FINITE-ELEMENT MODELING OF CREEP DAMAGE EFFECTS ON A MAGNETIC DETECTOR SIGNAL FOR A SEAM WELD HAZ-REGION IN A STEEL PIPE

Creep damage in steel causes a reduction of magnetic properties. A mat hematical model, previously formulated, accounts for this. Recently, t his model was used in finite element modeling (FEM) of a magnetic C-co re signal due to creep damage at a seam weld in Cr-Mo steam pipe. The FEM assumed unrealistically that in the absence of creep damage, the,v eld material and heat-affected zone (HAZ) and base metal all had the s ame magnetic properties. In this paper, new finite element simulations are presented for worst case relative permeabilities of 1271, 784 and 571 for base metal, HAZ, and weld material. Reduced permeability at t he weld results in a considerably reduced emf at low probe magnetic fi elds. However, creep damage does produce an additional emf reduction t hat is large enough to be detected, even when the creep damage does no t extend to the pipe wall surface. A method is suggested for calibrati ng the magnetic signal for weld, HAZ, and base metal effects.