Planning to add or replace a flame arrester on a tank already in service? You are not alone. Growth in biofuel, petrochemical, and pharmaceutical storage has pushed many operators to revisit vent-line protection. This guide walks you through the design checks that keep a retrofit safe, compliant, and leak-tight.
Many storage tanks were built before today’s vent-line standards caught up with modern service. You may be asked to revisit the protection on an existing tank for several reasons: the original arrester has plugged from product fouling or corrosion, the stored product has changed (for example, a shift toward renewable fuel blending), or local code updates now expect a documented flame-arrester specification where none existed before.
The expansion of chemical, edible-oil, and energy storage capacity across industrial regions has quietly raised the number of tanks that now require verified vent-line flame protection. When you treat a retrofit as a small engineering project rather than a swap-in part, you protect both the asset and the people who work around it.
Before you specify anything, you need a clear picture of what is already installed. Walk the tank and record the nozzle size, the flange rating and facing (ANSI, DIN, JIS, or GB), and the current arrangement of the breather valve and any existing arrester. A retrofit that ignores the as-built geometry will either not fit or will quietly raise the system pressure drop beyond what the tank shell was designed to tolerate.
Pay attention to whether the vent is end-of-line (atmosphere facing) or in-line (within a pipe run). This single detail changes the arrester type, the pressure rating you need, and the way you later verify performance. Photograph the nameplates and keep the drawings; you will reference them in the final record.
Every flammable mixture has a Maximum Experimental Safe Gap (MESG). Your arrester core must be fine enough to stop the specific flame for the gas group present in the tank vapor space. Identify the true vapor composition under normal and upset conditions, then match the arrester group (IIA, IIB, or IIC). Specifying on the “usual” product alone is a common retrofit mistake when tanks are reused for new service.
An arrester is a flow restriction. The selected end-of-line flame arrester must pass the tank’s full in-breathing and out-breathing rate without pushing the tank beyond its allowable pressure or vacuum. Confirm the calculated pressure drop against the tank’s mechanical design and against the relief setting of the associated breather valve.
A flame arrester rarely works alone. It sits downstream or upstream of a pressure-vacuum breather valve, and the two must be selected as a system. Check that the combined set resists clogging, drains condensate, and does not lift the valve off its seat during normal tank “breathing.” Where space and service allow, a combined breather valve with flame arrester can simplify the retrofit and reduce leak paths.
Confirm the body and core material against the stored product and any trace contaminants. Then verify the device is built and tested to the standards your authority having jurisdiction expects. For storage-tank venting, that typically means flame arrester with ventilation cap units reviewed against ISO 16852 and EN 12874, with the tank venting basis taken from API 2000 and any ATEX / zone-classification rules applied where applicable.
| Design check | What you verify | Why it matters |
|---|---|---|
| Gas group / MESG | True vapor composition and group | Core stops the actual flame front |
| Pressure drop | Flow vs. tank / valve limits | Protects tank shell from over-pressure |
| Breather valve match | System behavior, drainage | Prevents seizure and leakage |
| Standards | ISO 16852, EN 12874, API 2000 | Acceptance by inspectors and insurers |
Once the new arrester is fitted, you are not finished. Verify the installed device matches the approved specification, confirm there are no unintended flow restrictions, and (where the service demands it) witness a flow or pressure-drop test. Then close the loop with documentation.
Keep an engineering record for every retrofit: the as-found condition, the selected model and its certification, the installation date, and the verification results. These records are what inspectors, insurers, and your own future maintenance team will rely on. Treat the file as part of the safety system, not paperwork.
Not sure your tank vent passes these checks?
Send Zhenchao your tank drawing and service data. Our engineers will review your flame arrester retrofit against the right gas group, pressure drop, and standard — and recommend a verified, leak-tight configuration.
About this guide: Prepared by the Zhenchao engineering team. Zhejiang Zhenchao Petrochemical Equipment Co., Ltd. has manufactured tank protection equipment since 2006 and holds ATEX, Qingdao Institute, and Shenyang Institute certifications.
A deflagration arrester stops a slow flame that has not yet developed a pressure wave; a detonation arrester is built to survive and quench a fully developed detonation. Most storage-tank vent retrofits call for deflagration-grade devices at the ATM/vent, with detonation grades reserved for pipeline sections where a stable detonation can form. Match the grade to the worst credible event on that line.
Trace the pipe from the tank to where it meets the atmosphere. If the arrester is the last fitting before open air, it is end-of-line. If it sits inside a pipe run that continues to another vessel or a treatment unit, it is in-line. The nameplate and the P&ID will confirm it, and the answer decides the pressure rating and mounting you must specify.
Often yes, but only with a controlled plan. You can use a bypass leg, a double-block-and-bleed isolation, or (on suitably rated lines) a hot-tap fitting so the tank keeps operating. The safe answer depends on the product, the line pressure, and your site permit-to-work rules — never isolate a tank’s only relief path without a documented alternative.
MESG is the widest gap through which a flame will not propagate. Each gas group (IIA, IIB, IIC) has a maximum MESG, and the arrester core gap must be finer than that value for your specific vapor. If you change the stored product, the group can change, and a core that was safe for the old service may no longer be adequate.
A shared header is possible, but it demands careful flashback and cross-tank risk analysis. A single arrester on a common line must protect against a flame traveling from any connected tank, and you must prove no tank can become an uncontrolled ignition path. Many operators instead fit individual tank-vent arresters to keep the risk isolated and the verification simpler.
Ice and hydrate formation can block the core or the drain, raising pressure drop and defeating the vent. In cold or humid service, specify self-draining geometry, consider heating or an end-of-line location that sheds condensate, and add the blockage check to your inspection routine so the arrester keeps flowing through winter.
