Tube hole tolerance for baffle plate. 1

[mechengineer]

Hi experts,

The over tolerance of IOGP S-614 and TEMA RCB-4.2 shall be considered into the basic hole diameter of the baffle plate for HTRI analysis. The machining finishing/drill tolerance by CNC shall be as per GENERAL TOLERANCE DIN ISO 2768-mk if there is not surface finishing tolerance shown in the hole diameter. The surface finishing tolerance may not consider into HTRI analysis. We should not confuse the over tolerance in RCB-4.2 or IOGP with the surface finishing tolerance which limit by the accuracy what machining method used.

For example,
1. AS per TEMA standard TEMA RCB-4.2, the tube OD is 19.05 mm, the over tolerance is 0.4 mm (not pulsating conditions). So, the hole diameter on the baffle plate shall be 19.45 mm.
TEMA Standard RCB-4.2: Where the unsupported tube length exceeds 36 in. (914 mm) for tubes 1-114 in. (31.8 mm) diameter and smaller, standard tube holes are to be 1/64 inch (0.4 mm) over the OD of the tubes.
2. As per IOGP S-614 clause 7.5.3.5 "The standard tube hole diameter in the baffle and support plates shall be +0.4 mm (1/64 in.) over the outside diameter of the tubes. Tube hole tolerance shall be in accordance with TEMA RCB-4.2".
So, the hole diameter shall be 19.05+0.4+ 4 mm of the over tolerance of RCB-4.2 =19.45+0.4=19.85 mm.
3. To avoid confusing, the tolerance of RCB-4.2 and IOGP shall convert to the basic diameter in the drawing, not the finishing tolerance format as +/_0.0xx because the drawing is for machining. The machining tolerance shall comply with the applicable machning industry standards, not TEMA/IOGP.
4. How to understand so big different for hole diameter between TEMA and IOGP S-614?

Regards,

 

[Christine74]

I think you might be conflating two separate issues here. All baffle tube holes must be slightly oversized in order to be able to insert the tubes through the baffles. TEMA requires that the holes be oversized either 1/64 inch (0.4 mm) or 1/32 inch (0.8 mm) depending on the tube diameter and unsupported length of the tubes. Tighter tube holes are also occasionally specified in order to reduce "A" stream bypass and/or reduce the potential for tube vibration.

Additionally, since drilling tubes is imprecise TEMA allows for an additional tolerance above and beyond the oversize hole diameter of +0.010-0.015 inches (0.3-0.4 mm).

So really the only difference between the two standards is that TEMA allows you to use a 1/32" (0.8 mm) oversize drill in some cases but IOGP limits you to using a 1/64" (0.4 mm) oversize drill. This requirement will probably make it very difficult to install tubes into tube bundles that have a large number (20+) of baffles. As a practical matter it doesn't really improve heat transfer much either, so I don't see the point.

HTRI by default uses TEMA tube hole clearances but you can overwrite it if you want.


-Christine

 

[EdStainless]

And don't confuse hole size with drill size. The holes will be larger than the drill unless you are using drill+ream.
And different types of HX may have different size guidelines.
For example the HEI Condenser std lists support plate hole size for 0.750" nominal tubes as 0.760"-0.775".
(there is also an allowance for up to 4% of the holes to be slightly larger)
They presume that you are using standard ASTM tube tolerances, otherwise this needs to be modified.
There is also a roughness limit and deburr requirement.
It is common to see a larger chamfer used on the side of the support plate that faces the tube insertion direction.

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P.E. Metallurgy, consulting work welcomed