Determination of Explosion-Proof Performance for Oil Storage Tanks: Standards, Samples, Methods and

Oil storage tank explosion-proof performance testing verifies that storage tanks and their safety accessories can reliably prevent the ignition of flammable vapor-air mixtures, withstand internal deflagration pressure, and safely relieve hazardous overpressure. This technical guide explains the applicable international and national standards, typical test samples, core testing items, laboratory and on-site methods, and practical applications of explosion-proof performance determination for atmospheric and low-pressure oil storage tanks.

Technical Overview

Oil storage tanks containing crude oil, gasoline, diesel, kerosene, jet fuel and other flammable liquids continuously generate combustible vapor-air mixtures in their headspace. Potential ignition sources, including electrostatic discharge, lightning strikes, hot surfaces, and external flame propagation through vent lines, can trigger internal deflagration with severe structural and safety consequences. Explosion-proof performance determination is therefore a systematic evaluation that covers the complete protective chain of a storage tank: the structural pressure resistance of the tank body, the flame-arresting capability of venting devices, the set pressure and flow capacity of breathing valves, the emergency relief capacity, and the integrity of bonding and grounding systems.

The evaluation is governed by an interlocking framework of international and national standards, including ISO 16852 for flame arresters, the IEC 60079 series for equipment used in explosive atmospheres, API 650 and API 2000 for welded storage tanks and their venting requirements, EN 14015 for site-built vertical cylindrical tanks, NFPA 30 for flammable and combustible liquids, UL 525 for flame arresters, and the Chinese national standards GB 50074, GB 50160, GB/T 13347 and GB 5908 covering oil depot design, petrochemical fire prevention, and flame arrester performance. Accredited third-party laboratories conduct these tests to support regulatory compliance, hazardous area classification, and safe long-term operation.

Testing Samples

Flame Arresters

End-of-line and in-line flame arresters installed on tank vents and vapor recovery lines, including deflagration-type and detonation-type arresters with crimped metal ribbon, corrugated plate, or parallel plate elements. Detonation arresters with integrated relief are tested as complete assemblies.

Breathing Valves and Pressure/Vacuum Relief Valves

Weight-loaded, spring-loaded, and pilot-operated breathing valves that control vapor discharge and air ingress, together with combined breather valve and flame arrester units used on fixed-roof tanks.

Emergency Venting Devices

Emergency pressure relief manhole covers, hinged exhaust vents, and shear-pin or rupture-disc emergency vents designed to open under abnormal pressure caused by fire exposure or internal deflagration.

Tank Structural Components

Shell plates, roof sections, welded joints, nozzle reinforcements, and manhole assemblies sampled from vertical cylindrical tanks, internal floating roof seals, and underground or mounded storage tanks.

Explosion-Proof Electrical Equipment

Level transmitters, radar gauges, temperature sensors, and sampling devices mounted on tank nozzles, evaluated for flameproof enclosures, increased safety construction, or intrinsic safety in accordance with the IEC 60079 series.

Testing Items

The scope of explosion-proof performance determination typically includes the following items, selected according to the equipment type, the hazardous area classification, and the applicable standards:

• Flame transmission performance of flame arresters under deflagration and detonation conditions
• Endurance burning resistance and short-time burning behavior of arresting elements
• Explosion containment capability and pressure resistance of tank enclosures and covers
• Opening pressure, reseating pressure, and leakage rate of breathing valves
• Vacuum resistance and air intake performance of pressure/vacuum relief valves
• Emergency venting flow capacity at defined overpressure conditions
• Electrostatic bonding and grounding resistance of the tank and attached piping
• Lightning protection continuity and air terminal effectiveness
• Corrosion resistance of arresting elements, seals, and structural coatings
• Mechanical strength, vibration endurance, and thermal cycling behavior
• Explosion-proof marking, nameplate data, and technical documentation verification

Testing Methods

Flame Transmission Testing

Flame arresters are mounted on a test pipe filled with a standardized gas-air mixture corresponding to explosion group IIA, IIB, or IIC as defined in ISO 16852, such as propane, ethylene, or hydrogen mixtures. An ignition source is triggered at a defined location to produce a stabilized flame or an accelerated detonation that impinges on the element. The arrester passes only if no flame transmission to the protected side is observed across a consecutive series of ignitions, conducted at both atmospheric and elevated operating temperatures and at the limits of the specified installation orientation.

