[lucas]

There are a few methods used to inspect hydrogen damage. It is
important to know which type of hydrogen damage you are looking for (ie.
Wet Hydrogen Damage or High Temperature Hydrogen Damage).
WET HYDROGEN DAMAGE: This is a fairly easy failure mechanism to detect
and quantify if the proper testing equipment is utilized. I have used
Automated Ultrasonic systems which tend to remove a lot of the human
error, intern producing the best test results. There are several
multi-channel automated ultrasonic systems on the market today which
allow you to overlay the various shear wave angle (ie 45 degree) and
compression wave (ie 0 degree) transducer data. With both 0 degree and
45 degree data overlaid it is very easy to identify damaged areas and
also identify linkage between the swelling planer inclusions.
HIGH TEMPERATURE HYDROGEN DAMAGE: This one is a little more challenging
to detect and quantify in the early stages of damage. One method taught
by Chevron U.S.A. is a Velocity Ratio Comparison (VRC) and Shell Oil Co.
also has their own method. The VRC method initially uses a 0 degree
compression wave to locate noise ratio increase near the back 1/3 of the
backwall. When noise of a predetermined ratio is exceeded, a
oscilloscope is used in conjunction with a “0 degree shear” and “0
degree compression” wave transducers to determine the velocity of each
in the material at that point. The two velocities are then compared to
determine if they exceed the determined attenuation differences.