Reduced available energy to strike tube outside energy.

• Reduced by amount returned as the frontwall signal
• Reduced by amount returned by the sleeve tube interface signal (weld aperture is less than focal spot).
• Reduced by the dispersion expected after the sound passes through its focal spot.

Minimal energy returned

• The reflected sound (energy) must be perfectly perpendicular to the tube outside diameter to return back through the weld aperture.
• The backwalls signal's additional travel distance causes additional energy dispersion.
• The differing weld grain orientation may reflect a portion of the returning signal back into the tube rather than letting it travel back through the weld.

Tube outside diameter deposits

• Absorbs the UT sound
• Rougher outside diameter surface deflects more of the return energy away from the weld aperture.
• Increases the travel path with associated additional energy dissipation.

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