that means all of the weld will be x-rayed....sometimes only a small part of a weld is x-rayed. sometimes all of it is x-rayed. just depends on what the application requires.
It depends on how it is worded. Usually it means "ALL" welds must be x-rayed. In most cases, if a weld is shot, it will be shot for the entire length of the weld unless the PO, contract, specifications, code or whatever the case may be calls for spot radiography. in which case, you will take random shots on a weld, but not over the entire length of the weld.
For example, if your contract calls for spot radiography on all welds, you might take one exposure on each weld. Whatever is agreed upon.
But in my opinion, if the contract calls for 100% radiography, it means every weld made must be radiographed over their entire length.
It also means that your radiation source must be x-ray and not a gamma source, if in fact it states "100% x-ray". If your specification states "100% radiography" then either source of radiation may be used.
You are correct. There is a difference in radiation sources, but I don't believe their intent is to actually use an x-ray tube. Sometimes people will refer to radiography as x-ray, not knowing the difference. In Europe they call it "bombing". But they don't use explosives.
Unless the client insists on x-ray, I think gamma would suffice as long as you can obtain the proper density and sensitivity. However, if these welds are in thin wall stainless steel, then I would recommend x-ray, but not for normal c/s or s/s welds. Also, if they are mechanized GMAW welds in the short circuiting mode, then I would recommend UT and not RT at all.
Insisting on x-ray over gamma for typical manual welds is just not practical, and I believe anyone insisting on using x-ray simply because the drawing states 100% x-ray is being unreasonable.
Specifications are very important and drawings, depending upon their source, may ends up governing how your inspections must be made. Our company works to specifications that require x-ray to be used. Of course it is for aluminum tanks. Just because the drawing states 100% x-ray, you cannot always assume that it is unreasonable and even if it is, it is still an offical requirement and would require a deviation from the approving authority before you could deviate from the requirement.
There are circumstances in which x-raying is impossible and you must necessarily use gamma rays, as for example when eletric power is not available or in great shortage.
Back in my days of erector engineer I was responsible for the construction of a natural gas compressing station, 40 miles away from the nearest sign of civilization. Electric power was supplied by a 75 kW diesel set. Radiographing of welds was carried out at night because when you do it a large area around the welds must be isolated.
I wasn't going to keep the badly needed generating set running all night just to feed an x-ray equipment. So, gamma raying was the natural choice. This is true also for oil and gas pipelines and other jobs where electric power supply is of great concern.
By the way, gentlemen, remember that the ASME Code Section VIII has different formulae to calculate the thickness of a pressure vessel when welds are 100% radiographed, spot radiographed or not radiographed at all. While in most cases is up to the vessel designer to make the choice, in some other cases it's mandatory to carry out 100% radiograph, as for vessels containing lethal gases.
Giovanni S. Crisi
Sao Paulo - Brazil
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