Author: Site Editor Publish Time: 2026-10-07 Origin: Site
Buyers who specify ultrasonic testing (UT) on a steel purchase order usually end up juggling three standards: ASTM E2375 for bars and forgings shipped to North America, EN 10160 for plate going into European pressure equipment, and GB/T 2970 for plate rolled in Chinese mills. None of these is fully interchangeable with the others. A plate that clears EN 10160 Class S2/B2 can still fail GB/T 2970 Class II on the same scan line, and a forging that meets ASTM E2375 Level 1 does not automatically satisfy an EN 10228-3 requirement. This article lays out where each standard applies, how they compare on acceptance criteria, and what to write on the PO when you need cross-acceptance.
The first mistake to avoid is calling up the wrong document for the product form.
| Item | ASTM E2375 | EN 10160 | GB/T 2970 |
|---|---|---|---|
| Issuing body | ASTM International | CEN | SAC (China) |
| Title | Standard Practice for Ultrasonic Examination of Steel Bars, Billets, and Forgings | Ultrasonic testing of steel flat product of thickness equal or greater than 6 mm (reflection method) | Methods for ultrasonic testing of steel plates |
| Product form | Bars, billets, forgings (and certain tubulars when specified) | Flat products — plate and strip ≥ 6 mm thick | Steel plates 6–250 mm typical |
| Test method | Pulse-echo, contact (straight and angle beam) | Pulse-echo, contact, straight beam | Pulse-echo, contact, straight beam |
| Typical applications | Forged shafts, bars, seamless tube for oil & gas | Pressure vessel plate, boiler plate, shipbuilding plate | Pressure vessel plate, shipbuilding plate, structural plate |
Note that EN 10160 and GB/T 2970 are direct competitors on plate. ASTM E2375 sits alongside ASTM A578 (plate UT) and ASTM A388 (heavy forgings) for North American work. If you need plate UT to ASTM, the document is A578/A578M, not E2375 — E2375 covers bars, billets and forgings. Many purchase orders get this wrong, and the mill's response is usually to refuse the spec or quote the wrong test.
For European forgings, the counterpart to ASTM E2375 is EN 10228-3 (UT of fine-grained steel forgings). For Chinese forgings, the counterpart is GB/T 6402. We come back to this in the equivalence section.
All three standards use the pulse-echo technique with piezoelectric transducers. The differences are in probe frequency, coupling method, scanning pattern and reference block geometry.
ASTM E2375 is written around contact testing with straight-beam (longitudinal) and angle-beam (shear) probes. Probe frequency is typically 2.25 MHz for bars and forgings above 25 mm section, dropping to 1 MHz for coarse-grained or very thick sections, and up to 5 MHz for fine-grained bar under 25 mm. The standard requires calibration on a reference block of the same heat, similar section and heat-treat condition — most commonly an IIW Type V2 or ASME-type block for shear-wave calibration, or a notched bar of the same nominal diameter for axial examination. Immersion testing is permitted but is not the default method.
EN 10160 is purely a plate UT method. It defines four test categories — S0, S1, S2 and S3 — which differ in the number of probes and frequencies used:
S0 — single straight-beam probe, 4 MHz, scanning in the production direction only.
S1 — as S0, plus a 2 MHz probe for the central zone (Zone 2).
S2 — S1 plus additional probes for the subsurface zone (Zone 1), typically a 4 MHz + 2 MHz combination.
S3 — the most rigorous, with multiple probes for both zones and angled probes for near-surface examination.
The reference block is a stepped calibration block of the same nominal thickness, with a flat-bottom hole (typically 5 mm or 6 mm diameter) drilled from the bottom surface. Sensitivity is set against this FBH and corrected for transfer loss using a back-wall echo comparison.
GB/T 2970 uses straight-beam contact testing at 2.5 MHz or 5 MHz, with 2 MHz permitted for plate above 100 mm. Reference calibration is on a CB-1 or CB-2 block (per ISO 7963) with a 5 mm flat-bottom hole. Couplant is typically machine oil, glycerine or water-soluble gel. Scanning is performed along perpendicular grid lines spaced at 50–200 mm depending on plate size and quality class, with full 100% scanning reserved for Class I work.
This is where the three standards diverge most. Each uses different nomenclature and a different definition of a rejectable indication.
EN 10160 splits the plate thickness into two zones:
Zone 1 — the subsurface zone, the first 25% of thickness from each face (or to a defined midline for thin plate).
Zone 2 — the central zone, the middle 50% of thickness.
