Corrosion Rate Testing Service

Corrosion Rate Testing Service – Accredited ISO/IEC 17025 Metal Degradation Assessment for the Colombian Market

Corrosion rate is a fundamental parameter for evaluating the durability, safety, and service life of metallic materials, components, and equipment exposed to aggressive environments in industries such as oil and gas, mining, chemical processing, power generation, marine engineering, and infrastructure construction. Accurate measurement of corrosion rates allows engineers and asset managers to predict material loss, schedule maintenance, select appropriate materials, and ensure compliance with safety and environmental regulations. In the Colombian market, where the Agencia Nacional de Hidrocarburos (ANH), the Ministerio de Minas y Energía (MinMinas), the Superintendencia de Industria y Comercio (SIC), and the Dirección de Impuestos y Aduanas Nacionales (DIAN) enforce strict quality, safety, and environmental standards for materials used in the oil, gas, mining, and energy sectors, the accurate evaluation of corrosion rate is essential for product certification, supplier qualification, material selection, quality control in manufacturing, and import-export processes. Our laboratory offers a comprehensive corrosion rate testing service, applying standardized gravimetric, electrochemical, and accelerated exposure methods to determine the corrosion rate (in mm/year, mpy, or g/m²·day) of metals and alloys under a wide range of simulated service conditions. All tests are performed under our ISO/IEC 17025 (CNAS) accreditation, and the resulting reports are fully accepted by Colombian authorities, making them indispensable for regulatory compliance, asset integrity management, and market access in Colombia.

Test Samples and Materials We Regularly Examine

Our laboratory receives a wide variety of metallic materials and components for corrosion rate testing. Typical samples include:

• Carbon steels and low-alloy steels – used in pipelines, pressure vessels, and structural components in oil, gas, and mining.
• Stainless steels (austenitic, ferritic, duplex, and precipitation-hardening) – for chemical processing, food equipment, and marine applications.
• Aluminum and aluminum alloys – for aerospace, automotive, and construction applications.
• Copper and copper alloys (brass, bronze, cupronickel) – for heat exchangers, condensers, and plumbing systems.
• Nickel-based alloys (Inconel, Hastelloy, Monel) – for high-temperature and corrosive environments.
• Titanium and titanium alloys – for aerospace and biomedical applications.
• Galvanized and coated materials – zinc-coated, aluminized, and organic-coated steels.
• Prototype and new alloy formulations – submitted by manufacturers for corrosion resistance validation before series production.
• Field-exposed coupons and equipment sections – for failure analysis and remaining life assessment.

Gravimetric Corrosion Rate Testing – Weight Loss Method

The gravimetric (weight loss) method is the most widely used and standardized technique for determining the corrosion rate of metals exposed to liquids, gases, or atmospheric conditions. It measures the loss of mass of a metal specimen after a specified exposure period, from which the average corrosion rate is calculated. Our procedures follow international standards and the requirements of the Colombian oil, gas, and chemical industries.

• Immersion corrosion test (ASTM G31 / ISO 7539-1 / NTC 4703) – metal coupons (typically 25 mm × 50 mm × 3 mm) are cleaned, weighed, and immersed in the test solution (e.g., 3.5 % NaCl, HCl, H₂SO₄, or process water) at a controlled temperature (e.g., 23 °C, 40 °C, 60 °C, 90 °C) for a specified duration (e.g., 24, 72, 168, 504, or 1000 hours). After exposure, the coupons are cleaned of corrosion products (using mechanical or chemical cleaning) and re-weighed. The weight loss is used to calculate the corrosion rate in mm/year (or mpy) using the formula: Corrosion Rate (mm/year) = (Weight loss (g) × K) / (Area (cm²) × Density (g/cm³) × Time (hours)), where K is a constant (e.g., 87.6 for mm/year). We report the corrosion rate, the type of corrosion (general, pitting, crevice), and the appearance of the coupon.
• Alternate immersion test (ASTM G44 / NTC 4704 – for simulating wet/dry cycles) – the coupon is alternately immersed in the test solution and exposed to air (e.g., 10 minutes immersion, 50 minutes drying) for a specified number of cycles. This simulates the conditions in splash zones, marine atmospheres, and industrial environments with frequent wetting and drying. We report the corrosion rate and the surface condition.
• Atmospheric corrosion test (ASTM G50 / NTC 4705 – for outdoor exposure) – metal coupons are exposed to outdoor atmospheric conditions at a specified test site (e.g., an industrial, marine, or rural site) for a period of months or years. The weight loss is measured at intervals, and the corrosion rate is calculated. We report the corrosion rate and the environmental conditions.
• High-temperature immersion test (NTC 4706 – for elevated temperature service) – the immersion test is performed at temperatures up to 300 °C using an autoclave or a pressurized vessel, simulating conditions in heat exchangers, boilers, and chemical reactors. We report the corrosion rate at elevated temperatures.
• Corrosion rate in flowing conditions (ASTM G73 / NTC 4707 – rotating cylinder or flow loop) – we use a rotating cylinder electrode (RCE) or a flow loop to simulate the effect of fluid flow on the corrosion rate, which is relevant for pipelines and piping systems. We report the corrosion rate as a function of flow velocity.

