The programme succeeded first in the detection of cracks within the ring – confirming the results of the manufacturer’s inspections. TWI continued its work by carrying out an encoded inspection to achieve accurate measurement of crack length and through-wall extent.
In terms of acceptance criteria and applicability to any future work on this component, the inspections appear to lie outside the scope of current codes. With over 40 years’ experience in the Engineering Critical Assessment (ECA) approach or 'fitness-for-purpose analysis' widely accepted by a range of engineering industries, TWI considers it more appropriate to adopt ECA. This will allow NDT results to be interpreted against tolerable flaw sizes and enable classification of the root in terms of safe remaining life (e.g. Class 1: Unfit for purpose, Class 2: 1 year remaining life, Class 3: two years remaining life, etc.). The approach will make use of information from the inspection results on size (length and through-wall extent), position and orientation of flaws within the ring rather than just their circumferential extent.
For information please email contactus@twi.co.uk