Table D-5 TEMA Bolting Data - Root Area vs Conventional (UNC) root area 1

[takiyasamsama]

Guys,

Why is the root area between these two are different?

e.g. for M12 on Table D-5M the root area is 72.396 sq-mm while for for M12-1.75 UNC it is about 84.3 sq-mm.

Why is it different and what are the formula used for establishing TEMA root area? I'm wondering this since day one but just out of curiosity to ask while I'm currently designing vessel with removable ends.

Thanks in advance

 

[Shashvat]

Hi takiyasamsama

I think the reason for this has to do with the diameter used in the area calculations. If I am not wrong, the tensile stress area is equal to the area of the circle whose diameter is the average of the pitch diameter and the base diameter. This calculation might have been used for the UNC series.

However, the TEMA code, owing to the safety reasons, might have considered the tensile stress area as the area of the circle with the diameter as the base diameter. This might be the reason that the UNC area is greater than the TEMA table D-5M area.

I suggest you stick to the TEMA dimensions as the other dimensions mentioned in the table D-5M will pave a straight path for the flange design, if required. I do not have those big machinery handbooks at hand, but I think you might find the reason in the threads section of those book.

 

[takiyasamsama]

Hi Shashvat, thanks for the responds and yes I am currently using TEMA for the bolting data.

 

[r6155]

Both of you are wrong.
Table D-5 is not the same as Table D5-M (not equivalent)
See ASME B1.1 Unified Inch Screw Threads.

Regards
r6155

 

[takiyasamsama]

Hey r6155, it would be better if you could elaborate what is wrong and what is right. Simply point out a standard doesn't really helped at all, a kid could say that. Unless you also didn't know the difference between those two...

 

[r6155]

takiyasamsama.
Are you curious or comfortable? Minimum effort is required from you.
Take a look on ASME B1.1 and you can find the answer. I take my time to respond to you
I understand you are engineer.

Regards
r6155

 

[r6155]

Here the difference.

ASME B1.1. 8.3.1 (f) Minimum Minor Diameter (External Threads). When
it is desirable for design purposes to calculate the minimum
diameter, it can be obtained for all classes by the
formula: minimum pitch diameter minus 0.64951905P

In Table 6 for ½” 0.1257 sq in = section at minor diameter ( 0,126 sq.in in TEMA Table D-5 )

ASME B1.1 B-1 THREAD TENSILE STRESS AREA
The following thread tensile stress area formulas are
used for the purpose of product acceptance computations

In Table 6 for ½” 0.1419 sq in = tensile stress area

ASME SA-193 9.1.2 Full Size Fasteners, Wedge Tensile Testing—When
applicable, see 12.1.3, headed fasteners shall be wedge tested
full size. The minimum full size load applied (lbf or kN) for
individual sizes shall be as follows:
W 5 Ts 3At (1)
where:
W = minimum wedge tensile load without fracture,
Ts = tensile strength specified in ksi or MPa in Tables 2 and
3, and
At = stress area of the thread section, square inches or square
milimetres, as shown in the Cone Proof Load Tables in
Specification A962/A962M

SA962 /962M
TABLE 1 Cone Proof Load Using 120° Hardened
Steel Cone—Inch

1⁄2” x 13 0.1419 sq in = stress area

TABLE 2 Cone Proof Load Using 120° Hardened
Steel Cone—Metric

M12 x 1.75 84.3 mm2 = stress area USE FOR PRODUCT ACCEPTANCE (testing)


M12 x 1.75 72,398 mm2 = section at minor diameter USE FOR DESIGN CALCULATION

Regards
r6155

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