Test of the degradation effect of sulfur dioxide

Sulfur Dioxide Degradation Effect Testing Service – Evaluating Material Resistance and Corrosion Performance for Brazilian Industrial Environments

As an ISO/IEC 17025 accredited independent testing laboratory, we offer specialised sulfur dioxide (SO₂) degradation effect testing services to Brazilian manufacturers, importers, and infrastructure operators. Sulfur dioxide is a prevalent pollutant in petrochemical, mining, power generation, and metallurgical processes, as well as in urban atmospheres. Prolonged exposure to SO₂, especially in the presence of moisture, can cause severe corrosion, embrittlement, discolouration, and loss of mechanical integrity in metals, coatings, polymers, and electronic components. Our test protocols simulate controlled SO₂‑rich atmospheres under defined temperature and humidity conditions to quantify the degradation effects on your products. All methods are aligned with ABNT NBR standards, ISO 3231 (Coatings – Resistance to humid atmospheres containing SO₂), ASTM G87 (Conducting moist SO₂ tests), and IEC 60068‑2‑60 (Environmental testing – Flowing mixed gas corrosion), and are recognised by IBAMA (environmental licensing), ANP (oil and gas), and INMETRO for product certification in corrosive service conditions.

Product Samples We Regularly Test for SO₂ Degradation

Our environmental chambers accommodate a broad range of materials and assemblies that may be exposed to sulfur dioxide in service. Typical test specimens include:

• Metallic materials and coatings – carbon steel, stainless steels, galvanised steel, copper‑based alloys, aluminium, and electroplated or hot‑dip zinc coatings
• Protective paint and powder coating systems – epoxy, polyurethane, polyester, and alkyd coatings on metal substrates
• Polymeric seals and gaskets – EPDM, nitrile, silicone, PTFE, and fluoroelastomer components
• Electronic assemblies and printed circuit boards – with conformal coatings, connectors, and solder joints
• Electrical cable insulation and jacketing – PVC, XLPE, and other halogen‑free compounds
• Construction materials – galvanised structural steel, cladding panels, and fasteners
• Heat exchangers and process equipment – tube and fin materials used in flue‑gas or exhaust systems

Metals and Metallic Coatings – Corrosion Rate and Pitting Assessment under SO₂ Atmosphere

• Moist SO₂ exposure test (ASTM G87 / ISO 3231) – We place prepared metal panels or finished components in a sealed environmental chamber and expose them to a controlled atmosphere containing 1‑10 ppm SO₂ (or higher as required) with a relative humidity of 95‑100 % RH at a temperature of 35‑40 °C. The exposure duration typically ranges from 24 hours to 1,000 hours, depending on the product and performance requirement. We monitor the SO₂ concentration using an electrochemical sensor and replenish as necessary.
• Mass loss and corrosion rate calculation – Before and after exposure, test specimens are cleaned according to ASTM G1 (preparing, cleaning, and evaluating corrosion test specimens). The mass loss is measured (in grams) and converted into a corrosion rate (mm/year or µm/year) using the metal density and exposed surface area. We report both the average and maximum penetration rates, which are critical for predicting service life in Brazilian petrochemical and flue‑gas environments.
• Pitting depth and surface roughness change – Using a digital profilometer and optical microscopy, we measure the depth of individual pits (in µm) and the change in surface roughness (Ra) after SO₂ exposure. The number of pits per unit area and the maximum pit depth are recorded, following ASTM G46 (examination and evaluation of pitting corrosion). A maximum pit depth exceeding the client’s specified limit (e.g., 50 µm) results in a non‑conformity.
• Metallographic cross‑section evaluation – We prepare cross‑sections of exposed samples, mount them in resin, grind and polish, and examine under a metallurgical microscope per ASTM E3. We assess the extent of intergranular attack, subsurface delamination, and coating/substrate interface degradation. High‑resolution micrographs are included in the final report.

Protective Coatings and Paint Systems – Blistering, Adhesion Loss and Colour Change

• Visual evaluation and blistering rating – After SO₂ exposure, we inspect coated panels according to ASTM D714 (blistering rating) and ISO 4628‑2 (degree of blistering). We assign a rating from 0 (no blistering) to 5 (dense large blisters) and report the size (2, 4, 6, 8, 10) per standard. Any rating worse than 3 is generally considered a failure for high‑grade protective coatings.
• Adhesion (pull‑off and cross‑cut) test before and after exposure – We perform pull‑off adhesion testing per ASTM D4541 and cross‑cut per ASTM D3359 (Method A) on unexposed and exposed panels. The percentage loss of adhesion is calculated; a loss exceeding 30 % indicates that the coating system has degraded significantly in the SO₂ atmosphere, requiring a reformulation for Brazilian coastal or industrial zones.
• Colour change and gloss retention measurement – Using a spectrophotometer and gloss meter, we measure the CIELAB colour coordinates (L*, a*, b*) and 60° gloss before and after exposure, per ASTM D2244. The colour difference (ΔE*) and gloss retention (%) are reported. A ΔE* > 3.0 or gloss retention < 80 % may be unacceptable for architectural or automotive exterior finishes, and we provide this data to help formulators adjust pigment and binder systems.
• Electrochemical impedance spectroscopy (EIS) on coated panels – For advanced coating evaluation, we perform EIS at the beginning and end of the SO₂ test to quantify the coating’s barrier resistance (pore resistance) and capacitance. The test follows ASTM G106; a decrease in pore resistance by more than one order of magnitude indicates significant electrolyte permeation, which correlates with long‑term corrosion protection loss.

