Gray cast iron produces a spark stream about 25
may be one of the stainless steels. A reaction that
produces a brown-colored liquid indicates' a plain
inches long. It is small in volume with fewer
carbon steel. A reaction that produces a brown to
sparklers than white cast iron. The sparklers are small
black color indicates a gray cast iron or one of the
and repeating. Part of the stream near the grinding
alloy steels with its principal element either
wheel is red, and the outer end of the stream is
chromium, molybdenum, or vanadium. Nickel steel
straw-colored.
reacts to the acid test by forming a brown to
The malleable iron spark test will produce a spark
greenish-black liquid. A steel containing tungsten
stream about 30 inches long. It is of moderate volume
reacts slowly to form a brown-colored liquid with a
with many small, repeating sparklers toward the end
yellow sediment.
of the stream. The entire stream is straw-colored.
The wrought iron spark test produces a spark
You get a different result when you do an acid test
stream about 65 inches long. It has a large volume
on nonferrous metals and alloys. As the material
with few sparklers. The sparklers show up toward the
desolves you'll see shades of green and blue instead
end of the stream and are forked. The stream next to
of the brown-black colors that usually appear on
the grinding wheel is straw-colored, while the outer
ferrous metals. Except on nickel and Monel, the
end of the stream is a bright red.
reaction is vigorous. Nickel's reaction to nitric acid
proceeds slowly and develops a pale green color. On
Stainless steel produces a spark stream about 50
Monel the reaction takes place at about the same rate
inches long, of moderate volume, and with few
as on ferrous metals, but the characteristic color of the
sparklers. The sparklers are forked. The stream next
liquid is greenish-blue. Brass reacts vigorously, and
to the wheel is straw-colored, and white at the end.
the test material changes to a green color. Tin bronze,
Nickel produces a spark stream only about 10
aluminum bronze, and copper all react vigorously and
inches long. It is small in volume and orange in color.
the liquid changes to a blue-green color. Aluminum
The sparks form wavy streaks with no sparklers.
and magnesium alloys, lead, lead-silver, and lead-tin
alloys are soluble in nitric acid, but the blue or green
Monel forms a spark stream almost identical to
color is lacking.
that of nickel and must be identified by other means.
Copper, brass, bronze, and lead form no sparks on the
grinding wheel, but you can identify them by other
It's easy to see that you'll need good visual skill to
means, such as color, appearance, and chip tests.
identify the many different reactions of metals to
nitric acid. Acid test kits are available containing
You'll find the spark tests easy and convenient.
several different solutions to identify the different
They require no special equipment and are adaptable
metals. Some of the kits can identify between the
to most any situation. Here again, experience is the
different series of stainless steel (300, 400 series).
best teacher.
They also can quickly identify low-alloy steels, nickel
steels, and various bronze alloys. All large repair
Acid Test
ships and shore repair facilities have a NON
When you need to identify metal quickly, the
DESTRUCTIVE TEST (NDT) laboratory. The
nitric acid test is the most common and easiest test
personnel assigned to them will help you to identify
used in the Navy today, but you can use it only in
various metals in more critical situations, or when you
noncritical situations. It requires no special training
need a greater accuracy on a repair job.
in chemistry. It is most helpful in distinguishing
between stainless steel, Monel, copper-nickel, and
carbon steels. Whenever you perform an acid test, be
PLASTICS
sure to observe all safety precautions.
To perform the nitric acid test, place one or two
Plastic materials are increasingly being used
drops of concentrated (full strength) nitric acid on a
aboard ship. In some respects, they tend to surpass
metal surface that has been cleaned by grinding or
structural metals. Plastic is shock resistant, not
filing. Observe the resulting reaction (if any) for
susceptible to saltwater corrosion, and in casting,
about 2 minutes. Then, add three or four drops of
lends itself to mass production and uniformity of end
water, one drop at a time, and continue observing the
product.
reaction. If there is no reaction at all, the test material
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