ASNT NDT Level III PT cheat sheet

Capillary action draws penetrant into surface-breaking discontinuities; the driving force is the pressure differential across the curved meniscus, described by P = 2γcosθ/r.

Penetrant enters a discontinuity only if the surface is clean and the opening is not blocked; the effective radius r controls both fill speed and the amount of bleedout.

Bleedout is the reverse capillary flow that brings entrapped penetrant back to the surface; it is enhanced by the developer's absorptive and blotting action.

Penetrant systems are classified by type (I fluorescent, II visible) and method (A solvent-removable, B post-emulsifiable lipophilic, C water-washable, D post-emulsifiable hydrophilic).

Sensitivity levels 1/2 (low), 2 (medium), 3 (high), and 4 (ultrahigh) are assigned per AMS 2644; a family must be matched to the required sensitivity.

Fluorescent penetrants require UV-A illumination of at least 1000 µW/cm² (1000 µW/cm² = 1 mW/cm²) at the inspection surface in a darkened area.

Visible (color contrast) penetrants are evaluated under white light of at least 100 fc (1000 lux) at the surface being inspected.

Water-washable penetrants are highly susceptible to over-washing; excessive rinse removes penetrant from shallow discontinuities and produces false negatives.

Penetrant testing detects only discontinuities open to the surface; it cannot detect subsurface or internally closed flaws.

Pre-cleaning methods include solvent, alkaline or detergent cleaning, vapor degreasing, and mechanical methods; the chosen method must not close or smear discontinuities.

Penetrant application methods include dipping, spraying, brushing, and flowing; dwell time typically ranges from 5 to 30 minutes depending on material and specification.

Post-emulsification requires that the emulsifier contact time be tightly controlled; over-emulsification removes penetrant from discontinuities, under-emulsification causes high background.

Lipophilic emulsifiers are oil-based and used with Type I penetrants; hydrophilic emulsifiers are water-based concentrates and are usually applied by immersion or spray.

Hydrophilic emulsifier concentration is normally maintained in the 5–20 percent range by volume and monitored with a refractometer.

Developer types are dry powder, water-soluble, water-suspendable, and nonaqueous (solvent-based); each has a specific application method and drying requirement.

Aqueous developers require controlled drying; dry powder developer is applied after drying and provides a blotting action.

UV-A lamps must be checked periodically for output and for visible light contamination; the bulb's intensity is verified with a calibrated meter.

Black light filters must be checked for cracks or leakage; a cracked filter transmits visible light and degrades contrast.

A written procedure must address pre-cleaning, penetrant type and method, dwell time, removal, emulsifier time, developer type, drying, and inspection conditions.

AMS 2644 governs penetrant materials qualification; ASTM E1417/E1417M governs the practice for liquid penetrant testing; ASTM E165 covers general practice.

Procedure qualification is required when the specification demands it; the demonstrated technique becomes the baseline for production.

The penetrant family and sensitivity level must be selected based on the specification, the material, and the discontinuity size to be detected.

Dwell time is counted from the completion of penetrant application, not from the start of application.

Developer dwell time (development time) typically ranges from 10 to 30 minutes and must be allowed before interpretation.

Rinse water temperature should be maintained within a specified range (commonly 10–38 °C / 50–100 °F) to avoid chilling or over-removal.

Surface temperature during penetrant testing generally must be within 10–52 °C (50–125 °F) unless the procedure is qualified otherwise.

A procedure must specify acceptance criteria or reference the applicable code; the Level III cannot substitute personal judgment for the stated criteria.

Interpretation distinguishes relevant from nonrelevant indications; evaluation compares relevant indications to the acceptance criteria.

A relevant indication results from a discontinuity; a nonrelevant indication may arise from part geometry, machining marks, or penetrant trapped in threads or keyways.

A false indication results from improper technique, such as penetrant trapped under a lap or incomplete cleaning.

Linear indications are those with a length greater than three times their width; rounded indications have a length less than or equal to three times their width.

Indications are sized by their longest dimension; the applicable code defines the recording threshold and the acceptance limits.

Fluorescent indications are evaluated under UV-A in a darkened area; visible indications are evaluated under adequate white light.

Interpretation must occur during or immediately after the development time; delayed evaluation can allow bleedout to spread and obscure the true size.

The report should record the part number, material, procedure, penetrant system, sensitivity, results, and the inspector's identification.

All recorded indications should be documented with location, size, orientation, and disposition (accept, reject, rework).

ASNT SNT-TC-1A is a recommended practice; the employer's written practice defines the certification requirements and is the controlling document.

ANSI/ASNT CP-189 is a standard that mandates minimum training, experience, and examination requirements for NDT personnel.

Level III duties include procedure development and approval, technique qualification, personnel training and examination, and audit of the NDT program.

Level I personnel perform specific calibrations and tests under supervision; Level II personnel can set up, calibrate, interpret, and evaluate per written procedures.

Certification requires documented training hours, experience hours, and passing the general, specific, and practical examinations.

Vision requirements include near-vision acuity (Jaeger 1 at 12 in / 30 cm) and color perception sufficient to distinguish the colors used in the method.

Annual vision examinations are required; recertification intervals are defined by the written practice (commonly 5 years for Level III).

The Level III must maintain records of training, experience, examination results, and certification for each certified individual.

The NDT program should include periodic audits, calibration records, and a documented method for handling nonconforming product.

NDT methods include visual, penetrant, magnetic particle, ultrasonic, radiographic, eddy current, and leak testing; each has a distinct flaw-detection capability.

Penetrant testing detects only surface-breaking discontinuities; magnetic particle testing detects surface and near-surface flaws in ferromagnetic materials.

Ultrasonic testing detects internal flaws and measures thickness; radiographic testing reveals internal density differences.

Eddy current testing detects surface and near-surface flaws in conductive materials and is used for tube inspection.

Selection of an NDT method depends on material, geometry, discontinuity type and location, and the applicable code.

Codes such as ASME Section V define examination methods, while Section VIII defines acceptance criteria for pressure vessels.

AWS D1.1 governs welding inspection and acceptance for structural steel; acceptance criteria differ from pressure-vessel codes.

Calibration and verification of NDT equipment must be traceable to national standards and documented at defined intervals.

Qualification of NDT personnel must be documented and traceable; certification is employer-issued and method-specific.