This article presents a carbon footprint analysis of hydraulic cylinders coated with trivalent chromium plating. The objective is to quantify the environmental benefits of improved coating durability and to assess its influence on greenhouse gas (GHG) emissions caused by frequent component replacement in heavy-duty applications.
1. Introduction
Consideration of environmental impacts, driven by regulatory requirements and customer demand, is expected to play an increasingly influential role in corporate decision-making. In addition to technical performance and cost-efficiency, environmental aspects—such as carbon footprint—are becoming increasingly important factors in coating selection as well.
Reducing carbon emissions in industrial applications is increasingly urgent due to climate change and regulatory pressures. One critical pathway to sustainability in mechanical engineering is through component longevity. Hydraulic cylinders, integral to heavy-duty machinery, are susceptible to wear and corrosion, often leading to premature failure and replacement. This study investigates the environmental impact of using advanced trivalent hard chromium coatings on cylinder rods to improve their performance in a severe mining environment. The life cycle assessment (LCA) revealed that an innovative trivalent hard chromium coating multiplies the lifespan of hydraulic components compared to a conventional hexavalent chromium coating and thereby significantly reduces the greenhouse gas emissions resulting from their replacement.
The new coating achieves up to 70% higher hardness and 50% better wear resistance (Savroc Oy 2024a). Hexavalent chromium, although commonly used in hard chromium plating, is a known carcinogen and poses serious environmental risks. Due to regulatory pressures, including restrictions under the European REACH (European Commission 2006) regulation, industries are actively seeking safer and more sustainable alternatives, with ongoing pressure to phase it out entirely. Given the carcinogenic and environmentally harmful nature of hexavalent chromium, the move to trivalent alternatives also supports occupational health and environmental safety (European Chemicals Agency 2025). The Corporate Sustainability Reporting Directive (CSRD) (European Commission 2023), starting in 2024 for large firms and expanding to SMEs by 2026, introduces mandatory sustainability disclosures, including carbon footprints.
2. LCA methodology
The study employed a partial carbon footprint analysis aligned with ISO 14067 and the GHG Protocol Product Life Cycle Accounting and Reporting Standard (ISO 2018; WRI/WBCSD 2011). Using ISO 14067 and GHG Protocol standards, the carbon footprint of a hydraulic cylinder coated with Savroc Oy´s TripleHard® trivalent hard chromium (Räisä 2022a) was calculated and compared for the carbon footprint of the similar cylinders coated with traditional hexavalent hard chromium plating.
The carbon footprint calculation of an individual product progresses through several stages, each aimed at identifying and quantifying the greenhouse gas emissions generated throughout the product’s life cycle. In the first stage, Goal and Scope Definition, the boundaries of the assessment were established—determining which life cycle phases would be included in the carbon footprint calculation. A boundary that covers the entire life cycle is referred to as a cradle-to-grave approach (ISO 2018).
In this case the system boundary excluded the use phase of the hydraulic cylinder, focusing instead on material extraction, manufacturing, and transportation. This boundary was appropriate since the goal was to assess emissions related to component replacement, which is heavily influenced by coating durability. The emissions during use for a cylinder in a machine do not depend on the coating of the cylinder.
In the Life Cycle Inventory (LCI) phase, data on material and energy flows associated with each life cycle stage were collected to support the carbon footprint calculation. In the Life Cycle Impact Assessment (LCIA), the carbon footprint was calculated using collected data and emission factors. Calculations were performed using Excel, with emission factors sourced from literature and LCA databases.
Data was collected from a manufacturer of hydraulic cylinders. The functional unit was defined as one hydraulic cylinder with an average size of 1 meter in length and a mass of 100 kg. Emission factors were sourced from reliable databases including the World Steel Association (World Steel Association 2024), the VTT Lipasto emission database (VTT Technical Research Centre of Finland 2017) and Statistics Finland 2020–2023 (Statistics Finland 2023) as presented in table 1. The carbon footprint was calculated using operational data and emission factors multiplied for each lifecycle stage.
