When is CVN impact testing required?

When the structural code, contract, or AHJ specifies it. AISC 341 (Seismic Provisions) requires CVN for demand-critical welds. Some bridge codes (AASHTO) require CVN. Many ordinary building structures do not require CVN.

What's the difference between Table 6.6 and Table 6.8?

Table 6.6 is the baseline list of PQR essential variables for all qualifications. Table 6.8 is supplementary — it adds requirements only when CVN testing is part of the qualification. You apply both tables when CVN is required; only Table 6.6 when it isn't.

What changed in Table 6.8 from 2020 to 2025?

Two key changes: (1) Row 2(a) minimum thickness floor changed from 5/8 in [16 mm] (2020) to 1/2 in [12 mm] (2025); (2) Row 8 — preheat was dropped from supplementary scope, leaving only interpass-max increase as a requalification trigger.

If CVN isn't required, can I ignore Table 6.8 entirely?

Yes. Table 6.8 only applies when CVN impact testing is required. If your project has no CVN requirement, Table 6.6 is your sole essential-variable list.

CVN impact testing and AWS D1.1:2025 Table 6.8 supplementary essentials

When CVN (Charpy V-Notch) testing is required, Table 6.8 adds supplementary essential variables on top of Table 6.6. Here's what changed in 2025 and when it applies.

CVN — Charpy V-Notch — impact testing measures the toughness of a weld at low temperature. When the structural code requires CVN, AWS D1.1:2025 invokes Table 6.8 supplementary essential variables on top of Table 6.6. The supplementary list tightens several requalification triggers because toughness is sensitive to thermal history.

When CVN is required

CVN impact testing is mandated by:

AISC 341 (Seismic Provisions) for demand-critical welds in special moment frames and braced frames
AASHTO Bridge Welding Code for fracture-critical members
API 1104 for some pipeline applications
Owner / contract specifications that explicitly require it
AHJ requirements in some jurisdictions

Many ordinary building structures — standard moment frames in non-seismic regions, simple shear connections — do not require CVN. Read the structural drawings carefully; the welding callout will indicate.

What Table 6.8 adds

When CVN is required, Table 6.8 adds supplementary essential variables on top of Table 6.6. The key supplementary triggers:

Heat input maximum — tighter than the Table 6.6 baseline. A heat-input increase beyond a small tolerance requires requalification.
Interpass temperature maximum — increases beyond the qualified maximum require requalification.
Minimum thickness floor — the PQR's plate thickness sets a lower bound for the qualified range, with a code-defined minimum. In 2025, this floor is 1/2 in [12 mm]. In 2020 it was 5/8 in [16 mm].
Cooling rate / progression — vertical-down restricts toughness recovery; check progression rules.

What changed in 2025

Two row-level technical changes:

Row 2(a) — minimum thickness floor dropped from 5/8 in [16 mm] (2020) to 1/2 in [12 mm] (2025). This expands the range of plate thicknesses the PQR can support downward.
Row 8 — preheat was dropped from supplementary scope. Only interpass-maximum increase still triggers requalification under Table 6.8. (Preheat is still covered under Table 6.6 baseline rules.)

A 2020 PQR qualified for CVN at 5/8 in plate now supports a wider thickness range under 2025 rules. The CVN-supplementary preheat requalification trigger is gone in 2025.

Practical implications

For a fab shop that does CVN-required work, three changes matter:

Migrating PQRs to 2025 widens your qualified thickness range in many cases — no requalification needed, just an updated table citation on the WPS.
The preheat requalification trigger is gone. You can vary preheat (within Table 5.8 minimums and Table 6.6 essentials) without crossing Table 6.8.
Interpass max is still tight. Production welds that push interpass into a higher range than the PQR qualified will trigger a Table 6.8 violation — a rule engine flagging interpass on every CVN-required WPS prevents the audit finding.

Common audit findings on CVN-required WPSs

WPS cites Table 6.7 (the 2020 number for CVN supplementary) on a 2025-edition project
Interpass temperature recorded on the production log exceeds the WPS maximum, which exceeds the PQR-qualified maximum
A WPS imports a 2020 PQR's qualified thickness range without checking the 2025 floor change
The CVN requirement on the structural drawings is missed entirely — the WPS doesn't mention CVN; lab tests weren't run

The first three are mechanical and a rule engine catches them. The fourth is a reading-the-drawings problem and is harder to automate away.