards, John.

Bourdon Pressure - there are two other areas where this effect is commonly used.

1. Party toys - the paper tubes that are all coiled up and extend when you blow into them are "everybody's" first experience with the Bourdon effect. They are usually associated with noise and either the ice cream effect or the Bourbon effect.

2. Many dial-type pressure gauges use this effect. There may be some valuable analytical references in I&C books (we pipers aren't often permitted to read such hallowed tomes).

Eureka!!

After payment of an exorbitant fee, one of our I&C people permitted me access to a suitable reference. It is the WIKA Pressure & Temperature Measurement Handbook, a small hard-bound volume available from the WIKA Instrument Corporation. They are headquartered in Germany, and their US operations are at 1000 Wiegand Boulevard, Lawrencville, GA 30043.

Applicable discussion is on pages 30-41.

Craig,

It sounds as though you may have been subjected to the loathsome spectacle of some long winded piping seminar instructor blowing into the before mentioned party toy in support of an explanation of Bourdon Effect. Likely then you have also had to endure the misfortune of having bizarre colleagues (not of your choosing) forced upon you in the interest of "makin a living". You have my sympathy.

The payment of an exorbitant fee by any piping engineer in the search for wisdom and knowledge is indeed an unlikely occurrence. But on that subject, I wonder how the manufacturers of Bourdon tube pressure gages calibrate their instruments. There MUST be some design theory there that has been developed into a usable (nearly scientific) form by trial and error. In search of the grail....

Regards, John.

most likely propietary to the manufacturer..... also I suspect they build and test prototypes and use "in"finite element analysis as well in their designs....

Ok, here is the whole "ball of wax" as best we understand it. (I was really trying to avoid getting this deep into things, but oh well ...)

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Currently, there are no codes, equations, or technical papers that mention the Bourdon effect. We have hunted in vain for such a thing for years without success. Therefore we have a phenomenon that "everybody" knows how to use, how and when to apply, etc. but that nobody will put their name to. The reason, we believe, is because the traditional Bourdon implementation that everybody uses does not match up with reality.

Bourdon has little to do with the pressure translation of ovalized cross-sections into circular cross-sections - that is the pressure stiffening effect that most codes use to modify bend SIFs and flexibility factors. Bourdon is an attempt to take into account the strain that the piping undergoes when subjected to pressure. This strain is due to two components - the axial strain due to the pressure end cap effect (roughly PD/4tE) and then the Poisson effect (axial shrinkage due to radial and hoop expansion under pressure).

Virtually all pipe stress programs implement the Bourdon effect in the manner first developed for the MEC-21 pipe stress program, circa 1960. This method applies pressure elongation as a uniform strain to the entire piping system, in a way similar to thermal expansion (some codes, such as BS 7159, actually instruct the user to convert pressure strain to "equivalent temperature"). The actual pressure strain calculation is done as:

e = P(Ri * Ri) / (Ro * Ro - Ri * Ri) / E - V P(Ri) / (Ro - Ri) / E , or, slightly more exact,


but virtually identical for "thin" wall pipe:

e = [P(Ri * Ri) / (Ro * Ro - Ri * Ri) / E] (1 - 2 V)

Where:

e = uniform pressure strain

P = pressure

Ri = internal radius

Ro = outer radius

E = modulus of elasticity

V = Poisson's ratio

In the Bourdon method, this strain is then applied throughout the piping system, in the same manner as a thermal strain would be. The upshot of this is (think piping systems loaded with thermal strain):

1) On an unrestrained system (i.e., a cantilever), this leads to no stress, non-zero displacements, and no anchor loads.

2) On a restrained system (straight pipe anchored at both open ends), this leads to compressive stresses and compressive forces on the restraints and zero displacements.

3) On a restrained system (straight pipe with intermediate anchors), this leads to compressive stresses, zero anchor loads, and zero displacements.

