A913 Gr.70 Preheat for FCAW (H8) — over 2-1/2"

FCAW (H8) for A913 Gr.70 at over 2-1/2"

H8-certified FCAW (H8) for A913 Gr.70 at over 2-1/2": minimum preheat 150°F (65°C) under Category F. For FCAW wires like E71T-1C, achieving H8 certification requires careful control of flux moisture content during wire manufacturing. The flux core is the primary hydrogen source in FCAW, and H8-designated wires use moisture-resistant formulations with tighter quality controls.

FCAW (Flux Cored Arc Welding)

FCAW uses tubular flux-cored wire, available gas-shielded (E71T-1) or self-shielded (E71T-8) for field work. Category B in Table 5.11.

High-strength FCAW wire follows the steel's Table 5.6 base-metal group, not its Table 5.11 preheat category: Table 5.7 marks AWS A5.20 carbon-steel wire N/A for Groups III, IV and V and lists AWS A5.29 low-alloy classifications such as E8XTX-K2X for Group III and E9XTX-K2X for Group IV. The flux system in these wires is formulated for low diffusible hydrogen, often meeting H8 supplementary limits when tested per AWS A4.3. Wire storage requires climate-controlled conditions similar to SMAW electrodes to prevent moisture absorption.

FCAW Tips for High-Strength and TMCP Steels

For A913 Gr.70 TMCP column shapes, FCAW with E71T-1M at 220-260 A provides flat, horizontal, vertical-up and overhead capability for field column splice CJP welds. Stringer beads at controlled heat input (30-50 kJ/in) preserve the QST microstructure. Clause 7.7 heat input limits do NOT apply to A913.

Typical values for reference — always verify against your approved WPS and electrode manufacturer data.

Filler Metal for FCAW

Gas-shielded: E71T-1C (AWS A5.20, classified with 100% CO2) or E71T-1M (classified with 75 to 80 percent argon, balance CO2). The C and M designators identify the shielding gas used for classification; the actual gas must follow the electrode manufacturer and the qualified WPS. Self-shielded: E71T-8 (no external gas, field-ready). Diameter: 0.045" standard, 1/16" for high-deposition. Stick-out: 3/4" to 1-1/4" (longer than GMAW due to resistive heating of flux core).

Typical values for reference — always verify against your approved WPS and electrode manufacturer data.

A913 Gr.70

ASTM A913 Grade 70 (70 ksi yield, 90 ksi minimum tensile) is a TMCP structural shape used in heavily loaded columns and seismic applications requiring higher strength than Gr.50/60/65. It falls under Category C for standard low-hydrogen processes, with preheat requirements reflecting its higher strength level and CE-IIW of approximately 0.42-0.48. The TMCP QST microstructure provides inherent resistance to hydrogen cracking through its fine-grained bainitic structure, which is why H8 consumables unlock a reduced-preheat path not available for conventional Q&T steels at similar strength. A913 Gr.70 is primarily available in W14 sections ranging from W14x233 through W14x730, with limited W12 and W36 availability.

Why This Preheat for A913 Gr.70 with FCAW

TMCP 70 ksi shape with Category F reduced preheat using H8 consumables. H8-certified consumables with FCAW place this in Category F of Table 5.11. At 150°F, the preheat requirement reflects the TMCP microstructure's inherent resistance to hydrogen cracking combined with the controlled hydrogen input from H8 consumables.

Typical Applications for A913 Gr.70

Used in heavily loaded interior columns of super-tall buildings, transfer truss compression chords, mega-brace members in outrigger systems, stadium roof cantilever supports, and seismic collectors in high-rise cores. A913 Gr.70 TMCP shapes enable smaller column sections, freeing usable floor space on every floor of the building. Column splice butt welds at upper stories and moment connection flange welds carry the highest inspection priority. The 70 ksi yield enables using W14x398 where conventional Gr.50 would require W14x550, saving 38% in material weight and 3-4 inches of floor space per column. Erection splices at every 2-3 stories use CJP groove welds with backing bars removed and back-gouged per seismic detailing requirements.

Why Preheat Matters at over 2-1/2"

The heaviest sections demand the highest preheat in Table 5.11. Multi-pass sequences require maintaining interpass temperature throughout.

H8-Certified Consumables for A913 Gr.70

The H8 supplementary designator on a consumable classification (e.g., E7018-H8) certifies that the electrode deposits no more than 8 mL of diffusible hydrogen per 100g of deposited weld metal, tested per AWS A4.3. For A913 Gr.70, using H8 consumables qualifies for Category F with reduced preheat of 150°F at over 2-1/2" thickness. Verify the H8 designator on electrode packaging or manufacturer certification before claiming the reduced preheat category.

Try Different Combinations

Use the interactive preheat calculator to look up any steel, process, and thickness combination from D1.1:2025 Table 5.11.

A913 Gr.70 Welding Guides