Pipe Mill Tolerance and Required Reinforcement

Hello,

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I am trying to design a branch connection that will fully reinforce my header pipe and pass a burst test.

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Short Version:

Can mill over-tolerance be applied to both sides of the pipe wall at the same time?

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Extended Version:

Most piping designers would take the 12.5% under-tolerance to determine the worst case allowable pressure, I need to take the best case allowable pressure in order to assure that my part passes a burst test.

Per ASTM A530, over-tolerance is different for certain sizes ranges, however all the over-tolerances are more than 12.5%. As long as your over and under tolerance meets those tolerances, the pipe should be acceptable. (Please correct me if I'm wrong)

Initially I was under the impression that if you had an over-tolerance on one side of the pipe wall, the opposite side would have an under-tolerance. This means the pipe would fail at the under-tolerance side first. Additionally it would decrease the burst pressure of the pipe compared to if it were made "perfect".

However, if an over-tolerance was applied to both sides of the pipe simultaneously, it would increase the burst pressure of the pipe.

With regards to my design, if the under and over effect each other, I only have to design for "prefect" pipe as that would merit the max burst pressure. On the other hand if over-tolerance can be incorporated into both sides of the pipe, then I need to design for the (pipe wall) + (over tolerance %).

So again... Can mill over-tolerance be applied to both sides of the pipe wall at the same time?