5.3 Examiner Selection, Calibrations, and Acceptance Standards

Examiner Qualifications: ASNT SNT-TC-1A and CP-189

There is a strict regulatory distinction between the Authorized Piping Inspector and the Examiner under API 570:

• Authorized Piping Inspector: The API 570 certified inspector who is responsible to the owner-user for ensuring that all inspection, repair, and testing requirements are met. The inspector evaluates the NDE results and makes the final determination of piping fitness-for-service.
• Examiner: The technician who physically performs the NDE (such as RT, UT, MT, or PT). The examiner must be qualified and certified to perform these specific examinations but does not make the final decisions regarding piping repairs or retirement.

Certification Frameworks

API 570 recognizes two primary certification frameworks for examiners:

• ASNT SNT-TC-1A: This is a recommended practice published by the American Society for Nondestructive Testing. It provides guidelines for employer-based certification, meaning each employer must write their own "Written Practice" defining the education, training, experience, and examination requirements for their technicians. SNT-TC-1A is highly flexible and widely used.
• ANSI/ASNT CP-189: This is a national standard that establishes strict requirements for the qualification and certification of NDE personnel. Unlike SNT-TC-1A, CP-189 requires centralized certification and does not allow employers to waive specific training or examination requirements.

Examiner Certification Levels

• Level I: Qualified to perform calibrations, specific examinations, and record results under the direct supervision of a Level II or III. A Level I technician cannot independently interpret results or write reports.
• Level II: Qualified to set up and calibrate equipment, interpret and evaluate results according to applicable codes, standards, and specifications. They are authorized to sign off on NDE reports.
• Level III: Fully qualified to establish techniques and procedures, interpret codes, design training, and administer exams for Level I and II personnel.
• Vision Requirements: Examiners must pass an annual near-vision examination (Jaeger J-1 or J-2 letters at 12 inches / 300 mm) and must undergo color vision examinations to ensure they can distinguish colors used in penetrant and magnetic particle examinations.

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Calibration of NDE Equipment

All NDE equipment must be calibrated to ensure accuracy. ASME Section V defines specific calibration requirements:

• Densitometers (RT): Used to measure radiographic film density. Densitometers must be calibrated against a national standard step tablet that has been certified within the last 3 years. Densitometer calibration must be verified at the start of each work shift, after 8 hours of continuous operation, or whenever a change in the bulb or film type occurs.
• UT Instruments: Calibrations for distance and sensitivity must be verified using a calibration block at the beginning of each examination, at least every 4 hours of continuous operation, at the end of the job, or whenever there is a change of operator, battery, transducer, or cable.
• Black Lights (Fluorescent MT/PT): Black lights used for fluorescent examinations must be checked for intensity. The minimum intensity is 1000 \u03bcW/cm² at a distance of 15 inches (380 mm) from the light source. The meter used to measure this intensity must be calibrated at least once a year.

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NDE Acceptance Standards per API 570 and ASME B31.3

API 570 governs in-service piping inspections. However, it references the original construction code (typically ASME B31.3, Process Piping) for initial weld acceptance criteria. For in-service piping, API 570 also allows the use of Fitness-for-Service (FFS) methodologies (such as API 579-1/ASME FFS-1) to evaluate flaws that would be rejected under standard construction codes.

ASME B31.3 Table 341.3.2 Weld Acceptance Criteria

ASME B31.3 sets strict limits on weld discontinuities depending on the fluid service (Normal, Category D, Category M, High Pressure, etc.). The following rules apply to Normal Fluid Service:

• Linear Indications (Cracks): Any type of crack, lack of fusion, or lack of penetration is strictly unacceptable. If a weld shows a 1/16-inch crack, it must be rejected and repaired.
• Undercutting: Weld undercut is a groove melted into the base metal adjacent to the weld toe. B31.3 limits the depth of undercut to the lesser of 1/32 inches (0.79 mm) or 10% of the component wall thickness.
• Rounded Indications (Porosity & Slag): Slag inclusions and porosity are limited in length and cumulative distribution. For example, a single slag inclusion cannot exceed three times the nominal wall thickness, and the total length of slag in any 12-inch weld length is limited.

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Worked Scenario: Weld Undercut and Examiner Certification Checks

Scenario 1: Undercut Evaluation

An inspector is evaluating a weld on a newly modified carbon steel piping system (Normal Fluid Service). The nominal wall thickness of the pipe is 0.250 inches (6.35 mm). During visual inspection, the inspector notices a localized undercut at the toe of the weld. The depth of the undercut is measured using a weld gauge and is found to be 0.030 inches (0.76 mm).

To determine if this undercut is acceptable per ASME B31.3 Table 341.3.2:

1. Calculate 10% of the nominal wall thickness: $10\% \times 0.250 = 0.025\text{ inches}$
2. The code limit is the lesser of 1/32 inches (0.031 inches) or 10% of the wall thickness (0.025 inches).
3. The lesser of these two values is 0.025 inches.
4. The measured undercut is 0.030 inches, which exceeds the 0.025-inch limit.

Therefore, this weld undercut is unacceptable and must be repaired by grinding and re-welding (or qualified through engineering evaluation if under API 570 in-service rules).

Scenario 2: Examiner Qualification Verification

During an audit of NDE records for a piping replacement project, the API 570 inspector discovers that a radiographic examination (RT) report was signed off by a technician certified to ASNT SNT-TC-1A Level I. The report indicates that the weld is acceptable.

• The Issue: Under both ASME Section V and ASNT SNT-TC-1A, a Level I technician is only authorized to perform calibrations and examinations under the direct supervision of a Level II or Level III. They do not have the authority to independently interpret radiographs or sign off on the final weld acceptance.
• The Action: The inspector must reject the RT report. The radiographs must be re-evaluated and signed off by a certified Level II or Level III examiner.

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Exam-Focused Traps and Tips

• Inspector vs. Examiner Responsibility: The examiner performs the NDE, but the authorized piping inspector is ultimately responsible for accepting or rejecting the piping system.
• Undercut Limit Calculation: Always calculate the 10% wall thickness value and compare it to 1/32 inches. Take the lesser value. The exam will often give a thin-walled pipe where 10% is smaller than 1/32 in, or a thick-walled pipe where 1/32 in is smaller.
• Densitometer Verification Interval: Remember that a densitometer must be checked at the start of each shift (or every 8 hours), not just once a year. The 3-year interval is for the national standard calibration step tablet.

ASME Section V Article 1 — General Requirements

Article 1 sets the rules for using Section V as a referenced Code: scope, responsibilities of the owner/user and subcontractors, calibration expectations, definitions distinguishing inspection vs examination, and record keeping. API 570 inspectors do not replace certified examiners, but they must confirm that NDE performed for piping integrity uses a written procedure, calibrated equipment, and documented results consistent with Article 1 and the referencing Code (API 570 / ASME B31.3 Chapter VI).