Exchanger tubes AW tolerance for ASME VIII-1 Calculation 2

[FPPE]

Hi,

Should we consider a 10% tolerance on wall thickness for calculation of exchanger tubes (AW) according to ASME VIII-1?
I didn't find any requirement in the code about this.

Thanks in advance

 

[IdanPV]

See U-5: "The Code does not fully address tolerances...based on engineering judgment and standard practices determined by the designer"

 

[SnTMan]

The tube standards are usually either min wall or avg wall. Refer to the relevant standard, enter your data accordingly.

Regards

Mike

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

 

[r6155]

Use nominal thickness of tube.

Regards

 

[EdStainless]

For typical AW tubes the tol in almost all of the materials specifications will be +/-10%.
If you need to know the minimum wall then you should apply the tolerance.

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P.E. Metallurgy, consulting work welcomed

 

[Christine74]

Yes you must account for the undertolerance when specifying Average Wall tubing in your design calculations for internal/external pressure. See section UG-16(d) of ASME Section VIII-1.


-Christine

 

[FPPE]

Thank you all!

And what if there are no tolerances indicated in the material specifications in ASME II?

 

[EdStainless]

All of the tubing specifications have tolerances.

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P.E. Metallurgy, consulting work welcomed

 

[FPPE]

The manufacturer for sure, but I can't find it for example on SA 179 specification (ASME II).
Which spec shoul I refer to?

 

[david339933]

SA-450 as referenced in SA-179

 

[FPPE]

Thank you david339933.

Reading the following it would appear that the +-10% tolerance only applies to diameters above 50.8 mm:

However, from this table, considering for example a typical OD 25.4 and thk 2.11 mm tube, no negative tolerance is allowed:

Now, I had always thought that the 'average wall' referred to a +-10% tolerance, instead MW only with positive tolerance, but still considering the OD unchanged, as with standard pipes.

In which standard are these labels (AW or MW) mentioned and how exactly do they work? On various sites I find explanations that are not exactly congruent with each other.

Also, how is this distinction considered in software such as Compress or PV-Elite with regard to tolerances and outside diameters?

 

[EdStainless]

A179 says that it is for minimum wall tubing.
A450 is a general spec, it contains all of the options for applicable product specs.
And the product specs always override the general specs.
In software when you enter a specific material it should be pulling the data from the correct product spec.
Many product specs give both AW and MW tol ranges.
Because +/-10% is not exactly the same as +20/0, and some specs reflect this.
Tubing is specified as OD and wall.
Pipe is 'name of size' and 'schedule', neither of which are real dimensions since you have to look them up.

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P.E. Metallurgy, consulting work welcomed

 

[r6155]

The ordering information for tubes is outside diameter and minimum thickness.
Hence no tolerance is used for calculation.
I insist in my post 8May23: Use nominal thickness

Regards

 

[FPPE]

Just by reading the specifications in ASME II, it is clear (in my opinion) that the tolerance defined 'Average Wall' practically does not exist and it is not accepted by ASME.
So all suppliers offering AW exchange pipes are theoretically supplying a tube that is not in accordance with ASME, right?

And theoretically we manufacturers ourselves should not order an exchange tube, for example in SA 179, requesting for AW, which obviously has a lower price than the MW.

Honestly, I don't know if it works differently in the US, but in Europe (I understand that it may be wrong and not in accordance with the code, which would be serious) you are much more likely to see an AW pipe than MW.

 

[r6155]

The Average and Minimum Wall are used for dimensional control only and do not influence the design calculation.

Regards

 

[Christine74]

r6155, you are just plain wrong (again). Re-read UG-16(d).

It's very common to Average Wall thickness when working with stainless or nonferrous tubes and you need to account for the mill tolerance in your internal/external pressure calculations.


-Christine

 

[EdStainless]

There are many other ASTM/ASME tube specs where the default is average wall and min wall is an option.
Average wall is nearly always +/-10%.
The min wall can be anything from 18% to 40% depending on alloy/OD/wall combinations.

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P.E. Metallurgy, consulting work welcomed

 

[r6155]

Under tolerance of wall thickness of tubes (as table 2) is 0 (ZERO), hence no affect the calculation.

Christine74: try to avoid aggressiveness.

Regards

 

[Christine74]

r6155 your exact words "The Average and Minimum Wall are used for dimensional control only and do not influence the design calculation" are completely contradicted by UG-16(d).


-Christine

 

[FPPE]

r6155 and Christine74, I agree with both.
My doubt arises from the fact that for the most common carbon steel tubes (e.g. SA179 and SA210) the undertolerance according to the respective specifications is 0, whereas for a tube in SA 789 the specification explicitly states a tolerance of +-10% (e.g. for diameters between 12.7 and 38.1 mm) from ASME II part A-2 Table 5 page 1328).

So surely in the latter case, if you order the AW tube, the negative tolerance of 10% should be considered in the calculation.
This is why I ask my question again, when ordering tubes in SA179 or SA210 AW, we are theoretically ordering a product that does not comply with ASME, right?