Arc Machines 307 - Manual (Page 155)

Arc Machines, Inc. Model 307 Orbital Tube Welder Training
Document No. 740096 Chapter 16. Page 2.
Rev. A
Hydrogen mixtures
Additions of hydrogen to the shielding gas produces a reducing atmosphere
which inhibits the formation of oxides, reduces slag formation, and for this
reason is often used for welding nickel-based alloys.
The argon/hydrogen mixture produces a cleaner-appearing weld on stain-
less steel at similar levels of oxygen contamination than pure argon. It has
also been used as an I.D. purge for HP and UHP semiconductor applications
to reduce discoloration. However, hydrogen and hydrogen mixes from cyl-
inders typically contain higher amounts of oxygen and moisture than argon
supplied in dewars and thus oxygen contamination may outweigh any ben-
efits of using hydrogen additions to prevent discoloration.
Hydrogen mixes produce smoother weld beads as the wetting characteris-
tics are improved by the reduced surface tension of the weld metal. The
weld bead is typically narrower, but may not be narrower on very low-sulfur
materials. However, the arc is less stable with a tendency towards arc wan-
der, and tungsten life is se-
verely affected. Since the
addition of hydrogen affects
penetration, precise control of
the gas mixture is essential to
maintain the consistency of
the weld, especially for thin-
walled materials. Hydrogen is
detrimental to the properties
of some metals. It may cause
hydrogen induced cracking,
porosity, etc. Hydrogen gas
is flammable and
potentially explosive. Mix-
tures greater than 5% total
volume are not recommended
for safety reasons.
Verify that the gas type or
mixture is compatible with the
alloy being welded. For exam-
ple gas mixtures containing
hydrogen should never be
used on carbon steel or titani-
um. The helium/argon mix-
ture is the preferred gas for
welding carbon steel.
Cleanroom orbital welding operator adjusts flowrate
for purging. For high-purity applications separate
flowmeters are used for I.D. and O.D. purges.
Magnehelic ® gauges are mounted on the wall. Photo
courtesy of Murray Co.