How to Review an NDT Inspection Firm's Work (Quality Checklist)

I got the call at 3 PM on a Friday.

One of our largest clients had flagged a batch of ultrasonic inspection reports from a vendor we’d been using for two years. The findings looked solid on the surface — clean charts, professional formatting, all the right boxes checked. But when our engineering team dug into the actual data, something was off. The acceptance criteria didn’t match the contract specs. The calibration certificates were expired. And the technician signatures belonged to someone who’d left the company six months prior.

We didn’t catch it during delivery. We caught it during a third-party audit three months later. By then, we’d already paid the invoice and signed off on the work.

That’s when I learned that an NDT inspection report is only as good as the process that created it — and most companies have no idea what to actually verify when it arrives.

---

The Short Version: Review NDT inspection work against three core requirements: (1) personnel certifications and qualifications match the work performed, (2) procedures and acceptance criteria align exactly with your contract, and (3) equipment calibration is current and traceable. Use the checklist below before accepting any final report. If any item fails, issue a finding and request corrective action documentation.

---

Key Takeaways

• Personnel gaps kill NDT credibility fast. Expired certifications, unverified credentials, and inadequate training are red flags that most clients miss until an audit surfaces them.
• Contract misalignment is the #1 reason to reject NDT work. If the written procedures, acceptance criteria, or methods don’t match your purchase order or engineering specs, it’s not the vendor’s fault if they didn’t know — it’s yours for not verifying upfront.
• Equipment and calibration are non-negotiable. Uncalibrated probes, outdated certificates, or undocumented function checks introduce measurement error that can hide defects.
• A structured checklist catches 80% of common issues before they become audit findings.

---

The Problem Nobody Talks About: Vendors Do What They Think You Want

Here’s what most people miss: NDT inspection firms operate under your specifications. If you don’t give them crystal-clear requirements upfront, they’ll deliver to their interpretation of what you need — which often means their standard procedure, not yours.

Then they send the report. It looks professional. You sign off. Six weeks later, your internal auditor (or worse, a customer’s third-party auditor) asks to see the written procedure that governed the inspection. You dig into the inspection report. There it is, page 37 in 8-point font: “Visual inspection per ASTM D4417 using 500 lux minimum.”

Except your contract specifies 1,000 lux. Different standard. Different acceptance criteria. Now you’re explaining to your customer why their parts were inspected to the wrong standard.

The vendor didn’t screw up. You didn’t ask.

---

The Core Review Framework: Four Critical Areas

Most NDT audits follow the same structure, and you should too. According to SNT-TC-1A (the industry standard for NDT personnel qualification), any credible review includes four layers.

1. Personnel Qualifications

This is the easiest thing to verify and the most commonly ignored.

• ASNT Level II or III certification (or ISO 9712 equivalent) is required for the primary technician. Verify the certificate is current, hasn’t expired, and covers the specific method(s) used (ultrasonic, magnetic particle, radiography, etc.).
• Eye exams and medical fitness records should be documented. Some methods (radiography especially) have legal exposure limits that require formal tracking.
• Training documentation beyond the cert. ASNT Level II doesn’t mean someone was trained on your specific procedures. Look for evidence of method-specific training, equipment familiarization, and procedure sign-off.

Reality Check: I’ve seen firms submit reports signed by Level I technicians supervised by Level III inspectors. Technically compliant. Legally risky. The Level I doesn’t have authority to make independent accept/reject calls — every decision gets filtered through the Level III. Ask upfront who’s making the final call and whether they have signature authority for your contract.

2. Written Procedures and Documentation

Your contract probably specifies an inspection method. The vendor’s procedure should match it exactly. This is where the money goes wrong.

• Does the procedure document match your contract? If you specified “Ultrasonic inspection per ASTM E2375 with dual-element, 5 MHz transducer, 1.5-inch scan pitch,” the vendor’s procedure should say those exact things. Not “ultrasonic per ASTM standards” (vague) or “standard UT practice” (meaningless).
• Acceptance criteria clarity. “No indications greater than 3mm in the weld toe area, rejection threshold 5mm” is acceptable. “Indications shall be acceptable per industry standards” is not.
• Surface preparation requirements. How clean? How dry? Temperature limits? Couplant type? These aren’t decorative details — they affect measurement accuracy.

---

Three Checks That Catch 80% of Problems

Check #1: Equipment Calibration — Ask to See the Certificate

Calibration is where NDT either works or doesn’t. Bad calibration doesn’t just hide defects — it can create false positives, which then lead to unnecessary rework.

• Traceable certificates. The vendor should have documentation tying their calibration standards to NIST (National Institute of Standards and Technology). If they say “we calibrate in-house,” you want to see the documentation chain.
• Calibration date and frequency. For ultrasonic equipment, annual calibration is typical. For radiography, more frequent. Your contract probably specifies. Match them.
• Reference blocks and materials. What blocks were used for UT verification? IIW type or AWS? Flatness and surface finish matter — old, worn reference blocks give inaccurate readings.