Electrochemical Corrosion Rate Testing – Polarization Resistance and Tafel Extrapolation

Electrochemical methods provide rapid and highly sensitive measurements of corrosion rates, often in real time. The techniques are based on the relationship between the applied potential and the resulting current, and are especially useful for monitoring corrosion in process streams, for evaluating the effectiveness of corrosion inhibitors, and for performing accelerated tests in the laboratory. Our procedures follow international standards and the requirements of the Colombian oil and gas sector.

• Linear polarization resistance (LPR) test (ASTM G59 / ISO 17475 / NTC 4710) – a three-electrode electrochemical cell is used, with the metal specimen as the working electrode, a reference electrode (e.g., Ag/AgCl), and a counter electrode (platinum or graphite). A small potential scan (typically ±10 to ±20 mV around the open-circuit potential) is applied at a slow scan rate (e.g., 0.5 mV/s). The polarization resistance (Rp) is obtained from the slope of the potential vs. current density plot. The corrosion rate is calculated from Rp using the Stern-Geary equation: Corrosion rate = (B / Rp) × K, where B is a constant (typically 26 mV for active metals, or a value derived from Tafel slopes). We report the polarization resistance (in Ω·cm²), the corrosion current density (icorr, in μA/cm²), and the corrosion rate (in mm/year).
• Tafel extrapolation test (ASTM G3 / NTC 4711 – for determining corrosion kinetics) – a potentiodynamic scan is performed over a wider potential range (typically from -250 mV to +250 mV relative to the open-circuit potential) at a scan rate of 1 mV/s. The anodic and cathodic Tafel slopes (βa and βc) are determined from the linear regions of the E vs. log i plot, and the corrosion current density (icorr) is obtained from the intersection of the extrapolated Tafel lines. The corrosion rate is calculated from icorr using Faraday's law. We report the Tafel slopes, the corrosion potential (Ecorr), icorr, and the corrosion rate.
• Potentiodynamic polarization test for pitting and crevice corrosion (ASTM G61 / NTC 4712 – for stainless steels and alloys) – a potentiodynamic scan is performed at a higher scan rate (e.g., 0.5 mV/s) from the cathodic region to the anodic region, and the breakdown potential (Eb) and the protection potential (Ep) are determined. These parameters are used to assess the susceptibility to localized corrosion. We report Eb, Ep, the hysteresis loop area, and the susceptibility rating.
• Electrochemical impedance spectroscopy (EIS) – ASTM G106 / NTC 4713 – for detailed kinetic analysis – we perform EIS measurements at the open-circuit potential over a frequency range (e.g., from 100 kHz to 10 mHz) with a small AC perturbation (10 mV). The Nyquist and Bode plots are analyzed to obtain the charge transfer resistance (Rct), the double-layer capacitance (Cdl), and the diffusion-related parameters. The corrosion rate is derived from Rct. We report the EIS parameters and the corrosion rate.
• Corrosion monitoring in process streams (NTC 4714 – using corrosion probes) – for continuous monitoring in the field, we use corrosion probes (e.g., electrical resistance probes, LPR probes) to measure the corrosion rate in real time in pipelines, reactors, and storage tanks. We report the corrosion rate trend and the cumulative metal loss.

Accelerated Corrosion Testing – Salt Spray, Acidic Atmospheres, and Cyclic Conditions

Accelerated corrosion tests are used to simulate the effects of harsh environments on metals and coatings in a shorter time, allowing rapid screening of materials and evaluation of protective coatings. These tests are widely used for quality control in the automotive, construction, and metal finishing industries, and are required for certification by the SIC and the Ministerio de Ambiente.