The comparative study used data from field tests conducted in mining conditions, where cylinder rods were exposed to harsh environments. Mining conditions as an operating environment subject the cylinder rods to mechanical stress as well as factors that significantly promote corrosion. The combined effects of heat, moisture, salt, and dust create optimal conditions for corrosion damage, which can lead to severe performance issues in the cylinder rods.
3. Life cycle inventory and carbon footprint calculation results
3.1 Case study: durability and emission impacts
A field study was conducted in mining operations in Australia, where hydraulic cylinders coated with both hexavalent and trivalent hard chromium were deployed. The case study (Savroc Oy 2024b) presents a comparison of hexavalent chromium coating (made from a commercial Cr(VI) electrolyte) and trivalent TripleHard® (made from a commercial Cr(III) electrolyte) in mining conditions. To be clear, although reference is made here to the ionic form of the electrolyte, both coating products are non-ionic because the ions are reduced to the metallic form during electrolysis. There are differences in alloy composition and properties as stated later, but the coating is metallic.
For the test, similar hydraulic cylinder rods were coated with different coating options: for traditional hexavalent coating the base materials were AISI 329 and 20MnV6 and for TripleHard® coating, the base material was steel 20MnV6 coated with thin nickel strike layer. AISI 329 is a duplex-type stainless steel that resists corrosion in harsh environment and 20MnV6 is a common carbon steel. The hexavalent coating did not have a nickel underlayer because standard commercial hydraulic rods were used, which did not have a nickel strike option. There was one cylinder for each coating/base material combination.
The field test took place in an Australian mine environment, where the high temperature and saltiness cause even more challenges in extreme conditions. The salty, humid and temperatures above 30 °C mining environments especially are known for their corrosive nature. Equipment and infrastructure used in mining operations, such as metal structures and machinery, are likely to be susceptible for heavy corrosion. The complete duration of the field test was 34 months, and it started during 2018. During the test the hydraulic cylinder rods were regularly monitored. The results demonstrated strong contrasts in coating performance under severe environmental conditions.
The cylinder with traditional hexavalent chromium coating on 20MnV6 showed fast corrosion. After only two months of operating in the mine, a lot of rust had formed onto the cylinder rod, and the rod needed to be replaced.
The cylinder with hexavalent hard chromium coating on duplex stainless steel AISI 329 lasted a little longer. However, after four months rust had been formed on the cylinder, and it had to be replaced.
The cylinder with trivalent hard chromium coating (TripleHard®) on 20MnV6 lasted the whole test period without marks of rust or corrosion. After 34 months of continuous usage in the mine, there was no evidence of rust anywhere in the cylinder rod, see fig. 3. During the three years of operating there were no costs for replacing the cylinder (Savroc Oy 2024b).
3.2 Life cycle impact assessment
The carbon footprint for a single hydraulic cylinder is presented in table 1.
| Activity information | Emission factor kg CO2e | Source of the emission factor | Carbon footprint kg CO2e | |
|---|---|---|---|---|
| Materials | 0.1 t steel | 1.3 t CO2e/t | World Steel Association (2022) | 130 kg CO2e |
| Transportation of materials | Road freight 2,500 km | 0.039 kg CO2e/tkm | VTT Lipasto (2017) | 9.75 kg CO2e |
| Manufacturing | Energy consumption 97.5 kWh | 0.06 kg CO2e/kWh | Statistics Finland (2020–2023) | 5.85 kg CO2e |
| Transportation of the finished product | Road freight 500 km | 0.039 kg CO2e/tkm | VTT Lipasto (2017) | 1.95 kg CO2e |
| Transportation of the finished product | Sea freight 20,000 km | 0.028 kg CO2e/tkm | VTT Lipasto (2017) | 56 kg CO2e |
| Total | 204 kg CO2e |
This totaled a carbon footprint of 203.6 kg CO2e per cylinder unit. Steel was the largest contributor (63.8%), followed by transportation (33.3%) and manufacturing energy (2.9%).
