Tube to Tubesheet Joint in Claded surface

[krishsar]

Hi All,

We have a tubesheet which has a clad on tubeside but not on shell side.

According to specifiaction we require two grooves expaned tube to tubesheet joint. My doubt is where the grooves to be located.

As per my understanding one groove on clad (to avoid corrosion ) and other on base material but TEMA and API say (or do not recommend)no groove on clad portion. How to proceed please explain.


Regards,
KR

 

[Afox88]

Usually, I put both grooves in the base metal only. Some customer specifications ask to put a third groove in the clad portion but this is definitely not the norm. Also, it would require a thicker cladding (about 1/2" thk) in order to accommodate the groove.

I tend to include seal welding, if possible, when I use weld overlayed or clad tubesheets to prevent corrosion. The ability to do this of course depends on your material of construction.

 

[krishsar]

Afox88,

Thanks for the response i can understand we can provide a seal weld or strength weld or include groove in clad to prevent corrosion, but why does the API or TEMA does not specifically talk about that, our problem is the vendor has started to debate on the consideratinon of API and TEMA and requesting for extra price for performing a seal weld.


Regards,
KR

 

[Christine74]

TEMA RB-7.44 specifically says "all grooves should be in the base material unless otherwise specified by purchaser", presumably because cladding is generally not used as a load-bearing material.

I would double-groove the base material and then seal weld the tube-to-tubesheet joints to prevent crevice corrosion.

-Christine

 

[krishsar]

Thanks Christine, for your suggestion.

Regards,
KR

 

[plantprowler]

Out of curiosity what is the base metal and what is the clad MOC in your case? Also, what are the thicknesses.

 

[krishsar]

Base metal is SA-266 Gr.2 weld overlay Ni-Alloy and tubes are SA-268 TP405

Regards,
KR

 

[EdStainless]

And people still use grooves.
They only work (help) when the tubesheet is much stronger than the tubes.
If the strengths are close, or the tubes are stronger, or the tubes are very thick, then a series (5-15) of small shallow "vee" grooves help much more with joint strength and sealing.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[chevproe]

TEMA and API specifically prohibit any grooving in the clad portion.
However, you may need to consider the fact that Codes always stipulate only the bare minimum requirements, and the actual technical requirements are specified by the End user in the form of Project specifications.

Did you check the applicable Project specifications?
Has the Client specifically requested that Clad tubesheets be provided with seal welded joints in order to avoid crevice corrosion?
If no, you may just go ahaead with grooves in the base metal and expanded joints...
I think the Vendor is quite justified in asking for a price adder for seal welding since this is a big, unforeseen additional chunk of work for him to seal weld all the joints.

 

[r6155]

API 660: For shell-side-clad tubesheets, the tube shall be expanded to seal against the cladding material for a
minimum distance of 6 mm (1/4 in).
See more in API 660
Regards
r6155

 

[chevproe]

r6155,
The Exchanger under discussion is cladded on tubeside only, not on shell side.

 

[r6155]

chevproe, you say "TEMA and API specifically prohibit any grooving in the clad portion", but API 660 only shell-side is mentioned, hence for tube-side nothing prohibit.

Regards
r6155

 

[r6155]

chevproe, you say "TEMA and API specifically prohibit any grooving in the clad portion", but API 660 only shell-side is mentioned, hence for tube-side nothing prohibit.

Regards
r6155

 

[chevproe]

r6155,
Did you check API 660(9th Ed.),Par. 9.10.5??

 

[r6155]

chevproe
Sorry, I have only historical version 8th ed 2007 par 9.10.4. Most recent is 9th Ed 2015 not in my hands.

Regards
r6155