Hi

In my guess you can go for Thermography method. In this you have to supply a current on a steel member then u can check it.

best

dear Moawiah Mubarak, i think the best inspection method is the infrared electrical thermography survey you can result a significant results about the loss in cross-sectional area due to stresses accumulation and degradation.

you can read more in this reference:

http://carelabz.com/electrical-infrared-thermography-inspection-important/

Hi Moawiah Mubarak,

The best way I have found in the past, is using high energy X-ray Betatron to penetrate up to 1 M of concreate and the grouted pre-stressed cable. This clearly shows the corroded area of cable on the digital image or X-ray film.

Dear Moawiah Mubarak

Actually, you can use the infrared electrical thermography mapping.

Good luck