TEMA and Tolerance

[EuroWeld]

Hello,

Can somebody tell me if 9th edition TEMA standards describes tolerances of hole diameters in baffles for shell and tube heat exchangers? Meaning is their a maximum distance specified between tube and tube hole. I'm not an experienced STHE engineer but more experienced with Air Cooled Coolers.

The reason for this question is because I must know what are reasonable tolerances while fabrication? Must these holes be drilled or can these be lassercutted or produced in a different way? Depending on thickness and material, knowing that the surface of the baffle in contact with the tube must be smooth and deburred. Can anybody help me?

Baffles are made out of carbon steel, thickness 8mm, disign included a high amount so we like to produce as efficient as possible.

All our client specified was design according to TEMA.

Please inform me,

Euroweld

 

[gr2vessels]

Clause RCB-4.2 describes the hole size in the baffle as function of tube diameter and the unsupported tube length. For tubes larger than 31.8 mm and less than 914 mm unsupported length, the hole oversize is 0.8 mm on diameter. For smaller tubes and longer unsupported lengths, the oversize is only 0.4 mm. The hole tolerance is 0 to +0.3mm. For details refer to RCB-4.2.
Hope it helps,
Cheers,
gr2vessels

 

[EuroWeld]

Thanks for your reply. It's possible to lasercut this 8mm baffle including this tolerance. When using lasercutting how to execute the initial cut in the plate for cutting the hole? Is their a usual cut? From the middle or else?

 

[cloa]

Might want to put this new question in the laser engineering forum

 

[EuroWeld]

Yes, good suggestion.

 

[r6155]

Any burrs shall be removed and the tube holes given a workmanlike finish.

Regards

r6155

 

[EuroWeld]

r6155,

Is that mentioned in TEMA?

 

[gr2vessels]

The reply from r6155 is actually the excerpt from the TEMA 9th Edition. I would suggest buying TEMA if you intend to use it to this level of detail.
gr2vessels

 

[EuroWeld]

gr2vessels, thanks for your reply and your above given suggestion.
I was planned to buy the TEMA, but above question came to mind directly after the first one.(not good at waiting) I'm hoping to have my own version by the end of next week.



Thanks again

 

[SnTMan]

EuroWeld, experiences I have seen with laser cut tube holes has not been satisfatory. Problem with piercing, problem with finish. Potential problem with accurate diameter.

Suggest you get some samples done before heading whole hog down that road.

Yeah, drilling may cost more than laser cut, but less than warranty costs.

Regards,

Mike

 

[Duwe6]

Like everything else in the Machining world, it depends on the Machine and the Machinist. A new Laser Machining center [not just 'cutting table'] can hold =/- 0.001" all day, every day.

As for piercing, a good Machinist will pierce the hole inside the 'slug' and then spiral the cut out to the actual hole cut. And that cut will be continued past the starting point [overlap] so that any dross from where the spiral met the circular cut is cleaned off.

Get cheap work off a Laser Burning Table, expect +/- 0.020". Not the right machine.

 

[EuroWeld]

I understand that the machine and operator are the key issues here, knowing that this is a very accurate job that expects the most of both. SnTman and Duwe6 I am not trying to buy cheap at the expence of quality. We are aware of this issue. But knowing that competitors already applying the laser, we cannot fall beyond.

I opened a topic in the laser engineering forum for technical solutions. We are seriously trying to find out all possibilities for the future and hoping to get technical feedback there.

Additional I was wondering what the position of TEMA is about this issue. Is this a general exepted manner to produce the baffles? I tried to contact TEMA but they forwarded me to this forum, so knowing I am on the right spot to get the right answers.

 

[SnTMan]

EuroWeld, understood and good luck.

I doubt TEMA intends to mandate manufacturing processes, after all it is primarily a fabricator association. Meet the requirements, it's up to you what processes you use.

Regards,

Mike

 

[SnTMan]

EuroWeld, I might have added to my first post:

One thing that kind of argues against laser cut baffles is that baffles can normally be stack-drilled, laser cutting would have to be done individually I assume. I don't know enough about the economics to be able to guess where break-even might be.

Regards,

Mike

 

[EuroWeld]

I have asked our drilling specialist about stacked drilling today, he informed me that the break even point is reached already at low quantitys. It's more difficult to drill a stack when using a high speed drill because of the burrs that stick at the top of the drill.

I thought maybe TEMA had some guidelines fot applying the laser,I will wait and see what comes out the laser thread.

Thanks

 

[KevinCPE]

Although I'm reading this too late to help you specifically, I just wanted to add that CNC punching is a good way to go for baffle holes. Punch one baffle at a time on the press. One hole at a time, then either plasma cut or nibble the perimeter. Hole punches and dies are bought custom made right to the diameter you need. Most common materials can be done this way, within the tonnage of the punch machine.

If stack drilling, depending on baffle diameter you will need some tie-down bolts within the baffles to resist the chip friction. Drill these holes first, insert the bolts, tighten onto the machine table, then drill the rest of the tube pattern. Typically use a chip-breaker style.