Comparing Standards: SNT-TC-1A and AS 4037

Greetings ~ A little more information regarding the articles to be inspected would help here. If I'm not mistaken, B31.3 is for "Process Piping" whereas the Aussie Std. (4037) is more about "Pressure Vessels" (like ASME BPVC)...(?)

In my opinion, the determination as to "which Standard is better" (i.e.; Which Standard should be adhered to) needs to be made by someone who is thoroughly knowledgeable about the service and the environment that the article is subjected to.

Training for interpretation of (Radiographic) weld defects abounds:

If you were in the US, your top choices might be AWS themselves or...

Radiographic Interpretation Training (for Instructor) at:
ASNT_Instructor -

Radiographic Interpretation Training (for Student) at:
ASNT_Student -

The UK equivalent of AWS is TWI (The Welding Institute), which I can state first-hand offers some mighty fine instruction(!)

There exists a veritable plethora of books and manuals on Radiographic NDT, each of which offers sample images that delineate the various/typical discontinuities found in plate and pipe welds.

If I may say so, your question allows all-too-much room for imagination in a response.

The types of discontinuities that you might NEED to be seeking will hinge upon a number of factors, not the least of which would be "Which welding process" is used to produce the welds in question (and is it manual or automated)...

... and (not-to-forget), it is POSSIBLE that the discontinuity of MAJOR concern (with your particular welding process) just *might* be best located using an ultrasonic method in lieu of radiography.

Each method of NDT has its own specific capabilities and limitations, and these should be thoroughly understood before addressing a ("new") "inspection regimen".

Wishing you the best in your endeavors ~