Seawater full immersion corrosion test service

Seawater Full Immersion Corrosion Testing Service – Evaluating Material Durability in Marine Environments for Brazilian Offshore and Coastal Applications

As an ISO/IEC 17025 accredited independent testing laboratory, we provide comprehensive seawater full immersion corrosion testing services to Brazilian manufacturers, EPC contractors, and asset operators serving the offshore oil and gas, shipbuilding, port infrastructure, desalination, and renewable energy sectors. Full immersion in natural or synthetic seawater exposes materials to the combined effects of chlorides, dissolved oxygen, biofouling, temperature, and hydrostatic pressure – conditions that closely replicate subsea, tidal, and splash‑zone service environments. Our test protocols quantify general corrosion rates, pitting depth, crevice corrosion susceptibility, galvanic effects, and stress‑corrosion cracking under controlled and simulated field conditions. All methods are aligned with ASTM G31 (Laboratory Immersion Corrosion Testing), ASTM G1 (Cleaning and Evaluating Corrosion Test Specimens), NACE TM0169 (Laboratory Corrosion Testing of Metals), ISO 11306 (Corrosion of metals and alloys – Guidelines for exposing and evaluating in sea water), and ASTM D665 (for rust‑preventing characteristics). Our reports are recognised by ANP (oil and gas regulator), IBAMA (environmental agency), the Brazilian Navy (for naval certification), and INMETRO for product quality and safety compliance.

Test Specimens and Components We Regularly Evaluate

Our seawater immersion test facilities accommodate a wide range of material types and finished components. Typical test articles include:

• Carbon and low‑alloy steels – structural steel plates, pipes, flanges, and fasteners for offshore platforms and ship hulls
• Stainless steels – austenitic (304, 316), duplex (2205, 2507), and super‑austenitic grades for piping and heat exchangers
• Aluminium and its alloys – 5xxx and 6xxx series for hulls, superstructures, and marine equipment
• Copper‑based alloys – brass, bronze, and cupronickel (90/10, 70/30) for seawater piping and condensers
• Nickel‑based superalloys – Inconel®, Monel®, and Hastelloy®‑type alloys for critical offshore applications
• Organic and metallic coatings – epoxy, polyurethane, zinc‑rich primers, thermal‑sprayed aluminium, and galvanised layers
• Welded joints and heat‑affected zones – to evaluate galvanic and microstructural corrosion effects
• Composite materials – fibreglass‑reinforced plastic (FRP) and carbon‑fibre composites used in seawater contact

Metals and Alloys – General Corrosion Rate and Pitting Assessment

• Full immersion test in natural or synthetic seawater (ASTM G31 / NACE TM0169) – We suspend prepared test coupons (typically 50×25×3 mm) in a sealed glass or plastic vessel filled with seawater (either naturally collected from the Brazilian coast, with periodic replacement, or prepared according to ASTM D1141 for substitute ocean water). The temperature is controlled to the specified value (e.g., 25 °C for ambient, 40‑60 °C for elevated service, or 4 °C for deep‑water simulation). Test durations range from 30 days to 12 months, depending on the required corrosion rate and the client’s specification. Coupons are removed at intervals, cleaned of corrosion products per ASTM G1 (using chemical or electrolytic methods), and weighed to calculate the mass loss. The corrosion rate is expressed in mm/year or mpy (mils per year), with a typical uncertainty of ±5 %.
• Pitting depth and pit morphology – After cleaning, we examine the coupon surface under a stereomicroscope and measure the depth of the deepest pits using a digital profilometer or a depth gauge (resolution 0.01 mm). The pitting factor (ratio of deepest pit to average corrosion penetration) is calculated. We also classify pitting according to ASTM G46 (Examination and Evaluation of Pitting Corrosion), providing both numerical data and photographic records.
• Crevice corrosion test (ASTM G78) – For materials prone to crevice attack, we assemble specimens with a standard crevice former (e.g., a PTFE block or washer) to create a confined gap. After immersion, we disassemble and examine the contact area for any discolouration, etching, or pitting. The critical crevice temperature (CCT) can be determined by testing at multiple temperatures – a key parameter for Brazilian offshore equipment where tight seals and gaskets are common.
• Effect of flow velocity and aeration – In addition to static immersion, we offer a dynamic test using a recirculating seawater loop with controlled flow rate (0.5‑5 m/s) and aeration, simulating the conditions inside pipelines and pump impellers. The corrosion rate under flow is compared to static values, and the difference indicates flow‑accelerated corrosion sensitivity.

Stainless Steels and Duplex Alloys – Localised Corrosion and Susceptibility to Chloride Attack

• Critical pitting temperature (CPT) and critical crevice temperature (CCT) determination – We perform a series of full immersion tests at increasing temperatures (from 20 °C to 80 °C) in synthetic seawater, with ferric chloride added as an oxidising agent (per ASTM G48 Method A for pitting and Method C for crevice). The CPT is the temperature at which pitting becomes visible, and the CCT is the temperature at which crevice attack initiates under a standard crevice former. These values are essential for selecting stainless steel grades for Brazilian heat exchangers and seawater‑cooled systems.
• Critical chloride concentration test – We vary the chloride content (from 1% to 10% by weight) in the test solution at a fixed temperature to determine the threshold concentration above which pitting or stress‑corrosion cracking occurs. This is particularly relevant for produced‑water reinjection and desalination plant feed.
• Microstructural examination after immersion – We prepare metallographic cross‑sections of exposed coupons (per ASTM E3) to detect intergranular attack, sigma‑phase precipitation (in duplex steels), or selective leaching. High‑resolution images (SEM/EDS) are provided to identify corrosion products and elemental enrichment at the attack front.
• Electrochemical monitoring (potentiodynamic polarisation) – In parallel with mass‑loss coupons, we perform potentiodynamic scans on separate specimens in the same seawater to measure the corrosion potential (Ecorr), pitting potential (Epit), and protection potential (Eprot). These data are correlated with the long‑term immersion results to predict service life and to design cathodic protection systems for Brazilian subsea structures.

