Reading a Mill NDT Report: How GB/T, ASTM and EN Standards Map to Each Other
By Harris · FUSHUN METAL · Technical note for steel buyers
Viewpoint, stated up front. A Chinese mill’s MTC will almost always list GB/T, JB/T or NB/T standard numbers in the testing block. Those numbers are not a code you can ignore — they are a statement about the method, the calibration block, the scanning coverage and the acceptance level. The mistake most international buyers make is to read the method name (ultrasonic, magnetic particle, penetrant, radiographic, eddy current) and assume it is equivalent to the ASTM/ASME or EN standard they would have written into their own PO. The physics is the same, but the coverage, the reference notches, the acceptance class, and even the units of the report are not. This note is the bridge your supplier should be giving you — and the questions to ask when it is not.
The Five Conventional NDT Methods at a Glance
The Chinese NDT overview (GB/T 5616, GB/T 9445, GB/T 14693, GB/T 20737) recognises five conventional methods. Every one of them has a direct, named counterpart in the ASTM and EN systems — but the closest counterpart depends on the product form, not the method alone.
| Method | What it finds | Typical product forms |
|---|---|---|
| UT | Internal laminations, inclusions, cracks, delamination, lack of fusion | Forgings, plates, bars, tubes, welded joints |
| RT | Volumetric defects, porosity, slag, lack of penetration, cracks | Castings, welds, pressure equipment |
| MT | Surface and near-surface cracks, laps, seams on ferromagnetic parts only | Forgings, rolled bars, weld surfaces, crankshafts |
| PT | Surface-open cracks, porosity, laps on any non-porous material | Austenitic stainless, nickel alloys, aluminium, non-magnetic parts |
| ET | Surface and near-surface defects on conductive (typically non-magnetic) material | Tubes (especially austenitic SS and Ni alloy), heat-exchanger tubes, wire |
Ultrasonic Testing (UT) — Where GB/T and ASTM/EN Actually Differ
UT is the most frequently specified test in a mill’s MTC and the one with the widest gap between doing the test and doing the right test. The Chinese standard stack for UT is broad: GB/T 6402 covers steel forgings (and is widely cited as the practical Chinese equivalent of ASTM A388/A388M); GB/T 11343 covers contact pulse-echo on welds; GB/T 4162 covers steel rolled bars; GB/T 5777 covers seamless tubes; GB/T 7734 covers clad plates; GB/T 8361 covers cold-drawn rounds; GB/T 11259 covers reference blocks; JB/T 1581 covers turbine and generator rotor forgings.
The ASTM and EN counterparts are not one-to-one — they split by product form, and that is the point most cross-references miss:
| Product form | GB/T | ASTM / ASME | EN / ISO |
|---|---|---|---|
| Heavy steel forgings | GB/T 6402, JB/T 1581 | ASTM A388/A388M, ASME V T-560 | EN 10228-3 (ferritic/martensitic), EN 10228-4 (austenitic) |
| Rolled / forged bars | GB/T 4162, GB/T 8361 | ASTM A388 (as applicable), A745/A745M | EN 10308, EN 10160 |
| Seamless / welded tubes | GB/T 5777, GB/T 18256 | ASTM E213, A450, A999 | EN ISO 10893-8, -10; EN 10246-6/-8 (legacy) |
| Welds | GB/T 11343, GB/T 11345 | ASME V Art. 4, AWS D1.1 | EN ISO 17640, EN 1713 / 1714 |
| Clad / austenitic plate | GB/T 7734 | ASTM A578, A577 | EN 10160, EN 10307 |
The three traps buyers fall into: (1) accepting any UT report on a forging without checking whether the standard requires radial + axial + angle-beam scanning — GB/T 6402 and ASTM A388 both do, but a supplier may quote only one direction to save time; (2) ignoring that EN 10228-3 is ferritic/martensitic only, and austenitic forgings (e.g. duplex, super-duplex, austenitic stainless) must reference EN 10228-4 with different reference blocks; (3) missing the DGS versus reference-block methodology — the acceptance level you wrote into the PO often has no meaning if the supplier chose the other method.
Magnetic Particle Testing (MT) — Continuous vs Residual, North America vs Europe
The Chinese MT stack (GB/T 15822.1–.3 for general principles, medium and equipment; GB/T 9444 for castings; JB/T 6061, JB/T 8468, JB/T 9628, JB/T 9630.1, NB/T 47013.4 for pressure-equipment, crankshafts, turbine blades, castings) covers the ground. The ASTM side runs through ASTM E709 (the general-industry guide, the most-cited MT reference in North America, invoked by ASME Section V Article 7), ASTM E1444/E1444M for aerospace/critical components, and ASTM A275/A275M for steel forgings. The EN side runs through EN 1290 / EN ISO 9934 for welds, EN 10228-1 for steel forgings, EN 1369 for castings, and EN 10246-12 / -18 for ferromagnetic tubes.
The often-missed point is the method: continuous (current flowing while particles are on the part) versus residual (magnetise, stop current, then apply particles). E709 explicitly notes that the two have very different sensitivity, and a procedure that does not state which method it is using is essentially uncalibrated. The same defect on the same forging can pass one method and fail the other. Always ask the MTC or the inspection procedure to name the method.
