A1066 Gr.70 Preheat for SAW — 3/4" to 1-1/2"

SAW (Submerged Arc Welding)

SAW submerges the arc beneath granular flux for highest deposition rates, flat/horizontal only. Category B in Table 5.11.

SAW on high-strength plate selects wire-flux combinations by the steel's Table 5.6 base-metal group, not its Table 5.11 preheat category: Table 5.7 marks AWS A5.17 carbon-steel combinations N/A for Groups III, IV and V and lists AWS A5.23 low-alloy combinations such as F8AX-E(C)XXX-A2 for Group III and F9AX-E(C)XXX-A2 for Group IV. Heat input control is particularly important on TMCP grades because SAW naturally deposits high heat input due to the deeply penetrating arc.

SAW Tips for High-Strength and TMCP Steels

For A1066 Gr.70 plate, SAW provides highest deposition rates for long seam welds on bridge flanges — but Clause 7.7 heat input limitations DO apply to A1066 (unlike A913). Full Category C preheat mandatory regardless of consumable hydrogen designation. Limit parameters to 400-550 A with 3/32" EM12K wire, targeting heat input below 50 kJ/in. Neutral flux required for multi-pass.

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

Filler Metal for SAW

Wire: EM12K or EL12 with matching flux (AWS A5.17). Common combo: F7A2-EM12K. Diameter: 3/32" or 7/64". AWS A5.17 Figure 1U uses A for as-welded and P for PWHT, not flux activity. Annex A6.1 defines active versus neutral flux by weld-metal Mn and Si change with arc voltage (Wall Neutrality Number); primary use of neutral fluxes is multipass welding and of active fluxes is single-pass welds. Voltage: 28-34V. Current: 400-800A depending on joint size. Travel: 12-24 ipm.

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

A1066 Gr.70

ASTM A1066 Grade 70 (70 ksi yield, 85 ksi minimum tensile) is the highest-strength grade in this specification, produced as quenched-and-tempered or TMCP plate for demanding bridge and structural applications. It falls under Category C in Table 5.11 but notably does not qualify for any H8 reduced-preheat category — unlike Grades 50/60/65, Grade 70 must use full Category C preheat regardless of consumable hydrogen designation. This distinction exists because the higher alloying level needed for 70 ksi yield pushes the CE-IIW to approximately 0.48-0.54, a range where even H8 hydrogen control is not sufficient to offset the hardenability-driven cracking risk at reduced preheat. Fabricators working with A1066 Gr.70 should budget for full Category C preheating time on every joint, with no H8 shortcut available.

Why This Preheat for A1066 Gr.70 with SAW

Highest-strength A1066 at 70 ksi with no H8 preheat reduction available. 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 150°F minimum with SAW, the submerged arc process with granular flux produces controlled hydrogen levels, with flux condition being the primary variable, 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 A1066 Gr.70

Used in the most demanding bridge and structural applications: main girder flanges on record-span bridges, arch rib plates, suspension bridge stiffening truss chords, and heavy industrial crane runway girders. A1066 Gr.70 does not qualify for any H8 reduced preheat, so full Category C preheat must be applied regardless of consumable certification. This makes preheat management the primary production consideration for heavy-section joints where flange thicknesses of 2-4" are common. Fabrication bid costs for A1066 Gr.70 components must account for the full Category C preheat time in their labor estimates — typically 45-90 minutes per joint on plate over 2". Unlike Grades 50 and 60/65, there is no consumable-based path to reduce preheat duration on Gr.70 joints. Bridge fabrication shops working with this grade maintain dedicated preheat logs and temperature monitoring records for every CJP and PJP weld as part of their quality management system.

Why Preheat Matters at 3/4" to 1-1/2"

Preheat climbs at this range as thicker material slows heat dissipation, trapping hydrogen at crack-susceptible grain boundaries.

Category C Preheat for A1066 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 A1066 Gr.70 at 3/4" to 1-1/2", the 150°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 SAW at 3/4" to 1-1/2"

A1066 Gr.70 with SAW

Try Different Combinations

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

A1066 Gr.70 Welding Guides