Heat input - FCAW verses SMAW

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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=B0 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.=20


Les


Re: Heat input - FCAW verses SMAW

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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.

Re: Heat input - FCAW verses SMAW
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



Re: Heat input - FCAW verses SMAW

Randy Zimmerman wrote:
Quoted text here. Click to load it
no one
just
rate of
thicknesses.
with


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
Quoted text here. Click to load it
1inch wide across the fillet face *in one run*!

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


Re: Heat input - FCAW verses SMAW
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

Randy Zimmerman wrote:
Quoted text here. Click to load it
no one
just
rate of
thicknesses.
with


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
Quoted text here. Click to load it
1inch wide across the fillet face *in one run*!

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



Re: Heat input - FCAW verses SMAW
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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