Pro Tip: Ask the vendor for a copy of their equipment maintenance log — not just the calibration cert. You’re looking for evidence that they actually use the equipment properly between certs. Metal-to-metal couplant bottle contact, probe damage, gain drift — these get documented if someone’s paying attention.

Check #2: Method-Specific Essentials

The Stache Air NDI evaluation framework covers this well: each NDT method has 5 non-negotiables.

• Visual (VT): Lighting (minimum 500 lux per ASME, unless your contract specifies higher), magnification tools (mirrors, borescopes), defined visual acceptance criteria
• Liquid Penetrant (PT): Penetrant type and batch number, dwell time, developer application method, temperature control, acceptance per ASTM or your spec
• Magnetic Particle (MT): Magnetizing current (AC vs. DC), particle type (dry vs. wet), suspension medium stability, acceptance threshold in amps or gauss
• Ultrasonic (UT): Transducer freq., coupling agent type, scanning pattern (raster, point-by-point), reference calibration curve, distance-amplitude correction
• Radiography (RT): Film type, exposure time, kVp/mA settings, density range, viewing conditions
• Eddy Current (ET): Probe type, frequency, liftoff compensation, reference standards

If the report doesn’t specify these things, the vendor cut corners or doesn’t understand your standard.

Check #3: Defect Classification and Reporting

NDT reports classify findings as critical, major, or minor. The definitions vary by industry, but they should be explicit.

• Critical: Part fails and could cause safety issue or major system failure. Example: crack in pressure vessel wall.
• Major: Defect degrades function but part may still operate. Example: deep pit in bearing race.
• Minor: Surface-level or cosmetic, no functional impact. Example: small dent on exterior.

If the vendor’s report says “three indications found,” but doesn’t classify severity and doesn’t cross-reference your acceptance criteria, send it back. You need to know: is this a reject or a re-inspect-and-continue situation?

---

The Practical Checklist: Use This Before Accepting Delivery

Print this. Use it. Pass it to your QA team.

PERSONNEL

• Primary technician holds valid ASNT Level II (or Level III) certification covering the specific method used
• Certification is current (not expired) and includes eye exam records
• Training documentation exists showing method-specific instruction and sign-off on your procedures
• Level III supervisor (if applicable) has signature authority for accept/reject decisions

PROCEDURES & DOCUMENTATION

• Written procedure matches contract specifications exactly (method, transducer type, frequency, scan pitch, etc.)
• Acceptance criteria include specific numerical thresholds (not generic “per standards” language)
• Surface preparation requirements documented (cleanliness, dryness, temperature, couplant type)
• Procedures address all essential variables for the method used

EQUIPMENT & CALIBRATION

• Calibration certificate is current and includes traceable NIST reference
• Reference standards (blocks, materials) are documented and in acceptable condition
• Equipment function checks documented (probe response, gain stability, display accuracy)
• Calibration frequency matches contract requirements

REPORTING & FINDINGS

• All defect classifications (critical/major/minor) are explicitly defined and applied
• Findings reference contract acceptance criteria with specific measurements or thresholds
• Reporting format matches your purchase order requirements (electronic, film, report format)
• Technician signatures match certified personnel and are dated

If any item fails: Issue a written finding to the vendor specifying the gap, request a corrective action plan (root cause + fix + verification), and do not sign final acceptance until corrective documentation is submitted.

---

Reality Check: You might think “this is too detailed” or “the vendor knows what they’re doing.” Maybe. But I’ve watched a $2M aerospace contract get held up for three weeks because a technician’s certification had lapsed by 17 days. Not malice. Just missing one checkbox.

---

When to Request Re-Inspection

Some findings warrant a full re-do. Some don’t.

• Reject and re-inspect if: Personnel certs were invalid at time of inspection, procedures used don’t match contract specs, calibration was expired, or acceptance criteria were misapplied
• Accept with documented deviation if: Minor procedure variance (e.g., 480 lux instead of 500 lux) was recorded, equipment was within tolerance, and the defect findings are still valid under your actual specs. Document the deviation in writing and get sign-off from your engineering team.

The key: never hide it. If the inspection didn’t meet requirements, your customer’s audit will find it eventually. Better to catch and document it yourself.

---

Practical Bottom Line

You don’t need to become an NDT expert to oversee NDT work. You need a checklist.

1. Before work starts: Give the vendor a clear specification document. Don’t assume they know what you want.
2. When the report arrives: Use the four-area review framework above. Check personnel, procedures, equipment, and reporting.
3. If something’s missing: Send a written finding. Request documented corrective action. Don’t sign off until you have it.
4. Build a vendor history: Track which firms deliver clean reports on first submission. That data compounds.

The two hours you spend verifying an NDT report upfront saves you from the two weeks you’ll spend explaining to a customer why their parts were inspected to the wrong standard.

---

Related reading:

• The Complete Guide to NDT Inspection Firms — overview of how NDT vendors operate and what to expect
• More resources on ultrasonic testing standards and radiography procedures available in our resource library.