Why this approach
Corrosion is a chemical reaction that occurs between a material and its surrounding environment. This reaction can take place in various environments, including the atmosphere. Atmospheric corrosion typically leads to uniform corrosion, which can be effectively controlled through measures such as corrosion allowance and surface protection like protective coatings. Alternatively, corrosion may occur when a material comes into contact with a solution. One common example is corrosion caused by marine environments, which often affects structures such as boats, oil rigs, wind turbines, and sheet piles made of high-strength carbon steel grades. These structures require adequate corrosion protection to withstand the high chloride content and bacterial activity present in marine environments. Despite regular inspections conducted by the maritime sector, issues such as paint deterioration and the failure of sacrificial anodes tend to arise over time.
The maritime industry currently spends a significant portion, around 20% of its gross domestic product (GDP), on addressing corrosion-related problems through inspections and repairs. This raises questions about the potential for the Socorro system to improve corrosion management and whether there are more cost-effective ways to solve and manage corrosion. Additionally, it is worth exploring corrosion protection methods that are both economically viable and environmentally friendly.
In WP3, the primary objective is to develop a user-friendly strategy that enables companies to conduct life-cycle analysis (LCA) and life-cycle cost analysis (LCCA) for various types of corrosion protection methods suitable for their specific environmental conditions. The strategy aims to provide a comprehensive understanding of the environmental impacts and cost implications associated with different corrosion protection options.
To showcase the capabilities of this strategy, several specific aqueous environments have been selected for study in WP3. The main environment focuses on the harbour steel sheet piles exposed to a marine environment, which presents unique challenges due to high chloride content and bacterial activity. The second environment under investigation is wastewater treatment plants, where corrosion protection measures are crucial due to the corrosive nature of the (organic/inorganic) substances involved. These two cases were ultimately considered for the collection of the relevant data inventory.
By analysing these specific scenarios, the program aims to offer practical insights and recommendations for selecting the most effective corrosion protection strategies in each case. The ultimate goal is to provide companies with valuable tools and information to make informed decisions regarding corrosion protection throughout the life cycle of their assets.
Case study 1 - Marine/offshore installations
A sheet pile is a steel structure designed specifically for providing support during excavation and retaining soil or water. Its unique feature lies in its interlocked connections, allowing multiple sheet piles to fit together seamlessly. This interlocking mechanism enables the construction of both permanent and temporary seawalls, creating a continuous and sturdy barrier. The primary purpose of sheet piles is to ensure stability and resist lateral forces exerted by soil or water pressure. By interlocking the sheet piles, they form a cohesive structure capable of withstanding these external forces. This makes them suitable for various applications such as waterfront construction, flood protection systems, port infrastructure, and underground projects.
Sheet piles are typically manufactured using carbon steel, which is designed to have a lifespan of 25-50 years by a common average of 30 years in the literature. However, the aggressive corrosion attack from seawater poses a significant challenge to achieving this lifespan (Figure 1). Unlike stainless steel, plain carbon steel lacks a protective layer, making it susceptible to the corrosive effects of high-chloride seawater and resulting in alarming corrosion rates. To mitigate these issues, marine companies employ various protective techniques to inhibit corrosion.
While corrosion allowance has been widely implemented, there are alternative protection systems that offer both economic and ecological advantages. In WP3, the goal is to provide an overview of the commonly used protection systems and evaluate their economic and ecological impacts. Given the extensive research on sheet piles conducted by Antwerp Maritime Academy, this serves as an ideal case study to test the effectiveness of the LCA-LCCA strategy; thus, also allowing us to extrapolate these results to other marine installations.
By analysing different protection systems and their associated costs and environmental effects, WP3 aims to provide valuable insights for marine companies seeking the most suitable corrosion protection methods for sheet piles. This research not only addresses the challenges of corrosion in sheet pile applications but also explores more cost-effective and environmentally friendly alternatives.
Case study 2 - Wastewater treatment plants
As a partner in the Socorro project, KU Leuven brings extensive expertise in wastewater treatment plants (WWTP) to the table. Within the research group PETLAB, ongoing studies focus on improving the removal of toxic pharmaceuticals from wastewater. This research is of great significance as most biological WWTPs struggle to effectively degrade such organic compounds. While the group's expertise lies in advanced oxidation processes (AOP) and physico-chemical treatment of wastewater, there has been limited discussion regarding the corrosion effects associated with creating oxidizing conditions for degradation purposes.
Previous work conducted by Nagels et al. [2] has indicated that common austenitic stainless steel grades lack sufficient pitting resistance when exposed to oxidative wastewater. In light of this, lean-duplex grades have emerged as an interesting alternative despite their challenging weldability.
Wastewater treatment plants (WWTPs) often follow a straightforward guideline employed by manufacturers when selecting materials. If the chloride content remains below 200-250 ppm, AISI 304L stainless steel is commonly used for pipelines and process equipment. However, when the chloride content exceeds this threshold, a more corrosion-resistant material like AISI 316L is preferred. Storage tanks, utilized for controlling the pH of the wastewater and containing acidic or alkaline media, are typically constructed from stainless steel, with occasional usage of coated carbon steel. Concrete is the material of choice for constructing the basins in biological WWTPs.
One common misconception in WWTPs is the assumption that stainless steel is impervious to the aggressive nature of wastewater. Hence in wastewater with a chloride content exceeding 1000 ppm, many installations still rely on AISI 316L stainless steel. Unfortunately, when combined with elevated temperatures, which are beneficial for the biological processes and water quality of the WWTP, this chloride level becomes sufficient to initiate pitting corrosion.
In a field demonstration conducted as part of WP2 at PB Leiner company's industrial WWTP, AISI 304L and AISI 316L grades were utilized even in wastewater containing 4000 ppm chloride content. The combination of the aggressive wastewater and inadequate resistant materials resulted in valve failures (as depicted in the Figure 2). Despite companies being aware of the existence of more corrosion-resistant materials, it remains challenging to convince them to switch to these alternatives, which are often more expensive (in terms of higher initial costs) or require additional investment in coating/protection systems. Nevertheless, it is frequently disregarded that the long-term evaluation concerning life cycle assessment (LCA) and life cycle cost analysis (LCCA) may reveal that certain design solutions, despite their initial lack of cost efficiency, can ultimately emerge as the most economically and environmentally sustainable choices throughout their lifespan. Therefore, the LCA/LCCA program holds promise in convincing companies to consider using more expensive materials due to their associated economic and ecological benefits. By conducting life-cycle analyses and cost assessments, the program can provide valuable insights that may encourage companies to prioritize the long-term advantages offered by more resistant materials, outweighing the initial costs and highlighting the economic and environmental advantages.
By taking these two major case studies into account, our model framework for LCA/LCCA was built based on the extensive inventory that was collected on design parameters (e.g., material grades, thicknesses, corrosion protection systems, design life, etc.).
The full output of this work can be found in the report below
References
[1] P. Systems, PIER AND WHARF CONSTRUCTION PART I: FACILITY PLANNING THE INTERNATIONAL DEEP FOUNDATIONS AND MARINE CONSTRUCTION MAGAZINE STEEL SHEET PILE REPAIR METHODS HELICAL PIERS & HELICAL PILES, (n.d.).
[2] M. Nagels, B. Verhoeven, N. Larché, R. Dewil, B. Rossi, Corrosion behaviour of lean duplex stainless steel in advanced oxidation process (AOP) based wastewater treatment plants, Eng Fail Anal. 136 (2022). https://doi.org/10.1016/j.engfailanal.2022.106170.