The services of an Applied Inspection NDT Level 3 consultant were requested by one of our customers to investigate porosity issues relating to subsea welds. The problem related to the interpretation of radiographs of riser welds; the radiographs showed that there was a considerable amount of porosity in the welds but there were differences of opinion in quantifying the amount, size and shape of the porosity. This resulted in differing views as to the correct determination, in relation to compliance with the code.
An impasse had been reached between the Energy Group and their client. Eighteen welds had been rejected to the code by the Australian NDT sub-contractor for excessive porosity. However, the client’s NDT Level 3 recommended over-ruling the NDT sub-contractor’s results for all 18 welds, based primarily on the fact that the radiographs contained a large number of ‘non-relevant’ pores, i.e. they were smaller than 0.8 mm – the threshold specified in the ASME VIII code.
These pores tended to make objective viewing of the films almost impossible as in most cases there were so many non-relevant pores that this issue clouded the interpretation; it was not possible for the radiographic interpreter to compare only the relevant pores against the porosity charts, as required by the Code.
The Applied Inspection NDT Level 3 consultant suggested that a possible solution to the impasse might be to digitise the radiographs, then ask our operator – who is a qualified radiographer (PCN and ASNT Radiographic Interpreter Level 2) and a software specialist to remove all non-relevant gas pores digitally, then he would re-assess the radiographs to the ASME code as an independent NDT Level 3.
The client accepted the proposal and a representative sample of 17 radiographs was selected and digitised using a Computerised Information Technology Limited (CIT) DR3000 Radiograph Film Digitisation System. The Applied Inspection software expert created a computer program to digitally remove the non-relevant pores the TIF files generated. He then produced PDF print-outs scaled at 100 per cent. The scaling was confirmed on the print-outs by measuring the two adjacent 100mm ‘rulers’ on each image (see below).
The following are screen-shots from the application written by our software expert showing the porosity; firstly unfiltered and then filtered.