In real life, the situation would be:

1) On an unrestrained system (i.e., a cantilever), there would be tensile stress equal due to the end cap effect, non-zero displacements, and an anchor load (pressure thrust load).

2) On a restrained system (straight pipe anchored at both open ends), there would be tensile stresses equal to the Poisson's effect (due to hoop stress), tensile loads on the restraints, and zero displacements.

3) On a restrained system (straight pipe with intermediate anchors), there would be tensile stresses equal to the Poisson's effect (due to hoop stress), zero loads on the intermediate restraints, and zero displacements.

(Note that real life piping systems are much more complicated than any of these three scenarios.)

For all load cases containing pressure (whether Bourdon is activated or not), CAESAR II (and probably most other pipe stress programs) then adds the constant value P(Ri * Ri) / (Ro * Ro) to the stress due to other loads (since this is required by most piping codes).

So looking at the implications of different scenarios:

1) On an unrestrained system (i.e., a cantilever), with no Bourdon activated, this leads to a stress of P(Ri * Ri) / (Ro * Ro), no displacements, and no anchor loads. Technically this is correct for stress, incorrect for displacements, and incorrect for anchor loads.

2) On an unrestrained system (i.e., a cantilever), with Bourdon activated, this leads to a stress of P(Ri * Ri) / (Ro * Ro), displacements equal to length * P(Ri * Ri) (1 - 2V) / (Ro * Ro - Ri * Ri) / E, and no anchor loads. Technically this is correct for stress, correct for displacements, and incorrect for anchor loads.

3) On a restrained system (straight pipe anchored at both ends), with no Bourdon activated, this leads to a stress of P(Ri * Ri) / (Ro * Ro), no displacements, and no anchor loads. Technically this is incorrect (but conservative, as intended by most codes) for stress (the stress should probably actually be tension equal to only the Poisson term: -V P(Ri) / (Ro - Ri), correct for displacements, and incorrect for anchor loads.

4) On a restrained system (straight pipe anchored at both ends), with Bourdon activated, this leads to a stress equal to the end cap tension, less the Bourdon compression, or just the Poisson effect: V P(Ri) / (Ro - Ri), no displacements, and compressive anchor loads. So this would be correct for the stress, correct for displacements, and incorrect for anchor loads.

5) On a restrained system (straight pipe with intermediate anchors), with no Bourdon activated, this leads to a stress of P(Ri * Ri) / (Ro * Ro), no displacements, and no anchor loads. Technically this is incorrect (but conservative, as intended by most codes) for stress (the stress should probably actually be tension equal to only the Poisson term: -V P(Ri) / (Ro - Ri), correct for displacements, and correct for anchor loads.

6) On a restrained system (straight pipe anchored at both ends), with Bourdon activated, this leads to a stress equal to the end cap tension, less the Bourdon compression, or just the Poisson effect: V P(Ri) / (Ro - Ri), no displacements, and compressive anchor loads. So this would be correct for the stress, correct for displacements, and incorrect for anchor loads.

In our opinion, the correct answer is to model pressure elongation as two distinct effects:

(1) a primary (force driven) load equal to the pressure end cap thrust load, modeled at every elbow, valve seat, or other thrust surface; and

(2) a secondary (displacement driven) uniform strain equal to the Poisson's effect of the hoop stress.

This sort of model would make each of the above layouts (as well as all in between) work out correctly. The problem would be that this would buck a forty-year old trend, and probably would not be easily implemented by most pipe stress software available today, without modification. A secondary by-product is that this sort of analysis would not provide the sort of conservatism that is currently allocated to longitudinal pressure stress by most codes.
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Now, before anyone concludes that we need to fix CAESAR II - no we don't, there is nothing to fix. COADE does not perform research, or develop Codes and Standards. We take available, published, public domain Codes, Standards, and Papers - and develop software to implement them. If there is nothing published, there is nothing to put in the software. If someone can point me to a published, public domain procedure, we will be more than happy to evaluate it for possible implementation in the software.

whew!