Long-Term Marine Environment Exposure Effect on Butt-Welded Shipbuilding Steel

Goran Vukelic,Josip Brnic,Florian Sedmak,Goran Vizentin,Marino Brcic

doi:10.3390/jmse9050491

Goran Vukelic, Josip Brnic + Show 3 more

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https://doi.org/10.3390/jmse9050491

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Abstract

Extreme environments, such as marine environments, have negative impacts on welded steel structures, causing corrosion, reduced structural integrity and, consequently, failures. That is why it is necessary to perform an experimental research sea exposure effect on such structures and materials. Research presented in this paper deals with the mechanical behavior of butt-welded specimens made of AH36 shipbuilding steel when they are exposed to a natural marine environment (water, seawater, sea splash) for prolonged periods (3, 6, 12, 24, and 36 months). The usual approach to such research is to perform accelerated tests in a simulated laboratory environment. Here, relative mass change due to corrosion over time is given along with calculated corrosion rates. Corroded surfaces of specimens were inspected using optical and scanning electron microscopy and comparison, based on the numbers and dimensions of the corrosion pits (diameter and depth) in the observed area. As a result, it can be concluded that exposure between 3 and 6 months shows significant influence on mass loss of specimens. Further, sea splash generally has the most negative impact on corrosion rate due to the combined chemical and mechanical degradation of material. Pit density is the highest at the base metal area of the specimen. The diameters of the corrosion pits grow over the time of exposure as the pits coalesce and join. Pit depths are generally greatest in the heat affected zone area of the specimen.

Highlights

Structural integrity of marine steel structures can be greatly reduced by corrosive environments in which they are set
Research presented in this paper deals with the mechanical behavior of butt-welded specimens made of AH36 shipbuilding steel when they are exposed to a natural marine environment for prolonged periods (3, 6, 12, 24, and 36 months)
AH36 steel butt-welded specimens were exposed to a real marine environment for prolonged periods (3, 6, 12, 24, and 36 months) in order to determine the influence of these factors on corrosive behavior of such materials

Summary

Introduction

Structural integrity of marine steel structures can be greatly reduced by corrosive environments in which they are set. Marine propulsion systems are generally susceptible to corrosion, leading to a series of possible mechanical failures [3], which is why it is important to gain insight into their fracture behaviors, even if it is the case of marine shaft steels or marine exhaust steels with improved corrosion resistance [4,5]. Damage of masts on the training vessel was caused by deficient welds at the foundation of the masts [6] that accumulated water, enabled corrosion, and reduced the integrity of the structure. A cargo ship [7] sunk due to corrosive influence of the cargo where leaking acid accelerated corrosion of the floor panels, leading to failure. Finite element analysis revealed that a barge midship section can decrease for more than a third compared to its initial measure, due to corrosion [9]

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