A709 HPS70W Preheat for SMAW (low-hydrogen) — up to 3/4"

SMAW (Low-Hydrogen)

Low-hydrogen SMAW (E7018/E7016) uses basic-coated electrodes requiring rod oven storage, assigned to Category B in Table 5.11.

For high-strength shapes and plate, the Table 5.11 preheat category does not select the filler metal. Matching strength follows the steel's base-metal group in D1.1 Table 5.6: Table 5.7 lists AWS A5.1 carbon-steel electrodes such as E7018 for Group I and Group II base metals and marks A5.1 N/A for Groups III, IV and V, which take AWS A5.5 low-alloy electrodes such as E8018-C3 (Group III), E9018M (Group IV) or E10018M (Group V). Bead sequencing on thick TMCP flanges should follow qualified WPS parameters precisely to avoid overheating the refined microstructure.

SMAW-LH Tips for High-Strength and TMCP Steels

For A709 HPS70W (70 ksi yield, Q&T, Category C, maximum interpass per Table 5.11), a Table 5.6 Group IV steel, Table 5.7 lists AWS A5.5 E9018M or E9018-P2 as matching-strength SMAW electrodes. For exposed, bare, unpainted weathering applications, D1.1 5.6.3 requires the electrode to conform to Table 5.9, with single-pass groove and fillet exceptions. Category C preheat: 50°F up to 3/4", 150°F up to 1-1/2", 225°F up to 2-1/2", 300°F above. Maximum interpass must not exceed 400°F (up to 1-1/2") or 450°F (above).

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

Filler Metal for SMAW-LH

Electrode: E7018 (AWS A5.1). Table 5.7 lists it for Group I and Group II base metals only; Groups III, IV and V take AWS A5.5 low-alloy electrodes from Table 5.7. Diameter: 1/8" (general/out-of-position), 5/32" (production), 3/16" (heavy plate flat only). Storage: 250°F rod oven minimum per D1.1 §7.3.2.1. Exposure limit: 4 hours out of oven per Table 7.1, then re-bake at 500-800°F for minimum 2 hours per §7.3.2.4 (A5.1 classification).

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

A709 HPS70W

ASTM A709 HPS70W is the highest-strength weathering bridge steel with 70 ksi minimum yield and 85-110 ksi tensile range, used in long-span bridges and heavily loaded members where weight reduction is critical. Produced as quenched-and-tempered plate in thicknesses up to 4", its high strength places it in Category C of Table 5.11 with correspondingly higher preheat requirements. Table 5.11 footnote (b) sets a maximum preheat/interpass of 400°F for thickness up to 1-1/2” and 450°F for thicker material — this upper limit is unusual in D1.1 and exists because the Q&T microstructure can be degraded by excessive heat. The chemistry includes copper (0.25-0.40%), nickel (0.65-1.00%), and chromium (0.40-0.65%) for atmospheric corrosion resistance, with 0.19% max carbon keeping the CE-IIW in the 0.46-0.52 range.

Why This Preheat for A709 HPS70W with SMAW-LH

Highest-strength 70 ksi weathering bridge steel for long-span applications. 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 SMAW-LH, E7018 low-hydrogen electrodes produce typically 4-8 mL/100g diffusible hydrogen under proper rod oven conditions, 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 A709 HPS70W

Reserved for long-span bridge main girder flanges, cable-stayed bridge edge girders, arch rib plates, high-load interchange ramp girders, and situations where reducing member depth saves clearance or reduces dead load. HPS70W enables weight savings of 20-30% versus conventional Gr.50 designs, allowing shallower girder sections that reduce embankment costs on grade-separation bridges. Flange thickness often exceeds 2”, making preheat and interpass control critical at every CJP splice and web-to-flange joint. Note that Table 5.11 footnote (b) sets maximum preheat and interpass limits of 400°F for thicknesses up to 1-1/2" and 450°F above. This upper limit is unusual in D1.1 and requires monitoring both minimum and maximum interpass throughout the welding sequence. Fabricators must use dual-readout temperature monitoring to ensure the joint stays within the qualified band. Filler metals must match the 70 ksi minimum tensile while providing weathering-compatible chemistry for exposed joints.

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 A709 HPS70W

Category C in Table 5.11 applies to higher-strength steels where the combination of hardenability and residual stress requires elevated preheat. For A709 HPS70W 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 SMAW (low-hydrogen) at up to 3/4"

A709 HPS70W with SMAW (low-hydrogen)

Try Different Combinations

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

A709 HPS70W Welding Guides