thick walled expansion joint spring rate 1

[FSKeng]

dear All

have any body noticed that when "thickness of an expansion joint" exceeds that of the adjacent shell, the spring rate of expansion joint(calculated based on TEMA RCB.8) drops sudenly. while an increas in the spring rate is expected!!

example:
\
sheel thickness E.J. thickness Spring rate
20 mm 20 77108.547 Kgf/mm.
20 mm 21 48490.125 Kgf/mm.??

 

[gr2vessels]

FSKeng,
I ran several calculations on the PV Elite and I have had always an increase of the spring rate with the increase of the thickness of expansion joint wall, over the shell thickness. It would be interesting to share with us your explanation of the fenomena you noticed.
cheers,
gr2vessels

 

[DG72]

Are you looking at TEMA 8th edition or TEMA 9th edition? The flexible shell element section of TEMA was completely re-written in favor of a more accurate method. The rules are now based on finite element analysis and are much improved. TEMA contracted with Paulin Research Group to develop software, so the new software has been written in more of a "canned" FEA approach, similar to their NozzlePro software, which makes it simple for a non-FEA guy to use.

 

[FSKeng]

Yes I have heard about TEMA 9th edition but I have not seen or study it, but I checked several exampls with Ansys and NO such decrease of spring rate was observed.
as far as I followed the procedure of TEMA 8th edition, in RCB-8.31 a discontinuity in parameters C6 and C7 was found ::!!!??
(it is shown in the attached file)
C6 and C7 are functions of C2 which is the ratio of shell thickness to expansion joint thickness. probably this sudden jump in the value of C6 and C7 (which ocures at C2=1) will result in a decreas of spring rate when the thickness of expansion joint exceeds that of the shell!!

I do not know if this discontinuity was delibrately and has a mechanical justification or it is a mistake?

Any help is appreciated!!