Structural fab shops spend a lot of time worrying about cold-weather welding. Minimum preheat gets attention, cold cracking risks are well understood, and most CWIs have a procedure for verifying preheat at −20°F ambient. But the summer side of the temperature curve gets far less attention — and it causes real, documented weld failures.
Hot-weather structural welding under AWS D1.1:2025 isn't governed by a single dedicated clause the way minimum preheat is. Instead, the risks scatter across several requirements that all converge when ambient temperatures climb above 90°F and structural steel sitting in direct sun reaches temperatures the WPS wasn't written for. Understanding what the code actually requires — and where discipline has to fill the gap — is what separates field-ready quality programs from ones that fail in August.
Why High Ambient Temperature Creates Weld Quality Risk
The most common failure mode in hot-weather structural welding is exceeding the WPS interpass temperature maximum.
AWS D1.1:2025 Table 6.6 lists interpass temperature as an essential variable for SMAW, SAW, GMAW, FCAW, and GTAW procedures qualified under Clause 6. If the maximum interpass temperature recorded during the PQR test is, say, 400°F (204°C), then production welding must not exceed that value — a field exceedance is technically a departure from an essential variable and requires engineering disposition or requalification. (Rule library based on AWS D1.1:2025; verify against your governing edition.)
In cold weather, keeping interpass temperature above the minimum is the challenge. In summer, the opposite problem emerges. A preheated joint on a 90°F day with steel that has been baking in direct sun will cool slowly between passes. On thick plate with closely spaced weld passes, interpass temperature can drift 50–100°F above the WPS maximum before the first pass of the next sequence is even started. Welders who are focused on deposition rate rarely stop to check with a pyrometer between passes — especially when the WPS minimum preheat is easily maintained without any supplemental heat.
The second risk is filler metal handling. High ambient temperature and humidity can affect the conditioning of low-hydrogen electrodes. E7018 and similar low-hydrogen SMAW electrodes have specific handling requirements for atmospheric exposure once removed from sealed packaging or the rod oven. Elevated temperature alone doesn't drive hydrogen pickup the way humidity does, but hot and humid summer conditions in unconditioned fab bays can combine to compromise electrodes faster than cold-season norms suggest.
What AWS D1.1 Actually Requires in Hot Conditions
Minimum preheat still applies. AWS D1.1:2025 Clause 7 (Fabrication) requires that minimum preheat be maintained at the time of welding. There is no code provision that exempts this requirement because base metal is already warm. A CWI cannot assume sun-heated steel meets minimum preheat without verifying the actual temperature within 3 inches of the joint using a calibrated pyrometer or temperature-indicating crayons. Equally important: the code requires measuring within that 3-inch band, not on an arbitrary surface some distance away.
Maximum interpass temperature governs. The WPS specifies both the minimum preheat and the maximum interpass temperature as code-required parameters. AWS D1.1:2025 treats an exceedance of the maximum interpass temperature as a departure from the qualified procedure. If toughness testing (Charpy CVN) governs, maximum interpass temperature also appears in the supplementary essential variables under Table 6.8 — and the sensitivity there is higher because interpass temperature affects HAZ toughness directly.
Shielding gas performance. GMAW and FCAW-G shielding gas coverage degrades when hot convective currents disturb the gas envelope at the weld puddle. In summer, shop ventilation systems create more turbulence, and outside erection work contends with thermal updrafts over hot steel. The WPS shielding gas flow rate and nozzle-to-work distance requirements don't change in hot weather — but they become harder to maintain. Documenting gas flow checks in production weld logs is good practice.
Electrode storage. AWS D1.1:2025 Clause 7 sets conditioning requirements for low-hydrogen electrodes by H-designation. High-humidity summer conditions can shorten the permitted atmospheric exposure time for H4 and H8 electrodes compared to what welders may expect from winter experience. Shop quality programs should review electrode conditioning intervals seasonally, not just at initial procedure setup.
Field Practices That Support Compliance
The code sets the rules; the QC plan is where hot-weather controls get operationalized.
Mandatory interpass temperature checks. The single most effective control is requiring pyrometer or temperature crayon readings before each weld pass on thick plate or restrained joints. For SMAW multi-pass work on 1-inch plate or thicker, a brief cooldown interval — even five minutes in ventilated shade — can bring interpass temperature back into range without disrupting overall productivity.
Sun shading for staging steel. Steel sitting in direct summer sun can reach surface temperatures of 150–200°F before a single arc is struck. This creates two problems: the steel may be over-temperature for the first pass of a CVN-toughness WPS, and the inspector's first interpass check will be misleading because the base metal contributes thermal mass that extends subsequent pass cooling times. Storing structural members in shade or covering them with welding blankets before work begins is not a code requirement, but it substantially improves temperature control.
Documentation. The CWI or production welding log should record ambient temperature, base metal temperature at weld start, and interpass temperature at representative points during multi-pass work. This documentation protects the fabricator if an inspector or owner later questions whether the WPS was followed. It is also useful evidence if a weld is questioned due to apparent porosity or HAZ softening that might be attributed to excessive heat input or interpass exceedance.
Low-hydrogen electrode rotation. In summer months, consider reducing the permitted atmospheric exposure time for H4 electrodes from the standard interval and tracking rod-oven pull times by heat number. Some fab shops run a "one bundle out at a time" rule during peak humidity months regardless of season.
When to Consult the EOR
If your WPS was qualified at a maximum interpass temperature of 400°F and you have documented evidence that production work routinely exceeds that limit in summer conditions, the right answer is not to ignore it. Options include:
- Requalifying with a higher maximum interpass temperature in the PQR (requires new test coupon and mechanical testing)
- Implementing strict interpass cooling hold requirements in the quality plan
- Using the existing WPS but adding a notation that cooldown checks are required before each pass
If the project is governed by CVN toughness requirements, consult the structural engineer of record (EOR) before proceeding. Interpass temperature directly affects HAZ toughness and is a supplementary essential variable under Table 6.8. Exceedance in CVN-governed work may require engineering evaluation, not just procedural adjustment.
The CWI's Responsibility
AWS D1.1:2025 puts the inspection obligation squarely on the fabricator's quality organization. Contractor Quality Control (CQC) must verify that the WPS is being followed at the point of welding — including interpass temperature checks — not just at project closeout. The verification inspector (owner's CWI) typically performs surveillance, not full coverage, so the fabricator's CWI cannot assume the owner's inspector will catch interpass exceedances.
Practical surveillance plans for summer fieldwork should include spot pyrometer checks during multi-pass work on joints of 3/4-inch or thicker material, particularly on restrained connections like moment frames and column splice details.
Hot weather doesn't give structural welding a pass on code compliance. The WPS limits are the limits year-round — the season just changes how much active effort it takes to stay inside them.
Review interpass temperature controls on your active WPS procedures and compare your summer field protocol against the cold-weather welding requirements your QC plan already addresses. For WPS libraries with built-in preheat and interpass documentation, see the wpswelding.com plans.