BENDING OF FINNED TUBES OVER FIN

[lgracio]

My client wants to bend the finned tubes on each top end, but the bend area contains fins. What kind of requirements and criteria should I apply? My opinion is that I should comply with "International Standard for Dimensions, Tolerances, and Tests of High Frequency Resistance Welded fins". My concern, the bare tube surface can be affected on extrados/intrados due to tensile of bounded fin on that area, that can create cracking of the surface of bare tube.

Lufs Grßcio
Mechanical Engineer (Engineering Solutions)
Portugal-Set·bal

 

[EdStainless]

Go back and buy tubes that are not fined in the bend area.
Are these integral (roll extruded) fins or are they wrapped (and welded?) fins?
If they are wrapped then strip the fins off of the area and bend.
If they are integral forget trying it.

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P.E. Metallurgy, Plymouth Tube

 

[lgracio]

The finned tubes are carbon steel material, in a spiral strip finning machine wrapped around the bare tube (High Frequency Electric Resistance Welded Finned Tubes).
Due to conditions of boiler performance the client wants to have the same as designed, so wants fins on the bends.

Do you know any specific requirements for this situation?

Lufs Grßcio
Mechanical Engineer (Engineering Solutions)
Portugal-Set·bal

 

[Duwe6]

"Due to conditions of boiler performance. . . " bet you an adult beverage that there will not be enough difference to measure.

Yes, the boiler will lose efficiency. Just like standing on a dock at a lake, and pouring your beverage out into the lake. You just raised the level of that lake, obviously. Now try to measure the difference.

If the client will not listen to reason, bend up a few test pieces. Then peel or grind off the fins. Use a sensitive dye-penetrant* to check for cracking at the extrados.
*NOT the common red dye; needs to be at least a sensitivity "Level II" if not Level III to detect the tiny cracks you are looking for. Probably will not find any; the stretching from the bending is perpendicular to the line of fin welds.