Coated Systems and Galvanic Couples – Barrier Performance and Galvanic Corrosion

• Full immersion of coated panels with scribe (ASTM D1654 / ASTM B117 combined with immersion) – We apply organic coatings (paint, epoxy, or powder) on steel or aluminium panels, introduce a standard scribe down to the metal, and immerse them in seawater for 500‑2,000 hours. We evaluate the degree of blistering, rust creepage from the scribe, and coating disbondment. The results are reported using standard ratings (e.g., ASTM D714 for blistering, ASTM D610 for rusting) and are critical for Brazilian shipyard and offshore coating qualification.
• Galvanic couple testing (ASTM G71) – We assemble couples of dissimilar metals (e.g., steel‑copper, steel‑aluminium, stainless‑carbon steel) in a seawater bath, connected through a zero‑resistance ammeter to measure galvanic current, and monitor the potential difference over time. The corrosion rate of the anode and the protection of the cathode are quantified. The test provides the galvanic corrosion rate (mm/year) and the galvanic current density (µA/cm²), which are used to size anodes for cathodic protection systems in Brazilian offshore platforms.
• Under‑film corrosion evaluation – After immersion, we remove the coating in selected areas and examine the substrate for pitting or general corrosion; the extent of under‑film corrosion is measured and reported as a percentage of the total area.
• Effect of biofouling on coating performance – In selected tests, we add a natural seawater microbial consortium (or use raw seawater with natural fouling organisms) and periodically inspect the coated panels for attachment and any differential aeration cells that may accelerate corrosion under the deposit.

Welded Joints and Heat‑Affected Zones – Localised Attack and Stress Corrosion Cracking

• Full immersion of welded coupons (NACE TM0177 / ASTM G36 adapted) – We machine welded panels with the weld bead centred in the test coupon. After immersion in seawater for a specified period (e.g., 90 days), we perform a visual and microscopic inspection of the weld metal, heat‑affected zone (HAZ), and parent metal. Any preferential attack in the HAZ is measured, and the corrosion rate in each zone is reported separately. This is critical for Brazilian pipeline girth welds and structural welds in marine environments.
• Stress‑corrosion cracking (SCC) susceptibility using U‑bend or C‑ring specimens (ASTM G30 / NACE TM0177) – We prepare stressed specimens (U‑bends, C‑rings, or four‑point bent beams) from the material, immerse them in seawater at controlled temperature (e.g., 60 °C) and periodically inspect for cracks using dye‑penetrant or ultrasonic methods. The time to crack initiation and the crack morphology (intergranular vs. transgranular) are reported. This is essential for components subject to tensile stresses, such as bolting and pressure vessels in Brazilian offshore production units.
• Sulfide stress cracking (SSC) for sour service – optional – For materials that may contact H₂S in addition to seawater, we perform a separate test with hydrogen sulfide bubbled through the seawater (per NACE TM0177 Method A), and we report the time to failure under the defined stress level.
• Residual stress measurement before and after immersion – Using X‑ray diffraction (XRD) or hole‑drilling method, we measure the residual stresses near the weld, and correlate any stress relaxation with corrosion attack patterns.

Composites and Non‑Metallics – Water Absorption and Strength Retention

• Seawater immersion for composites (ASTM D5229 / ISO 22524) – For FRP and carbon‑fibre composites, we immerse test specimens (tensile, flexural, or compression coupons) in seawater at 25 °C, 40 °C, and 60 °C for 1,000‑4,000 hours. We measure the water absorption (mass gain) at intervals and determine the diffusion coefficient. After immersion, we test the residual mechanical properties (tensile, flexural, and interlaminar shear) and report the retention percentage. A retention below 80 % may indicate hydrolysis or fibre‑matrix debonding.
• Visual inspection for blistering and delamination – We examine the edges and surfaces for any blistering, cracking, or delamination; any such defects are documented with photographs and measured for size and density.
• Effect of biofouling on polymer surfaces – For non‑metallic materials used in marine growth‑prone areas, we also observe the extent of slime or hard fouling adhesion after long‑term immersion, and we report the cleaning difficulty (e.g., ease of removal by water jet).

Report Acceptance & Compliance with Brazilian Offshore and Maritime Regulations

All seawater full immersion corrosion tests are conducted under our ISO/IEC 17025:2017 accreditation, using temperature‑controlled water baths, calibrated mass balances (0.0001 g resolution), digital callipers, and reference electrodes that are periodically verified with standard seawater and certified corrosion coupons. Our final reports include a comprehensive test plan (seawater source, temperature, duration, specimen preparation), mass‑loss data with calculated corrosion rates (in mm/year and mpy), pit depth and distribution statistics, any localised attack observations, photographic documentation (macro and micro), analysis of corrosion products (by SEM/EDS or XRD where applicable), and a clear pass/fail verdict against the specified acceptance criteria (e.g., maximum corrosion rate < 0.1 mm/year for stainless steels). We also provide an uncertainty budget for key measurements. These reports are widely accepted by ANP for offshore platform equipment qualification, by IBAMA for environmental impact assessments, by the Brazilian Navy for naval vessel material certification, by INMETRO for marine product safety, and by Brazilian shipyards and oil‑field service companies for material selection and asset integrity management. Bilingual (Portuguese/English) versions are available to facilitate submissions to regulators and communication with project stakeholders. With our rigorous seawater corrosion testing, you can confidently evaluate material durability in Brazil’s challenging marine environments, ensuring safe, reliable, and cost‑effective operations.