6.4 Relevant vs Non-Relevant Indications

6.4 Relevant vs Non-Relevant Indications

Quick Answer: Not every NDT response is a rejectable defect. Relevant indications come from discontinuities that must be evaluated to acceptance criteria. Non-relevant indications come from geometry, surface condition, magnetic artifacts, or other causes that the procedure treats as not significant discontinuities. Level III owns the written rules, training, and documentation that keep those calls consistent.

Official Basic exam competencies include applying NDT methods and distinguishing relevant from non-relevant indications, including those related to manufacturing and geometry. This section is pure Level III judgment territory: physics plus procedure plus ethics of not inventing criteria in the field.

Indications Are Not Automatically Defects

An indication is a response or evidence from an NDT method that requires interpretation: a PT bleed-out, an MT powder line, a UT echo, an RT density change, a VT mark.

A discontinuity is an interruption in the physical structure (crack, pore, LOF, etc.).

A defect (in code language often a rejectable discontinuity) is a discontinuity that does not meet acceptance criteria.

Flow:

1. Detect indication
2. Interpret: real response vs noise/artifact
3. Classify: relevant vs non-relevant (and false call risk)
4. If relevant, characterize (type, size, location, orientation)
5. Evaluate against written acceptance criteria → accept, reject, or repair/rework path
6. Document

Skipping to "defect" at step 1 is how false rejects and customer disputes are born.

Relevant Indications

A relevant indication is caused by a condition that the governing procedure or code treats as a discontinuity requiring evaluation. Examples:

• Linear MT indication from a crack or seam meeting size thresholds for evaluation
• PT bleed-out from a surface-breaking crack or open pore beyond allowed limits after evaluation
• UT reflector from LOF, crack, or lamination that must be sized/compared to tables
• RT image of porosity or slag within the weld that must be measured against porosity charts

"Relevant" does not automatically mean "reject." Many relevant indications are acceptable after measurement (e.g., porosity within chart limits). Relevant means you must evaluate—you may not ignore it.

Non-Relevant Indications

A non-relevant indication is a method response not caused by a discontinuity that requires rejection evaluation under the procedure—or is explicitly recognized as geometric/process background.

Common sources:

Non-relevant does not mean "always ignore forever." If geometry hides a real crack (e.g., undercut plus crack), the crack portion is relevant. Reclassification can occur when technique improves or when a second method confirms a true discontinuity.

Manufacturing-Related Confusion

Level III candidates must expect manufacturing features that look like flaws:

• Weld reinforcement and undercut: geometry for VT; undercut may be rejectable as geometry even without a crack; a crack in the undercut is separately relevant for surface methods.
• Mismatch / high-low: RT and UT geometric responses; evaluate to fit-up criteria, not as slag by default.
• Backing bars, consumable inserts: RT density and UT reflectors if not accounted for in technique.
• Heat tint, spatter, arc strikes: VT conditions; arc strikes may be rejectable surface damage under some specs.
• Grain flow and banded structure: UT anisotropy, not necessarily laminations.
• Cast surface roughness: PT background; may need surface prep standards before calling relevant porosity.

Procedure notes and technique sheets should list expected geometric reflectors so Level I/II personnel do not false-call them.

False Calls: Two Directions

Controls Level III owns or influences:

• Written practice and method procedures with clear indication definitions
• Acceptance criteria tables and examples
• Surface preparation requirements
• Calibration and sensitivity (IQI, DAC/TCG, contrast, field strength)
• Demonstration of technique on known reflectors or sample welds
• Training and eye examination compliance
• Dual review or Level III audit of borderline calls on critical hardware
• Complementary methods when one method is geometry-blind or crack-weak

Procedure and Acceptance Criteria Role

Acceptance criteria come from codes, standards, specifications, and customer requirements invoked by contract, and from the company's written NDT procedures approved under SNT-TC-1A or CP-189 frameworks as applicable. The Level III develops, approves, and ensures personnel use those documents.

Critical rules:

1. Do not invent tighter or looser criteria in the field without authorized change control.
2. Different codes differ—ASME porosity charts, AWS visual limits, API pipeline criteria, aerospace specs are not interchangeable.
3. Method-specific criteria—a linear indication limit for MT is not a porosity chart for RT.
4. When criteria are silent, escalate; do not guess.
5. Repair and reinspection paths must be procedural, including when a relevant indication is removed.

Relevant vs non-relevant classification is often defined inside the procedure (e.g., MT: linear indications longer than X are relevant; magnetic writing is non-relevant after demagnetization/retest). Basic exam items test whether you know that the procedure and code—not memory of a single shop rule—govern.

Evaluation Practice Pattern

For a disputed MT line at a weld toe:

1. Verify magnetization direction, field adequacy, surface cleanliness, particle application.
2. Clean and retest; try alternative magnetization if orientation may hide a crack.
3. Use PT or high-magnification VT if allowed to corroborate opening.
4. If still ambiguous on critical parts, consider light grind and retest per approved procedure (not uncontrolled metal removal).
5. Compare final characterized indication to acceptance table.
6. Record photos/sketches, sizes, instruments, and criteria paragraph.

For UT geometric root signals: map with multiple angles, compare to joint design, use ID creeping or TOFD if procedure allows, and avoid calling every root echo "LOP" without characterization.

Documentation Requirements

Defensible Level III systems record:

• Part identity, material, process stage (as-welded, after PWHT, in-service)
• Method, procedure number/revision, technique details (angles, media, kV, etc.)
• Operator identification and certification level
• Calibration / system checks
• Indication maps: location, length, amplitude/height, depth if applicable
• Classification: relevant / non-relevant / rejectable / acceptable
• Criteria reference (code section, procedure paragraph)
• Disposition: accept, reject, repair, use-as-is with engineering approval if the quality system allows
• Date/time and review signatures where required

Audits (customer, code, internal) reconstruct decisions from this record. "Looked OK to me" is not a Level III answer.

Ethics and Communication

Pressure to ship product can push over-acceptance (missed relevant). Pressure to "look thorough" can push over-rejection of non-relevant geometry. The Level III protects both safety and process integrity by making criteria visible, training consistent calls, and backing personnel who follow the written practice. When production disputes a call, resolve with data and the document hierarchy—not with personality.

Exam Synthesis

Expect scenarios such as:

• MT powder held on a sharp corner with no residual after demag and retest → likely non-relevant geometry/magnetic effect
• Linear bleed-out that reappears after clean retest at a weld toe → relevant; evaluate to criteria
• UT mid-wall 0° reflector in plate → relevant lamination candidate; evaluate to plate UT quality level—not "ignore as geometry"
• RT density change exactly at a known thickness transition with IQI sensitivity met and no rounded porosity pattern → geometric, non-relevant as a weld discontinuity

Connect this section to method chapters: each method has its own artifact zoo. The universal Level III skill is indication → cause hypothesis → confirm/refute with technique → criteria → document.

Exam traps: Treating every indication as a defect; treating every geometric response as safe without verification; changing acceptance limits informally; failing to document non-relevant calls on critical jobs when the procedure requires recording; assuming Level I can invent classification rules without procedure support.