Emergency Shutdown and Depressuring (Blowdown) Study

Emergency Shutdown and Depressuring (Blowdown) Study

A well designed emergency shutdown (isolation) and depressuring (blowdown) system can greatly reduce the consequence of a process safety event such as a gas leak or fire and may reduce the likelihood of cascading events from occurring.  In some instances, such as an unwetted vessel being exposed to a fire, it is one of the few ways to reduce the likelihood of a catastrophic rupture of that vessel. Properly isolating a process into distinct sections reduces the volume of fluid that can be released from any one section, minimizing contributions to a possible gas cloud or to fueling a nearby fire. Sectionalization also allows for a more controlled facility depressuring, if required. API 521 provides some additional background on vapor depressurization.

Key blowdown analysis considerations based on Inglenook’s experience:

A higher resolution version of the above graphic can be downloaded below.  The file is password protected.  To receive the password, please use the contact us form with the request “blowdown graphic password”:

Pressure Relief Design Basis Revalidation Depressuring and Blowdown Infographic (111 KB)

A well-defined emergency shutdown and depressuring study will:

  • Evaluate the circumstances that lead to depressuring (blowdown) events
  • Evaluate the capability of the systems to provide shut down and depressuring
  • Evaluate the hydraulic impact of blowdown loads on the effluent handling system

Inglenook Engineering has experience developing internal client standards and guidelines related to emergency and non-emergency shutdown and depressuring as well analyzing and/or designing these systems for both existing and new facilities.

A typical analysis has the following work process:

  • Establish project guidelines based on relevant company and industry best practices as well as recognized and generally accepted good engineering practices
  • Review plant design for isolation points and fully define each isolated section
  • Identification of scenarios that should result in emergency shutdown and/or depressuring of each isolated section
  • Analysis of the capability of the blowdown systems to provide the required shutdown and/or depressuring
  • Analysis of the system in the event of non-emergency blowdown such as for maintenance operations
  • Identification of potential adverse effects, such as low temperatures, exceeding the downstream system MAWP, high velocity or high radiant heat caused by the depressuring of equipment
  • When deviations from standards or best practices are identified, specific design solutions may be provided at the request of the client
  • Generation of a final report including comprehensive documentation of the emergency shutdown and depressuring system design and all the supporting calculation.

Check out our Resource Library, particularly our Fireside Chats blog, for more insights.

Use the CONTACT US form to ask specific questions about emergency shutdown and depressuring studies.