The Standard Diameter Ratio (SDR) is a key dimensional characteristic used for pipes. It is defined simply as the ratio of the pipe's Outer Diameter (OD) to its wall thickness.
Definition and Application
SDR = OD / wall thickness
In many calculations, particularly for pressure pipes, the mean diameter (OD minus wall thickness) is often used, leading to expressions involving SDR-124. For example, the SDR is a crucial parameter in Barlow's formula used to calculate the pressure rating (PN) of a pipe.
The values for the Outer Diameter used in ISO standards for pipes are often ISO values +1, related to the SDR definition. The ISO standard uses so-called Renard or ISO figures for OD, materials strength, and safety factors, based on constant percentage steps.
While the source defines SDR and shows its use in formulas, it does not detail the calculation process itself.
FAQ Section
What is the significance of the SDR value for a pipe?
The SDR value directly relates the pipe's diameter to its wall thickness24. For pressure pipes, it is a critical parameter used in conjunction with the material's strength (MRS) and a safety factor to determine the pipe's pressure rating (PN)13.
Why is "SDR-1" sometimes used in pipe calculations?
Calculations for pipe pressure often use the mean diameter of the pipe wall (Outer Diameter minus the wall thickness) rather than the outer diameter24. Using the mean diameter in the ratio with wall thickness leads to the expression SDR-124.
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Albert Vaartjes
