Arnab For evaulation of hydrogen damage, U.T attenuation principle will give better information. U.T attenuation if done systemmatically and with a refernce standard of the same material as that is being evaulated for hydrogen attack will give more info than back scatter to detect hydrogen related damages. U.T Back scatter may not give the same degree of reliabiity. Trust this is of help to you C.V.Srinivasan Nishi Engineers Pvt Ltd India April 28 E-mail:nishi@vsnl.com . >How does UT back scatter technique evaluate hydrogen attack >and what factor does make it superior than velocity or >attenuation principle?