Non-Invasive Inspection 

NII Non-Invasive Inspection – is the application of NDT techniques to the outside of a closed vessel or tank as an alternative to opening the tank or vessel up and performing NDT from the inside.
Non-Invasive is not a new term but with the move away from statutory periodic inspections, which usually required that internal inspections be performed, to a risk-based approach, the term has taken on a new interpretation.

Performing internal inspections carries a large preparation cost: draining contents; preparing access; monitoring the confined space. If equivalent inspections can be performed using non-invasive techniques applied to the outside then the cost savings can be marked.

However, it is important to show that the non-invasive techniques have a capability either equal to the internal inspections they replace or sufficient to show that the vessel or tank is fit for purpose.
Of course, for those in the nuclear industry NII really means the Nuclear Installations Inspectorate!

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