Cryogenic tanks are designed and built to API 620 Appendix R, not API 650.
Sorry, I don't have the standard on hand to see if what you propose is allowed.
Giovanni S. Crisi
Sao Paulo - Brazil
API 620 appendix U ut in liu of radiography. Yes there are many restrictions. the Key one being the minimum Charpy V notch values. I am on one of these projects now.
APPENDIX Q--LOW-PRESSURE STORAGE TANKS FOR
LIQUEFIED HYDROCARBON GASES
APPENDIX U--ULTRASONIC EXAMINATION IN LIEU OF RADIOGRAPHY
You will have to pay particular attention to those two appendixes of 620.
Welding material will likely be SFA 5.11 and 5.14 ECRNIMO 3 through 6 depending on your project spec. The plate will be ASTM A553M
There is also some restrictions on use of TOFD. The filler will end up around 60 to 65 percent NI. This gives you effectively a dissimilar weld that is prone to center line hot cracking when it goes south. Combined with the large grain structure of the weld vs the fine grain structure of the base metal, the primary constituents of the AUT exam will likely be (all refracted longitudinal) round trip tandem, creep wave, and direct wave. The Aut primarily consisting of composites of those methods with limited use of the TOFD function.
Shoot me an email if you need any further info.