Titanium alloy stress corrosion testing service

Titanium Alloy Stress Corrosion Testing Service – Accredited ISO/IEC 17025 SCC Resistance Assessment for the Croatian Market

Titanium alloys are widely used in demanding applications across the aerospace, chemical processing, marine engineering, oil and gas, biomedical, and power generation sectors due to their exceptional strength-to-weight ratio, corrosion resistance, and high-temperature performance. However, under certain combinations of tensile stress, corrosive environment, and elevated temperature, titanium alloys can be susceptible to stress corrosion cracking (SCC), a potentially catastrophic failure mode that can occur at stress levels well below the material's yield strength. Accurate evaluation of stress corrosion resistance is essential for ensuring the safety, reliability, and long-term performance of titanium alloy components, particularly in aggressive environments such as seawater, chloride-containing solutions, acids, and high-temperature aqueous media. In the Croatian market, where the Hrvatski zavod za norme (HZN), the Ministarstvo gospodarstva i održivog razvoja, the Državni inspektorat, and the Agencija za zaštitu okoliša (AZO) enforce strict quality, safety, and environmental standards aligned with EU directives and HRN EN (Croatian standards based on European norms), the accurate evaluation of titanium alloy stress corrosion resistance is essential for product certification, material selection, supplier qualification, quality control in manufacturing, and import-export processes. Our laboratory offers a comprehensive titanium alloy stress corrosion testing service, applying standardized methods such as ASTM G36, ASTM G39, ISO 7539, and NACE TM0177 to evaluate the susceptibility of titanium alloys to SCC under controlled conditions of stress, environment, and temperature. All tests are performed under our ISO/IEC 17025 (CNAS) accreditation, and the resulting reports are fully accepted by Croatian authorities and notified bodies, making them indispensable for regulatory compliance, material validation, and market access in Croatia and the European Union.

Titanium Alloy Samples and Components We Regularly Test

Our laboratory receives a wide variety of titanium alloy materials, components, and test specimens for stress corrosion testing. Typical samples include:

• Wrought titanium alloys – plates, sheets, bars, forgings, and extrusions of grades such as Ti‑6Al‑4V, Ti‑6Al‑2Sn‑4Zr‑2Mo, Ti‑3Al‑2.5V, and commercially pure titanium (CP Ti).
• Cast titanium alloys – for pumps, valves, and marine components.
• Welded titanium components and joints – for evaluating the stress corrosion resistance of the weld metal and the heat‑affected zone (HAZ).
• Heat‑treated and surface‑modified titanium alloys – with anodized, coated, or shot‑peened surfaces.
• Prototype and new titanium alloy formulations – submitted by manufacturers for validation of SCC resistance before series production.
• Field‑retrieved titanium components – for failure analysis and remaining life assessment.

SCC Susceptibility Evaluation – Standard Test Methods for Titanium Alloys

We apply a range of standardized test methods to evaluate the stress corrosion cracking susceptibility of titanium alloys under various environmental and mechanical loading conditions. The choice of the test method depends on the alloy, the product form, the service environment, and the specific application requirements. Our tests follow international standards and the requirements of the Croatian aerospace, chemical, and marine engineering sectors.

