A516 Gr.65/70 Preheat for SAW — 1-1/2" to 2-1/2"

SAW (Submerged Arc Welding)

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

For pressure vessel longitudinal and circumferential seams, SAW is the primary process. Tandem or multi-wire configurations on specialized manipulators achieve consistent quality over seam lengths exceeding 40 feet. Flux basicity index per ASME Section II Part C determines the mechanical properties of the weld deposit.

SAW Tips for Pressure Vessel and Low-Temperature Steels

For A516 Grades 65/70 pressure vessel plate (35–38 ksi yield, Category B only), SAW F7A2-EM12K at 550–650 A is the standard for vessel longitudinal and circumferential seams. Annex A6.1.1 states that the primary use for neutral fluxes is multipass welding, especially when the base metal exceeds 1 in. [25 mm]; even then, strength and impact properties can change with depth of fusion, heat input, and number of passes. Category B minimum preheat is 50°F [10°C] over 3/4 thru 1-1/2 in, 150°F [65°C] over 1-1/2 thru 2-1/2 in, and 225°F [110°C] over 2-1/2 in.

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.

A516 Gr.65/70

ASTM A516 Grades 65 and 70 are the higher-strength pressure vessel plates in this specification, with 65 and 70 ksi minimum tensile strength and 35/38 ksi minimum yield respectively. Used in higher-pressure vessels, distillation columns, and reactor shells, they require low-hydrogen welding processes (Category B only in Table 5.11) due to their higher carbon equivalent compared to Grades 55/60. Carbon limits are 0.28% max for Gr.65 and 0.31% max for Gr.70 on thicker plate, pushing the CE-IIW into the 0.43-0.48 range where non-low-hydrogen SMAW is no longer prequalified. A516 Gr.70 is the single most specified plate grade for ASME Section VIII Division 1 pressure vessels, accounting for an estimated 40%+ of all vessel plate orders in North America.

Why This Preheat for A516 Gr.65/70 with SAW

Higher-strength pressure vessel plate requiring low-hydrogen processes only. This steel is prequalified only with low-hydrogen processes under Table 5.11. With SAW, the submerged arc process with granular flux produces controlled hydrogen levels, with flux condition being the primary variable. The 150°F minimum preheat balances the steel’s strength level and carbon equivalent against the hydrogen control provided by SAW. Non-low-hydrogen SMAW is not an option for this grade under D1.1 prequalified WPS.

Typical Applications for A516 Gr.65/70

Used in higher-pressure process vessels, distillation columns, reactor shells, thick-wall accumulators, high-pressure heat exchangers, and flare knockout drums. A516 Gr.70 plate is common in ASME VIII Division 1 vessels above 250 psi design pressure and in columns operating under hydroprocessing conditions. Longitudinal seams on heavy-wall vessels and nozzle-to-shell set-on welds are critical joint configurations requiring strict preheat compliance. Wall thicknesses in high-pressure service can exceed 3" on large-diameter vessels, with shell diameters from 24" to over 15 feet. Post-weld heat treatment per ASME Code is frequently required for A516 Gr.70 above 1-1/4" wall thickness, adding PWHT soak temperature (typically 1100-1200°F) and hold time (1 hour per inch of thickness) to the fabrication sequence. PWHT stress-relieves the weld and HAZ but does not change the preheat requirements during the initial welding operation.

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

Heavy plate with significant restraint and thermal mass — preheat is critical to maintain slow cooling for hydrogen escape.

Other Steels with SAW at 1-1/2" to 2-1/2"

A516 Gr.65/70 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.

A516 Gr.65/70 Welding Guides