Definition
Drift Diameter — Drift diameter is the guaranteed minimum internal diameter of a tubular, verified by passing a standard-sized drift mandrel through the full length, ensuring that tools, bits and inner strings of a specified size will pass freely.
Also known as: drift diameter, drift, drift ID
What drift diameter is
Drift diameter is the minimum bore a tubular is guaranteed to have along its entire length. It is verified with a drift test: a cylindrical mandrel of a standardized diameter and length is passed through the pipe, and if it goes fully through, the pipe drifts. The drift is deliberately smaller than the nominal internal diameter, giving a safe working clearance.
Drift matters because anything run inside the tubular — a bit, a packer, a smaller tubing string, a logging tool — must be sized to the drift, not the nominal ID, to be certain it will pass.
Why it matters
- Tool clearance — bits and downhole tools are selected to pass the drift of the string above.
- API standards — drift mandrel dimensions are defined in API specifications (5DP, 5CT).
- Design margin — drift is smaller than ID, so calculations for pass-through use drift.
Renting drift-verified tubulars
Confirming drift before running avoids expensive hang-ups downhole. We rent drill pipe, workstring tubing and casing accessories with documented drift — contact us to confirm your tools will pass.