Issue 78

A. Sancak et alii, Fracture and Structural Integrity, 78 (2026) 186-206; DOI: 10.3221/IGF-ESIS.78.11

For the preparation of 3 L substitute seawater, 2.7 L of distilled water was first added to a glass jar. Then, 12.282 g of anhydrous Na ₂ SO ₄ , corresponding to 4.094 g/L, and 73.602 g of NaCl, corresponding to 24.534 g/L, were added and dissolved. Subsequently, 60 mL of stock solution I and 30 mL of stock solution II were added. The solution was then completed to a final volume of 3 L using distilled water. The final mixture was stirred until all compounds were fully dissolved. The pH of the prepared substitute seawater was initially measured as 7.8 and was adjusted to 8.2 by adding a small amount of NaOH solution. The pH values of both substitute seawater and seawater were measured using an OHAUS ST10 pH meter and were recorded as 8.2. Immersion corrosion exposure The immersion corrosion procedure was arranged based on the principles of ASTM G31-21 for laboratory immersion corrosion testing of metals [34]. The specimens were placed in glass jars and fully immersed in the test medium under static laboratory conditions. The exposure durations were selected as 10 and 30 days. All immersion tests were performed at room temperature, with an average ambient temperature of approximately 20 °C. The relative humidity during the exposure period was recorded in the range of 65–70%. For each exposure setup, six specimens were immersed in approximately 3 L of the corresponding test medium. This volume was selected according to the solution-volume requirement calculated from the specimen surface area, using a minimum solution volume of 0.2 mL/mm². During immersion, the specimens were positioned inside the glass jar so that they did not touch each other. This arrangement was used to minimize unintended contact effects between specimens and to provide comparable exposure conditions. The specimen arrangement in the glass jar is shown in Fig. 3.

Figure 3: Arrangement of Charpy specimens in the glass jar during immersion corrosion exposure. The specimens were fully immersed and positioned without mutual contact. The solutions were not designed to simulate flowing seawater conditions. Instead, the exposure procedure was designed as a controlled static immersion test to compare the relative effects of substitute seawater and seawater on the impact behaviour of the investigated chain steel. The pH of the exposure media was monitored during the immersion experiments and was recorded as 8.2. An important aspect of the experimental procedure was that corrosion products were not removed before Charpy impact testing. After the immersion period, the specimens were tested in their corroded surface condition. This approach was selected to preserve the actual surface condition generated by seawater exposure and to avoid modifying the corroded surfaces before impact loading. Corrosion products were removed only after the impact tests for mass-loss assessment. Fig. 4 shows representative views of the Charpy V-notch specimens at different stages of the experimental procedure. The images include uncorroded notched specimens, specimens removed from seawater before Charpy impact testing and representative corroded specimens. These views illustrate the surface condition of the specimens prior to impact testing. Charpy V-notch impact testing Charpy V-notch impact tests were carried out using a Zwick/Roell RKP450 pendulum impact testing machine. The tests were performed according to ISO 148-1 [32], and the absorbed impact energy was recorded in joules for each specimen.

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