Relief Valve Networks

Proxion Process provides a full range of services relative to the sizing, verification and modelling of Flare Systems and Pressure Safety Relief Valves (PSVs or PSRVs)


Proxion Process generate all calculations and associated documentation for the sizing and selection of PSVs per API and/or ASME Code requirements. This includes:

  • Identification of and calculations for all credible scenarios, not just the controlling scenario
  • Physical properties generated by CHEMCAD process simulation models for each stream.
  • Flare stack or vent stack sizing (height, diameter, tip configurations, etc.) to fall within API Code requirements. Flare manufacturers are also consulted to ensure the best available technology is included in the design. Knockout drums and blowdown systems are also designed and sized for each particular installation, possibly including specialised features such as; knockout drum vaporization or pump-out capabilities.
  • Generate all documentation needed to meet OSHA requirements and any specific company requirements
  • Generate required PSV specifications (spec sheets)
  • Construct a flare header pressure drop simulation model in CHEMCAD, including both inlet and outlet PSV piping configurations
  • Perform flare header pressure drop evaluations for specific PSV combinations associated with global relief scenarios.

Our Methodology

In general, Proxion Process follows methodology set forth in the American Petroleum Institute (API) 520 and 521 guidelines. When performing an evaluation to determine if adequate relieving systems are in place for an existing system and if the flare header is adequately designed, the following steps are typically involved.

Relief Device Evaluation:

  1. Collect information on the existing system (PSV data, P&IDs, protected equipment information, flare header isometrics, inlet/outlet line sizes, etc.).
  2. Work with the clients’ technical staff to develop the credible relief scenarios, both for individual pieces of equipment and especially for those effecting entire units or sections of the plant (blocked flow, external pool fire, loss of cooling, loss of power, etc.).
  3. Calculate the required flow rate capacity for the relieving streams along with the required orifice sizes for each credible scenario.
  4. From this information, the controlling scenario is determined and the valve is sized. Proxion Process uses state-of-the-art commercial process simulation software to obtain the relieving stream physical properties required to perform the flow rate calculations.
  5. For evaluation of existing valves, the required flow rate and actual flow rate capacity for the relief valves are calculated along with the required orifice size for each scenario. From this information, the controlling scenario is determined to check if the existing valve is sized appropriately.

What we provide:

  • Drawing Diagram
  • Equipment Summary Sheet
  • Calculation & ratings Sheet
  • PSV sizing
  • Reference sheet

Safety First (HSE)

Proxion Process HSE