A nondestructive in situ electrochemical polarization method has been evaluated to measure the degradation of 347 grade SS superheater tubes used in fossil fuel-fired power stations. Polarization in 1 M NaOH gave good reproducibility and the measured electrochemical parameter (anodic peak current density i(p)) correlated well with increasing [Cr]/[Fe] ratio of sigma/carbide precipitates in both service and artifically aged tubes. The relationship between i(p) and the creep damage ratio for artificially aged specimens was established and it is proposed that for plant tests, using the portable cell, tubes should be examined with a view to repair or replacement when i(p) exceeds 30 muA cm-2.