When considering the need to replace cylinders, it was significantly lower in devices equipped with a trivalent coating. Cylinders with traditional hexavalent coating on carbon steel had to be replaced after two months of usage and cylinders with traditional coating on duplex stainless steel after four months (Savroc Oy 2024b). There was no need for replacement for cylinder with TripleHard® coating during the whole test period. Emission savings were calculated by multiplying the number of replacements by the carbon footprint per cylinder calculated in table 1. The outcome was a reduction in lifecycle emissions from 610.7–1221.3 kg CO2e per year to just 71.2 kg CO2e for one steering cylinder of one mining machine, which corresponds to reduction of up to 94%, see table 2.
| Coating | Base material | Lifetime (months) | Replacements/year | CO2 emissions per year |
|---|---|---|---|---|
| Cr(VI) type | 20MnV6 | 2 | 6 | 1221.3 kgCO2e |
| Cr(VI) type | AISI 329 | 4 | 3 | 610.7 kgCO2e |
| TripleHard® CR(III) | 20MnV6 | 34 | 0.35 | 71.2 kgCO2e |
4. Coating properties extend life cycle
There are obvious reasons why the TripleHard® chromium coating is superior compared to traditional hexavalent chromium coating. Composition and microstructure of the coating provide high hardness. An oxide layer is formed on the surface because of heat treatment, which provides excellent corrosion and wear resistance even in harsh environments.
4.1 Composition and microstructure
The composition of trivalent chromium plating is an alloy. EDS analysis, X-ray diffraction, and Scherrer-based grain size measurement reveal that TripleHard® is a Cr–C–Fe–Ni alloy with a nanocrystalline structure (4–23 nm) that hardens via the Hall–Petch mechanism (Wu et al. 2013). The chromium alloy was analyzed to contain 2% carbon, 1.5 % iron and 1.9 % nickel. Fe and Ni dissolution enhances toughness and corrosion resistance, which helps to make corrosion resistant coating.
The cracking structure of chromium coating is also essential for corrosion resistance. As the internal stress of the coating is released, the coating cracks. Macrocracks that penetrate through the layer should be avoided. However, the microcrack network is acceptable. Microcracks are not extending through the entire coating structure. When the coating is considered as microcracked there are typically more than 300 cracks/cm in traditional hexavalent hard chromium coating (Anke, Kleinz & Specht 1981; Jones 1989). It can be seen from Figure 4 that there are no macrocracks in the TripleHard® sample.
Based on Figures 4 and 5, it can be concluded that the microcrack network (600-1200 cracks/cm) that is typical of traditional hard chromium plating also occurs in trivalent coating.
When excellent wear and acid resistance is required, typically in harsh environments like offshore and mining, the TripleHard® coating may be post heat treated at 400 °C (Räisä 2022b). It will harden the coating up to 1800 HV. Heat treatment after plating will cause the coating to crack more and even macrocracks may be formed. When TripleHard® coating was heat treated 6 hours at 400 °C, there will be a thick oxide layer on the coating surface that may also block the cracks, which enhances the corrosion resistance significantly, see Fig. 6. Traditional chromium plating cannot be heat treated at such high temperatures since it starts to soften after 350 °C.
4.2 Leakage performance
Leakage performance of hydraulic cylinders is an important functional parameter. When TripleHard® coating was tested and compared to hexavalent coating, a significant improvement was observed: the cylinder with the TripleHard® coating lasted over 200,000 cycles without leakage, while the hexavalent coating showed increasing leakage from the start. (Savroc Oy 2024b).
