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Out-of-roundness pipeline bends

asked Oct 13, 2014 in Piping by guyredumis (540 points)
What is the recommended out-of-roundness pipeline bends when designing the pipeline and pigging system?

2 Answers

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answered Oct 13, 2014 by bxander (1,180 points)
The bend internal diameter out-of-roundness should be 5% or less.

You should use a minimum of one pig length of straight run pipe either upstream and/or downstream of all bends, outlets, valves.
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answered Oct 13, 2014 by bxander (1,180 points)

Also, consideration should be given to specifying a constant internal diameter and varying the pipe outside diameter accordingly.  If internal diameter changes are unavoidable, the maximum deviation of internal diameter from nominal should be kept to the minimum according to the table below.

Nominal Pipe Diameter, in. Maximum Deviation, in.
4 0.016
6 0.024
8 to 12 0.039
14 to 20 0.055
20 to 36 0.063
36 and over 0.079

All internal diameter changes should be made with tapered transition pieces of 1.5 minimum slope.