Charpy V-Notch (CVN) impact testing adds a layer of scrutiny to PQR qualification that most fab shops never encounter until they take on a project that specifies it. When CVN is required, the standard essential variables in Table 6.6 are no longer enough — AWS D1.1:2025 Table 6.8 introduces a second set of supplementary essential variables that govern when you must requalify. Miss one of these triggers in production and you may have impact-tested welds that are no longer supported by the PQR.

When Table 6.8 Activates

Table 6.8 is a supplementary table. It does not apply to every WPS or every PQR — it activates only when CVN impact testing is required as part of the PQR qualification record.

CVN is specified when the design, the engineer, or the contract documents identify welds that must demonstrate a minimum notch toughness — typically a minimum absorbed energy (in ft-lbs or J) at a specified temperature (e.g., 20 ft-lbs at −20°F). This is common in:

  • Seismic applications (often specified through AWS D1.8 or AISC 341)
  • Fracture-critical bridge members (AWS D1.5)
  • Owner or EOR specifications for low-temperature service
  • Applications where the AHJ or project contract requires it

If none of your project specifications call for CVN testing, Table 6.8 does not apply and your PQR is governed solely by Table 6.6. If CVN is specified for even a subset of welds, those joints require a CVN-qualified PQR with Table 6.8 compliance.

Rule library based on AWS D1.1:2025; verify against your governing edition.

Structure of Table 6.8

Table 6.8 lists supplementary essential variables that, when changed beyond the qualified range, require a new PQR with new CVN test welds. The rows cover:

  • Heat input range — CVN properties are sensitive to heat input; a higher heat input slows cooling, coarsens the HAZ grain structure, and can reduce impact toughness
  • Preheat and interpass temperatures — changes in these affect the thermal cycle and therefore the impact properties of both the weld metal and HAZ
  • Base metal thickness — different thicknesses experience different cooling rates; the PQR must bracket the thickness range in production
  • Base metal group/type — changing the base metal to a different chemistry or strength category affects CVN outcomes
  • Filler metal classification and heat number — impact properties can vary with filler chemistry; Table 6.8 treats filler classification as an essential variable at a finer level than Table 6.6 does for standard qualification
  • PWHT changes — adding or eliminating post-weld heat treatment, or changing PWHT parameters, can significantly alter CVN values

Key 2025 Edition Changes to Table 6.8

AWS D1.1:2025 made two substantive changes to Table 6.8 that are worth tracking if your shop maintains PQRs originally qualified to the 2020 edition:

Row 2(a) — minimum base metal thickness floor. The 2025 edition lowers the minimum thickness floor to 1/2 in [12 mm]. In the 2020 edition this was 5/8 in [16 mm]. This matters for shops welding lighter structural members with CVN-required joints — a PQR that was borderline compliant at 5/8 in may now cover a wider thickness range without requalification.

Row 8 — preheat scope. In the 2025 edition, preheat is removed from the scope of this row; only an increase in maximum interpass temperature triggers requalification. A preheat increase (while interpass temperature holds within the qualified range) no longer forces a new CVN PQR. This reduces unnecessary requalification in cold-weather production scenarios.

If your PQRs were written to the 2020 table, review these two rows against your current procedures. Work qualified under the 2020 table may remain valid under your governing contract edition, but new qualifications should use the 2025 numbering and logic.

Heat Input and CVN: The Core Relationship

Heat input is the dominant variable in Table 6.8 because the CVN toughness of the weld and heat-affected zone is largely a function of the thermal cycle — how fast or slow the weld cools after deposition.

High heat input → slower cooling → coarser grain structure in the HAZ → typically lower CVN values. Low heat input → faster cooling → finer grain structure → typically higher CVN values, but also higher risk of hydrogen cracking in susceptible steels.

For CVN-required welds, the PQR must document the heat input used during test welding, and the WPS must specify a heat input range that stays within what the PQR tested. Production welds that drift above the upper bound — driven by welders slowing travel speed or increasing amperage to fill large gaps — are outside the qualified range even if the visual and UT results look fine.

This is the most common compliance gap for CVN-qualified procedures: the metallurgical acceptance criterion (CVN toughness) is invisible to visual inspection but is negated by heat input violations that any CWI with a calculator and the WPS can detect.

