Both stamps certify pressure vessel fabrication under ASME Section VIII, but they come from different divisions of the code and produce different commercial outcomes.
U Stamp — Section VIII Division 1
Division 1 uses design-by-rule formulas with generous safety factors. It is the standard route for most industrial vessels and requires a quality control program with an Authorized Inspector reviewing and stamping the U-1A form.
U2 Stamp — Section VIII Division 2
Division 2 permits higher allowable stresses, which usually means thinner walls and less weight, but demands more analysis (including fatigue screening where applicable) and a more extensive examination program. It pays off on large or heavy vessels where wall thickness drives cost.
How to choose
- Start from the process design conditions: pressure, temperature, fluid and cyclic service.
- Ask engineering to compare wall thickness under Div.1 and Div.2.
- Compare the material savings against the extra analysis and inspection cost.
- Confirm the fabricator holds the matching Certificate of Authorization.
Repairs still run through the R Stamp
Neither U nor U2 covers field repair. Repairs and alterations on existing pressure equipment require the National Board ‘R’ Stamp, which Daniel Steels Manufacturing holds alongside its ASME ‘U’ Stamp.
Need help deciding? Send the design conditions and our engineering team will compare both routes.