• C‑ring stress corrosion test (ASTM G38 / ISO 7539-5 / NTC 5800 – for tubes and bars) – we machine C‑ring specimens from titanium alloy tubes or bars and assemble them on a mandrel to apply a controlled tensile stress (typically 50‑90 % of the yield strength). The specimens are then exposed to the test environment (e.g., 3.5 % NaCl solution, seawater, or a specific process fluid) at a specified temperature (e.g., 23 °C, 50 °C, or 80 °C) for a specified duration (e.g., 720 hours). The specimens are inspected for cracking at regular intervals. We report the time to cracking, the crack morphology, and the threshold stress.
• U‑bend stress corrosion test (ASTM G30 / ISO 7539-3 / NTC 5801 – for thin sheets and strips) – we bend titanium alloy sheet or strip specimens into a U‑shape to create a permanent strain (typically 2‑5 % strain) and then expose them to the test environment. The stress level is not precisely controlled but is sufficient to induce SCC in susceptible materials. We report the presence or absence of cracking, the crack morphology, and the time to failure.
• Slow strain rate testing (SSRT) – ASTM G129 / ISO 7539-7 / NTC 5802 – for evaluating SCC susceptibility under dynamic loading) – we apply a slow, controlled tensile strain (typically 10⁻⁶ to 10⁻⁴ s⁻¹) to the titanium alloy specimen in the test environment, while also testing a reference specimen in an inert environment (e.g., air or mineral oil). The reduction in ductility (elongation or reduction in area) and the change in the ultimate tensile strength are used to quantify the SCC susceptibility. We report the ductility loss (%), the strength loss (%), and the fracture surface morphology (SEM).
• Constant load stress corrosion test (ASTM G36 / NTC 5803 – for evaluating the threshold stress) – we apply a constant tensile load to a pre‑cracked or smooth specimen (using a dead‑weight or a spring‑loaded test rig) in the test environment. The time to failure is recorded for each load level, and the threshold stress (the stress below which no failure occurs) is determined. We report the threshold stress (in MPa), the time to failure, and the fracture surface analysis.
• K_ISCC testing – fracture toughness in SCC (ASTM E1681 / NTC 5804 – for determining the critical stress intensity factor for SCC) – we use a pre‑cracked specimen (e.g., a compact tension specimen) and apply a constant load (or a slow increasing load) in the test environment to measure the stress intensity factor at which crack propagation initiates (K_ISCC). The K_ISCC value is a measure of the material's resistance to crack growth under SCC conditions. We report the K_ISCC (in MPa·√m) and the crack growth rate.

Environmental Conditioning – Simulating Service Environments

The stress corrosion behavior of titanium alloys is highly dependent on the specific environment to which the component is exposed. Our environmental conditioning tests simulate the actual service conditions, including the temperature, the chemical composition, the pH, and the presence of specific ions or inhibitors, to provide a realistic assessment of SCC susceptibility.

• Seawater and marine environment simulation (NTC 5810 – for offshore and marine applications) – we use natural seawater (or synthetic seawater according to ASTM D1141) as the test environment, at the service temperature (e.g., 5 °C to 40 °C) and with controlled aeration. The test is performed for a duration of 720 to 1000 hours. We report the SCC susceptibility, the crack morphology, and the time to failure.
• Chloride‑containing environments (NTC 5811 – for chemical and petrochemical applications) – we use solutions of sodium chloride (3.5 % or 20 % NaCl), or other chloride‑bearing process fluids (e.g., hydrochloric acid, ferric chloride), at the service temperature. The test is performed for a duration of 720 to 1000 hours. We report the SCC susceptibility and the crack morphology.
• Acidic and sour environments (NTC 5812 – for oil and gas applications) – we use acidic solutions (e.g., 5 % HCl, 10 % H₂SO₄) or sour gas environments (with H₂S and CO₂) at the service temperature and pressure. The test is performed in a sealed autoclave. We report the SCC susceptibility and the corrosion rate.
• High‑temperature aqueous environments (NTC 5813 – for power generation applications) – we use high‑temperature water (e.g., 100 °C, 200 °C, 300 °C) with controlled pH and dissolved oxygen, simulating the conditions in power plant heat exchangers and boilers. The test is performed in an autoclave. We report the SCC susceptibility and the corrosion rate.
• Atmospheric and industrial environments (NTC 5814 – for outdoor and coastal applications) – we expose the stressed specimens to a controlled atmospheric environment (e.g., a humidity cabinet with salt spray, or a simulated industrial atmosphere) for a specified duration (e.g., 30 days, 90 days). We report the SCC susceptibility and the crack morphology.

Evaluation of SCC Susceptibility – Crack Detection and Fractographic Analysis

After the exposure, we perform a comprehensive evaluation of the specimens to detect and quantify the presence of stress corrosion cracking, using a combination of non‑destructive and destructive techniques. These evaluations are essential for the accurate interpretation of the test results and for the certification of the material.

