Intergranular corrosion (IGC) testing of stainless steel woven wire mesh is a critical quality control process that evaluates the material's resistance to grain boundary attack caused by sensitization during welding, heat treatment, or service in corrosive environments. Our laboratory provides comprehensive IGC testing services for stainless steel woven mesh products in accordance with ASTM A262, GB/T 4334, and ISO 3651 standards, ensuring material integrity for demanding filtration, chemical, and pharmaceutical applications.
Technical Overview
Intergranular corrosion is a localized form of corrosion that attacks the grain boundaries of austenitic and ferritic stainless steels, often without visible warning signs on the surface. In stainless steel woven wire mesh, this degradation mechanism is particularly dangerous because the fine wire diameters—commonly ranging from 0.02 mm to 3 mm—leave very little material margin before structural failure occurs. When a mesh wire suffers grain boundary attack, individual grains can drop out of the matrix, causing wire breakage, mesh aperture distortion, and premature screen failure.
Sensitization is the primary cause of intergranular corrosion in stainless steel woven mesh. During weaving, annealing, welding of mesh panels, or high-temperature service exposure in the range of 425°C to 815°C, chromium carbides (Cr23C6) precipitate at grain boundaries. This precipitation depletes the chromium content in zones adjacent to the grain boundaries to below the ~12% threshold required for passivation, leaving these depleted zones vulnerable to preferential corrosive attack. Stabilized grades containing titanium or niobium, and low-carbon grades (L grades), are engineered specifically to mitigate this risk.
Intergranular corrosion testing subjects mesh specimens to standardized accelerated corrosion environments, followed by metallographic examination and bend testing, to determine whether the material has been sensitized and whether the grain boundaries can resist attack. The test results are essential for qualification of mesh intended for chemical processing, petrochemical service, nuclear applications, and other aggressive environments.
Testing Samples
Austenitic Stainless Steel Woven Mesh
Specimens prepared from AISI 304, 304L, 316, 316L, 321, and 347 woven wire mesh in plain weave, twill weave, and Dutch weave configurations. Both as-woven and post-welded (welded mesh panel) conditions can be evaluated to assess the heat-affected zone sensitivity.
Ferritic and Duplex Stainless Steel Mesh
Specimens from ferritic grades such as 430 and 446, tested per ASTM A763, and duplex grades including 2205 (UNS S32205) and 2507 woven mesh, which require modified test solutions and evaluation criteria appropriate to their mixed microstructure.
Product Forms and Sample Requirements
- Mesh sheet or coil sections with minimum dimensions of 30 mm × 100 mm per test method
- Individual wire samples extracted from warp and weft directions for selective evaluation
- Welded mesh joints including the weld bead and heat-affected zone
- Sensitized (heat-treated) and as-received specimens for comparative assessment
- Specimens must be degreased, pickled, and passivated prior to testing to remove surface contamination and oxide scale
Testing Items
Our intergranular corrosion testing program for stainless steel woven wire mesh covers the following evaluation parameters:
- Determination of sensitization susceptibility in as-supplied, as-welded, and heat-treated conditions
- Corrosion rate measurement by gravimetric weight-loss analysis (mm/year conversion)
- Metallographic examination of grain boundary ditching and attack depth after etching
- Bend test evaluation for intergranular cracking and grain dropping after exposure
- Microstructure verification of grain size, carbide precipitation, and sigma phase presence
- Verification of material compliance with purchase specifications and code requirements
- Heat treatment validation for solution annealing effectiveness
- Evaluation of welded mesh joints and heat-affected zone corrosion resistance
Testing Methods
ASTM A262 Practice A – Oxalic Acid Etch Test
A rapid screening method in which specimens are electrolytically etched in a 10% oxalic acid solution at 1 A/cm² for 90 seconds. Metallographic examination at 250× to 500× classifies the etch structure as step, dual, or ditch. Ditch structures indicate sensitization and require confirmatory testing by Practices B, C, or E. This method is suitable for rapid acceptance screening of 304 and 316 mesh production lots.
ASTM A262 Practice B – Ferric Sulfate–Sulfuric Acid Test
Specimens are immersed for 120 hours in a boiling solution of 50% sulfuric acid with 25 g of ferric sulfate. The corrosion rate is calculated from weight loss and is compared against the specified maximum, typically 1.14 μm/h (0.045 in/month) for acceptance. This test is the most widely specified quantitative method for chromium carbide sensitization in mesh materials.
