# The Multistate Reliability Assessment of Ship Hull Girders
## 1 Introduction  
The numerous maritime incidents with vessels in operation have motivated researchers to investigate the causes that lead to these accidents. Research published by [PERSON] et al. [1] and [PERSON] [2] showed that general and dry cargo vessels exhibit the highest likelihood of casualties. Research conducted by EMSE 2019 showed that collision, fire, explosion, flooding, loss of control, hull failure, contact, damage to ship equipment, grounding, and capsizing [3] are the main causes of casualties at sea, while research published by [PERSON] [4] presented a model for assessing the impact of various factors on maritime accidents. Structural damage inside the ship can partially damage the construction and affect the stability of the ship, while cracks in the structure or leaks can cause fuel spillage inside or outside the vessel, which results in environmental pollution and significant economic losses for their repair. In addition to the aforementioned findings, studies conducted in previous decades support the significance of adopting additional regulations. Research conducted between 1997 and 2001 recorded more than 15% hull failures [5], research between 2002 and 2006 recorded around 4% of hull defects [5], and recent research from 2019 by European Maritime Safety Agency (EMSA) announced that the number of casualties associated with hull failure was around 1% [3]. The most significant contribution to the prevention of corrosion was achieved through the application of Performance Standards for Protective Coatings (PSPCs), implemented in April 2006, which significantly enhance coating quality and efficiency [6]. As corrosion takes place in a monotonous manner, it is very important to identify critical areas and carry out regular visual inspections and measurements regarding the assessment of the condition of corroded surfaces. Visual inspections and thickness measurements aim to assess the condition of the surface protection and the thickness of the metal structure. The rules of classification societies define the state of surface protection as good, fair, and poor, while the state of corrosion is classified as acceptable wear, substantial corrosion, and extensive corrosion, for which immediate reaction should be conducted in order to replace the corroded structure. Additionally, the most significant contribution to preserving the structural integrity of ships, tankers, and bulk carriers was achieved with the introduction of common structure rules--CSRs [7]. These rules were established to create the minimum classification requirements to mitigate the risks of major hull structural failure that can occur during ship operation, improve safety and environment protection, and ensure the ship's service life of twenty-five years. Common structure rules were created based on a comprehensive analysis of empirical data on the condition of ship structures in service and actual corrosion values [8]. Through statistical modeling, with a data reliability level of 95%, the corrosion margin was calculated during the designed life cycle of each structural element of the structure depending on the type of ship and the location of the structural element [9]. Thus, the rules define the net thickness of the structural element that meets the strength and resistance criteria of the structure, as well as the gross value that considers allowances for corrosion and safety margins. In addition, these rules ensure greater structural strength and reliability of the hull in relation to corrosion, but increase the weight of the vessel by several percent. Marine environment and ship-specific factors significantly influence the deterioration of ship structures over time [10]. The corrosion margin is directly influenced by the complex marine environment to which a certain structural element is exposed, and it is under the direct influence of different factors such as atmosphere, cargo, cargo operation, operation procedures, the ship's route, etc.