• Salt spray (fog) test (ASTM B117 / ISO 9227 / NTC 4750 – for coatings and metals) – metal specimens (coated or bare) are placed in a salt spray chamber and exposed to a continuous 5 % NaCl fog at 35 °C for a specified duration (e.g., 24, 48, 96, 240, 500 hours, or more). The specimens are inspected for corrosion products (rust, pitting), blistering, and loss of adhesion (for coatings). The corrosion rate is determined by weight loss or by visual rating. We report the corrosion appearance, the weight loss, and the rating according to ASTM D610 (rust grade) or ASTM D714 (blistering).
• Cyclic corrosion test (ASTM G85 / NTC 4751 – for simulating wet/dry cycles with salt spray and humidity) – the specimen is exposed to alternating cycles of salt spray (e.g., 4 hours), drying (e.g., 2 hours), and high humidity (e.g., 2 hours) at elevated temperatures. This test is more realistic than continuous salt spray and is used for automotive and marine coatings. We report the weight loss and the visual condition.
• Acidified salt spray test (ASTM G85 – Annex A1 / NTC 4752 – for acidic environments) – the salt spray solution is acidified with acetic acid or sulfuric acid to a pH of 3.0 to 3.5, simulating the conditions of industrial and acidic atmospheric environments. We report the corrosion rate and the appearance.
• Alternate immersion test (ASTM G44 / NTC 4753 – for simulating tidal and splash zones) – the specimen is alternately immersed in the test solution (e.g., 3.5 % NaCl) and exposed to air, simulating the conditions in marine environments, including tidal and splash zones. We report the corrosion rate and the pitting depth.
• High-temperature salt spray test (NTC 4754 – for automotive exhaust and high-temperature components) – the salt spray test is performed at elevated temperatures (e.g., 50 °C, 60 °C) to simulate the conditions of automotive exhaust systems and high-temperature industrial equipment. We report the corrosion rate and the appearance.

Pitting and Crevice Corrosion Testing – Localized Corrosion Susceptibility

Localized corrosion, such as pitting and crevice corrosion, can be more dangerous than general corrosion because it leads to rapid perforation and failure with minimal material loss. Our specific tests evaluate the resistance of metals and alloys to these localized forms of corrosion, which is critical for materials used in chloride-containing environments (e.g., seawater, brine, and chemical process streams).

• • Pitting potential measurement by potentiodynamic polarization (ASTM G61 / NTC 4760 – for stainless steels) – the potentiodynamic polarization curve is obtained in a chloride-containing solution (e.g., 3.5 % NaCl). The pitting potential (Eb) is determined as the potential at which the anodic current density increases sharply, indicating the initiation of pitting. A more noble (positive) pitting potential indicates a greater resistance to pitting. We report Eb, the current density at the breakpoint, and the susceptibility rating.
  • Ferric chloride pitting test (ASTM G48 / NTC 4761 – for stainless steels and nickel alloys) – metal specimens are immersed in a 6 % FeCl₃ solution (acidified with HCl) at a controlled temperature (e.g., 22 °C, 40 °C, 50 °C) for a specified duration (e.g., 24, 72, or 168 hours). After exposure, the specimens are examined for the presence of pits, and the maximum pit depth is measured. We report the pit count, the maximum pit depth (in mm), and the corrosion rate.
  • Crevice corrosion test (ASTM G48 – Method B / NTC 4762 – for crevice resistance) – metal specimens are assembled with a crevice former (a PTFE block or washer) to create a narrow gap, and then immersed in the FeCl₃ solution (or another aggressive solution) for a specified duration. The crevice region is inspected for attack. We report the presence and depth of crevice corrosion.
  • Critical pitting temperature (CPT) test (ASTM G150 / NTC 4763 – for stainless steels) – a metal specimen is immersed in a 10 % FeCl₃ solution, and the temperature is gradually increased (0.5 °C/min) while the potential is monitored. The critical pitting temperature is defined as the temperature at which a sudden increase in current (indicating pitting) occurs. We report the CPT (in °C).
  • Pitting depth and density measurement (NTC 4764 – optical microscopy and profilometry) – after the localized corrosion tests, we measure the depth and the distribution of pits using an optical microscope, a scanning electron microscope, or a contact profilometer. We report the maximum pit depth (in μm), the average pit depth, and the pit density (pits/cm²).

Complementary Tests – Corrosion Product Analysis and Material Characterization

To provide a comprehensive assessment of the corrosion process and to identify the mechanisms of attack, we complement the corrosion rate tests with chemical and microstructural analyses. These tests are essential for failure analysis, material selection, and for understanding the long-term behavior of materials in the corrosive environments of the Colombian oil, gas, and mining sectors.

