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T/O Certificate of Authorization

The National Board offers the Certificate of Authorization and T/O mark for the inservice testing of pressure relief valves. Requirements are described in NB-528, Accreditation of T/O Test Only Organizations.



Organizations seeking a National Board T/O Certificate of Authorization must complete and submit the following:


  1. have a written quality system that complies with the requirements of the current edition of the National Board Inspection Code (NBIC), NB-528, Accreditation of T/O Test Only Organizations, and includes the expected scope of activities,
  1. have the current edition of all parts of the NBIC. Organizations have the option of using either a printed version or an electronic version, including a subscription from a National Board licensed reseller, to fulfill this requirement; and,
  1. have available a copy of the Code of Construction appropriate for the intended scope of work.

Prior to issuance of a National Board T/O Certificate of Authorization, the organization and its facilities are subject to a review of its quality system. An important part of that review will be the witnessing of the repair of several sample pressure relief valves.

An independent test for operation and capacity of these sample pressure relief valves will be conducted at a National Board-accepted laboratory. The test is to verify the repaired valves meet applicable ASME Code requirements for performance.

  • The National Board Testing Laboratory is available to perform this testing, along with several other major valve manufacturers which operate National Board-accepted testing laboratories.
  • A National Board representative will witness the valve testing.

Return forms by e-mail to: or mail the forms to:

          National Board Test Laboratory
          7437 Pingue Drive
          Worthington, Ohio 43085

Pressure Relief Department staff will contact you to schedule a date for the review of the T/O Quality System and its implementation, and to witness the repair of the required sample pressure relief valves.


Estimated Fees

Certification Fees:

The certificate fee for the T/O Certificate of Authorization is $660 USD for a three-year period.

Review Fees:

The review of an organization’s quality control system for T/O certification, conducted by the National Board, can be performed in conjunction with its ASME review, where applicable, or as a standalone T/O review. The National Board requires an advance deposit to schedule reviews for ASME and T/O certifications or the standalone T/O certification, as shown below:

Within the Continental US $5,500 USD
Canada $6,000 USD
Alaska, Caribbean, Hawaii, Mexico $7,000 USD
Europe $8,000 USD
Africa, Asia, Australia, Russia, South America $9,000 USD

If your location is not included in the above list, please contact the National Board Pressure Relief Department.

Cancellation Fees:

Withdrawal of an application in-process will result in a $330 USD cancellation fee. If a review has been scheduled and is cancelled, other cancellation fees may apply.


Organizations holding a T/O Certificate of Authorization who are having a name change prior to renewal must submit an NB-519, National Board VR, T/O, and/or NB Certificate of Authorization Name Change Application, along with a copy of their Quality Control Manual revisions. There is a fee of $50 USD for a name change to a certificate.

NOTE:  If the name change is being done at the time of renewal, an NB-519 does not need to be submitted, and the $50 revision fee is not needed. The name change should be noted on the NB-550 application for renewal.

Organizations holding a T/O Certificate of Authorization who are having a location change or scope change, must submit an NB-550, Application for the National Board VR and/or T/O Certificate of Authorization.  A review of your facility may be required prior to issuance of a revised certificate. Cost will be determined upon receipt of the NB-550.

If there are questions on the certification program, please Contact Us or email the Pressure Relief Department at


Payment Options

Payment of the certificate fee and advance deposit, if applicable, can be made as follows:

  • By check payable in U.S. Dollar, drawn on a U.S. Bank, to The National Board of Boiler and Pressure Vessel Inspectors and remit to the address below, to the attention of the Accounting Department.

  • For all other payment types, please contact the Accounting Department as follows:
    • ACH (preferable) — send your ACH authorization form to the Accounting Department for banking information by mail or fax.
    • Credit Cards (VISA, MasterCard, American Express) — send credit card information by fax or call the Accounting Department.

  • Accounting Department contact information:
    Address 1055 Crupper Avenue
    Columbus, OH 43229
    Telephone 614.888.8320 ext. 217
    Fax 614.985.4615