What is the UD stamp and why is it important?
The UD stamp is an ASME Code Symbol Stamp with the designator ‘UD’ below it. ‘UD’ is the ASME code that refers to pressure relief devices. It confirms that a rupture disc, or bursting disc, complies with the ASME Boiler and Pressure Vessel Code section for pressure relief devices.
A rupture disc with the ASME stamp has been verified as meeting the ASME standards for quality and safety. The precise values for a product (minimum and maximum burst pressures as well as the MNFA – Minimum Net Flow Area) are specified when submitting an application for ASME certification.
The certification process
Part of the initial process for obtaining UD certification for a rupture disc involves bursting three discs of three differently sized examples of a single product, e.g. three different sizes of an Opti-Gard. This makes nine tests in total and the statistical deviation of burst tests allowed for all nine tests is very tight.
Each disc must burst within the previously defined minimum and maximum burst pressures for the product to pass. Additionally, the deviation of the burst tests in each size is measured and the deviation of the three groups of tests must also be within an acceptable range.
Following a successful burst test, the discs are mounted on an ASME certified flow test rig and flow tested to determine their flow resistance value, or ‘Kr value’. This certified Kr value is then published in the National Board Pressure Relief Device Certifications, known informally in the industry as the Red Book.
Authorisation to continue using the UD stamp must be renewed every three years through an audit by an ASME representative. Recertification does not require the nine-disc burst test but does involve a witnessed flow test.
Why is the UD stamp important?
Providing rupture discs with ASME certification demonstrates a company’s commitment to quality and safety. ASME certification is the required standard for many states and provinces in the USA and Canada. In addition, over 100 countries accept it as a means of meeting government safety regulations. Even where the ASME stamp is not a requirement, it demonstrates that the rupture discs conform to established safety standards.
Use a bursting disc marked with a UD stamp to give you reassurance that the product has been through a leading, universally recognised, independent quality assurance programme.
You can therefore be confident that the disc:
- is safe;
- is of a high quality;
- will perform reliably;
- will perform consistently.
Elfab’s ASME certified product range
Elfab provides a range of rupture discs certified to ASME standards. These include:
As an additional demonstration of our commitment to providing customers with the highest standards of quality and service, we have invested in our own ASME certified flow test rig. We are the first rupture disc manufacturer outside the USA to do so.
Importantly, National Board representatives can now authorise our rupture discs on-site. This avoids having to go through the lengthy process of sending the discs abroad for testing and waiting for results. This considerably speeds up both the initial certification process and audits to re-authorise UD-stamped discs. This allows us to work smoothly with customer’s timelines and production requirements.