Tubesheet hole tolerance and size per ASME

[MikeG7]

Is there any restrictions or roles for how close fitting a tube is in a tube sheet that is to be welded?
For clarification, tubesheet design per ASME VIII D1 l, tube thickness 1.2 mm

Fabricator wants to cut holes bt lazer or similar process but is concerned that some ASME requirements are in place for hole tolerance

Thanks

 

[SnTMan]

MikeG7, I am not aware of any Sec VIII Div 1 hole tolerances. Most likely TEMA (RCB-7.21) is applicable. I tend to doubt laser-cut holes will be suitable.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[EdStainless]

Laser cut hole would not be acceptable, you would need to ream them to remove the re-cast layer of material.
I would worry about welding to as-cut laser material.
HX standards (TEMA or HEI) give very precise guides for hole sizes.

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P.E. Metallurgy, Plymouth Tube

 

[MikeG7]

Thanks both EdStainless and SnTman for your input! The fabricator (most) want to do the least extra processes as possible. I can point them to the Tema guidelines, but I can see predict the question "we are doing this to ASME so show me what the code says".

 

[EdStainless]

I have seen hundreds of ASME code HXs built to TEMA or HEI rules. It is very common.
You are buying, you set the rules. All that they can do is charge you for it.
Be very wary of the guys that say sure we can do that and then don't change their price.
If they want to not do that then ask them for their detailed quality plans.
How thick is this tubesheet?
The hole quality is critical for a few reasons, the fit influences the quality of the weld, and when the tubes are rolled for mechanical support you need reliable hole size in order to get proper expansion.

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P.E. Metallurgy, Plymouth Tube

 

[SnTMan]

If nothing else, you can put the tolerances and so forth on the drawing, There IS a drawing, right?

Edit: I had sort of assumed you were buying out the tubesheet, rather than the exchanger. If the latter is the case, you need to specify by appropriate means.

I'd guess that a fabricator offering laser-cut tube holes is on his first tubesheet. Ever.

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[MikeG7]

Thanks again for the responses both above.
The tubesheet in question is 32mm thick final size.

It was also my opinion that this method of lazer cut holes is not an option and I agree that the hole finish is important to achieve a reliable support for expansion. The advice/comments recieved above echo this.

But only for curiosity purpose , if the strength is in the weld and not in the expansion (correct me if wrongly interpreted) for a welded tube, and that the expansion process is only a means of locating the tube for the welding process, in such case, would a this be an "time saver" that is appropriate?

 

[EdStainless]

A laser cut hole will have a rough surface.
This is because you get some melted material re-deposited on the surface.
Sometimes this material is very different from the base material and need to be removed.
Even when you are doing strength welds you need a good fit (usually just a contact roll) in order to get a good uniform weld, and you need to then fully roll for mechanical support (you don't want the welds resisting vibration).

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P.E. Metallurgy, Plymouth Tube

 

[MikeG7]

well that kind of says it all then!...thanks