| A
section of the tube not less than 63 mm in length shall be
flattened cold between two parallel flat surfaces to a
distance between the plates (H) as calculated by the formula
given below, without showing any sign of a crack or flaw.
(1 + e) t
H
=
-----------------
E + t/D
where
t
= specified thickness of tube (mm)
D = specified outside diameter of the tube (mm)
e
= a constant, as given below
e
= 0.07 for Carbon steel with maximum specified carbon 0.19% or
greater
e
= 0.09 for Carbon steel with
maximum specified carbon 0.18% or less
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