PetroStreet

As per Annex E of API 941, Velocity Ratio Ultrasonic method has the detection capability of not only detecting fissures in base metal away from weldments but also differentiate between HTHA damage and plate laminations. What successful commercial techniques are available to meet this?
2) Why spectral analysis and backscatter could not differentiate between laminations and HTHA damage?

That's right but practically what's happening is application of combining advanced UT imaging & physics-based analysis. That is where Advanced backscatter comes in.
HTHA would be distributed microfissuring + methane voids however laminations would be planar reflectors. That is where the difference gets picked.
Commercially you can check with Eddyfi, Zetec, Olympus systems.

A thread found at PetroNavigator:
viewtopic.php?t=994&sid=759b58261e63bd1 ... a2f83b8a6d

There is a basic core issue why spectral analysis and backscatter could not differentiate between lamination and hydrogen attack as both defects affect ultrasonic energy in similar ways.
Spectral analysis looks at frequency dependent attenuation which both damages reflect.
Backscatter focuses on energy scattered which happens again in both the damages.