Forming Strains under ASME VIII-1 vs ASME VIII-2

[MchA]

Hello everyone,

I am seeking clarification on the classification of forming strains under ASME VIII-1 UG-79 and ASME VIII-2 Table 6.1, particularly for spherical caps, such as those used in floating head heat exchangers or intermediate heads with Y-forgings.

Under ASME VIII-1 Table UG-79-1, these components appear to fall under Case 2, which applies to parts with double curvature (e.g., heads). This typically includes elliptical and torispherical heads, but would it also apply to hemispherical heads or spherical caps, despite having a constant radius of curvature?

My interpretation is that hemispherical and spherical caps are still double-curved since they have curvature in both the meridional and circumferential directions. Can anyone confirm whether this is correct? Or is Case 2 specifically intended for heads with two different radii (i.e., crown and knuckle)?

Turning to ASME VIII-2 Table 6.1, classification seems to depend on the fabrication process. If a spherical cap is formed from a single plate, would it fall under the first row:

“For all one-piece, double-curved circumferential products, formed by any process that includes dishing or cold spinning (e.g., dished heads or cold spun heads)”

Could a spherical cap, even with a constant radius of curvature, qualify as a “one-piece, double-curved circumferential product” under this definition?
Alternatively, if the cap is formed from multiple segments, I assume it would fall under the third row:

“For heads that are assembled from formed segments (e.g., spherical dished shell plates or dished segments of elliptical or torispherical heads)”

Could one argue that a spherical cap, even when formed from a single piece, is conceptually similar to the top portion of a segmented head and therefore classified under the third row? Or is classification strictly based on the fabrication method (i.e., one-piece vs. welded segmented)?

I’d appreciate any feedback or insights based on your experience.
Thanks in advance!

 

[TGS4]

My interpretation is that hemispherical and spherical caps are still double-curved since they have curvature in both the meridional and circumferential directions. Can anyone confirm whether this is correct?

Correct. Cylinders would have single-curvature, but any head would be doubly-curved.

Could a spherical cap, even with a constant radius of curvature, qualify as a “one-piece, double-curved circumferential product” under this definition?

Yes

Could one argue that a spherical cap, even when formed from a single piece, is conceptually similar to the top portion of a segmented head and therefore classified under the third row? Or is classification strictly based on the fabrication method (i.e., one-piece vs. welded segmented)?

For Table 6.1, classification is strictly based on the fabrication method.

 

[r6155]

"For Table 6.1, classification is strictly based on the fabrication method" : Incorrect
The difference is ONE-PIECE or segments.

 

[TGS4]

"For Table 6.1, classification is strictly based on the fabrication method" : Incorrect
The difference is ONE-PIECE or segments.

Which is what I said, in the context of the question asked.

 

[r6155]

The calculated strain is an estimate and must be verified with post-forming measurements. A procedure is required for this.