Welding Inspection & Metallurgy API ICP Self Study Notes

Proof Stress
Re0.2%
Since it is difficult to measure
elastic limit, proof stress is the
maximum stress a material can
withstand without taking more
than a small amount of set. The
amount is usually specified as
the smallest that can be
measured by the extensometer,
namely, 0.01 percent in 2 inch.
As with the yield strength, the
preferred method of measuring
proof stress is by using a 0.01
percent offset. This is shown in
the figure given below (the
proportional limit and yield
strength are also shown to
explain the term clearly).