Hi BB, Thanks for your reply, I completely understand your interpretation now!
My interpretation is slightly different, the 6 monthly prolongation verifies the welder has been working within his range of approval within the last 6 months rather than continuously for the past 6 months. Meaning if I break my leg and take a month off or if I go on holiday for a month or 3, I wont come back 'unqualified'.
I'm not particularly saying my interpretation is the correct one, the standard is actually quite vague under section 9.2 with the requirements for prolongation.
It's good to see different interpretations and highlight vague areas in the standards though!