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ASME UV stamp and National Board

The UV mark on a pressure relief valve shows that it was built under an ASME certificate for pressure vessel relief valves. The NB mark shows that the National Board has certified its capacity. Luofu Valve Group holds both authorizations.

The short answer

UV is the ASME designator for pressure relief valves that protect pressure vessels. A valve with the ASME certification mark and the UV designator was made by the holder of an ASME Certificate of Authorization. The NB mark means its relieving capacity is certified by the National Board.

Luofu holds the ASME UV Certificate of Authorization and the National Board authorization certificate for the UV designator.

What the UV mark covers

ASME issues a Certificate of Authorization after it reviews the manufacturer's quality control system and shop. With the UV designator, the holder may apply the ASME certification mark to pressure relief valves for pressure vessels.

Valves for power boilers carry a different designator, V. The certificates listed on this page cover UV.

Project specifications often ask for the UV stamp on valves that protect ASME vessels. Write it on data sheet line 38 so that the quotation covers the stamp.

What the NB mark adds

The National Board of Boiler and Pressure Vessel Inspectors certifies relieving capacities. A valve design is flow tested at a laboratory the National Board accepts. The certified capacities are published in the National Board list NB-18.

A manufacturer with National Board authorization may add the NB mark to the nameplate next to the UV designator. Inspectors and owners use the mark to trace the certified capacity of the valve.

What the nameplate shows

The nameplate of an ASME-marked pressure relief valve carries the data the code requires, such as:

  • The name of the manufacturer
  • The model or type number
  • The inlet size
  • The set pressure
  • The certified capacity, with the test medium
  • The year built, or a code that gives it
  • The ASME certification mark with the UV designator, and the NB mark where it applies

Check the nameplate against the data sheet at receipt. Set pressure and capacity should match the values confirmed for the tag.

Luofu certificates

Luofu Valve Group holds these two certificates:

ASME UV Certificate of Authorization
ASME UV stampCertificate of Authorization
National Board Certificate of Authorization, UV designator
National BoardAuthorization certificate, UV designator

Ask for copies of the current certificates in your inquiry. Tell us which tags must carry the UV and NB marks.

Questions engineers ask

Is the UV stamp the same as the U stamp?

No. The U designator is for the pressure vessels themselves. UV is for the pressure relief valves that protect them.

Do API 526 and the ASME UV stamp cover the same thing?

No. API 526 sets orifice letters, sizes, pressure classes, and dimensions. ASME sets the rules for construction, testing, marking, and capacity certification. A valve for an ASME vessel often has to meet both.

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