Well there are a few reasons,

1) There are many NDT techniques, the best technique is usually selected to meet the need of the inspection. You question might be rephrased "why not use liquid penetrant instead of RT" and the answer would be that PT can't detect defects that are not open to the surface.

2) TOFD requires expensive gear and requires a highly trained technician. Even so for some welds, especially for looking for IGSCC in stainless material various ultrasonic techniques are used including TOFD, but for plain old carbon steel RT works well.

3) RT is a well established technique, gives accurate flaw sizing (harder to do with ultrasonic) and if you did you baseline with RT back in the day before there were fancy UT techniques then why not do it again to compare against baseline.

Here is a link that might help.

http://en.wikipedia.org/wiki/Nondestructive_testing

Its very nature things, once you get used to nde /ndt,

There are many method to detect fault of an object without destroy it. generally we divide them into RT, UT, Eddy, PT and MT etc 5 large classes.

They have different usage for different fault. sometime they can exchange each other. others not.

TODF is one of UT. and developped since last 70's. and place more and more important role. Hoever they are not as direct view as photograph does. so they cannt replace RT.

From RT you can view almost all inside of object. so you can judge what take place.

Today color RT has been invented sothat we get more information from it.

CT is also belong to the RT.

Hello Guest,

Just some advice for you.

CAPITALS IN A FORUM, are regarded as shouting at the reader.

In that, the use of all CAPITALS is regarded as bad manners.

Could you consider that, please, when you next place a Post in an Internet Forum, including CR4 Forum.

Thank you in anticipation.

Kind Regards....