Corrosion Resistance and Air Permeability Testing for Oil Fume Filter Mesh

Oil fume filter mesh, the core grease-filtration component of range hoods and kitchen exhaust systems, must simultaneously withstand corrosive cooking fumes and maintain stable airflow. Corrosion resistance and air permeability testing verifies these two critical properties through salt spray exposure and airflow pressure-drop measurement in accordance with ISO, ASTM, and GB standards. This article explains the sample requirements, test methods, evaluation criteria, and applications of oil fume filter mesh corrosion resistance and air permeability testing performed by accredited third-party laboratories.

Technical Overview

Oil fume filter mesh (also known as grease filter mesh or grease trap mesh) is installed in household range hoods, commercial kitchen exhaust systems, and oil-mist separation equipment to intercept grease particles from cooking fumes. During service, the mesh operates in a harsh environment containing oil vapor, water vapor, salt-containing condensates, high humidity, and periodic contact with alkaline or acidic cleaning agents. Over time, these conditions can corrode the mesh surface, causing white rust, red rust, coating degradation, pore blockage, and structural weakening.

Corrosion damage directly affects two essential performance attributes of the filter mesh: its structural durability and its air permeability. If corrosion products block the mesh openings, the pressure drop across the filter increases, the exhaust airflow rate of the range hood decreases, noise rises, and grease filtration efficiency deteriorates. Conversely, a mesh with excellent permeability but poor corrosion resistance will fail prematurely in service. Therefore, corrosion resistance testing and air permeability testing are typically performed together as a combined qualification program to demonstrate long-term reliability.

Corrosion resistance is commonly evaluated using neutral salt spray (NSS) and copper-accelerated acetic acid salt spray (CASS) tests in accordance with ISO 9227, ASTM B117, and GB/T 10125, while air permeability and airflow resistance are measured using a dedicated permeability test bench that determines the pressure drop of air passing through the mesh at specified face velocities. These tests are widely performed by accredited third-party laboratories for product certification, supplier qualification, and export compliance.

Testing Samples

Aluminum Alloy Oil Fume Filter Mesh

Multi-layer expanded aluminum mesh and aluminum honeycomb grease filters are the most common types used in household range hoods. Aluminum alloy mesh is lightweight and offers good thermal conductivity, but it is susceptible to pitting corrosion and white rust when exposed to chloride-containing salt spray or alkaline degreasers, making it a primary candidate for CASS corrosion evaluation and permeability verification.

Stainless Steel Oil Fume Filter Mesh

Mesh woven or stamped from austenitic stainless steel such as grade 304 or 316 is used in mid-to-high-end range hoods and commercial kitchen exhaust purification systems. Stainless steel mesh offers superior corrosion resistance, and testing typically focuses on confirming pitting-free performance after extended neutral salt spray exposure, together with pressure-drop verification of the woven or sintered structure.

Galvanized and Coated Steel Mesh

Galvanized steel mesh, epoxy-coated mesh, and PTFE-coated aluminum mesh are used in cost-sensitive or low-maintenance applications. For these samples, testing emphasizes the integrity of the protective coating, the appearance of white rust on zinc layers, and whether coating degradation after corrosion exposure causes measurable loss of air permeability.

Sample Preparation Requirements

• Sample dimensions are typically cut to fit the salt spray cabinet specimen racks and the permeability test fixture, commonly 100 mm × 150 mm or full-size filter panels for airflow testing.
• Samples must be cleaned with appropriate solvents to remove oil, dust, and fingerprints without damaging the surface coating before testing.
• Corrosion specimens and permeability specimens must be prepared separately, because salt spray exposure permanently alters the mesh surface and would invalidate baseline airflow measurements.
• A sufficient quantity of replicate specimens, typically at least three per test condition, is required to ensure statistical validity of the results.

Testing Items

The combined test program for oil fume filter mesh generally covers the following items:

• Neutral salt spray (NSS) corrosion resistance test
• Copper-accelerated acetic acid salt spray (CASS) corrosion resistance test
• Post-corrosion appearance evaluation and defect rating
• Mass loss or corrosion extent determination where required
• Air permeability measurement (pressure drop versus face velocity)
• Permeability retention comparison before and after corrosion exposure
• Optional supplementary items such as coating adhesion after salt spray, oil resistance, and thermal aging

The acceptance criteria for corrosion resistance typically specify no red rust, no more than a defined level of white rust or pitting, and an appearance rating number above a specified threshold. For air permeability, the criteria normally require that the pressure drop at the rated face velocity remain within a specified tolerance band, for example within ten percent of the design value, and that permeability retention after corrosion exposure exceed a defined percentage.

Testing Methods

Neutral Salt Spray Test (NSS)

The neutral salt spray test is conducted per ISO 9227, ASTM B117, and GB/T 10125. A 5% sodium chloride solution is atomized at a cabinet temperature of 35 °C with a collected solution pH between 6.5 and 7.2. Specimens are positioned at an angle of 15 to 30 degrees from vertical so that condensate flows freely over the mesh surface. Common test durations for oil fume filter mesh include 24, 48, 96, 168, and 240 hours, selected according to the material grade, coating type, and the quality level claimed by the manufacturer. After exposure, specimens are gently rinsed and dried, and the corrosion morphology is assessed for white rust, red rust, pitting, blistering, and coating loss.

