Pipeline Ovality
Pipeline Ovality
(OP)
There are 2 main methodologies in industry for calculating ovality, API & DNV.
In API 5L out-of-roundness is defined as the difference between the maximum (orminimum diameter) and the nominal diameter, expressed as a percentage of the nominal diameter. In DNV-OS-F101 and ISO 3162, out-of-roundness is defined as the difference
between the maximum and minimum diameters, expressed as a percentage of the nominal diameter. Assuming symmetric ovality, the API 5L definition gives half the percentage ovality of the ISO 3162 definition.
Given one method gives half the value of the other, which methodology would you use to assess ovality in steel pipelines and why? Looking for any background / insight in experiences and why these 2 methods are different? Does acceptance criteria generally differ then when using one method or the other?
Thanks.
In API 5L out-of-roundness is defined as the difference between the maximum (orminimum diameter) and the nominal diameter, expressed as a percentage of the nominal diameter. In DNV-OS-F101 and ISO 3162, out-of-roundness is defined as the difference
between the maximum and minimum diameters, expressed as a percentage of the nominal diameter. Assuming symmetric ovality, the API 5L definition gives half the percentage ovality of the ISO 3162 definition.
Given one method gives half the value of the other, which methodology would you use to assess ovality in steel pipelines and why? Looking for any background / insight in experiences and why these 2 methods are different? Does acceptance criteria generally differ then when using one method or the other?
Thanks.





RE: Pipeline Ovality
Yet another standard ISO 2531 for ductile iron pipe defines "out-of-roundness" I suspect to avoid confusion of words instead with an algebraic expression and also as a percentage:
100%(A1-A2)/(A1+A2)
Where A1 and A2 are the maximum and minimum measured diameters. Again I believe you will get very similar result, with yet this third way of expression!
All this sort of makes sense to me, and while these standards are expressed differently, all would appear to me to basically give similar result!
RE: Pipeline Ovality
API 100% Dmax – Dmin / Dmax + Dmin
= 1.2% with this method
ISO 100% Dmax – Dmin / Dnom
= 2.4% with this method
RE: Pipeline Ovality
I get Dmax 170.3 mm - Dnom 168.3 / Dnom 168.3 = ~0.012 or 1.2%
RE: Pipeline Ovality
RE: Pipeline Ovality
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso
RE: Pipeline Ovality
API 5L defines out-of-roundness as:
"the out-of-roundness shall be determined as the difference between the largest outside diameter and the smallest outside diameter, as measured in the same cross-sectional plane."
The unit is distance (mm) and the tolerances shown in API 5L are also in mm given such as 0.015D
there is also no mention about the word "ovality" in API 5L.
I don't have the DNV but I can not understand the comparison of API 5L (mm) and DNV (%). Where does the API formula in your calculations come from?
At any rate, what we use as the pipe vertical deflection (ovality) in water sector is:
percent deflection= (change in diameter)/(nominal diameter) x 100