FOERSTER
Application notes
Residual Magnetic Field Testing on Non-Magnetic Drill Collars

Residual Magnetic Field Testing on Non-Magnetic Drill Collars

Residual magnetism in non-magnetic drill collars can distort borehole measurements and jeopardize drilling. The residual magnetic field test reliably detects such magnetism before use.

The challenge

In directional drilling, drill collars must not influence compass-based navigation systems. Mechanical processing, heat treatment or handling can alter magnetic properties and create local magnetic anomalies (“HotSpots”). According to API Spec 7, deviations must not exceed ±0.05 µT. Precise residual magnetic field testing is therefore essential to ensure drilling accuracy and safety.

The solution

Residual magnetic field inspection is performed using MAGNETOSCOP or MAGNETOMAT systems with a differential probe. Measurements can be carried out with either moving probe or rotating drill collar. Differential sensing minimizes environmental magnetic disturbances. Data acquisition and evaluation are supported by MAGDATA HotSpot software with API-compliant reporting.

The result

The system enables reliable detection of magnetic anomalies within the ±0.05 µT tolerance specified by API Spec 7. Differential measurement improves sensitivity and reproducibility under controlled environmental conditions. Automated data processing and reporting support compliance verification and safe deployment of non-magnetic drill collars in deep-bore operations.