Upstream, midstream and downstream hydrocarbon facilities around the world regularly employ depressuring systems to limit the consequences of leaks or equipment rupture due to fire exposure. Performance requirements for the design and operation of depressuring systems are outlined in API 521 and are widely used as the benchmark within the industry.

The design of depressuring systems can be complex and should consider the following as a minimum:

  1. Flare capacity – Required to accommodate all credible relief and depressuring scenarios and understand any constraints in the flare system.
  2. Blowdown valve/RO sizing – Sized to depressure each process segment in line with the facility blowdown philosophy.
  3. Fire survivability – Assess the survivability of vessels and piping to fire exposure and ensure acceptance criteria for rupture is met.
  4. Low temperature assessment – Establish appropriate materials of construction to ensure minimum metal design temperatures are not violated within process equipment, piping and flare system.

The workflow to design a depressuring system which meets the performance requirements of API 521, whilst ensuring fire survivability and low temperature constraints are not violated, is highly integrated and benefits from a holistic modelling approach. During the design process there are opportunities to optimise the design, especially when mitigations are required to resolve fire survivability or low temperature violations. Also, by incorporating dynamics into the assessment the additional capacity inherent due to packing of headers and the true flowrates from sources can be solved simultaneously.

This webinar will showcase PSE’s dynamic modelling capabilities for combined depressuring, fire survivability and low temperature assessments of coupled process and flare systems. An example of a depressuring system will demonstrate the benefits of performing the design using a coupled dynamic model of the process and flare system in an integrated workflow.

The topics covered include:

  1. Depressuring system performance
    1. Industry Standard requirements influencing design.
    2. Complexity of introducing segregated or staggered depressurising systems.
  2. Fire survivability & low temperature assessment
    1. Overview of fire survivability assessment as per API 521 and Scandpower Guidelines.
    2. Overview of low temperature assessment in process equipment and propagation through flare networks.
    3. Typical mitigations employed to prevent rupture due to fire or violating minimum metal design temperature.
  3. Integrated workflow
    1. Benefits of utilising coupled process and flare system models to design and optimise depressuring systems in a dynamic environment.
    2. Optimised design in conventional and complex depressuring systems.
    3. Summary of an integrated workflow to improve design efficiency.


Francisco Borralho
Francisco Borralho, Senior Consultant Engineer, PSE

Francisco Borralho is a Senior Consultant Engineer, within PSE’s Process Safety group. He is a chemical engineer with a MSc from Instituto Superior Técnico, Portugal. Francisco has over six years of experience working on a wide variety of safety consulting projects, using PSE’s proprietary gFLARE technology.

More Information



40 minutes plus Q&A

Who should attend?

This webinar is aimed at process design engineers, safety relief engineers and operator technical authorities, and those responsible for the design and management of flare and relief systems at upstream and midstream energy companies.

A recording will be made available to all registered attendees one day after the broadcast.