Our B&W boiler has a number of tube

[DRight]

Our B&W boiler has a number of tubes that are cold drawn. and asked about substituting with a hot finished tube. Initially we were told that This does not matter as it has no impact on properties. The Cold Drawn has better tolerance but you will pay a premium. A Boiler Manufacturer may have used Cold Drawn to manufacturer ie. walls because the tighter tolerance better suited their processes.The materials that went into the original design may no longer be available, you will have to use what is commercially available. Or be prepared to wait for a mill run.
Upon further discussion with a design engineer I was told The use of cold drawn tubes are critical to ensure a balanced equal flow especially in area's such as superheaters because of the close tolerance the C.D. tubes provide as opposed to the H.F. tubes . If this fact is ignored you could possibly cause some overheating of a particular leg which would cause long term overheating and failure This may happen and we may not even be aware of the original cause.
Hot finished tubes can be ordered to Cold Drawn tolerance, I am a bit confused on the industry standard
I would appreciate your opinion on this matter.
Thanks

 

[davefitz]

1.. Not all tube suppliers can supply hot finished to the same tolerance and cold drawn.

2. Design engineer is sort of right- in some applications the cold finished tolerance is critical, such as on the long waterwall tubes of supercritical steam generators ( 0.5" ID tubes). But on standard 3" NPS tubed waterwalls, the tolerance is not critical.The sensitivity of this issue increases by the -3 power of the tube diameter.

Likewise , in superheaters it is usually the case that inelt orificing was provided to provide the appropriate flow distribution thru the superheater- a bigger effect than the tube tolerance is probably the apparent outlet orificing effect caused by the socket weld at the tube to header weld.

 

[kenvlach]

The boiler tubes that I have seen are swaged against the endplates when installed. I don't think a tiny variation in tolerance matters; rather, the cleaner surface and higher strength of the cold drawn tubes may be why they are used. Also, cold drawing uses better,'drawing quality' initial material.