FINITE-ELEMENT SIMULATION OF MAGNETIC DETECTION OF CREEP DAMAGE AT SEAM WELDS

Using appropriately modified magnetization curves for each element of creep-damaged material, a finite element calculation has been carried out to simulate magnetic detection of non-uniform creep damage around a seam weld in a 2.25 Cr 1 Mo steam pipe. The magnetization curves for the creep-damaged elements were obtained from an earlier model for th e magnetic effect of a uniformly creep-damaged material as given by Ch en, et al. In the finite element calculation, a magnetic C-core with p rimary and secondary coils was placed with its pole pieces flush again st the specimen in the vicinity of the weld. The secondary emf was sho wn to be reduced when creep damage was present inside the pipe wall at the cusp of weld and in the vicinity of the cusp. The C-core detected the creep damage best if it completely spanned the weld seam width. A lso, the current in the primary needed to be such that the C-core was not magnetically saturated.