CEMP-E
TI 809-26
1 March 2000
(4) A primary disadvantage of ultrasonic testing is that it is highly dependent upon the skill of the
UT technician.
(6) The cost of the equipment is considerably more that MT, but also much less than RT. The cost
of more sophisticated UT units capable of computer-generated imaging approaches, and sometimes
exceeds, the cost of RT equipment.
(7) UT indications are difficult to interpret in certain geometric applications. It is ineffective for fillet
welds unless very large, and then only for the root area for fillet welds above approximately 18 mm (3/4
in.). When backing bars remain in place, it is difficult to distinguish between the backing bar interface
and cracks, slag lines, or lack of penetration or fusion at the root. With partial joint penetration groove
welds, it is difficult to distinguish between the unfused root face and discontinuities near the root. In
welded beam-to-column moment connections, the interference of the web with inspection of the bottom
flange makes direct evaluation of the area beneath the weld access hole difficult. Second-leg
inspections, not as accurate or as reliable as first-leg inspections, are necessary to evaluate the entire
depth of many welds unless the weld face is ground flush. Discontinuities located just below the weld or
material surface are also difficult to detect.
(8) UT is best suited for planar discontinuities such as cracks and lack of fusion, discontinuities
which are generally most detrimental to joint performance when oriented transverse to the direction of
loading. These discontinuities tend to be irregular with rough surfaces, and therefore reflect signals even
when not exactly perpendicular to the direction of the pulse. Laminations and lamellar tears are also
easily detected. Smooth surfaces, such as unfused root faces, would redirect a signal and provide a
weak response unless oriented perpendicular to the pulse. Rounded and cylindrical discontinuities such
as porosity disperse the signal, also providing a weak response, but such rounded discontinuities are
rarely detrimental to joint performance. Slag inclusions are irregular and provide easily identifiable
responses. See Table D-4.
(9) The cost of ultrasonic testing is considerably more than PT or MT, and considerably less than
RT. However, UT is the best method for detection of the most serious weld discontinuties in a wide
variety of thicknesses and joints. The time, and therefore cost, of UT inspection can vary greatly,
depending upon the quality of the weld to be inspected. A good quality weld will provide few responses,
requiring little evaluation time. A difficult configuration, or a poor quality weld, will require numerous
time-consuming evaluations and recording of test data.
D-8
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