The deviation of ellipsoidal head

Dear all friend

I have question to asking you about the deviation of ellipsoidal head as per ASME Sec VIII div.1 UG-81 (a).
That involving the outside and inside deviation of inner surface.

The deviation can be checked by fit the temporary template into the inner surface and check the gap between template and surface.

Tolerance mention below;
Outside deviation not more than 1.1/4% of I.D.
Inside deviation not more than 5/8% of I.D.

My question is what does the outside deviation mean (dent inside or dent outside)? And what does the inside deviation mean (dent inside or dent outside)?

Thank you for all your guy reply.
Chatchai S.

In my opinion, measurement of head shall be met U-81 and additional measurement thickness after forming. Drawing normally specified the min. thickness of knuckle areas.

Regard to inside, you are mounting temporary templates fit inside surface, then you should be measuring the gap from inside surfaces to edge of template,normally at knuckle area .Acceptance when the gap values is smaller 5/8% of ID.
Outside is the same

Thank you for your reply.
So that’s mean we need to prepare 2 temporary template. 1 piece for inside and 1 piece for outside by plywood.

in my opinion, Only one template (inside) and UTM the formed areas.

dimensional checking of formed heads, based the fact that the UG-81 inner surface shall not deviate outside of the specified shape more than 11⁄4% of D and inside the shape more than 5⁄8%of D.

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Ok I am agree with you 1 piece for internal is enough. And thank you for all your kind reply. I hope that my problem will have useful to every person whose interface same problem.


UTM shall be measured.

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