Spot Radiography & Full Radiography

Full radiography would require that every inch of weld length be radiographed. For a big vessel this would mean hundreds of shots and a long process to complete, but you could then be assured that there are no flaws that will cause you a failure later.

Spot radiography on the other hand would use a philosophy like shoot 1% of the total weld length, at 10 spots, particularly critical spots like junctions to get 10% of the length. If there are no flaws found then pass. If a flaw is found then do another 10% just to make sure it is a one off. (repeat if another flaw is found, and if flaws continue to be found you will end up doing full radiography).

Typically if the vessel is very critical (high pressure, containing toxic or corrosive material) then you would do full radiography. If the vessel is a water tank, or as you mention an atmospheric tank, spot radiography is generally good enough.

Ok i understand Sir..

So, the meaning of 10 % spot radiography is 10 % of total weld length.

Then Sir, what is the relationship to Joint Efficiency (E), why ASME stated that joint efficiency for spot radiography is 0.85 then for full radiography is 1?

Thanks.

For pressure vessels go to ASME VIII UW-11. Joint category or joint efficiency.

Spot: A % of the total lenght of the weld.

Random: (For pipe welds): Total lenght of the weld, over the determinate lot of welds.

Full: 100% of the welds

Spot Radiography requires one (1) shot for every 50' of weld and all tee joints...

i am not understand of the meaning -

every 50' of weld and all tee joint