Your post lacks information, so Ill take a shot by assumption(s).
It depends on the desing code you use, and engineering design requirements (i.e. client specifications). If you're using ASME B31.3, either your client specs will tell you RT percentages. Otherwise B31.3 by means of 341.4 will tell you 5% RT for circ. butt and miter groove welds in Normal Fluid service fully by random radiography. For cat. D (341.4.2), no RT is required. For cat M, 20% RT fully by random radiography. For severe cyclic, 100% RT (341.4.3). For percentages on VT check para 341.
Please make sure to discuss with your client (e.g. during a kickoff meeting) what is defined as a lot when applying random NDE.
And to add a bit to XL83NL's post: I think know the root of your question. Under ASME B31.1 & B31.3, there is no recognized 'Spot' requirement. When a weld is RT's, the entire weld is RT'd; not just a 'spot'. So under 'Normal Fluid Service', 5% of all buttwelds [pipe-to-pipe circumferential buttwelds] are RT'd, 100% of the way around.
"Spot' RT is almost always associated with pressure vessel fabrication, not pipe fab/construction.
Clause 341.5.1 clearly states the requirements of Spot Radiography as defined in B31.3.
The Inspector selects or approves the locations of spot radiography,
Regards,
Kiwi
Gotta [respectifully] disagree: 341.5 sez: Supplementary Examination " . . . may be specified by the engineering design to supplement the examination required by para. 341.4." Spot RT is a Supplementary Examination that is not required by ASME B31.3, but may be specified by the designer to supplement the required testing. All Code-required RT has to be 100% of the weld being RT'd.