ASTM A262 Practice C – Nitric Acid Test (Huey Test)
Five consecutive 48-hour boiling periods in 65% nitric acid, with weight loss measured after each period. This practice detects sensitization plus sigma phase and other nitric acid-specific intergranular attack, making it essential for mesh intended for nitric acid service and nuclear fuel reprocessing applications.
ASTM A262 Practice E – Copper–Copper Sulfate–16% Sulfuric Acid Test (Strauss Test)
Specimens are exposed for 24 hours in contact with copper shot in a boiling 16% sulfuric acid solution with copper sulfate, followed by a 180° bend test over a mandrel equal to the specimen thickness. Cracking or fissuring on the bent surface reveals intergranular attack. This method is frequently applied to welded mesh and stabilized grades.
GB/T 4334 and ISO 3651-2 Equivalent Methods
Chinese national standard GB/T 4334 (Methods A through E) and international standard ISO 3651-2 provide equivalent test procedures—the 16% sulfuric acid–copper sulfate test and the 35% sulfuric acid–copper sulfate test—with acceptance criteria aligned to ASTM A262. We perform testing to all three standard families and report results in formats acceptable for domestic and international certification.
ASTM A763 for Ferritic Stainless Steels
Ferritic mesh grades are tested using the ferric sulfate–50% sulfuric acid practice (Practice X or Y) with appropriate exposure times and evaluation criteria specific to ferritic microstructures, addressing chromium carbide and chromium nitride precipitation at grain boundaries.
Applications
Intergranular corrosion testing of stainless steel woven wire mesh supports quality assurance across diverse industries:
- Petrochemical and chemical processing: catalyst recovery screens, distillation column internals, and filter elements exposed to acidic media
- Pharmaceutical and food processing: sanitary filtration mesh requiring validated corrosion resistance and product purity
- Nuclear power: fuel assembly components and radioactive waste filtration systems requiring Huey test qualification
- Marine and offshore engineering: seawater intake screens and hydraulic filtration mesh subject to chloride-bearing environments
- Aerospace: fluid filtration screens and composite molding mesh requiring verified material integrity
- Export certification: compliance documentation for stainless steel mesh shipped to international buyers specifying ASTM, EN, or ISO acceptance criteria
- Material failure analysis: root cause determination when mesh exhibits unexpected cracking, wire breakage, or leakage in service
FAQ
What causes intergranular corrosion in stainless steel woven mesh?
Intergranular corrosion is primarily caused by chromium carbide precipitation at grain boundaries when the mesh is heated in the sensitization range of 425°C to 815°C—typically during welding, improper annealing, or slow cooling after heat treatment. The chromium-depleted zones adjacent to the boundaries lose corrosion resistance and are preferentially attacked in corrosive media.
How long does an intergranular corrosion test take?
Test durations vary by method: the oxalic acid etch screen (Practice A) can be completed within one day; the Strauss test (Practice E) requires approximately 24 hours of exposure plus bend testing; the ferric sulfate test (Practice B) requires 120 hours of boiling exposure; and the Huey test (Practice C) requires 240 hours across five 48-hour periods. Total turnaround including sample preparation, metallography, and reporting typically ranges from 3 to 12 working days.
Which test method should I choose for my mesh product?
Practice A is recommended for fast production screening; Practice B is the standard quantitative method for most austenitic mesh; Practice C is specified for nitric acid and nuclear service; Practice E is preferred for welded mesh and stabilized grades. Our engineers can recommend the most appropriate method based on your alloy grade, product condition, and end-use environment.
Can low-carbon and stabilized grades still fail IGC testing?
Yes. Although 304L, 316L, 321, and 347 grades are designed to resist sensitization, improper heat treatment, extended service above 400°C, or heavy cold work followed by sensitizing heat treatment can still produce susceptibility. Independent verification through testing remains essential for critical applications.
Do you accept small mesh samples and individual wires?
Yes. We routinely test small mesh coupons and individual wires extracted from woven mesh. Our metallographic preparation techniques are adapted to fine wire diameters down to 0.02 mm, ensuring reliable bend testing and microstructural evaluation even for ultra-fine Dutch weave products.
What reports and certificates are provided?
Each test is documented with a formal test report containing specimen identification, test method and standard reference, exposure conditions, corrosion rate calculations, bend test results, metallographic photomicrographs of the etch structure, and a clear pass/fail conclusion against the specified acceptance criteria. Reports can be issued in English and stamped with laboratory accreditation where applicable.