Reference profile
- Designation
- API 521
- Title
- Pressure-relieving and Depressuring Systems
- Issuing body
- API
- Current edition
- [verify]
- Status
- Library record: published; official standard status [verify].
- Category
- Safety & Relief Devices
Overview
Applies to pressure-relieving and vapor depressuring systems. Gives guidelines for examining the principal causes of overpressure, determining relief rates, and designing disposal systems.
Scope & Applicability
Covers
- Overpressure Scenarios
- Relief Load Calculation
- Flare Header Design
- Depressuring Systems
- Knockout Drums
- Thermal Radiation
Does NOT cover (exclusions)
- Exclusions are not documented in this library record. Confirm the official publication, neighbouring codes, the adopted edition, and jurisdictional boundaries before application.
Key Requirements
Lifecycle requirements
- Flare System Design
- Relief Load Summary
- Blowdown Design
Technical Details
Applies to pressure-relieving and vapor depressuring systems. Gives guidelines for examining the principal causes of overpressure, determining relief rates, and designing disposal systems.
Components: Flare Header, Knockout Drum, Blowdown System, Flare Stack.
Engineering Notes
- Used to determine WHAT causes overpressure and HOW MUCH fluid needs to be relieved.
Related Standards
- API 520
Companion or referenced standard; verify its exact relationship in the adopted edition.
- API 537
Companion or referenced standard; verify its exact relationship in the adopted edition.
- ISO 23251
Companion or referenced standard; verify its exact relationship in the adopted edition.
Source, Edition & Status
- Publisher
- API
- Edition Year
- N/A
- Industries
- Petrochemical, Refinery, Chemical, Oil & Gas
- Content Status
- published
- Last Reviewed
- 2026-07-01
- Last Updated
- 2026-07-01
- Verified By
- Engineering Reviewer
- Official Link
- N/A
This paraphrased summary is a discovery aid. Do not reproduce or substitute it for the copyrighted official publication or jurisdictional requirements.