CASS Test for Aluminum and Coated Mesh

The CASS test is a more aggressive accelerated corrosion method particularly relevant to aluminum alloy and coated filter mesh. The spray solution contains 5% sodium chloride with the addition of copper(II) chloride, acidified with acetic acid to a pH of 3.1 to 3.3, and the cabinet is operated at 50 °C. Because the copper ions accelerate cathodic reactions, the CASS test reproduces, in a short period, the degradation caused by long-term exposure to corrosive kitchen fumes and cleaning agents. Typical durations are 24, 48, or 72 hours, after which specimens are rated for pitting density, corrosion area percentage, and protective coating integrity.

Corrosion Rating and Evaluation

Post-exposure evaluation is performed with reference to ISO 10289 and GB/T 6461 for the rating of corroded specimens and protective coatings on metallic substrates. The number and size of corrosion defects are used to calculate an appearance rating, and results are reported together with photographic documentation. For mesh samples, particular attention is paid to corrosion products within the mesh openings, because pore blockage directly reduces airflow performance.

Air Permeability and Pressure Drop Test

Air permeability testing measures the resistance of the filter mesh to airflow and is performed on a dedicated test bench in which the specimen is clamped in a holder with sealed edges. Air is drawn through the mesh at controlled face velocities, commonly in the range of 0.5 to 2.5 m/s, which represents typical operating velocities in range hoods and kitchen exhaust systems. At each velocity, the static pressure difference across the mesh is measured with a calibrated pressure transducer, and a pressure-drop versus velocity curve is generated. For sintered metal mesh, the fluid permeability determination can be carried out in accordance with ISO 4022 and the related GB standard methodology, which characterizes the viscous and inertial permeability coefficients of the porous structure. The reported results include the pressure drop at the rated face velocity, the permeability coefficient, and the uniformity of flow across the specimen.

Permeability Retention After Corrosion

To quantify the combined effect of corrosion on airflow performance, identical specimens are first measured for baseline pressure drop, then subjected to the specified salt spray duration, dried, and re-measured on the same test bench under identical conditions. The permeability retention rate is calculated as the ratio of the post-corrosion airflow performance to the baseline value. A high retention rate confirms that the mesh does not shed blocking corrosion products and that the pore structure remains stable after corrosive aging.

Test Report Contents

• Sample description, material grade, coating type, mesh layer count, and dimensions
• Test standards referenced and test conditions, including salt solution concentration, pH, temperature, and duration
• Corrosion appearance rating, defect description, and photographic evidence
• Pressure drop values at each test velocity and the derived permeability data
• Permeability retention rate where before-and-after comparison is performed
• Conclusion on conformity with the specified acceptance criteria

Applications

Corrosion resistance and air permeability testing of oil fume filter mesh supports quality control and compliance across multiple industries and use cases:

• Household range hood manufacturers verifying grease filter durability and confirming that exhaust airflow performance is maintained over the product life cycle
• Commercial kitchen exhaust and fume purification equipment suppliers demonstrating filter reliability in high-load, continuous-operation environments
• Mesh and filter material producers performing material grade comparison, coating development, and incoming quality control
• E-commerce platform compliance, where test reports are used to substantiate durability and airflow claims for listed products
• Export certification support, providing data packages aligned with ISO, ASTM, EN, and GB standard requirements for international markets
• Oil-mist filtration components for machine tools and industrial air purification equipment, where salt spray and permeability verification are equally applicable

FAQ

Question: How long should the salt spray test last for oil fume filter mesh?

There is no single mandatory duration, because the requirement depends on the material, coating system, and quality grade. For household range hood filters, 24 to 96 hours of neutral salt spray is common for coated or galvanized mesh, while stainless steel mesh is often subjected to 240 hours or longer. Aluminum alloy mesh intended for premium products is frequently assessed with a 24 to 48 hour CASS test. The acceptance duration is usually agreed between the manufacturer and buyer or defined in the product specification.

Question: What are typical pass criteria for the corrosion test?

For stainless steel mesh, the typical criterion is no red rust or pitting visible to the naked eye after the specified duration. For galvanized mesh, a limited area of white rust may be acceptable, but red rust on the substrate is rejected. For coated mesh, blistering, coating loss, and under-film corrosion beyond the defined rating threshold constitute failure. These criteria should be clearly stated in the test plan before testing begins.

Question: Can the same specimen be used for both corrosion and permeability testing?

No. Corrosion exposure permanently modifies the mesh surface and may deposit corrosion products, so baseline permeability must be measured on separate reference specimens. A common practice is to measure baseline airflow on one group of specimens, run the corrosion exposure on a second identical group, and then compare results to calculate permeability retention.

Question: Why does air permeability matter as much as corrosion resistance?

A range hood or exhaust purifier is an airflow system, and the filter mesh is a key resistance element in that system. If permeability is too low, exhaust airflow drops, noise and energy consumption increase, and grease capture efficiency can fall. If permeability is excessively high, grease interception becomes inadequate. Testing ensures the mesh maintains the correct balance between filtration performance and airflow resistance throughout its service life.

Question: How should samples be submitted for testing?

Manufacturers typically submit full-size filter mesh panels or representative cut specimens along with material specifications, coating information, target test standards, required durations, and acceptance criteria. Working with an accredited third-party laboratory ensures that the salt spray cabinets and airflow measurement systems are properly calibrated and that the reported results are traceable and recognized by buyers and regulatory bodies.