4.3 Corrosion tests
Normally, the hexavalent coating resists neutral salt spray for 24–120 hours. Typical specification levels are 48 h. In some applications like marine environments nickel underlayer is applied to enhance corrosion resistance, which increases the salt spray test resistance up to 200 hours. The thickness and microstructure of the coating significantly affect corrosion resistance. However, when the environment is acidic, warm and contains a lot of moisture, the performance is very poor. Even if the base material is duplex or stainless steel it is not durable.
Corrosion resistance of TripleHard® is excellent, and it exceeds industry standards. The plated specimen withstands 200–2000 hours in neutral salt spray (NSS) testing (Savroc Oy 2024a). However, NSS or even copper assisted salt spray test (CASS) correlates poorly with mining conditions. Therefore, a test was conducted in Savroc’s laboratory with simulated mine water (contains sodium chloride, magnesium chloride and sulfuric acid, pH <1, total salt content 16%). The test time was 72 hours.
After 20 hours, green corrosion products began to form on the hexavalent coating, but the TripleHard® sample was still clear, see Fig. 7. The trivalent chromium coating TripleHard® (Räisä 2022a) used in this study lasts until the end of the test, 72 hours. It also resisted real mining environment conditions as was seen.
4.4 Hard chromium coating properties
Table 3 presents a summary about the properties of the coatings tested by Savroc.
| Features | Hexavalent Coating | TripleHard® coating |
|---|---|---|
| Hardness (HV) | 800–1000 | 900–1500 |
| Friction Coefficient | 0.2–0.3 | 0.15–0.2 |
| Cost (€/unit) | Low | Low |
| HSE Impact | Hazardous (Cr⁶⁺) | Safe (no Cr⁶⁺, no boric acid) |
| Corrosion Resistance | Good | Excellent |
| Temperature Resistance (°C) | 350–400 | 700 |
| Impact Resistance | Moderate | High |
| Coating Thickness (μm) | 5–200 | 5–70, in some cases up to 150 |
| Suitability for Sliding Parts | Limited | Excellent |
| Process Complexity | Low | Moderate |
The findings reinforce the value of surface engineering in climate mitigation strategies. Traditional coatings contribute to frequent component failure and high lifecycle emissions. Trivalent chromium coatings not only offer technical superiority but also reduce exposure to toxic substances, aiding in regulatory compliance (e.g., REACH) (European Commission 2006).
This technology is particularly relevant considering the EU’s Corporate Sustainability Reporting Directive (CSRD), which mandates that companies account for environmental impacts, including product-level emissions (European Commission 2023). Integrating LCA data into sustainability reports positions companies as forward-thinking and environmentally responsible.
5. Conclusion
Advanced trivalent chromium coatings present a dual opportunity: enhancing the functional longevity of hydraulic machinery while leading to substantially lower carbon emissions. These benefits support broader environmental targets and corporate sustainability efforts. For mechanical engineering firms, adopting such coatings represents a strategic investment in both performance and regulatory readiness.
Trivalent chromium coatings represent a breakthrough in sustainable surface engineering. By dramatically improving the durability of hydraulic cylinders, they reduce the frequency of component replacement and the associated emissions. The reason for superior performance lies behind the alloy composition and microstructure of trivalent coating. Better resistance for heat treatment enables very high hardness combined with strong oxide layer, which results in high wear and corrosion resistance. A single customer case for one cylinder in a mining machine demonstrated annual carbon savings of over 1,000 kg CO2e. For mechanical engineering companies, especially those in high-wear environments, adopting such coatings supports both regulatory compliance and operational efficiency.
References
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Authors
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Henna Pohjola
Alumna, Metropolia UASHenna Pohjola graduated from Metropolia University of Applied Sciences as a materials and surface engineer in 2025.
About the author -
Jussi Räisä
CEO, Savroc OyTechnology executive specialized in industrial surface technologies and advanced plating solutions.
About the author -
Arto Yli-Pentti
Surface Engineering Specialist & Lecturer, Metropolia UAS / Savroc OySurface and materials engineering specialist with extensive experience in research, industry and education.
About the author