Polymers and Elastomers – Mechanical Property Degradation and Surface Cracking

• Change in tensile strength and elongation after SO₂ exposure – We condition dumbbell‑shaped specimens of polymers (e.g., seals, gaskets, cable insulation) in the SO₂ chamber for 7 to 28 days. After removal, we perform tensile testing per ASTM D638 (plastics) or ASTM D412 (elastomers) and compare the results to unexposed control samples. The percentage retention of tensile strength and elongation is calculated; a retention below 70 % indicates severe degradation, often due to chain scission or cross‑linking induced by SO₂ oxidation.
• Hardness variation and surface micro‑crack evaluation – We measure Shore A or D hardness before and after exposure and examine the surface under a stereomicroscope (10‑50×) for micro‑cracks, crazing, or surface bloom. Any visible cracking that penetrates more than 0.1 mm is recorded and classified as a failure. This is particularly important for sealing materials used in Brazilian oil‑field valves and flanges.
• Change in volume and mass (swelling or leaching) – We weigh and measure the volume (by immersion in water or by geometric calculation) of elastomer specimens before and after SO₂ exposure. An increase or decrease of more than 5 % is reported as dimensional instability, which may affect seal compression and tightness.
• Chemical analysis (FTIR) for degradation products – We perform Fourier‑transform infrared (FTIR) spectroscopy on the surface of exposed polymers to identify oxidation products (e.g., carbonyl groups, sulfonic acids) that indicate chemical attack. The FTIR spectra of exposed and unexposed samples are overlaid, and the change in absorbance ratio (e.g., carbonyl index) is calculated, following a modified approach from ASTM E168.

Electronic Components and Assemblies – Contact Resistance, Insulation and Solder Joint Integrity

• Corrosion of electrical contacts (fretting and creep) – We expose connectors, relay contacts, and PCB edge connectors to SO₂ atmosphere (with humidity) for 96 hours per IEC 60068‑2‑60 (Method 4). The contact resistance (milliohms) is measured before and after using a four‑wire method per ASTM B539. An increase of more than 20 % of the initial value is considered a failure, as it may lead to intermittent electrical signals in Brazilian power and control systems.
• Insulation resistance and dielectric strength of printed circuit boards – After SO₂ exposure, we measure insulation resistance between adjacent traces and vias per IPC‑TM‑650 (method 2.5.4) and perform a dielectric withstand test (500 V DC for 60 seconds). Any leakage current exceeding 10 μA or breakdown indicates degradation of the solder mask or conformal coating.
• Solder joint corrosion and surface morphology (SEM/EDX) – We examine exposed solder joints using scanning electron microscopy (SEM) with energy‑dispersive X‑ray analysis (EDX) to identify corrosion products (e.g., sulfides, sulfates). The presence of sulfur‑containing compounds on the solder surface is documented, and the extent of intermetallic phase degradation is assessed. This is critical for Brazilian electronics used in polluted industrial atmospheres.
• Metal migration and dendrite formation check – Under humid SO₂ conditions, silver and copper may migrate and form dendrites. We inspect the board under a microscope at 50‑200× magnification and report any visible dendritic growth that could cause short circuits. Testing follows the guidelines of IPC‑9201 (surface insulation resistance testing).

Report Acceptance & Compliance with Brazilian Regulatory and Industry Standards

All SO₂ degradation tests described above are conducted within the scope of our ISO/IEC 17025:2017 accreditation, using calibrated environmental chambers with verified temperature, humidity, and SO₂ concentration control (traceable to NIST and international reference materials). Our comprehensive test reports include: a full description of the test parameters (concentration, temperature, RH, duration), pre‑exposure and post‑exposure property data for each specimen (mechanical, physical, electrical, visual), statistical analysis (mean, standard deviation, percent change), photographic documentation of macroscopic and microscopic degradation, FTIR or SEM/EDX results where applicable, and a clear conformity statement against your specified acceptance criteria or reference standard limits. We also provide an uncertainty budget for key measurements (mass loss, thickness, hardness, resistance). These reports are widely accepted by IBAMA for environmental compliance demonstrations, by ANP for equipment qualification in corrosive oil‑and‑gas processing, by INMETRO for product safety certification, and by Brazilian mining, steelmaking, and automotive industries for supplier validation and material selection. Bilingual (Portuguese/English) versions are available to facilitate submissions to regulatory authorities and internal quality reviews. With our rigorous SO₂ degradation testing, you can confidently assess and improve the durability of your products against sulfur‑induced deterioration, ensuring reliable performance in Brazil’s demanding industrial and atmospheric environments.