For each zone, EN 10160 defines four quality classes: B1/B2/B3/B4 for Zone 1 and C1/C2/C3/C4 for Zone 2. A typical specification reads "EN 10160 S2/B2/C2" — test category S2 with class B2 for Zone 1 and class C2 for Zone 2. The number goes up as the requirement tightens; B4/C4 is essentially defect-free plate, used for nuclear or cryogenic service.
Acceptance is by reference reflector: each class corresponds to a maximum allowable flat-bottom-hole equivalent diameter. For 30 mm plate at test category S2:
Class B1 — 6 mm FBH equivalent
Class B2 — 3 mm FBH equivalent
Class C1 — 9 mm FBH equivalent
Class C2 — 6 mm FBH equivalent
GB/T 2970 has four quality levels, I, II, III, IV, where I is the strictest:
Class I — no indication ≥ 50% of the distance-amplitude correction (DAC) curve from a 5 mm FBH.
Class II — no indication ≥ 80% DAC.
Class III — no indication ≥ 100% DAC (i.e. equal to a 5 mm FBH at the same depth).
Class IV — no indication exceeding 100% DAC by more than a defined amount (effectively a fit-for-purpose grade).
Class II is the typical pressure vessel plate specification. Class III is the structural plate default. Class I is reserved for nuclear, cryogenic and high-pressure hydrogen service.
ASTM E2375 takes a different approach. It does not set fixed FBH equivalents. Instead, it defines the examination quality level (Level 1 through Level 4) and leaves the acceptance criteria to the supplementary specification or purchaser-seller agreement. The levels govern scanning sensitivity, coverage and calibration, not the rejectable flaw size.
Level 1 is the highest coverage: 100% scanning of all surfaces with both straight and angle beams, calibrated against a 1.5 mm or 3 mm side-drilled hole (SDH). Level 4 is essentially a perimeter-and-spot check used for non-critical bar. Forgings are typically specified to ASTM A388 for the test method, with acceptance per ASTM E2375 Level 1/Level 2, plus a back-reflection requirement (typically 80% of a flat, parallel back-wall with no loss greater than 3 dB relative to a reference reflector).
| Item | ASTM E2375 | EN 10160 | GB/T 2970 |
|---|---|---|---|
| Reference reflector | Side-drilled hole or notch | Flat-bottom hole | Flat-bottom hole |
| Typical FBH diameter | 1.5 / 3 / 5 mm SDH, by quality level | 3, 5 or 6 mm FBH by class and zone | 5 mm FBH (3 mm optional) |
| Calibration block | IIW V2, ASME block, or block of same heat | EN 12223 stepped block (Stepanov type) | CB-1/CB-2 per ISO 7963 |
| Probe frequency | 1–5 MHz, typical 2.25 MHz | 2 and 4 MHz (4 MHz primary) | 2.5 and 5 MHz |
| Surface roughness | Ra ≤ 6.3 µm | Ra ≤ 6.3 µm for S2; ≤ 12.5 µm for S0 | Ra ≤ 6.3 µm (Grade A/B plate) |
| Scanning coverage | 100% surface at Level 1; spot/perimeter at Level 4 | Continuous line scan at S0; raster at S2/S3 | Grid scan, 50–200 mm pitch |
A practical note: EN 10160 Class S2/B2 sits between GB/T 2970 Class I and Class II in terms of detectable flaw size, but the test geometries and scanning density differ enough that you cannot certify "equivalence" from the FBH diameter alone.
This is the question our procurement desk gets weekly: if a Chinese mill certifies a plate to GB/T 2970 Class II, will a European customer accept it as EN 10160 Class S2/B2?
The honest answer is: not automatically, and not always. Three points drive the response.
1. Methodology mismatch. EN 10160 Class S2 mandates two probe frequencies (4 MHz and 2 MHz) on the central zone, plus additional probes on the subsurface zone. GB/T 2970 uses a single frequency (typically 2.5 MHz) for the entire scan. A plate that passes EN 10160 S2 will almost certainly pass GB/T 2970 Class II on the same surface, but the reverse is not guaranteed — a 4 MHz probe catches small laminar defects that a 2.5 MHz probe at the same DAC level will miss.
2. Acceptance geometry. EN 10160 measures each indication against a flat-bottom-hole equivalent computed from the actual reflector response, using DGS (distance-gain-size) curves. GB/T 2970 measures against the DAC of a 5 mm FBH at the equivalent depth. For thin laminar defects (≤ 3 mm), the two methods can disagree by 2–3 dB, which is enough to flip a borderline call.
3. Acceptance by the notified body. European Pressure Equipment Directive (PED 2014/68/EU) work requires UT to a "harmonised standard" — EN 10160 is one. GB/T 2970 is not harmonised under PED. For a Chinese-mill plate going into a PED Category III/IV vessel, the customer or notified body will usually re-test to EN 10160 in their own shop, or insist on a dual-spec certificate.
