The guidelines and dimensions for safety relief valves vary by country, applied standards and dimensions. Abbreviations such as PED, API, DIN and ASME are common. In this blog, I explain what they mean, where they come from and what to consider when applying spring relief valves.
Directive 97/23/EC
Let me start with the European Pressure Equipment Directive. This Directive 97/23/EC (Pressure Equipment Directive, PED) applies to the design, manufacture, assembly, and conformity assessment of pressure equipment with a maximum allowable pressure (PS) exceeding 0.5 bar.
Pressure equipment includes pressure vessels, piping, safety accessories, other pressure accessories, and elements attached to these products (including flanges, nozzles, couplings, support structures, and lifting eyes).
Manufacturers of safety valves are primarily responsible for the CE marking of pressure equipment. As an importer of safety valves and other pressure protection products, we ensure that foreign manufacturers apply the CE marking in accordance with the directive.
American Petroleum Institute (API)
The American Petroleum Institute, abbreviated as API, is an American organization that develops technical standards for the oil and gas industry and the petrochemical industry. It is the largest American trade association with approximately 400 industry members. API develops technical standards and represents industrial interests with government agencies in the field of safety (plant safety).
In addition, setting up and certifying industrial standards is an important part of their work.
An example is the API 526 standard, which focuses on flanged steel pressure relief valves (safety valves).
The standards set forth in this document include:
- Capacity per discharge opening
- Inlet and outlet nominal sizes (1 – 10 inches)
- Dimensions of 'center to face'
- Maximum set pressure
- Maximum back pressure
- Material for body, spring, and housing
- Pressure and temperature limits
- Adjusting ring
Companies that adopt API as a standard are therefore brand-independent.
All safety valves manufactured according to API guidelines are interchangeable. This American standard is the most widely used and represents the largest market in the world for safety valves.
If you are looking for a safety valve that falls within the API standard, I can always offer you a solution according to the same API guidelines.
American Society of Mechanical Engineers (ASME)
The American Society of Mechanical Engineers is a professional association founded in North America as an engineering society focused on mechanical engineering. Today, ASME operates worldwide.
An important standard is the ASME Boiler and Pressure Vessel Code (BPVC). The BPVC provides rules for the design, manufacture, installation, inspection, maintenance, and use of boilers, pressure vessels, and nuclear components. The code also includes standards for materials, welding and brazing procedures and qualifications, non-destructive testing, and in-service nuclear inspection. If a company receives a stamp from this code, it is re-evaluated every 1 to 3 years. In our industry, we deal with 3 different stamps:
- ASME I (V-stamp): steam boilers in power plants
- ASME VIII (UV-stamp): pressure vessels
- ASME III (NV-stamp): nuclear applications
Safety valves that comply with the ASME standard are used worldwide (in Europe both on- and offshore in the oil and gas refining and (petro)chemical industries).
Important! Pay Attention to Differences Between API and ASME
There may be differences between the discharge openings and discharge coefficients proposed by API and the actual ASME values used.
According to API 520 Part 1, the API orifice sizes and discharge coefficients are assumed values that should only be used for the initial selection of the safety valve. They are designed to simplify the selection of a valve at an early stage of a project and to ensure that the eventually purchased valve will have a certified capacity that meets or exceeds the required overpressure capacity.
Differences in capacity may occur between the initial choice of the API orifice and the actual ASME orifice.
For most projects, the actual ASME orifice may provide a much higher flow rate. Calculated orifice sizes usually fall between the standard letter and the designated API sizes. When this happens, the next larger orifice is chosen, resulting in a valve that is larger than desired but necessary due to the API sizing.
Certification Standards
Although not all the guidelines described above are standardized (API is the only one), other standards are used for certification. This means that the safety valve is tested according to the standards of the relevant authority. In America, for example, this involves the National Board of Boiler and Pressure Vessel Inspectors, and in Europe, you may deal with TÜV, Bureau Veritas, Vinçotte, or Lloyds.
In addition to guidelines such as API and ASME, you may also need to consider the following certifications:
- National Board (NB-stamp)
- PED 2014/68 EC (Pressure Equipment Directive for EU countries)
- TÜV BKZ (German inspection agency)
- DIN (Deutsches Institut für Normung)
I will discuss DIN (Deutsches Institut für Normung) in a separate blog soon.
If you want to know more about guidelines and certification of safety valves after reading this blog, feel free to ask your questions. I am happy to help you.
