Radiography Testing and Heat Exchangers

I suspect/assume you are talking about ASME markings when you refer to RT1, RT2, .....

As per the BPVC Section VIII Div-1, UG-166:

(e) When radiographic or ultrasonic examination has
been performed on a vessel in accordance with UW-11,
marking shall be applied under the Code Symbol as
follows:
(1) "RT 1" when all pressure-retaining butt welds,
other than Category B and C butt welds associated with
nozzles and communicating chambers that neither exceed
NPS 10 (DN 250) nor 11⁄8 in. (29 mm) wall thickness
[except as required by UHT-57(a)], satisfy the full radiography
requirements of UW-11(a) for their full length; full
radiography of the above exempted Category B and C butt
welds, if performed, may be recorded on the Manufacturer's
Data Report; or
(2) "RT 2" when the complete vessel satisfies the
requirements of UW-11(a)(5) and when the spot radiography
requirements of UW-11(a)(5)(b) have been applied; or
(3) "RT 3" when the complete vessel satisfies the

spot radiography requirements of UW-11(b); or

(4) "RT 4" when only part of the complete vessel
has satisfied the radiographic requirements of UW-11(a)
or where none of the markings "RT 1," "RT 2," or "RT

3" are applicable.

Or are you asking something else?

thank u