What triggers supplementary essential variables under AWS D1.1:2025?

Supplementary essential variables (Table 6.8) are invoked when the contract documents, project specification, or engineer of record requires Charpy V-notch (CVN) impact testing of the weld metal. This commonly occurs for cold-service structures, seismic demand-critical welds, fracture-critical members, or owner specifications citing AWS D1.1 Table 6.8.

What is the difference between Table 6.6 and Table 6.8 in AWS D1.1:2025?

Table 6.6 lists the standard essential variables that apply to all tested WPS — a change to any of these requires a new PQR. Table 6.8 lists supplementary essential variables that are only required when CVN notch-toughness testing of the weld metal is specified. Table 6.8 applies in addition to Table 6.6, not instead of it.

How does Table 6.8 change the minimum base metal thickness that requires CVN testing?

Under AWS D1.1:2025 Table 6.8 Row 2(a), the minimum base metal thickness floor for CVN supplementary essential variable testing is 1/2 in [12 mm]. This was 5/8 in [16 mm] in the 2020 edition, so more joints now require CVN-tested PQRs on projects that invoke supplementary variables. Verify against your governing edition.

Does every change to preheat require a new PQR when Table 6.8 is invoked?

No. AWS D1.1:2025 Table 6.8 Row 8 removed preheat from the supplementary essential variable scope. Only an increase in maximum interpass temperature triggers requalification under the CVN supplementary variable framework. A decrease in preheat or a change that does not increase the maximum interpass temperature does not require a new PQR under Table 6.8. This was a significant change from the 2020 edition.

Supplementary Essential Variables: CVN PQR Program Impact

When a project specification invokes AWS D1.1:2025 Table 6.8 supplementary essential variables, the CVN testing requirements can multiply your WPS count and PQR cost. Here's what to expect and how to plan.

Most structural welding projects live comfortably within the standard essential variable framework of AWS D1.1 Table 6.6. The WPS gets written, the PQR gets run, the CWI reviews and signs, and production moves forward. But when the contract documents specify notch-toughness testing of the weld metal — Charpy V-notch (CVN) testing — a second tier of requirements activates: the supplementary essential variables of AWS D1.1:2025 Table 6.8.

Understanding when Table 6.8 applies, what it requires, and how it affects WPS program cost is essential for any QC manager writing a welding program for a seismic, cold-service, or owner-specified CVN project.

Rule library based on AWS D1.1:2025; verify against your governing edition (the AHJ or contract may specify 2020 or earlier).

What Are Supplementary Essential Variables?

AWS D1.1:2025 defines two tiers of essential variables for tested WPS:

Table 6.6 — Standard essential variables. These apply to every tested welding procedure for the covered processes (SMAW, SAW, GMAW, FCAW, and GTAW). A change to any Table 6.6 variable invalidates the existing WPS and requires a new PQR.

Table 6.8 — Supplementary essential variables. These apply only when CVN impact testing of the weld metal is required by the contract, specification, or engineer of record. They are applied in addition to Table 6.6, not as a replacement.

The distinction matters because Table 6.8 introduces additional parameters that can drive WPS requalification even when nothing in Table 6.6 has changed. The most common surprise for fabricators encountering this for the first time: changing the electrode heat or lot number becomes an essential variable. Under standard Table 6.6 procedures, a filler metal substitution from one lot to another within the same AWS classification is typically not an essential variable. Under Table 6.8, it can be.

For background on standard essential variables, see AWS D1.1 Table 6.6 essential variables explained.

What Triggers Table 6.8?

The specification document — not the fabricator — activates Table 6.8. Triggers include:

Project specification language such as "weld metal shall meet minimum CVN impact energy of ___ ft-lb at ___ °F" or "welding procedures shall qualify supplementary essential variables per AWS D1.1 Table 6.8."

Seismic demand-critical welds under AISC 341. The seismic provisions require CVN testing of weld metal for demand-critical welds in intermediate and special moment frames, eccentrically braced frames, and buckle-restrained braced frames. The WPS for these welds must be tested with CVN specimens, invoking Table 6.8. See CVN supplementary essential variables and Table 6.8 for the seismic context.

Cold-service applications where operating temperatures are well below ambient and the owner has specified CVN requirements. Liquefied natural gas (LNG) terminals, Arctic structures, and cold-storage facilities are typical examples. See cold-service structural WPS and CVN toughness requirements for that specific application.

Owner-specified fracture control plans that reference AWS D1.1 Table 6.8 or require impact-tested WPS documentation.

