INVESTIGATION AND IDENTIFICATION OF SHIP HULL STEEL GRADE FOR MAINTENANCE AND REPAIR PROCEDURES ON SCIENTIFIC RESEARCH VESSEL RSV 421 "ST. ST. CYRIL AND METHODIUS"

Abstract

The Bulgarian scientific research vessel RSV 421 "St. St. Cyril and Methodius" conducts regular maritime expeditions from Bulgaria to Antarctica. During these missions, the ship navigates through diverse global waters, encountering a wide range of seawater temperatures and salinity levels, extreme weather conditions, and severe environmental challenges. Ensuring the structural integrity of the ship's hull under such harsh marine environments is of major importance for the safety of the crew, cargo and the success of these polar expeditions. The present study is focused on the precise identification of the ship's hull steel grade as a fundamental prerequisite for executing adequate and high-quality maintenance and repair procedures. To establish the exact classification and properties of the material, a comprehensive analytical approach was applied. The experimental methodology encompasses optical microscopy for microstructural evaluation, X-ray diffraction (XRD) for phase composition analysis, Vickers microhardness testing to assess the mechanical characteristics, potentiodynamic Tafel and Open Circuit Potential (OCP) corrosion resistance tests to evaluate the electrochemical corrosion behaviour of the tested material. Determining the precise steel grade through these combined methods is a crucial step that dictates the correct technological approach to future maintenance. Ultimately, this accurate material identification significantly enhances the reliability, durability, and overall longevity of the ship's hull, ensuring the safe and uninterrupted conduct of future challenging expeditions.