Heat input - FCAW verses SMAW

I'd like to hear some opinions on heat input of FCAW verses SMAW when welding a 1-1/2" thick reinforcing pad to a 1-1/2" thick rolled and welded cylinder. Both items are SA516-70. The weld required is a 3/4"
fillet weld, with a min. pre-heat of 200 F. This would be welded with one welder on each side of the cylinder.
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
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Self-Shielded FCAW, or Gas-Shielded FCAW? Makes a huge difference.
If you are welding this outside then it would be self-shielded. Gas-Shielded FCAW will be hotter, but will also give you a better cleaner weld.
You haven't specified your filler metals. What diameters, and types, of wire and electrode.
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I doubt that the total heat input would be greatly different however no one in their right mind makes a nickel welding with stick these days. It just takes too long!!! Your preheat, interpass and post heat will control the cooling rate of the HAZ. On just 44w structural we preheat to 250 on these thicknesses. Randy
I'd like to hear some opinions on heat input of FCAW verses SMAW when welding a 1-1/2" thick reinforcing pad to a 1-1/2" thick rolled and welded cylinder. Both items are SA516-70. The weld required is a 3/4" fillet weld, with a min. pre-heat of 200 F. This would be welded with one welder on each side of the cylinder.
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
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Randy Zimmerman wrote:

Les
Not expert on practice - defer to Ernie and Randy on this! But looked at these issues as scientific investigator back in 1990's.
In general, you are always looking at the heat input per unit length *per weld run* - not the summed heat input for all the runs.
FCAW can achieve very high properties, but there can be a *maximum* heat input (kJ/mm, ie. heat/length) which you must not exceed. In North Sea oil practice in the 1990's, welding tough HSLA steels for oil rigs in the cold and stormy North sea, there was a restriction for some high-toughness welds that the fillet face or bead width should not exceed 12mm (1/2inch). Easy to do, easy the check, and hits the technically needed target. So run many "stringer" beads, rather than few big ones. This one, about max ht input, is about the weld freezing quickly from molten metal and having a fine structure.
OTOH, many specs have mentioned a *minimum* heat input. That is about the weld not cooling quickly, so you don't get a hard HAZ. Only a concern if the HAZ is a quench-hardenable material - ie. carbon steel. But what you can achieve with a high heat input, you can get from applying preheat. And the weld will still freeze fast if the weld run is small. 1700C going for 200C is about as fast as 1700C going for 20C in the initial 1700C to say 1500C range. So if you have a maximum heat input for toughness, you can still get a soft HAZ and/or hydrogen dispersion by preheat (and post-heat if this is a really challenging case).
You can slow down a FCAW a lot and make huge runs - I know from playing around, which would give slow cooling rates and a softer HAZ if the material being welded were a steel with significant carbon - say

Don't know the material spec. you refer to - or even if it is a steel! Mention made of Nickel. The Continental European and Japanese low-carbon (0.03%C to 0.06%C) TMCR HSLA steels (the type which US steelmakers *do not* (?) make - despite proclaiming "TMCR" and "HSLA" on their websites) never harden their HAZ and low heat input, so short HAZ temperature excursion, limits grain-growth and improves HAZ toughness.
RS
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Good points Richard. My Canadian strucural code book is over twenty years old but I do know that later codes have heat input guidlines in joules per metres in Canada. I imagine the D1.1 has similar guidlines in Joules per foot? My codes limit single pass to 3/8 inch fillets or 10 mm on prequalified joints unless you go to submerged arc. Randy

Les
Not expert on practice - defer to Ernie and Randy on this! But looked at these issues as scientific investigator back in 1990's.
In general, you are always looking at the heat input per unit length *per weld run* - not the summed heat input for all the runs.
FCAW can achieve very high properties, but there can be a *maximum* heat input (kJ/mm, ie. heat/length) which you must not exceed. In North Sea oil practice in the 1990's, welding tough HSLA steels for oil rigs in the cold and stormy North sea, there was a restriction for some high-toughness welds that the fillet face or bead width should not exceed 12mm (1/2inch). Easy to do, easy the check, and hits the technically needed target. So run many "stringer" beads, rather than few big ones. This one, about max ht input, is about the weld freezing quickly from molten metal and having a fine structure.
OTOH, many specs have mentioned a *minimum* heat input. That is about the weld not cooling quickly, so you don't get a hard HAZ. Only a concern if the HAZ is a quench-hardenable material - ie. carbon steel. But what you can achieve with a high heat input, you can get from applying preheat. And the weld will still freeze fast if the weld run is small. 1700C going for 200C is about as fast as 1700C going for 20C in the initial 1700C to say 1500C range. So if you have a maximum heat input for toughness, you can still get a soft HAZ and/or hydrogen dispersion by preheat (and post-heat if this is a really challenging case).
You can slow down a FCAW a lot and make huge runs - I know from playing around, which would give slow cooling rates and a softer HAZ if the material being welded were a steel with significant carbon - say

Don't know the material spec. you refer to - or even if it is a steel! Mention made of Nickel. The Continental European and Japanese low-carbon (0.03%C to 0.06%C) TMCR HSLA steels (the type which US steelmakers *do not* (?) make - despite proclaiming "TMCR" and "HSLA" on their websites) never harden their HAZ and low heat input, so short HAZ temperature excursion, limits grain-growth and improves HAZ toughness.
RS
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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
I'd like to hear some opinions on heat input of FCAW verses SMAW when welding a 1-1/2" thick reinforcing pad to a 1-1/2" thick rolled and welded cylinder. Both items are SA516-70. The weld required is a 3/4" fillet weld, with a min. pre-heat of 200 F. This would be welded with one welder on each side of the cylinder.
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
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