Endurance Burning Testing

A stabilized flame is held directly against the arrester element for the specified endurance period to simulate an external fire or sustained flame condition. The element must resist burn-through, prevent flame passage, and retain mechanical integrity, confirming the time rating marked on the device.

Hydrostatic and Pneumatic Pressure Testing

Tank bodies, manhole covers, and relief enclosures are subjected to hydrostatic testing, in which the component is filled with water and pressurized to the specified test pressure, held for the required duration, and inspected for leakage, permanent deformation, or weld defects. Where hydrostatic loading is impractical, pneumatic testing with air or nitrogen is performed under strictly controlled safety measures. Explosive mixture containment tests may also be conducted in which a deflagration is initiated inside a closed representative enclosure to verify structural survival without rupture.

Breathing Valve Set Pressure and Leakage Testing

Valves are placed on a calibrated pressure and vacuum bench, and pressure is ramped gradually to record the opening point, full-flow point, reseating pressure, and seat leakage. Results are compared against the design set pressures specified by API 2000, GB 50074, or the manufacturer rating.

Venting Capacity and Flow Testing

Airflow benches measure the discharge and intake capacity of breathing valves, emergency vents, and combined units at defined overpressure and vacuum levels. The measured capacity is compared with the calculated thermal and liquid movement venting demand for the tank to confirm adequate emergency relief under fire exposure scenarios.

Static Grounding and Lightning Protection Testing

Earth resistance and bonding continuity are measured using dedicated earth testers and micro-ohmmeters at tank grounding terminals, flange bonding straps, and floating roof shunts. Grounding resistance values are verified against the limits specified in the applicable GB and IEC design standards, and lightning protection systems are checked for down-conductor continuity and air terminal coverage.

Environmental and Mechanical Durability Testing

Salt spray exposure in accordance with ASTM B117 evaluates the corrosion resistance of arresting elements and hardware, while vibration, impact, and thermal cycling tests confirm that critical clearances and flame path dimensions remain within tolerance throughout the service life of the device.

Applications

Explosion-proof performance determination supports safety, regulatory approval, and asset integrity across the entire petroleum and chemical storage supply chain. Typical applications include:

• Crude oil and refined product tank farms at refineries and shipping terminals
• Gasoline, diesel, and kerosene storage at distribution depots and bulk plants
• Aviation fuel hydrant systems and airport fuel farms
• Underground and mounded storage tanks at fuel service stations
• Flammable solvent and chemical storage vessels at petrochemical plants
• Vapor recovery units and vent manifold systems requiring detonation arresters
• In-service inspection and periodic recertification of aging storage assets

FAQ

What is the difference between a deflagration flame arrester and a detonation flame arrester?

A deflagration arrester is designed to stop a subsonic flame front over short, straight pipe runs, while a detonation arrester must stop supersonic flame fronts and the associated shock waves generated in long or complex piping systems. Detonation arresters are structurally reinforced and are tested under stable and unstable detonation conditions in accordance with ISO 16852.

How often should explosion-proof performance be verified?

Type testing of new safety accessories is performed before market introduction or installation, while in-service tanks and accessories are typically subject to periodic inspection on an annual to five-year cycle depending on the applicable national regulations, the service severity, and the risk assessment. Any device exposed to fire, corrosion damage, or mechanical impact should be retested before being returned to service.

Which standards are most commonly applied?

The most frequently referenced standards include ISO 16852, IEC 60079, API 650, API 2000, EN 14015, NFPA 30, UL 525, GB 50074, GB 50160, GB/T 13347 and GB 5908. The governing combination depends on the tank design pressure, the stored fluid classification, the hazardous area zoning, and the jurisdiction of installation.

Can testing be performed on tanks that are already in service?

Yes. Structural pressure resistance, grounding resistance, lightning continuity, venting capacity verification, and in-situ flame arrester condition assessment can be carried out on operating sites after cleaning and gas-freeing, while full flame transmission and endurance burning tests require laboratory type testing of representative or production samples by accredited third-party laboratories.

What test gases are used in flame transmission testing?

Standardized mixtures of propane, ethylene, and hydrogen with air are used to represent explosion groups IIA, IIB, and IIC respectively. The selection depends on the vapor classification of the stored liquid and the marking group claimed for the arrester, ensuring the device is qualified for the most severe mixture it may encounter in service.