• X‑ray diffraction (XRD) of corrosion products – ASTM E1857 / NTC 4770 – the corrosion products (scale, rust, deposits) are scraped from the metal surface and analyzed by XRD to identify the crystalline compounds (e.g., Fe₂O₃, Fe₃O₄, FeOOH, sulfides, chlorides). The phase identification helps understand the corrosion mechanism and the environmental conditions. We report the mineral phases present.
• Scanning electron microscopy (SEM) and EDS analysis – ASTM E1508 / NTC 4771 – the corrosion morphology (pitting, intergranular attack, cracking) is examined using SEM, and the elemental composition of the corrosion products is determined by EDS. We report the SEM images, the elemental maps, and the chemical composition of the corrosion layers.
• Metallographic examination (ASTM E3 / NTC 4772 – for microstructure analysis) – we prepare cross‑sections of the metal specimens to observe the depth of intergranular attack, the microstructure, and the presence of any secondary phases (e.g., carbides, sigma phase) that may have promoted corrosion. We report the microstructure and the depth of attack.
• Hardness and tensile testing (ASTM E18 / NTC 4773 – for mechanical property assessment after corrosion) – we measure the hardness (Rockwell, Vickers) and the tensile properties (tensile strength, elongation) of the metal specimens after the corrosion test to evaluate any loss of mechanical integrity caused by the corrosion. We report the changes in hardness and tensile properties.
• Corrosion rate prediction using the NACE model (NTC 4774 – for oil and gas pipelines) – we use the NACE (National Association of Corrosion Engineers) empirical models for predicting the corrosion rate in sour (H₂S) and sweet (CO₂) service based on the measured parameters (temperature, pH, flow velocity). We report the predicted corrosion rate and compare it with the laboratory-measured value.

Test Report and Recognition in the Colombian Oil, Gas, and Industrial Sector

All procedures described are within the scope of our ISO/IEC 17025 accreditation, with equipment calibrated periodically (balances, potentiostats, salt spray chambers, immersion baths, etc.) and traceability to international standards (NIST, PTB). Our test reports are issued in Spanish and include:

• Full identification of the material (grade, heat number, dimensions, surface finish, and manufacturer).
• Detailed description of the test methods applied (ASTM/ISO/NTC standards, exposure conditions, temperature, solution composition, and duration).
• Numerical results: corrosion rate (mm/year, mpy, or g/m²·day), weight loss (mg), pitting potential (Eb), crevice corrosion depth (mm), polarization resistance (Ω·cm²), Tafel slopes (mV/decade), and corrosion current density (μA/cm²).
• Graphical data: weight loss vs. time, polarization curves, Nyquist and Bode plots, and pitting potential curves.
• Comparative tables against the values specified by the client or against the limits of the NTC 4703 (Immersion), NTC 4710 (LPR), NTC 4750 (Salt spray), and the requirements of the ANH, MinMinas, SIC, and DIAN for corrosion resistance in oil, gas, and mining equipment.
• Photographs and micrographs (SEM, optical) of the specimens before and after the tests, showing the corrosion patterns, pits, and the microstructure of the corrosion layer.
• Recommendations for material selection (e.g., upgrading to a more corrosion‑resistant alloy), the use of corrosion inhibitors, the application of protective coatings, or the adjustment of operating conditions (e.g., temperature, pH, flow rate) to reduce the corrosion rate.
• Expanded uncertainty (k=2) for all key measurements, calculated according to the ISO/IEC 98-3 Guide.

These reports are fully accepted by the Agencia Nacional de Hidrocarburos (ANH) for the certification of materials used in oil and gas production and transportation, by the Ministerio de Minas y Energía (MinMinas) for the approval of materials in mining and energy projects, by the Superintendencia de Industria y Comercio (SIC) for product registration and quality certification, and by the Dirección de Impuestos y Aduanas Nacionales (DIAN) for tariff classification and quality verification in the import of metals and alloys. Additionally, we offer consulting services for corrosion risk assessment, the selection of corrosion‑resistant materials, and the implementation of corrosion monitoring and mitigation programs, contributing to the safety, integrity, and economic efficiency of industrial assets and infrastructure in the diverse and growing Colombian market, from the oil fields of the Llanos Orientales to the coastal refineries and the mining operations in the Andes.