Thanks sonikk. Now i am mostly happy i intend to get busy with the wire brush and give it a good sorting out.
I may well do the process again when its clean.
If in doubt, its always worth another application to settle your mind. We do several applications if the first attempt is dubious. And then if there is any further doubt we then call in the NDT team to do a Eddy current or ultrasound scan dependant on the material.