Side-Drilled Hole (SDH)
A side-drilled hole is a cylindrical reference reflector drilled perpendicular to the inspection surface, used as a length-independent angle-beam target for building DAC curves and verifying sensitivity.
Definition
An SDH is a small-diameter (typically 1.5 mm or 3 mm) hole drilled through the side of a calibration block. Its long cylindrical surface presents the same echo amplitude regardless of axial position, making it ideal for angle-beam DAC curves.
What it is
A calibration reflector drilled parallel to the examination surface so its cylindrical wall presents a consistent reflector to a beam at any angle — which is why it is the standard reference for angle-beam DAC construction.
Correct use
Where flat-bottom holes suit normal-beam sensitivity, SDHs serve angle-beam work: the same hole set builds distance-amplitude curves across angles, and code blocks specify their sizes and depths.
Governing standards
ASME Section V Article 4 basic calibration blocks are SDH-based; ISO 17640 references equivalent reflectors.
The usual mistake
Comparing amplitudes between SDH-calibrated and FBH-calibrated setups as if equivalent. The reflector geometries respond differently with angle and distance; sensitivities transfer only through the code's own correlations.
Where Side-Drilled Hole fits in an inspection programme
A term is only useful when it connects to a decision. Side-Drilled Hole appears in written procedures, in technique sheets, and in the records an owner or accreditation body reviews afterwards — which means the way it is defined in your documentation has to match the way it is applied on site. Where the two drift apart, audits find it. Atlantis writes and reviews procedures against the governing codes, trains inspection personnel to apply them, and builds the record-keeping that makes the evidence retrievable years later. Procedure development and code consulting · NDT training and certification · Ask us about your programme.
Related terms
- Calibration Block — A calibration block is a reference specimen with known geometry and reference reflectors (side-drilled holes, flat-bottom holes, notches) used to set ultrasonic instrument sensitivity, range, and angle prior to inspection.
- Flat-Bottom Hole (FBH) — A flat-bottom hole is a reference reflector drilled into a calibration block to a precise depth with a flat bottom perpendicular to the beam axis, used as a known disc-shaped target for normal-beam sizing.
- Distance-Amplitude Correction (DAC) — DAC is an ultrasonic calibration curve plotted on the A-scan display that shows expected echo amplitude from a reference reflector at varying depths, used to evaluate flaw size while compensating for beam spread and attenuation.
Further reading
reference standards and block calibration in ut
More equipment terms
Transducer · Dual-Element Probe · Angle-Beam Probe · Normal-Beam Probe · Couplant · Reference Reflector · Notch Reference · X-Ray Tube · Gamma Source · Iridium-192
Where this comes up in practice
Terms like this one appear in three places that matter commercially: the written practice that governs how your personnel are qualified, the procedures and technique sheets that define how an examination is actually performed, and the evidence an auditor or client asks for when they want to know why an inspection was accepted. Getting the terminology right is the easy part; being able to produce the qualification record, the calibration traceability and the procedure revision that applied on the day of the inspection is the part that decides audits.
Atlantis NDT provides NDT training and certification against ASNT SNT-TC-1A and ISO 9712, ASNT Level III consulting for written practices and procedure approval, inspection management software that holds qualification, calibration and procedure-revision evidence in recoverable form, and an asset integrity platform that binds inspection results to the asset they describe. Browse the full NDT glossary or ask a Level III directly.