Calculate API 5L line pipe out of roundness and ovality from diameter and tolerance.
Out of roundness is equal to the maximum diameter minus the minimum diameter measured at the same cross section. Out of roundness ratio equals the out of roundness divided by either the nominal diameter or the mean diameter. DNV or ISO ovality is equal to the out of roundness ratio. API ovality is equal to half the DNV ovality (DNV or ISO ovality is equal to 2 x API ovality).
`Davg = (Dmax + Dmin) / 2 `
`OOR = (Dmax - Dmin) `
`ro = (OOR) / (Davg) `
`fa = (Dmax - Dmin) / (Dmax + Dmin) = (OOR) / (2.Davg) = (ro) / 2 `
`fd = 2.(Dmax - Dmin) / (Dmax + Dmin) = (OOR) / (Davg) = 2.fa = ro `
where :
OOR = out of roundness
ro = out of roundness ratio
Dmax = maximum diameter
Dmin = minimum diameter
Davg = average or mean diameter
fa = API ovality
fd = DNVGL or ISO ovality
Out of roundness can be calculated from API 5L, from user defined out of roundness, or from user defined maximum and minimum diameter. For diameter D ≥ 0.2191 m, the out of roundness can be calculated from the inside diameter. For D < 0.0603 m the out of roundness is included with the diameter tolerance. For D ≥ 1.422 m the out of roundness tolerance is to be agreed with the supplier. All tolerances should be entered as positive (+ve) values.
References :
API 5L : Specification for Line Pipe (2007)
ISO 3183 : Petroleum and Natural Gas Industries - Steel Pipe For Pipeline Transportation Systems (2007)
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