16.3 Acceptance Criteria and Quality Control

16.3 Acceptance Criteria and Quality Control

Quick Answer: Domain 5.5–5.6 expects Level IIIs to help develop acceptance criteria when none exist (with proper engineering/owner interface) and to apply quality-control protocols to NDT work. On the exam and on the floor, separate relevant indications (must be evaluated) from rejectable indications (fail the acceptance criteria). Document evaluations so a second qualified person can reconstruct the decision.

Sections 16.1–16.2 got the requirements and procedures right. This section is the decision and control layer: what “pass” means, how quality systems keep NDT honest, and how the Level III interfaces with design when the package is incomplete.

Acceptance Criteria: What They Are For

Acceptance criteria are the rules that convert examination results into accept, reject, or repair dispositions. They may be expressed as:

• Maximum discontinuity length, height, or area
• Amplitude relative to a reference (DAC, DGS, notch, side-drilled hole)
• Film density / image quality thresholds plus discontinuity charts
• “No cracks” or “no incomplete fusion” absolute rules
• Statistical or lot-based rules for some product forms
• Hybrid rules combining size and location (for example toe cracks vs buried porosity)

Acceptance criteria are product quality decisions, not pure physics. A detectable indication can be relevant and still acceptable if it is within limits. A non-relevant geometric indication should not be treated as a rejectable defect merely because it produces a signal.

Relevant vs rejectable (and non-relevant)

Use precise language—Basic loves these distinctions:

Exam trap: Equating “I saw an indication” with “the part fails.” Evaluation is a two-step process: characterize relevance, then apply criteria.

Assisting When Acceptance Criteria Do Not Exist

Domain 5.5 specifically includes helping develop acceptance criteria when none are provided. This is not a license for the Level III to invent secret shop limits for pressure equipment or safety-critical parts without design authority.

Proper interface model

1. Confirm silence — verify the code/spec/drawing truly lacks applicable criteria for this product form and examination.
2. Escalate — notify engineering, design authority, owner, or customer quality as required by the contract and quality manual.
3. Propose technical input — the Level III contributes method capability, typical discontinuity morphology, sizing uncertainty, and industry-precedent options.
4. Document the decision — formal criteria (drawing note, ECR, specification revision, approved deviation) before production acceptance.
5. Freeze uncontrolled acceptance — do not ship “best judgment” accepts on critical product while waiting for criteria unless a documented engineering disposition explicitly authorizes interim controls.

What good Level III input looks like

When assisting criteria development, contribute:

• Detection capability and limitations of the selected method/technique
• Expected discontinuity types from the process (welding, casting, forging, service)
• Measurement uncertainty (sizing accuracy, orientation effects)
• Consistency with related code families if the product is analogous and the design authority chooses that path
• Repair/re-exam practicality

What not to do:

• Copy unrelated product criteria blindly without design review
• Set criteria only to maximize shop throughput
• Use “we always accepted that” tribal memory as the sole basis for safety-critical parts
• Confuse reporting thresholds (record everything above X) with acceptance limits (reject above Y) without clarifying both

Applying Quality Control Protocols to NDT

Domain 5.6—apply QC protocols—means NDT is run as a controlled process, not as artisanal craft. QC elements Level IIIs own or strongly influence:

Process control

• Only approved procedures/work instructions in use (current revision)
• Personnel certified and current (vision, method, technique limits)
• Equipment calibrated or performance-checked within intervals
• Materials (penetrants, particles, film, couplant) within shelf life and system family
• Environmental conditions within procedure limits (temperature, lighting, ambient UV, humidity as applicable)

In-process checks

• System performance checks at required frequency (sensitivity, field strength, densitometer, UV intensity)
• Coverage verification (scan plans, overlap, exposure calculator records)
• Independent review or dual interpretation when specified (common in RT programs)
• Hold points observed; customer witness arranged when the ITP requires it

Nonconformance and product control

• Rejected items identified and segregated
• Nonconformance reports routed to material review/engineering
• Repair procedures approved before blend/weld repair
• Re-examination after repair using the governing method/extent
• Trend analysis: recurring reject causes may trigger process corrective action upstream (welding, machining, heat treat)

Audit and surveillance

• Internal process audits of NDT (not only personnel-file audits—see 15.3)
• Surveillance of technicians for procedure compliance
• Corrective actions with effectiveness checks

QC is how you keep Domain 2 “application of methods” from drifting into uncontrolled practice.

Engineering Interface and Evaluation Documentation

Engineering interface

NDT does not replace design. The Level III’s interface responsibilities include:

• Clarifying whether an indication is in a critical location relative to design stress or fatigue concern (often requires engineering input beyond NDT sizing alone)
• Supporting fitness-for-service discussions with measured data, not vague “looks bad” language
• Explaining method limitations so engineering does not assume NDT found “everything”
• Aligning repair acceptance with the same or more stringent criteria as original fabrication when codes require it

Documentation of evaluations

Evaluation records should allow a qualified reviewer to answer:

• What was examined (part ID, heat/serial, weld ID, location map)?
• Which procedure/revision and acceptance document/revision applied?
• Who performed the exam (certification evidence available)?
• What equipment/calibration state was used?
• What indications were recorded, with measurements and sketches/images as required?
• What was the disposition (accept/reject/repair) and who authorized it?

Incomplete reports are a classic audit failure mode: the part may be fine, but the quality system cannot prove it.

High-Yield Exam Traps for This Section

• Treating all relevant indications as automatically rejectable.
• Treating all non-relevant indications as optional to document when the procedure requires recording.
• Inventing acceptance criteria for code-stamped or customer-critical work without design/owner authority.
• Confusing sensitivity settings with acceptance levels.
• Skipping re-examination after repair.
• QC that checks only certificates and never watches actual technique compliance.

If you can explain relevant vs rejectable, describe how you would develop missing criteria through engineering, list core QC controls for an NDT process, and specify what belongs in an evaluation record, you are aligned with Domain 5.5–5.6.