Penetrant Testing (PT) — The “Equivalent” That Is Only Mostly Equivalent
PT is the most deceptively simple method — and the one where the international “equivalents” diverge most in the details the report does not show. The Chinese series is GB/T 18851.1 to .5 (general, penetrant materials, reference blocks, equipment, verification), plus GB/T 9443 for castings and JB/T 6062 / JB/T 6064 for welds and test blocks. The ASTM counterparts are ASTM E165/E165M (general industry) and ASTM E1417 (broader PT practice); the European counterparts are EN 571-1 (being replaced by EN ISO 3452-1), EN 1371-1 / -2 for castings, EN 10228-2 for forgings, and EN 10246-11 for tubes.
In practice, the differences show up in three numbers buyers never see on the MTC but always see in a rejection:
- Penetrant dwell time. ISO 3452-1 mandates 10–30 min; ASTM E165 permits 5–20 min. A 7-minute dwell is valid under ASTM and non-conforming under ISO/GB.
- Ambient humidity. GB/T (adopted from ISO) caps humidity at 80 %; ASTM E165 sets no explicit humidity limit. A report done in monsoon weather may be perfectly valid for an ASTM buyer and invalid for a GB/T buyer.
- UV source intensity. EN 571-1 requires calibrated black-light intensity at the part surface; GB/T 18851 inherits this; ASTM E165 is silent. A fluorescent indication that passes in a Beijing lab with a freshly calibrated lamp can fail under a Western buyer’s audit lamp.
If your end-use is ASME-stamped pressure equipment or nuclear, write ASTM E1417 + ASME V Article 6 into the PO, not just E165. If it is EN 13445 / PED equipment, write EN ISO 3452-1 with the relevant acceptance level from EN 12889 or EN 23277.
Radiographic (RT) and Eddy Current (ET) — Two Methods Where Coverage Class Matters
RT. The Chinese system is GB/T 3323 (welds), GB/T 5677 (castings), GB/T 12604.2 (terminology), plus the JB/T 6220 / 7412 / 7413 / 9402 / 6221 / 6440 / 7260 / NB/T 47013.2 stack for equipment and pressure-equipment practice. The Western counterparts split again by product form: ASTM E94 / E1742 (general radiographic), ASTM E1030 (castings), ASTM E1032 (welds), ASME V Article 2 (pressure-equipment), EN 1435 / EN ISO 17636 (welds), EN 12681-1 (castings, film), EN 12681-2 (castings, digital), and the umbrella EN 444 / EN ISO 5579 (general rules). The European system introduces a testing class (A = basic, B = improved) that ASTM does not. If you specify only “RT per ASTM”, you may receive a class-A-equivalent image quality; the same call under EN ISO 5579 gives you a defined class.
ET. Chinese ET standards include GB/T 5126 (Al and Al-alloy tubes), GB/T 5248 (Cu and Cu-alloy tubes), GB/T 7735 (steel tubes), GB/T 11260 (round bars), GB/T 12969.2 (Ti tubes), GB/T 14480.3 (equipment), GB/T 28705 (pulsed ET), and NB/T 47013.5. The most direct ASTM counterpart for austenitic stainless and titanium tubes is ASTM E426; for aluminium tubes it is ASTM E215. The European equivalent is the EN ISO 10893-2 family (which replaced the older EN 10246-3), with ISO 9712-qualified operators and reference notches calibrated to the standard.
ET is the one method where the calibration is everything. E426 explicitly requires reference standards of the same alloy and heat-treatment condition as the production material, with artificial defects (drilled holes and EDM notches) of defined depth. A mill that supplies an ET certificate without naming the reference notch depth and the acceptance level is selling you a paper exercise — regardless of whether the report header says GB/T 7735, ASTM E426, or EN ISO 10893-2.
A Buyer’s Quick-Reference Checklist
Before you accept any MTC with an NDT block, walk through these six questions. A good supplier answers them in writing; a poor one will not.
- Method ↔ product form ↔ standard. Does the standard cited actually cover the product form you are buying? (GB/T 6402 is a forging standard; it is not appropriate for a plate.)
- Scanning coverage. 100 %? What directions? UT reports on a forging should name radial + axial; on a bar, full perimeter and end-to-end.
- Acceptance level. ASTM A388 §6 acceptance levels 1–5? EN 10228-3 quality class 1–4? GB/T 6402 § quality grade? The grade — not the method — is what the buyer is actually buying.
- Calibration artefact. Reference block, flat-bottom hole, DGS, or side-drilled hole? Depth in mm or % of wall? These are not interchangeable.
- Personnel certification. Operator qualified to which scheme — ASNT SNT-TC-1A, NAS 410 / EN 4179, or ISO 9712 / PCN? Note: SNT-TC-1A is employer-issued and does not travel between employers; ISO 9712 / PCN is third-party and portable. The two are not interchangeable for cross-border orders.
- Report units and language. Are amplitudes in % of full screen height (ASTM/ASME convention) or in dB (ISO/EN convention)? Are reference notches reported in inches or millimetres? Will the report be bilingual if your end customer requires it?
Closing Note
The five conventional NDT methods are universal. The standards that govern them are not. A Chinese mill quoting UT to GB/T 6402 is not automatically equivalent to UT to ASTM A388 and not automatically equivalent to UT to EN 10228-3 — and a buyer’s PO that lists only the method name is leaving the equivalence to chance. The shortest path to a clean acceptance at your customer’s dock is to specify the standard, the acceptance grade, the scanning coverage, the calibration artefact, the personnel scheme, and the report format — and to confirm that your supplier has all six in writing before the heat is poured. FUSHUN METAL provides this bridge on every enquiry as a matter of course, and we are happy to walk any incoming spec against any of the standards listed above.
Harris has been on the technical side of alloy, stainless and nickel-base steel supply since 2014, with a focus on translating Chinese mill practice into the ASTM / EN language of international B2B buyers.
