Hardness tests are made either on the outside or the inside surfaces on the end of the tube as appropriate.
The standard 3000-kgf Brinell load may cause too
much deformation in a thin-walled tubular specimen. In this
case the 500-kgf load shall be applied, or inside stiffening by
means of an internal anvil should be used. Brinell testing shall
not be applicable to tubular products less than 2 in. (51 mm) in
outside diameter, or less than 0.200 in. (5.1 mm) in wall
thickness
The Rockwell hardness tests are normally made on
the inside surface, a flat on the outside surface, or on the wall
cross-section depending upon the product limitation. Rockwell
hardness tests are not performed on tubes smaller than 5⁄16 in.
(7.9 mm) in outside diameter, nor are they performed on the
inside surface of tubes with less than 1⁄4 in. (6.4 mm) inside
diameter. Rockwell hardness tests are not performed on annealed tubes
with walls less than 0.065 in. (1.65 mm) thick or
cold worked or heat-treated tubes with walls less than 0.049 in.
(1.24 mm) thick. For tubes with wall thicknesses less than
those permitting the regular Rockwell hardness test, the
Superficial Rockwell test is sometimes substituted. Transverse
Rockwell hardness readings can be made on tubes with a wall
thickness of 0.187 in. (4.75 mm) or greater. The curvature and
the wall thickness of the specimen impose limitations on the
Rockwell hardness test. When a comparison is made between
Rockwell determinations made on the outside surface and
determinations made on the inside surface, adjustment of the
readings will be required to compensate for the effect of
curvature. The Rockwell B scale is used on all materials having
an expected hardness range of B0 to B100. The Rockwell C
scale is used on material having an expected hardness range of
C20 to C68
Superficial Rockwell hardness tests are normally
performed on the outside surface whenever possible and
whenever excessive spring back is not encountered. Otherwise,
the tests may be performed on the inside. Superficial Rockwell
hardness tests shall not be performed on tubes with an inside
diameter of less than 1⁄4 in. (6.4 mm).
