you are asking specific supplementary from specific end user (Shell). Better to consult with their representative or your counterpart in this case.
Would not find it anywhere in the net, at least the updated version one.
Yes, as per Obturator recommend, it is MESC SPE 77-302.
In summary, Inspection Level criteria is segregated into 4 categories, having Level 1 is very basic (industrial standard) up to Level 4 (things like 100% X-ray, full PMI, full DPI, etc.). of course there are a lot more details in it.