Hello, my name is Nina Giombetti
and I’m a sales engineer for Olympus Ultrasonic Thickness Gages.
Today, we are going to discuss
the differences between Echo to Echo and
Thru-Coat measurements on the 38DL PLUS.
The 38DL PLUS has two unique features
for measuring the remaining wall thickness of pipes,
tanks or other metal material
that may be externally painted or coated.
In this discussion I am going to be using a thin piece of plastic
to simulate a coating thickness.
The first feature is called Echo to Echo.
In this feature the 38DL PLUS
measures the time of flight
between multiple back wall reflections within the metal
to display the true metal thickness
underneath the painted or coated surface.
Echo-to Echo is the most common method of measuring
remaining wall thickness on materials
that are painted or coated.
A limitation of this feature
is that when the internal surface becomes extremely eroded or corroded
multiple back wall echoes may not exist,
as displayed in this signal here.
Another limitation of Echo to Echo
concerns thick materials,
where material attenuation and irregular back wall surface conditions
make it difficult to get two back wall echoes to occur.
On materials over 15 millimeters
there can be echo interference
of unwanted mode converted echoes,
which occur between the first and second back wall echoes.
Here I am coupled to a 20 millimeters test block
and the gage is making detection of the first back wall echo
but the second back wall echo is very low in amplitude
and difficult to measure.
The last limitation regarding Echo to Echo
concerns measuring thin materials,
it is extremely difficult or impossible
to separate the time of flight between multiple back wall echoes
when the wall thickness is below 2.5 millimeters.
In this case here we are coupled
to a 1 millimeter test block
and you cannot clearly separate the time of flight
between multiple back wall echoes.
The second feature the 38DL PLUS has
to measure the remaining wall thickness
for pipes or tanks that may be externally painted or coated
is called Thru-Coat.
In this technique the gage uses
a single back wall echo to measure
both the coating thickness
and the steel thickness at the same time.
The advantages of Thru-Coat
are that it can make proper thickness measurements
when multiple back wall echoes do not exist
or when measuring thick and thin materials
as demonstrated here.
Here is a Thru-Coat measurement
when multiple back wall echoes do not exist.
Here is a Thru-coat measurement
on a 20 millimeter test block.
Here is a Thru-coat measurement
on a 1 millimeter test block.
The limitations of Thru-Coat
are it may not work properly
If the thickness of the coating
is below 0.125 millimeters
or if the external coated surface is rough or irregular
it may be difficult for Thru-Coat to resolve
the thickness of the coating
and the thickness of the steel.
When measuring a painted material
if Thru-Coat can not resolve the coating
and steel thickness properly
then the thickness value of the coating
will be blank and the thickness of the material
will be incorrect.
The truly unique feature of the Thru-Coat transducers
are that they can be used in Thru-Coat mode
where they can measure the thickness of the coating
and the thickness of the steel using a single back wall echo.
These transducers can also be used
in Echo to Echo mode
where they will measure the true metal thickness
using a multiple back wall echoes
or in standard measurement mode,
measuring to the first back wall echo.
This completes the discussion
of the differences of Echo to Echo
and Thru-Coat measurements on the 38DLPLUS.
For more information, please visit our website
at www.olympus-ims.com,
or contact your local sales representative.