Expanded Tube Joint Calc (Sect VIII Po & Pt)

[BigTank]

Gents,

I have expanded-only TEMA-type tube joints in a fixed tubesheet S&T exchanger. I need a methodology for estimating (calculating or emprical reference) Po and Pt (Section VIII-Appendix A variables).

Can anyone help? I'm working on developing something, but a reference of some kind would certainly help things along (that is if someone can't just GIVE me something to use...wink wink).

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Fitter, happier, more productive

 

[BigTank]

Gents and Ladies, that is...my ignorant mistake.

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Fitter, happier, more productive

 

[SnTMan]

BigTank, I have never been able to find much on this, particularily something easy to use along the lines of other ASME design rules, say as a hand calculation.

I have developed the following means of addressing this variable.

Per Appendix A the quantities Po, Pt appear as a ratio in the calculation for Lmax. As a ratio it can increase, decrease or not change Lmax. Therefore, I never use it to increase the joint strength, max (Po+Pt)/Po = 1.0

I may use it to decrease the joint strength, (Po+Pt)/Po < 1, if the coefficient of thermal expansion of the tubesheet material is greater than the COTE of tube material, selecting Po, Pt such that the calculated ratio is equal to the ratio of the COTE's, i.e. Po = 1, Pt = -0.25, ratio = 0.75.

Not perfect by a long shot, but something.

I find it a little odd that there is not more readily available on the subject after all this time.

Regards,

Mike

 

[BigTank]

i think that's as sound a method as anything, mike. i was trying to develop something based on the yield strength of the tubesheet, working inwards and treating the joint as a press fit or some derivative thereof...until i asked myself 'and how do i consider friction loss in there?' (which would be substantial, i'm sure), and then 'how do i account for the change in pressure based on the thermal expansion?'

i guess i gave up when i realized how many variables there were in considering this joint strength (strain-to-stress relationships above yield, work hardening of the tube material and/or tubesheet, the relative tribology of the interfacing materials and it's change due to friction). i knew i could come up with something, but it would most likely be light years away from reality.

that being said, i'm sure there would be a value in emperical data and their associated trends. i'm with you...i find it odd that there isn't SOMETHING available to estimate the strength of this type of joint.

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Fitter, happier, more productive

 

[SnTMan]

BigTank, I think if you search the site, you will find references to a few papers on the subject. I found one of them at the local public library, from "Journal of Pressure Technology" May, 1992.

What I have not found is the time to plow through it and see if anything conveniently useful can be squeezed out.

Regards,

Mike

 

[AllHandlesTaken]

Hi BigTank,

Send me an email at Spammmemailll,,,,,,at,,,,,,gmail(dot)com

(and I am not joking - that is my, as you can guess "Spam" email)

 

[sjrfc2]

Harvey's book on pressure vessel design discusses it a little. I don't have the book with me know but he addresses the need for the tube sheet yield to be higher than the tube yield strength. He also provides a graph showing relative pull-out strengths and impact of having either one or more serrations in the tubesheet (from memory).

I looked for info in the early-mid 90's and found very old papers (30's, 40's, 50's). I was also able to find test data. The US Navy and industry was doing testing around that time as they were increasing the working pressure of boilers.

From what I rememeber the pull out strength in the test data could vary a lot based on how the tube was expanded. The tube yields as it is expanded (rolled) and compressed against the seat. If the mechanic continues to try to roll the tube it extrudes axially along the seat shearing at the tube-to-tube seat interface. So there is an optimum expansion of the tube (beyond which the joint is weakened) that is largely attributed to the mechanics judgement.

The later papers in the 90's seemed like they were more based on validation or optimization of a hydraulic expansion method that took the mechanical rolling process out of it.

 

[AllHandlesTaken]

Yes, there is (also?) some info in Harvey's "Pressure Component Construction" - see attached (fair use copyright exempt

 

[AllHandlesTaken]

....... which, after checking, is the exact same material in "Theory and Design of Pressure Vessels" {Harvey}

 

[saplanti]

The following thread might be helping somehow I guess:

http://www.eng-tips.com/viewthread.cfm?qid=225601

Additionally, this kind of connections must be tested in accordance with Australian Standards (I can't remember the number right now). So, you may need to consider the test samples option if you need to continue doing this kind of jobs.

Many companies have developped some kind of expansion connection standards by their experience over the years in accordance with the thickness range of the tubesheet and the occupation. Therefore they become their job secrets. However if you contact one of the reputable expansion company that you are going to deal with for the job they may be helping you.

Ibrahim Demir