Length of tube expansion on Tubesheet 2

[vesselrajj]

We are fabricating a steam generator for WHB.In client spec for tube expansion, they specified to expand 1/8inch beyond the tubesheet thickness (to the backside of the tubesheet). The tubes are to be strength welded and expanded to 3-8%. We used to expand as per TEMA i.e.tubesheet thickness minus 1/8in. Is this advisable to expand beyond the tubesheet thickness? I fear it may cause bulging of tubes.

 

[SnTMan]

vesselrajj, normally not done, but they may want to eliminate any crevice between tube / tubesheet. I would comfirm.

Regards,

Mike

 

[chicopee]

I am a little confused by the statement "...they specified to expand 1/8inch beyond the tubesheet thickness..." are you referring about projecting the tube ends 1/8" past the tube sheet?

 

[vesselrajj]

Chicopee,Its not the projection. They insist to expand the tube beyond the backside of tubesheet thickness. So the length of expansion will be the sum of tube projection+ Tubesheet thickness + 1/8inch. Hope I am clear.

 

[chicopee]

Another word, your customer wants to flare(expand) the projections of the tube ends simultaneously to tube rolling in addition to strength welding (not seal welding) the tube ends. If this is the case, it seems to be overkill. Normally the rolling and tube end expansion should be enough. So what type of a boiler is it, what are the max. working pressure and temperature, who is the manufacturer and what is the application of the boiler?.

 

[vesselrajj]

chicopee, it is a steam generator for waste heat boiler.As stated by Mike,their concern is to eliminate the crevice between tube & tubesheet. I will come up with other details soon.

 

[chicopee]

So,are we talking about a steam drum or are we discussing an unfired pressure vessel that reclaims the hot exhaust flue gases for the waste heat boiler?

 

[vesselrajj]

Its of 2nd type. The name of the equipment is Reaction furnace steam generator and it is a part of Reaction furnace WHB package.The inlet is from combustion chamber and the outlet is connected to steam drum. Since I am fabricating only steam generator, i don't have much information about other equipments.

 

[chicopee]

"...their concern is to eliminate the crevice between tube & tube sheet.." to me that would mean a seal weld not a strength weld. Which code is being used to build this steam generator ASME Code I or code VIII?

 

[SnTMan]

chicopee, vesselrajj is talking about the backside of the tubesheet...

So, vesselrajj, if you have confirmed this is what the client is after, you must take care that the tube is not cut by the expansion process. The tubehole will have to be square edged to eliminate the crevice, but this aggravates the cutting issue. Better would be a small radius on the tubehole, but this could possibly leave a small crevice still. I would get complete buy-in from the customer on your proposed details & process before proceeding.

Regards,

Mike

 

[chicopee]

Semantics is a son of a gun to a lot of people, so one has to determine the actual messages that authors try to convey in their OP's, many of which are not what the authors have intended to convey, therefore, the reference to backside means nothing to me as it is either the waterside or fireside. If the author had been descriptive as to the type of boiler or ASME code and other pertinent information such as the code 9 I,IV or VIII being used, then a proper response would have been provided.

 

[gr2vessels]

The proposed expansion of the tubes on the 'other side' of the tubesheet is meant to reduce the chance of a deep crevice, not to eliminate it all together. There will always be some degree of elastic spring back of tubes, resulting in opening a small crevice. The small radius on tube hole end is probably the best bet for controlling the potential rupture of the square end of tube hole and allowing a better material flow of the tube during the extended rolling. As far the Client concerns, you are suppose to tell the Client the proposed solution is the best he can get, unless he has an even better alternative.
Cheers,
gr2vessels