Can anybody explain me this item?

Thanks,

Fabiano,

You can get a little explanation in PVElite manual but you will find more in and around fig. UHX-11.2 (ASME VIII) and fig. 13.7.3-1(EN 13445-3). If your tubesheet has an area without tubeholes (for cleaning purposes or pass partition) then this an untubed lane area. It is used to work out the effective ligament efficiency. If your tubesheet is fully tubed then you would enter 0.

Thanks Stan,

Does this untubed area include also the region below the nozzles (for impigement plate) or only the area due to pass partition?

Fabiano,

I'm not sure I understand your question.

The untubed area would include areas within the tube bundle pattern that extend right across the complete tube layout. Any 'untubed' areas outside of the outer tube limit would not apply. Equally, if there was a small area within the tube pattern left untubed then I would ignore this and assume tubed.

Does this answer it?

This is what I think, but I am not 100% sure about this,

The section UHX shows untubed lane area around the pass partition lanes (Fig. UHX-11.2). On the outer edge you need to specify the Outer tube limit diameter (Do). Then you do not have to worry about the nozzle clearances.

If you have unsymmetrical tube arrangement with large untubed areas then you can include those areas as well.

The most the untube area can be is 4 * Do * p

where,

Do - equivalent diameter of outer tube limit
p - tube pitch

From what I understand TEMA is working on a procedure to allow for large untubed areas. That method will provide factors to modify the UHX rules. But, this is no easy task.

OK. So if the there are untubed areas within the outer tube limit I must include those. Even if it is not for pass partition plates, isn`t it?

Fabiano,

I will tell you what I know,

1. You do not take area between the tubes in a normal tube arrangement. For example away from the partition lanes.

2. The part UHX indicates that the untubed area, AL is meant for the partition lanes.

3. You can extend partition lanes to mean other lanes (non-partition).

4. If you have large number of tubes missing that are not in a lane, then you are outside the range of section UHX (in my opinion). You may experiment including that other area and use that value of AL. But, the total AL is still limited to 4 * Do * p.

Review the applicability of UHX in detail. There is a white paper on the background of the UHX, available at the following link

http://www.coade.com/support_reference.asp?vartype=13&varflag=PVElite

I also saw this discussion on www.eng-tips.com,

http://www.eng-tips.com/viewthread.cfm?qid=198964&page=1

http://www.eng-tips.com/viewthread.cfm?qid=198964&page=15

I hope that helps.