Once any of these triggers exists in the contract documents, Table 6.8 is not optional.

Key Changes in AWS D1.1:2025 Table 6.8

Two important changes from the 2020 to 2025 edition affect how supplementary essential variables work in practice:

Row 2(a): Minimum Thickness Floor Lowered

The minimum base metal thickness above which Table 6.8 supplementary variables must be applied for groove welds was reduced from 5/8 in [16 mm] in the 2020 edition to 1/2 in [12 mm] in the 2025 edition. This means fabricators working on projects that invoke Table 6.8 will now encounter CVN-tested PQR requirements on thinner material than they did under the 2020 rules. Structural steel in the 1/2 to 5/8 in range is common in bracing, beam webs, and secondary members, so this change can significantly increase the number of PQRs required for a building program.

Row 8: Preheat Removed from Scope

In the 2020 edition, certain changes to preheat temperature were supplementary essential variables. AWS D1.1:2025 Table 6.8 Row 8 removed preheat from scope. Now only an increase in maximum interpass temperature triggers requalification under the supplementary variable framework. A reduction in preheat, a change in preheat maintenance method, or the addition of preheat where none was previously required does not force re-testing under Table 6.8. This is a meaningful relaxation — it means a fabricator can adjust preheat protocols in response to cold ambient temperatures without invalidating CVN-tested PQRs.

How Table 6.8 Multiplies WPS Count

Under standard Table 6.6 procedures, a well-designed PQR test plate can support a WPS that covers a broad range of production welding. Under Table 6.8, several variables that are non-essential under Table 6.6 become essential, which fragments that broad coverage:

Filler metal lot or heat number. When CVN requirements are invoked, the filler metal used in the PQR test weld must match — within the Table 6.8 constraints — the filler used in production. A change in filler lot or heat number may require re-testing or re-certification. This forces fabricators running large CVN-sensitive programs to maintain tighter filler metal inventory control and in some cases requires separate PQRs for different filler lot qualifications.

Electrode diameter or wire size. Some electrode-size changes that are non-essential under Table 6.6 become essential under Table 6.8 because wire size affects heat input and thus the microstructure of the heat-affected zone and weld metal.

Welding position. While position is an essential variable under Table 6.6, the CVN test specimens must be taken from a position that represents the production welding. A PQR that qualifies flat and horizontal positions for standard work may need a separate test for overhead or vertical production welds when CVN requirements apply, because position affects heat input distribution and cooling rate.

The net effect: a fabricator who might manage a standard structural program with 3–5 WPS documents may find that the same project with Table 6.8 invoked requires 10–15 WPS documents, each backed by its own PQR with CVN specimens.

PQR Testing Requirements Under Table 6.8

The PQR for a CVN-qualified WPS must include Charpy V-notch specimens in addition to the standard tensile and bend tests. AWS D1.1:2025 specifies:

The number of CVN specimens per weld zone (weld metal and heat-affected zone).
The notching location relative to the weld center line and heat-affected zone edge.
The test temperature at which specimens must be evaluated.
The minimum absorbed energy (ft-lb or joules) that must be demonstrated.

The project specification or engineer of record will specify the required test temperature and minimum energy. The code sets the framework; the specification sets the acceptance criterion. If the specification is silent on test temperature, the fabricator must clarify with the EOR before qualifying — running PQR specimens at an assumed temperature that does not match the project requirement is a common and costly error.

For a full breakdown of PQR mechanical test requirements, see PQR tensile and bend test requirements under AWS D1.1.

Practical Planning Advice

Get the specification before budgeting PQR costs. Table 6.8 can triple or quadruple the test laboratory cost for a project. The filler lot restrictions also increase purchasing complexity. Identify whether CVN requirements apply before estimating the welding program.

Coordinate with your filler metal supplier. If filler lot number is an essential variable, you need to know which lots are available and buy sufficient quantity to complete the project. Mid-project lot changes that force re-testing are expensive and delay production.

Centralize PQR records. A firm maintaining a library of CVN-tested PQRs can reuse them across projects if the essential variables match. Tracking which PQR supports which WPS, and which lots were used in each test, becomes critical record-keeping under Table 6.8.

Use software to manage WPS-to-PQR linkage. When essential variable tables are complex and WPS counts are high, a spreadsheet introduces significant error risk. A purpose-built WPS management system can flag when a production change would require a new PQR, before it becomes a nonconformance.

For related reading on managing a multi-WPS library, see WPS library management for multi-project AWS D1.1 programs.