1. General wall thickness tolerance rules
Tubes with outer diameter ≥73mm
Wall thickness <20mm: tolerance +15% / -12.5%.
Wall thickness ≥ 20 mm: tolerance +17.5% / -10%.
Hot-expanded steel tubes
Tolerance of wall thickness is ±15%.
2. Additional tolerances for special wall thicknesses
Thin-walled tubes (wall thickness ≤ 0.10 mm)
The tolerance is the greater of ±12.5% or ±0.40mm.
3. Examples of tolerance calculations
| OD(mm) | WT(mm) | Tolerance range |
|---|---|---|
| 73 | 10 | +1.5mm / -1.25mm |
| 219.1 | 25 | +4.375mm / -2.5mm |
4. Other key requirements
Unroundness and wall thickness unevenness: not more than 80% of the tolerance of outer diameter and wall thickness.
Pipe end perpendicularity: for steel pipes with OD ≤60mm, the pipe end slant cut should not be more than 1.5mm.
Summary
The wall thickness tolerance of API 5L is dynamically adjusted according to the outer diameter, wall thickness and manufacturing process (e.g. hot expansion) of the steel pipe, and the core rules are:
+15%/-12.5% for wall thickness <20mm for OD ≥73mm; +17.5%/-10% for wall thickness ≥20mm. For wall thickness ≥20mm, +17.5%/-10% is applied.
For hot-expanded tubes a uniform ±15% applies.
