A913 Gr.70 Preheat for FCAW — up to 3/4"

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 all-position capability for field column splice CJP welds. Stringer beads at controlled heat input (30-50 kJ/in) preserve the QST microstructure. With H8-certified E71T wire, qualifies for Category F reduced preheat (32°F up to 2-1/2", 150°F above). 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. With H8-certified consumables, it qualifies for Category F — 32°F up to 2-1/2”, 150°F above. 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. The higher strength level of this steel places it in Category C of Table 5.11, which carries elevated preheat requirements compared to Category B grades. At 50°F minimum with FCAW, flux-cored wire in FCAW provides a combination of deoxidizers and low-moisture flux formulations that control hydrogen, but the preheat must still ensure the cooling rate stays slow enough to prevent hydrogen-induced cracking in this higher-hardenability material.

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. The Category F path with H8 consumables (32°F up to 2-1/2", 150°F above) provides a practical alternative to full Category C preheat on these thick-flange column splices.

Why Preheat Matters at up to 3/4"

Thin material sheds heat quickly, allowing hydrogen to escape the HAZ readily — lowest preheat tier in Table 5.11.

Category C Preheat for A913 Gr.70

Category C in Table 5.11 applies to higher-strength steels where the combination of hardenability and residual stress requires elevated preheat. For A913 Gr.70 at up to 3/4", the 50°F minimum preheat slows the weld cooling rate to prevent formation of crack-susceptible martensite in the heat-affected zone. Maintaining interpass temperature at or above this minimum is especially critical for multi-pass welds on restrained joints.

Other Steels with FCAW at up to 3/4"

A913 Gr.70 with FCAW

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