BENDING OF FINNED TUBES OVER FIN
BENDING OF FINNED TUBES OVER FIN
(OP)
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





RE: BENDING OF FINNED TUBES OVER FIN
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
RE: BENDING OF FINNED TUBES OVER FIN
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
RE: BENDING OF FINNED TUBES OVER FIN
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.