S32760 Yield and Tensile strength, ASME Sec IID

[31KT]

The yield ( Table Y-1) and tensile (Table U)strength for S32760 are significantly different between ASME Sec IID Metric and Customary. From Customary Sy is 64.6ksi @200F , where as from Metric its 455MPa (65.9ksi) @ 100C(212F). Can someone point me the obvious that I am not able to decipher. I noticed this trend on the tensile strength as well, the material is somehow stronger in metric units when compared to customary. I understand mathematical correction during unit conversion but the difference in this case appears to be significant.

 

[EdStainless]

If you look at the material spec you will see that the english and metric values for yield and UTS are not direct conversions.
This is likely where the difference is from.

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P.E. Metallurgy, Plymouth Tube

 

[31KT]

Noted, but 1.3ksi of difference in yield between metric and English can make or break when on the edge. For wall thickness calculation, we can simply adopt metric units to our advantage , but at the same time we fall short when replaced with English units, what is the rationale?

 

[EdStainless]

Your design has to be all one or the other, you can't switch units to 'make it work'.
If you design to the metric values then all of the material must be bought to the "M" spec, not converted from english.
The strengths and tolerances do not hard convert.
Just pick one set and go with it.

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P.E. Metallurgy, Plymouth Tube

 

[r6155]

See NONMANDATORY APPENDIX
GUIDANCE FOR THE USE OF U.S. CUSTOMARY AND SI UNITS IN THE ASME BOILER AND PRESSURE VESSEL CODE.

Regards

 

[CuMo]

If you have an ASME design - the units have to be consistent throughout the whole design.
Using values from Imperial or SI "to suit" is not permitted.
Stick to one or the other.

 

[gtaw]

I believe it is called a "soft" conversion. 25.4 mm = 1-inch, but using soft conversion we use 25 mm = 1-inch. Similar rounding assumptions are used for other units of measure.

Best regards - Al