Alloy B-2
Alloy B-2 is an alloy, rich in
nickel and molybdenum, which
has been developed primarily
for resistance to reducing acid
environments, particularly hydro-
chloric, sulfuric and phosphoric.
Its resistance to these acids in
pure forms is unsurpassed, but
the presence of ferric and other
oxidizing ions in quantities as
low as 50 ppm can dramatically
degrade the resistance of this
alloy.
Alloy C-276
Alloy C-276 is a nickel chro-
mium-molybdenum alloy having
perhaps the broadest general
corrosion resistance of all
commonly used alloys. It was
developed initially for use with
wet chlorine, but it also offers
excellent resistance to strong
oxidizers such as cupric and fer-
ric chlorides, and to a variety of
chlorine compounds and chlorine
contaminated materials. Because
of its broad chemical resistance,
Alloy C-276 is the second most
popular alloy, following T316SS,
for vessels used in research and
development work.
Nickel 200
Nickel 200 is one of the
designations of commercially
pure nickel. It offers the ultimate
in corrosion resistance to hot
caustic environments, but
its applications are severely
restricted because of its poor
machinability and resultant high
fabrication costs.
Titanium
Titanium is an excellent
material for use with oxidizing
agents, such as nitric acid, aqua
regia and other mixed acids. It
also offers very good resistance
to chloride ions. Reducing acids,
such as sulfuric and hydrochlo-
ric, which have unacceptably
high corrosion rates in their pure
form can have their corrosion
rates in titanium reduced to
acceptable levels if relatively
small quantities of oxidizing ions,
such as cupric, ferric, nickel or
even nitric acid are present to act
as corrosion inhibitors.
This phenomenon leads to
many successful applications for
titanium in the hydrometallurgy
field where acids, particularly
sulfuric acid, are used to leach
ores. In these operations the
extracted ions act as corrosion
inhibitors.
Prospective users must
remember that titanium will burn
vigorously in the presence of
oxygen at elevated temperatures
and pressures. While there have
been many successful applica-
tions in hydrometallurgy where
oxygen and sulfuric acid are
handled in titanium equipment,
the danger of ignition is always
present and must be protected
against whenever titanium and
oxygen are used together.
Commercially pure titanium
is available in several grades.
Grade 2 is the material most
commonly used for industrial
equipment since it can be fabric-
ated by welding and is approved
by the ASME Code for Unfired
Pressure Vessels. Grade 4, which
has slightly higher trace levels
of iron and oxygen, has higher
strength than Grade 2 but it is
not suitable for welding and it is
not covered by the ASME Code.
Since most Parr vessels are
not welded, they usually are
made of Grade 4 to obtain higher
working pressures than can be
obtained with Grade 2. Grade
7, containing small amounts of
palladium, and Grade 12 contain-
ing small amounts of nickel and
molybdenum, offer enhanced
resistance to certain environ-
ments and can be used for Parr
reactors and pressure vessels if
suitable billets can be obtained.
Zirconium
Zirconium offers excellent
resistance to hydrochloric and
sulfuric acids, however, as with
Alloy B-2, oxidizing ions such as
ferric, cupric and fluorides must
be avoided. Zirconium also offers
good resistance to phosphoric
and nitric acids, and to alkaline
solutions as well. Two different
grades are available: Grade 702
which contains hafnium is the
standard commercial grade offer-
ing the best resistance to most
corrosive agents, Grade 705
contains small amounts of both
hafnium and niobium which
increases the strength charac-
teristics and allows for higher
maximum working pressures
for a vessel. Grade 702 typically
offers better corrosion resistance
than Grade 705. Grade 702
is also more widely available
from commercial stocks of raw
materials.
Carbon Steel
Carbon Steel is usually used
for laboratory reactors only
when it is desired to duplicate
construction material used in
plant equipment. Because it rusts
easily, carbon steel vessels are
not carried in stock and must be
made to order, often resulting in
costs higher than stainless steel
equipment despite the lower
material cost for carbon steel.
12
P a r r I n s t r u m e n t C o m p a n y
Materials, Continued
