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Join Date: Oct 2011
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Pipe Mill Tolerance and Required Reinforcement

05/03/2012 11:19 PM

Hello,

----

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?

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#1

Re: Pipe Mill Tolerance and Required Reinforcement

05/04/2012 3:17 AM

<...a branch connection that will fully reinforce my header pipe and pass a burst test....> will be satisfied by many proprietary clamp-on branch connections intended for hot-tapping. So there is no need to do a design from scratch. Simply enter "hot tapping" into any internet search engines and a number of suppliers will come up. Simply filter them on the basis of location and then start ringing them.

"Simples!ξ"

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#2
In reply to #1

Re: Pipe Mill Tolerance and Required Reinforcement

05/04/2012 5:31 AM
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#3
In reply to #2

Re: Pipe Mill Tolerance and Required Reinforcement

05/05/2012 12:22 AM

MR. Slack, what is the pressure rating of the bolt-on you have pictured? I appears to be fairly robust compared to some bolt-ons I have seen.

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#4

Re: Pipe Mill Tolerance and Required Reinforcement

05/05/2012 12:23 AM

What is the operating pressure?

What is the burst pressure test value you need to pass?

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#9
In reply to #4

Re: Pipe Mill Tolerance and Required Reinforcement

05/09/2012 1:31 AM

I have to do this for multiple header sizes all at Maximum Working pressure....

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Working pressures are to be calculated per B&PV Section VIII

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Theoretical bursting shall be per B ≈ St/r

B - Burst Pressure

S - Tensile Strength of Material

r - Radius of Pipe

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Fitting must reinforce at 105% of calculated Burst Pressure

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#5

Re: Pipe Mill Tolerance and Required Reinforcement

05/05/2012 1:18 AM

I think the answer is NO to either version, under any reasonable interpretation.

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#6
In reply to #5

Re: Pipe Mill Tolerance and Required Reinforcement

05/06/2012 5:50 PM

GA Tornado, I completely overlooked the safety factor component of this issue. How can the mill allowance be reliably known to be always on the plus side consistantly?

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#7
In reply to #6

Re: Pipe Mill Tolerance and Required Reinforcement

05/06/2012 6:03 PM

Also, in the case of seamless pipe, overtolerance on one side of the pipe equates to undertolerance on the other. Then how can it be ensured that the branch will occur on the thicker side of the pipe?

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#8
In reply to #5

Re: Pipe Mill Tolerance and Required Reinforcement

05/07/2012 8:47 AM

I was curious how you gaurantee an over-tolerance during manufacturing.

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