Eddy current inspection of stainless steel steam/methane
reformer tubes is employed to identify crack-like defects. The principal behind
eddy current inspection is that a defect changes the energy flux induced in the
material through a magnetic field. Caution
should be taken when applying eddy current as variations in material
permeability can result on false positives.
For austenitic stainless steels, the energy field penetrates up to 1-in.
deep which is greater than the wall thickness of most tubes. This technique can
be is performed both externally and internally.
Therefore, so that catalyst removal is not required does not need to be
removed and allows rapid inspection of tubes at travel speeds up to 1 ft/s (0.3
m/s).
Some operators have found it useful to assess data from a
combination of technologies, i.e., diametral, laser profilometry, eddy current,
and ultrasonic. The advantage of using multiple technologies is a
cross-comparison of results, particularly for the case where a damage mechanism
may be sensitive to multiple methods.
Most commercial equipment will grade each tube in terms
of relative creep damage based on characteristic signals within a particular
type of material. In addition, some equipment can also measure wall thickness
ultrasonically and tube diameter as it travels along the tube. Diametric
changes in tubes can also be determined through laser profiling from the tube
ID. These additional measurements combined with eddy current and/or ultrasonic
test results can allow an assessment of relative creep damage. Grading of
individual tubes combined with subsequent repeat examinations may enhance tube
damage trending and ultimate tube replacement planning.
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