heat input is commonly measured by the product of amperage and voltage normalized over the travel speed. The formula is given as
Heat Input = Amps x Volts x 60 / travel speed
and the output is in joules per inch or joules per mm depending on the units with which you started. The formula gets a little goofy with pulsed arc processes since the amps and volts can be effected to a significant extent by the wave shape of the votage and amperage trace and that will affect the cooling rate of the weld deposit.
Your minimum preheat of 200F will tend to hold down the maximum HAZ hardness. 516 Gr 70 is basically a carbon manganese steel that can get a pretty hard HAZ since the carbon content is upwards of 0.2%. You also need to consider what your maximum interpass temperature is going to be if you have two welders banging away at the job at the same time. I'd think you'd want to keep the part under 400 F or so to minimize grain growth in the HAZ. Make sure the preheat is of the uniform soaking type. All too often the parts are locally at the preheat range, but by the time the welder gets his stinger ready and his hood on, the parts have cooled to less than the required preheat. I like to train the welders to go 50 F or so over the min preheat just to make sure...
Electrode selection will pretty much tell you your productivity. Some flux core wires are quite productive, as well as large diameter stick electrodes. But the common "all position" E71-T1 wire in the 0.045 diameter isn't much more productive than 5/32 E7108 SMAW. If you have the opportunity to use large diameter SMA wire, by all means go ahead. If you're looking for maximum productivity, 1/16 diameter FCAW using E70T-1 that works in the flat and horizontal positions is a good bet. But I'm old fashioned. I like big diameter SMA (3/16 and up) or 1/16 spray GMA.
Self shielded FCAW wire doesn't have a good history of high notch toughness. The 516Gr 70 is usually selected for a base material when there's a need for low temperature notch toughness. (It gets its toughness with grain size control). So if you're using the self shielded wire, you might want to pay attention to toughness in the weld deposit too. If you're using the 71-T1 you might want to pay attention to how fresh the wire is. It definitely has a shelf life. The older it is, the more hydrogen it picks up. If you see chicken tracks on the bead or under the slag, the wire is tired.
If you're concerned about a hard HAZ you might employ a temper bead technique. I'd think you'd want to keep your heat inputs in the 50-70 Kj per inch range. If you're worried about underbead cracking, using a butter layer technique can be quite effective too. The very first time I saw underbead cracking was in a 516 Gr 70 pressure vessel. It was a highly restrained weld joint on an internal baffle welded to the shell. IIRC it was a half inch double welded fillet but since the baffle was curved there was no way distortion could relieve any of the residual stresses from welding.
Make sure the plate is clean of all oily residue. Don't use spray type anti spatter compounds. And don't weld over the temperature indicating crayon marks.
Good luck.
J
Would one process be more suited to this to avoid an extremely hard HAZ? My thoughts are that FCAW will put more heat into the material.
Any thoughts on this would be appreciated.
Les