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Flame Arresters in Piping Systems: An Analysis of API Publication 2028 (1991)
Foundational Guidance for Safe Design and Operation of Flame Arresters in Process Piping
Scope and Purpose of API Publ 2028-1991
API Publ 2028-1991, titled Flame Arresters in Piping Systems, is a historic first-edition publication by the American Petroleum Institute (API) that provides comprehensive guidance on the selection, installation, operation, and maintenance of flame arresters used in piping systems containing flammable fluids. Despite being superseded by later editions (e.g., 2002, 2014), it remains a cornerstone document for process safety professionals seeking to understand the fundamental principles of flame propagation prevention.
The publication applies to both deflagration and detonation flame arresters installed in piping systems handling flammable gases or vapors at or near atmospheric pressure. It addresses the critical parameters that influence flame arrester performance, including flame speed, gas group classification, piping geometry, and operating conditions. The scope explicitly covers in-line and end-of-line arrester configurations, providing a risk-based framework for determining when flame arresters are necessary.
Core Technical Provisions
Flame Arrester Classification
API Publ 2028-1991 categorizes flame arresters based on their ability to quench flames under different propagation regimes. The two primary types are:
- Deflagration Arresters — Designed to stop subsonic flame fronts (typical propagation velocities below the speed of sound). These are most commonly applied in short pipe runs or at vent outlets where the risk of transition to detonation is low.
- Detonation Arresters — Capable of withstanding and extinguishing supersonic flame fronts (above the speed of sound) that generate significantly higher pressure and thermal loads. They are required for long piping systems where flame acceleration may occur.
The standard also distinguishes between end-of-line (vent) arresters and in-line (pipe) arresters, each with distinct design considerations related to weather exposure, mounting, and pressure drop.
Performance Requirements and Gas Group Classification
A crucial element of API Publ 2028-1991 is the use of Maximum Experimental Safe Gap (MESG) to classify flammable gases and vapors into groups. The gas group determines the arresting capability required:
| Gas Group | MESG Range (mm) | Typical Gases |
|---|---|---|
| Group I | > 1.14 | Methane (mining applications) |
| Group IIA | 0.90 – 1.14 | Propane, butane, ammonia |
| Group IIB | 0.55 – 0.90 | Ethylene, town gas |
| Group IIC | < 0.55 | Hydrogen, acetylene, carbon disulfide |
Flame arresters must be tested and certified for the specific gas group(s) in which they will operate. The publication emphasizes that a single arrester design may not be suitable for multiple groups, particularly when Group IIC gases are involved.
Installation and Maintenance Guidelines
API Publ 2028-1991 provides detailed recommendations for proper installation to ensure flame arrester effectiveness. Key provisions include:
- Location — The arrester should be installed as close as possible to the potential ignition source or at the end of the piping run. For in-line systems, multiple arresters may be required to cover long distances.
- Piping Configuration — Avoid sharp bends, tees, and obstructions upstream of the arrester, as these can accelerate flames and reduce the safety margin.
- Maintenance — Regular inspection for corrosion, fouling, or mechanical damage is required. The standard recommends establishing a routine cleaning schedule based on service severity and testing the arrester’s pressure drop periodically to detect blockage.
Implementation Best Practices
Although the 1991 edition is no longer current, its implementation principles remain valuable for existing installations or legacy system reviews. The following table summarizes key selection and operational parameters drawn from the publication:
| Parameter | Description | Recommended Practice per API Publ 2028-1991 |
|---|---|---|
| Gas Group | MESG-based classification of flammables | Select arrester tested and listed for all gases in the system |
| Flame Arrester Type | Deflagration vs. Detonation; End-of-line vs. In-line | Use detonation arresters for lines > 10 m or where flame speed may exceed 0.5 Mach |
| Pressure Drop | Allowable drop across the element | Verify at maximum and minimum flow conditions; monitor for increasing drop |
| Housing Material | Corrosion resistance and mechanical strength | Use materials compatible with process environment; ensure pressure rating exceeds maximum anticipated back pressure |
Proper documentation of arrester specifications, test certificates, and maintenance history is emphasized to demonstrate compliance during audits.
Compliance and Safety Considerations
Operators and engineers applying the guidance of API Publ 2028-1991 should be aware of both its strengths and limitations in today’s regulatory environment.
Tip: When selecting a replacement flame arrester for a legacy system designed under the 1991 edition, always verify that the new unit meets the current edition’s more stringent performance test requirements, including endurance burn and detonation stability tests.
Warning: The 1991 edition does not address some modern challenges such as cyclic flows, pulsating services, or multiphase conditions. These scenarios require additional risk assessment beyond the original scope.
Success: Facilities that have maintained systems using the principles in API Publ 2028-1991 often achieve excellent safety records, provided that regular inspections and element replacements are carried out.
Danger: Never modify the internal element gap or bypass the flame arrester to reduce pressure drop. Such actions can render the device incapable of stopping a flame, leading to catastrophic fire or explosion.
The publication’s guidance on testing methods (e.g., using propane or ethylene test gases) remains a reference for many manufacturers, but users must confirm that their current equipment conforms to the latest ISO or API test protocols.
Frequently Asked Questions
Q: Is the 1991 edition of API Publ 2028 still considered applicable today?
A: No, the 1991 edition has been superseded by later revisions (e.g., API Publ 2028, 3rd edition, 2014). However, for existing installations designed to the 1991 version, it can still be used as a baseline for maintenance and safety reviews, provided gaps with current best practices are addressed.
A: No, the 1991 edition has been superseded by later revisions (e.g., API Publ 2028, 3rd edition, 2014). However, for existing installations designed to the 1991 version, it can still be used as a baseline for maintenance and safety reviews, provided gaps with current best practices are addressed.
Q: What are the main limitations of API Publ 2028-1991 compared to the current edition?
A: The 1991 edition does not include guidance on mitigation of endurance burn (continuous flame exposure) or the latest testing protocols for detonation arresters in large-diameter pipes. It also lacks coverage of risk-based selection tools that appear in later editions.
A: The 1991 edition does not include guidance on mitigation of endurance burn (continuous flame exposure) or the latest testing protocols for detonation arresters in large-diameter pipes. It also lacks coverage of risk-based selection tools that appear in later editions.
Q: How is MESG used in flame arrester selection under this publication?
A: MESG determines the gas group, which directly affects the gap dimensions and quenching capability required for the flame arrester element. The standard provides tables correlating MESG to gas groups, enabling engineers to select an arrester that has been successfully tested for that group.
A: MESG determines the gas group, which directly affects the gap dimensions and quenching capability required for the flame arrester element. The standard provides tables correlating MESG to gas groups, enabling engineers to select an arrester that has been successfully tested for that group.
Q: Are flame arresters always required for atmospheric vents handling flammable vapors?
A: Not always. The 1991 edition recommends a case-by-case analysis considering vent location, wind conditions, the nature of the vapor, and presence of ignition sources. In many cases, a flame arrester is recommended unless a detailed risk assessment justifies its omission.
A: Not always. The 1991 edition recommends a case-by-case analysis considering vent location, wind conditions, the nature of the vapor, and presence of ignition sources. In many cases, a flame arrester is recommended unless a detailed risk assessment justifies its omission.
© 2026 API Publ 2028-1991 Analysis. This article is provided for informational purposes and does not replace official standard documents.