expansion joints acc. to VIII-1

[Frohnert]

Hi
In former times it was possible to calculate expansion joints made from carbon steel according to Appendix 26. Since today only austenitic items can be calculated with this rules, I would like to know which rules you guys apply to perform a calculation of an expansion joint according to VIII-1, e.g. made from 516-70.
Best regards
michger

http://www.OneTB.com

 

[Frohnert]

Correction: Not austenitic steels are permitted in the current Code, but only Nickel/Nickel Alloys.

The carbon and low alloy steels were allowed in the 1998 Edition, however disappeared in the Add. 00 where only high alloy and the above mentioned nickels remained.

Has anybody an idea why these materials where deleted?

Michael

http://www.OneTB.com

 

[eeromatti]

Appendix 26 says only that material shall comply with UG-4?!?

 

[Frohnert]

Please read a little bit further. In 26.6.6.3.2 for the fatique analysis (which is the important matter for the expansion joint) is written:

"The following equations are valid for:
(a) austenitic chromium-nickel stainless steel, UNS N066XX and UNS N04400 ..."

That´s it. No equations for carbon material anymore means no number of allowable cycles.

http://www.OneTB.com

 

[eeromatti]

OK, now I understand your point.

We are talking about fatigue, and SN (stress-life) curve for carbon steel differs significanly from curve of stainless steel (or nickel alloy) or curve of welded bellows.

Standard EN 13445 provides SN curves for austenitic (cold formed) and ferritic steels (welded and non-welded) and AD 2000 Code provides about the same curves. Or use some book of strength of materials, but remember to use reasonably factor of safety!

And because there is no equation for carbon steel, doesn't mean that numbeer of allowed fatigue cycles is 0. It's only calculation method missing...

 

[SnTMan]

I've never seen a CS bellows joint for HX use, all were stainless or nickel alloys, but truthfully, I don't remember if a fatigue equation for CS was present in earlier editions or not.

Flange & flues are often made of CS, per Appendix 5.

Regards,

Mike

 

[Frohnert]

Thanks a lot for your answers.
@eeromatti
The curves for ferritic steels you are refer to deal with "ferritic and martensitic steels", the product no. of these materials are 1.4xxx and these are not carbon steels like 516-xx you know from Sec. II. Therefore you cannot use these curves for carbon steels.

@SntMan
I have it on my desk. It´s not unusual here. The only disadvantage is that the manufacturer of the expansion joint provides a calculation according to the 1998 Ed. of the ASME Code, which is indeed unpleasant if the HE is acc. to Ed. 04 Add. 05.

Has anybody the faintest idea why the equations for CS bellows disappeared 1999?

Michael

http://www.OneTB.com

 

[SnTMan]

michger, it may be possible, with agreement between the involved parties, to use the older equations, etc. under U-2(g).

Regards,

Mike

 

[metengr]

michger;
I don't believe that the current revision of Appendix 26 necessarily prohibits the use of carbon steel. In fact, I laid out the 1998 edition/2000 Addendum of App 26 and the 2004 Edition of Appendix 26 and compared them side by side. The 2004 edition of Appendix 26 seems to have added substantial information concerning expansion joint design in comparison to the 2000 Edition of Appendix 26. However, in the 1998 Edition/2000 Addendum of App 26 there is still verbiage that limits the fatigue equations in 26-3 to only series 3xx,high alloy, nickel alloys... There is no mention of prohibiting fabrication using carbon steel. So, you can still fall back on U-2 (g).