There is a single 'V' butt joint without backing strip - circumferential/ longitudinal joint of OD < 24" (Type 3 as per table UW 12). Is it possible to upgrade the joint to Type 1 by any means like using GTAW process or Performing RT/additional NDT?

The most popular interpretation of the difference between Type 1 and Type 3 I have met so far is that the Type 1 needs a visual inspection of the root of the finished weld. If you can't get inside the vessel and you can't get a boroscope there- you have a Type 3. But it's up to an accord with your AI, just like all the not-so-well defined bits and bobs around the Code.

Type 3 does not have E's for radiographed joints, because automatically they become Type 1. But when the Code does not require radiography- the only way you can tell the difference between Type 1 and 3 is visual appearance of the root. It's nice=Type 1, it's ugly=Type3. As simple as that!

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Konrad Anikiel

Regarding visual inspection of the root, as an AI I act this way: Place a Hold Point for root pass (GTAW process) on that weld. Visually examine (the welder does the same) the root pass done through the gap of the weld preparation whilst the welder is welding. Of course the last (approx.) four inches of root are not seen, but if all the rest is good I can reasonably assume all is good. Instruct your GTAW welder and your welding inspector to do the same. Propose your AI to do the same. However a weld with a regular preparation of the joint, first pass GTAW (or any other method which is proved to obtain good root pass, e.g. GMAW STT or SMAW with proper electrode), made by a good, qualified welder, and RT examined, is considered "Type 1" by everybody (with common sense).
Mauro
Mauro