Hazard-free anti-seize paste for gas & steam turbines

Safe and Sustainable Chemicals, Germany

A leading initiative by DuPont.

In recent years, concerns have arisen regarding the formation of hexavalent chromium (Cr(VI)) on threaded connections in turbine and turbocharger applications operating at elevated temperatures. Hexavalent chromium is known to be cancerogenic and toxic, posing serious health risks. To combat this issue, a new lubricant with an environmentally friendly profile has been developed, aiming to suppress the formation of Cr(VI) and safeguard the health of operators while ensuring smooth maintenance processes.  

Regular maintenance of gas and steam turbines is crucial to maintain reliable power generation, especially in the modern era. Anti-seize pastes, or lubricants, have long played a vital role in these maintenance procedures. They provide controlled friction during assembly, facilitating precise tensioning and safe disassembly, even after extended exposure to high temperatures. However, in recent years, the emergence of hexavalent chromium residues on heat-exposed lubricated parts, such as flanges, has raised significant concerns. Turbine Original Equipment Manufacturers (OEMs), like Siemens and GE, and industry associations, including Energy UK, have addressed this safety issue in their publications.  

DuPont, a company with a well-established portfolio of anti-seize pastes under the MOLYKOTE® brand, recognised the importance of addressing this issue. As part of its responsible care philosophy and commitment to product safety, DuPont initiated a project in 2019 to develop a new generation of anti-seize pastes that could prevent the formation of hexavalent chromium. The primary objective was to create a product that would not require hazardous labeling under current EU legislation. This entailed using high-purity ingredients devoid of sulfur and halogens while maintaining the performance level expected from anti-seize pastes used in threaded connections.  

Investigating the Formation of Hexavalent Chromium  

Research began by investigating the causes of hexavalent chromium formation (Cr(VI)). Importantly, anti-seize pastes themselves do not contain any chromium components. Scientific literature and both internal and external evaluations revealed that the critical factors triggering the formation of Cr(VI) are temperature (typically exceeding 300°C), the type of alloy used (with a higher chromium content increasing the risk), and the presence of calcium or magnesium-containing materials (which can be found in anti-seize paste formulations). All three factors need to be present for hexavalent chromium to form.  

Modern turbines, which often use superalloys containing 15-20% chromium and operate at temperatures exceeding 300°C, are particularly susceptible to Cr(VI) formation. The most effective approach to preventing Cr(VI) formation is to use an anti-seize paste that does not contain critical ingredients like calcium and magnesium.  

Developing a Solution  

The project team devised an internal test method to simulate the formation of Cr(VI). This test involved applying samples of pastes to a sandblasted chromium alloy plate with approximately 20% chromium. The plates were then exposed to temperatures exceeding 500°C for specific durations, ranging from 72 to 500 hours. After cooling, any paste residues were collected, and the hexavalent chromium content was analyzed according to DIN 19734 (1999-01).  

This test method guided the development of an anti-seize paste that did not support the formation of Cr(VI) when applied to chromium-containing alloys. The final prototype demonstrated a significant reduction in hexavalent chromium formation, with levels approximately 200 times lower, approaching the detection limit, compared to currently available commercial products.  

The New Solution  

The resulting product, MOLYKOTE® P-3700 anti-seize paste, was introduced to the market in 2022. Engineers and customers received training through a technical webinar, which highlighted the critical factors contributing to hexavalent chromium formation and how MOLYKOTE® addressed this issue.  

DuPont™ MOLYKOTE® positions this new product as a sustainable solution with an environmentally friendly profile, aligning with four United Nations Sustainable Development Goals. By addressing the challenges of Cr(VI) formation, DuPont has taken a significant step towards safer and more sustainable maintenance practices in high-temperature applications.