A516 Gr.65/70 Preheat for SAW — over 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. Neutral flux is mandatory for multi-pass seams on these higher-strength grades to prevent alloying element dilution in the weld deposit from pass to pass. Preheat to 150°F for plate 3/4"–1-1/2"; 225°F above.

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". Flux type: active (A) for single-pass, neutral (N) for multi-pass. 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 225°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 over 2-1/2"

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

Other Steels with SAW at over 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