Preheat and Interpass Under Table 6.8

For standard Table 6.6 qualification, preheat and interpass temperature changes are essential variables when they fall outside qualified limits. Table 6.8 tightens these requirements because small changes in thermal cycle have larger effects on CVN results than on tensile or bend properties.

Preheat decrease — triggers requalification under Table 6.8 because a lower starting temperature means faster initial cooling. The HAZ sees a sharper thermal gradient, which can coarsen grain structure near the fusion line in ways that reduce toughness.

Interpass temperature increase — triggers requalification in the 2025 edition. Running hotter between passes is equivalent to adding heat input after the first pass, degrading the refined structure that the earlier passes established. This is why a CWI monitoring a CVN-required joint should track interpass with a contact thermometer, not just preheat before the first arc strike.

Preheat increase without interpass change — per the 2025 Table 6.8, this alone does not trigger requalification. A shop running cold-weather work that needs to raise minimum preheat to prevent condensation has some flexibility here.

Filler Metal Traceability for CVN PQRs

Table 6.8 treats filler metal at a finer level of detail than Table 6.6. For CVN-qualified procedures, the PQR records the specific heat number or lot of filler metal used in the test welds. A change in filler classification or — in some specifications — a change in brand or lot without demonstrated equivalent CVN performance may require requalification or at minimum a data letter from the electrode manufacturer showing heat-to-heat CVN consistency.

This makes filler metal procurement and traceability critical for shops with standing CVN-qualified WPS procedures. A purchasing change to an "equivalent" electrode from a different manufacturer is not automatically covered. See welding consumable cert traceability for how to structure your receiving inspection and documentation.

PWHT and CVN

Post-weld heat treatment (PWHT) appears in Table 6.8 because it directly alters the as-welded microstructure and therefore the CVN result. Adding PWHT to a WPS that was CVN-qualified without it — or removing PWHT from one that was tested with it — requires re-running CVN test welds under the new thermal condition.

The temper embrittlement phenomenon is relevant here: some steels lose CVN toughness when PWHT is held at certain temperature ranges. If your project spec requires both PWHT and CVN acceptance, the test welds in the PQR must have been PWHT'd before the CVN specimens were machined and tested.

How This Plays Out in a Fab Shop Audit

During an AISC or owner CWI audit of a project with CVN-required welds, the auditor will cross-reference:

  1. The PQR: what heat input, preheat, interpass, and base metal thickness were used during qualification?
  2. The WPS: does it specify ranges within the PQR's qualified bracket?
  3. Production records: did actual heat input, preheat, and interpass during production stay inside the WPS range?

A gap at any of these three levels constitutes a nonconformance. The tightest scrutiny falls on heat input logs — few shops record these automatically unless their WPS software or welder tracking system is capturing amps, volts, and travel speed by joint.

For an overview of how Table 6.6 and Table 6.8 relate to the overall PQR structure, see AWS D1.1:2025 Table 6.6 explained: PQR essential variables row by row and PQR tensile and bend test requirements.

Setting Up Your WPS Correctly for CVN Joints

If you have CVN-required joints in your current project:

  1. Verify the PQR covers the base metal, thickness, and heat input range for those joints specifically.
  2. Confirm the WPS specifies a heat input range — not just amperage and voltage, but the calculated range derived from them with travel speed.
  3. Brief welders on the interpass temperature limit. Use a contact thermometer and require recording of preheat and interpass by joint or by shift.
  4. Track filler metal lot numbers against the PQR documentation for CVN-critical welds.

For a platform that tracks these parameters and flags when a production weld is outside the qualified WPS range, see our WPS and qualification management software.

Summary

AWS D1.1:2025 Table 6.8 supplementary essential variables activate only when CVN impact testing is part of your PQR qualification. They add stricter controls on heat input, preheat, interpass temperature, base metal thickness, and filler metal than the standard Table 6.6 variables. Two rows changed substantively in the 2025 edition: the minimum thickness floor dropped to 1/2 in [12 mm], and preheat alone no longer triggers requalification (only an interpass maximum increase does). If your shop is taking on CVN-required work for the first time, build the Table 6.8 checklist into your WPS drafting process and your production inspection protocol before welding begins.