We have inspected a tube bundle using RFT, and the output was the remaining thickness of each tube, how can I determine the tube remaining thickness below which I would plug the tube?
Is this a CODE compliant HX?
What is the design min wall?
That is your answer.
For other applications it depends on what you are comfortable with.
I have seen anything from 40% to 90% wall loss used as a plugging criteria.
It depends on how critical it is when a tube fails and how fast they are thinning.
Do you know the thickness at the thinnest location in each tube?
Have you removed a tube to verify the readings?
May also check with the fixed equipment inspection team, if existed in your plant, who may set up the minimum thickness of the tubes as required to meet the mechanical integrity criteria and the possible remaining service life.