Advanced Development of Sensors’ Roles in Maritime-Based Industry and Research: From Field Monitoring to High-Risk Phenomenon Measurement

Marine Structural Health Monitoring with Optical Fiber Sensors: A Review

Real-time monitoring of large marine structures' health, including drilling platforms, submarine pipelines, dams, and ship hulls, is greatly needed. Among the various kinds of monitoring methods, optical fiber sensors (OFS) have gained a lot of concerns and showed several distinct advantages, such as small size, high flexibility and durability, anti-electromagnetic interference, and high transmission rate. In this paper, three types of OFS used for marine structural health monitoring (SHM), including point sensing, quasi-distributed sensing, and distributed sensing, are reviewed. Emphases are given to the applicability of each type of the sensors by analyzing the operating principles and characteristics of the OFSs. The merits and demerits of different sensing schemes are discussed, as well as the challenges and future developments in OFSs for the marine SHM field.

The Influence of Water Flow Characteristics on the Physical and Mechanical Qualities of Underwater Wet Welded A36 Marine Steel Plate

Underwater welding has proven to be a successful method of joining two similar or dissimilar metals and takes place underwater. This technique is frequently used for maintenance purposes, such as repairing piping systems, ships, and other marine structures. This study investigates the effect of different water flow types on an underwater weld’s physical and mechanical properties of welded bead on the A36 steel plate. The SMAW method with an E7018 electrode is used for welding A36 steel in saltwater. In this simulation, underwater welding is performed using three types of flow (without flow, non-uniform flow with a baffle plate, and non-uniform flow without a baffle plate) to compare metallography, hardness, tensile, impact, and bending testing results. The findings revealed that the saltwater flow caused more porosity defects. Moreover, the highest penetration depth was observed in specimens with the non-uniform flow with a baffle plate. The heat energy is concentrated due to droplets accumulating in the weld area. The microstructure of welding metals such as acicular ferrite and ferrite with the second phase grows as the water flow becomes non-uniform. Furthermore, as the rate and variability of the water flow increased, the value of the mechanical properties of the specimens increased relatively.

Mechanical and Microstructural Properties of A36 Marine Steel Subjected to Underwater Wet Welding

Underwater wet welding (UWW) is applied to repair basic offshore structures, underwater pipelines, water transportation, docks, and port equipment. The underwater wet welding method used in the current research was shield metal arc welding (SMAW), and this was conducted on an A36 steel plate. We investigated the effect of a water temperature of 10 ± 5 °C and different types of water flow (without flow, non-uniform flow with baffle bulkhead, and non-uniform flow without baffle bulkhead). The defects found on the specimen included spattering, irregular surfaces, porosity, and undercutting. A high cooling rate led to the formation of more acicular ferrite (AF) phases in the weld metal area than a slow cooling rate. The microstructure of the heat affected zone (HAZ) area led to the formation of finer and small grains. Values of tensile, impact, and hardness strength were greater with higher cooling rates. The highest tensile strength value was 585.09 MPa, and this occurred with non-uniform flow without a baffle bulkhead. The highest values of absorbed energy and impact strength were 41.9 J and 2.05 J/mm2, respectively, and these occurred with a non-uniform flow without a baffle bulkhead. The greatest hardness values were found with a non-uniform flow without a baffle bulkhead in the weld metal area.