For North American pressure vessels (ASME Section VIII Div. 1), the relevant method is ASME Section V Article 5, with acceptance per ASME Section VIII Div. 1 Appendix 12 — neither EN 10160 nor GB/T 2970 is accepted as-is, but a Chinese mill with an ASME U-stamp can issue test reports that map directly to ASME criteria. ASTM E2375 is the underlying practice for forgings and bars.
For forgings rather than plate, the European counterpart to ASTM E2375 is EN 10228-3 (UT of fine-grained steel forgings). The Chinese counterpart is GB/T 6402. If you are buying forged shafts in AISI 4340 or DIN 34CrNiMo6 for export to Europe, specifying "ASTM E2375 Level 1 + EN 10228-3 Class 3" on the PO is the safest way to land both markets.
| Buyer / market | Specification to write on PO | Notes |
|---|---|---|
| European pressure vessel plate | EN 10160 S2/B2/C2 (or S3/B3/C3 for cryogenic) | Default for PED work; specify test category and both zone classes |
| ASME Section VIII vessel plate | UT to ASME Sec. V Art. 5, accept per App. 12 | If mill is ASME U-stamped, dual cert with GB/T 2970 Class I/II possible |
| North American forging buyer | ASTM E2375 Level 1 + ASTM A388 for shear wave | Combine practice (E2375) and test method (A388) in two clauses |
| Chinese domestic structural plate | GB/T 2970 Class III | Default for shipbuilding and structural plate to GB/T 712 / GB/T 1591 |
| Heavy-walled bar for oil country goods | ASTM E2375 Level 1 + EN 10228-3 Class 3 for export | Dual-spec covers both markets — common in 4340 and 34CrNiMo6 bar |
| Wind turbine main shaft forgings | EN 10228-3 Class 3 + ASTM E2375 Level 1 | Large forgings to EN 10213 / EN 10083-3 with dual UT |
A short example from our own dispatch log: a 38 mm SA516-70 plate rolled for a Japanese pressure vessel maker was specified "EN 10160 S2/B2/C2 + GB/T 2970 Class II". The plate was tested at the mill to GB/T 2970 Class II at 2.5 MHz and passed; a second scan at 4 MHz per EN 10160 S2 picked up a 4 mm laminar indication that was below the GB/T 2970 Class II threshold but exceeded the EN 10160 B2 limit. The plate was downgraded and re-rolled. This is the kind of mismatch you pay attention to.
Q: Can a Chinese-mill plate certified to GB/T 2970 Class II be re-certified to EN 10160 S2/B2 without re-testing?
No. The methodology and acceptance differ. A re-test to EN 10160 by a European-recognised lab is normally required, and the customer's notified body will often insist on witnessing it.
Q: What is the equivalent of ASTM E2375 Level 1 in EN terms?
There is no clean linear mapping. ASTM E2375 Level 1 governs coverage and methodology; the actual acceptance is governed by the supplementary specification. For forgings, the European counterpart is EN 10228-3 Class 3 (best quality), not EN 10160.
Q: Does EN 10160 cover plates below 6 mm?
No. EN 10160 starts at 6 mm thickness. For thinner flat product, EN ISO 17640 (general UT) or a customer-specific procedure is used. ASTM A578 also covers plate down to around 6.4 mm.
Q: Why do some European customers ask for both EN 10160 S2/B2 and GB/T 2970 Class II?
Usually because the customer is buying plate from a Chinese mill and wants the GB/T 2970 certificate for traceability but the EN 10160 certificate for the notified body file. A dual-spec PO is normal and acceptable — the mill re-tests to EN 10160 after the GB/T 2970 scan, often with a third-party inspector (SGS, BV, TÜV) witnessing.
Q: Is ultrasonic testing the same as eddy current testing for steel?
No. UT detects internal laminar defects and inclusions; eddy current (per ASTM E243 for tube, EN ISO 15549 generally) catches surface and near-surface flaws. For through-thickness inspection of plate, UT is the standard method.
If you are specifying UT on plate, bar or forgings and need help matching the right standard to the right market — or need a Chinese-mill product certified to both GB/T 2970 and EN 10160 — Qilu Metal can supply plate and forged bar with mill test reports, third-party UT witnessing and dual-spec certification. We stock pressure vessel plate, AISI 4140 and AISI 4130 forged bar to ASTM, EN and GB/T specifications. Email enquiry@qilumetal.com with the grade, section size, applicable code (ASME, PED, GB 150) and the acceptance class you need — our metallurgy team will confirm the UT procedure and issue a quotation with the test plan attached.
