The Performance of Dissimilar Metal Welds Under Cyclic Loading and Corrosive Environments
Dissimilar metal welds (DMWs), which involve joining two different metallic materials, are commonly used in various critical industries such as power generation, oil and gas, nuclear energy, and chemical processing. The project Dissimilar Metal Welding (ERIPARI) deals with issues concerning nickel base alloy dissimilar metal welds. Dissimilar metal welds are used in nuclear power plants and in oil refineries at locations where two different types of materials, e.g., carbon steel and stainless steel are joined (Ramon, Basu, Vander Voort, & Bolar, 2021).
The nickel-base alloy dissimilar metal welds are typically made of Alloy 182 and Alloy 82. Recently, Alloy 52 has started to be used both in new constructions as well as in repair welding.
The trend towards alloys with higher amounts of chromium is driven by the observed cracking in Alloy 182, and recently also in Alloy 82. One driving force towards what are today believed to be more resistant alloys is also the challenges and costs related to non-destructive examination of dissimilar metal welds. Although all the parameters affecting cracking susceptibility of nickel-base weld metals are not yet known, weld repairs increase the susceptibility, e.g. by increasing the residual stresses. Weld defects, such as hot cracks, are probably also playing a key role in crack initiation (Zerbst, 2020).
These joints are often exposed to extreme operational environments, including cyclic mechanical loading and corrosive media, making them susceptible to degradation and failure, the long-term performance of DMWs in such conditions is a key area of concern because it can affect the safety, reliability, and longevity of infrastructure, Cyclic loading, which introduces repeated stress and strain, leads to fatigue in welded joints. Fatigue is one of the leading causes of failure in metallic structures, and in the case of DMWs, it is more complex due to the difference in material properties, thermal expansion, and mechanical behavior of the joined metals. This mismatch in properties creates stress concentrations at the weld interface, which can initiate cracks and significantly reduce the fatigue life of the joint (Jambor, Pokorný, Trško,
Oplt, Jacková, & Hutař, 2022).
Corrosion occurs wherever water can leak onto the superstructure or areas where water and debris can accumulate. The corrosion of the steel can be particularly severe where road salt and dust are present in the water. The places most commonly found with corrosion are on the bottom flange where water collects from dew or splash, and on the webs near the abutments and joints. For instance, the examination of four bridges in Alaska by Albrecht et al (1984) showed that the most significant amount of corrosion occurred on the bottom flange of the seaward girders. This location on the steel would have the greatest amount of condensed water blown inland from the sea. The corrosion under moist conditions is related to the time of wetness (Niazi, Eadie, Chen, & Zhang, 2021).
The corrosive environments in which many DMWs operate accelerate the deterioration of the welded joint. Corrosion mechanisms such as stress corrosion cracking (SCC) and galvanic corrosion are prominent in DMWs due to the electrochemical potential difference between the dissimilar metals. These corrosive processes, combined with cyclic loading, can lead to accelerated material degradation, crack initiation, and failure. Understanding the long-term performance and endurance of DMWs in cyclic loads and corrosive conditions is crucial for predicting their service life and ensuring the safe operation of critical systems, the behavior of DMWs under such harsh conditions remains an ongoing challenge due to the complexity of material interactions and environmental factors. Therefore, investigating the endurance of DMWs in these environments will provide valuable insights into optimizing welding practices, material selection, and maintenance strategies to enhance the durability and performance of these joints in industrial applications (Liu et al., 2023).
The corrosive environments in which many DMWs operate accelerate the deterioration of the welded joint. Corrosion mechanisms such as stress corrosion cracking (SCC) and galvanic corrosion are prominent in DMWs due to the electrochemical potential difference between the dissimilar metals. These corrosive processes, combined with cyclic loading, can lead to accelerated material degradation, crack initiation, and failure. Understanding the long-term performance and endurance of DMWs in cyclic loads and corrosive conditions is crucial for predicting their service life and ensuring the safe operation of critical systems. Despite extensive research on weld performance, the behavior of DMWs under such harsh conditions remains an ongoing challenge due to the complexity of material interactions and environmental factors, investigating the endurance of DMWs in these environments will provide valuable insights into optimizing welding practices, material selection, and maintenance strategies to enhance the durability and performance of these joints in industrial applications (Das, Kumar, Sahu, & Gollapudi, 2022).
1.2 Statement of the problem
Dissimilar Metal Welds (DMWs), which involve joining different metallic materials, are crucial in industries such as power generation, oil and gas, nuclear energy, and chemical processing. These joints, typically composed of nickel-based alloys like Alloy 182, Alloy 82, and the recently adopted Alloy 52, are used in nuclear power plants and oil refineries to connect dissimilar materials such as carbon steel and stainless steel. However, DMWs are subject to extreme operational environments, including cyclic mechanical loading and corrosive conditions, which accelerate degradation and pose a significant risk to the safety and reliability of critical infrastructure.
One of the major challenges in DMWs is fatigue failure due to cyclic loading, which introduces repeated stress and strain, exacerbated by the mismatch in material properties. This leads to stress concentrations at the weld interface, causing crack initiation and reducing fatigue life.
Furthermore, corrosive environments, such as those found in nuclear plants and oil refineries, promote stress corrosion cracking (SCC) and galvanic corrosion, further accelerating the degradation process. These combined factors cyclic loading and corrosion make predicting the long-term performance and endurance of DMWs difficult.
Despite ongoing research, understanding the complex interactions between different metals in DMWs under cyclic loads and corrosive conditions remains an unresolved challenge. Current welding practices and materials may not sufficiently address the susceptibility of these welds to cracking and failure, particularly in highly demanding environments. Therefore, investigating the performance of DMWs in such conditions is critical to optimizing welding techniques, improving material selection, and developing effective maintenance strategies to enhance the durability and safety of welded joints in critical industrial applications.