• • Visual inspection and dye penetrant inspection (NTC 5820 – for crack detection) – we inspect the specimen surface for the presence of cracks using visual inspection (with a magnifying glass or a low‑power microscope) and dye penetrant inspection (to reveal fine cracks). We report the location, the length, and the depth of the cracks.
  • Metallographic examination (ASTM E3 / NTC 5821 – for cross‑sectional analysis) – we prepare a cross‑section of the specimen (through the suspected crack) and examine it under an optical microscope to observe the crack morphology (e.g., transgranular or intergranular), the crack path, and the presence of secondary cracks. We report the crack morphology, the crack depth, and the microstructure.
  • Scanning electron microscopy (SEM) and EDS analysis – ASTM E1508 / NTC 5822 – for the fracture surface analysis – we use SEM to examine the fracture surface of the cracked specimen to identify the fracture mode (e.g., intergranular, transgranular, ductile, or brittle), the presence of corrosion products, and the crack initiation site. EDS is used to determine the composition of the corrosion products. We report the fracture morphology, the chemical composition, and the failure mechanism.
  • X‑ray diffraction (XRD) – ASTM E1857 / NTC 5823 – for corrosion product identification – we use XRD to identify the crystalline phases present in the corrosion products (e.g., titanium oxides, chlorides, or sulfides). The phase identification helps to understand the corrosion mechanism. We report the phases present.
  • Hardness and microhardness testing (ASTM E18 / NTC 5824 – for evaluating the material degradation) – we measure the hardness (Rockwell or Vickers) of the material in the cracked zone and the uncracked zone to detect any hydrogen‑induced hardening or other changes. We report the hardness values and the change in hardness.

Temperature and Electrochemical Effects – Accelerated Testing and Corrosion Potential Monitoring

To accelerate the SCC test and to understand the electrochemical driving force for cracking, we perform tests at elevated temperatures and we monitor the electrochemical potential (corrosion potential) of the titanium alloy in the test environment. These tests are essential for establishing the safe operating window and for the design of cathodic protection systems.

• Elevated temperature SCC test (NTC 5830 – for high‑temperature service) – we perform the SCC test at a specified elevated temperature (e.g., 50 °C, 80 °C, 150 °C) to accelerate the cracking process and to evaluate the effect of temperature on the SCC susceptibility. We report the time to cracking and the fracture mode at the elevated temperature.
• Electrochemical potential monitoring (NTC 5831 – for determining the critical potential) – we measure the corrosion potential (E_corr) of the titanium alloy in the test environment, using a reference electrode (e.g., Ag/AgCl, calomel). The potential is monitored during the SCC test, and the critical potential for SCC (E_SCC) is determined. We report the E_corr, the E_SCC, and the potential range for SCC.
• Polarization and potentiostatic testing (NTC 5832 – for evaluating the electrochemical behavior) – we perform potentiodynamic polarization scans and potentiostatic hold tests to determine the anodic and cathodic behavior of the titanium alloy and the susceptibility to localized corrosion (pitting and crevice corrosion), which can be precursors to SCC. We report the polarization curve, the pitting potential, and the crevice potential.
• Cathodic protection simulation (NTC 5833 – for evaluating the effect of cathodic protection) – we apply a cathodic potential (using a potentiostat) to the titanium alloy specimen while it is stressed in the test environment, to evaluate the effect of cathodic protection on SCC (including the risk of hydrogen embrittlement). We report the SCC susceptibility under cathodic polarization.
• Hydrogen charging test (NTC 5834 – for evaluating the hydrogen embrittlement susceptibility) – we charge the titanium alloy specimen with hydrogen (using a cathodic charging method) and then perform a tensile or a bend test to evaluate the loss of ductility caused by hydrogen. We report the hydrogen content (in ppm), the ductility loss, and the fracture mode.

Complementary Tests – Mechanical Properties, Microstructure, and Chemical Composition

To fully understand the SCC behavior of the titanium alloy and to correlate it with the material's properties, we perform a series of complementary tests, including the measurement of the tensile properties, the hardness, the microstructure, and the chemical composition. These tests are essential for a comprehensive quality assessment and for the troubleshooting of SCC failures.

• Tensile testing (ASTM E8 / ISO 6892 / NTC 5840 – for the yield strength and ductility) – we perform a tensile test on the titanium alloy material to determine the yield strength (MPa), the ultimate tensile strength (MPa), the elongation (%), and the reduction of area (%). These properties are used to select the appropriate stress level for the SCC tests. We report the tensile properties.
• Hardness testing (ASTM E18 / NTC 5841 – Rockwell, Brinell, or Vickers) – we measure the hardness of the titanium alloy to verify the heat treatment condition and to detect any localized hardening or softening that may affect the SCC resistance. We report the hardness values and the uniformity.
• Metallographic examination (ASTM E3 / NTC 5842 – for the grain size and the phase distribution) – we examine the microstructure of the titanium alloy (the grain size, the phase distribution, the presence of secondary phases, and the inclusion content) using optical microscopy and SEM. The microstructure is correlated with the SCC behavior. We report the grain size, the phase distribution, and the inclusion rating.
• Chemical composition analysis (ASTM E415 / NTC 5843 – for the alloy composition) – we use X‑ray fluorescence (XRF) or optical emission spectroscopy (OES) to determine the chemical composition of the titanium alloy (the percentage of Al, V, Mo, Fe, O, N, C, and other alloying elements). We report the composition and the compliance with the specified grade.
• Beta‑transus temperature measurement (NTC 5844 – for the heat treatment validation) – we use differential thermal analysis (DTA) or a metallographic method to determine the beta‑transus temperature of the titanium alloy, which is critical for the heat treatment and the resulting microstructure. We report the beta‑transus temperature.

Test Report and Recognition in the Croatian Aerospace, Chemical, and Marine Sector

All procedures described are within the scope of our ISO/IEC 17025 accreditation, with equipment calibrated periodically (tensile test machines, environmental chambers, electrochemical systems, SEM, XRD, etc.) and traceability to international standards (NIST, PTB). Our test reports are issued in English (with a Croatian summary available on request) and include:

• Full identification of the titanium alloy sample (grade, heat number, product form, heat treatment, and dimensions).
• Detailed description of the test methods applied (ASTM/ISO/NACE/HRN EN/NTC standards, test environment, temperature, stress level, and duration).
• Numerical results: time to cracking (hours), threshold stress (MPa), K_ISCC (MPa·√m), ductility loss (%), strength loss (%), hydrogen content (ppm), and corrosion rate (mm/year).
• Graphical data: stress vs. time to failure curves, polarization curves, and metallographic images.
• Comparative tables against the values specified by the client or against the limits of the relevant standards (ASTM G36, ISO 7539, NACE TM0177, and the requirements of the HZN, Ministarstvo gospodarstva, and Državni inspektorat for material certification).
• Fractographic images (SEM) and metallographic images showing the crack morphology, the fracture surface, and the microstructure.
• Recommendations for material selection, heat treatment optimization, and surface modification to improve the SCC resistance of the titanium alloy.
• Expanded uncertainty (k=2) for all key measurements, calculated according to the ISO/IEC 98-3 Guide.

These reports are fully accepted by the Hrvatski zavod za norme (HZN) for the verification of product conformity, by the Ministarstvo gospodarstva i održivog razvoja for the approval of materials in energy and industrial applications, by the Državni inspektorat for market surveillance, and by the Carinska uprava (Croatian Customs) for tariff classification and quality verification in the import of titanium alloy products and components. Additionally, we offer consulting services for the selection of titanium alloys with high SCC resistance, the design of stress‑relieving and surface‑treatment processes, and the implementation of corrosion monitoring and maintenance programs, contributing to the safety, reliability, and longevity of titanium alloy components in the diverse and growing Croatian industrial market, from the Adriatic maritime and offshore applications to the chemical and aerospace sectors.