China has completed what it describes as the world’s first 537-day deep-sea material corrosion exposure test at a depth of 6.8 miles (11,000 meters), marking a major milestone in long-duration deep-sea engineering research.
The test aimed to study how different materials and protective coatings behave after prolonged exposure to one of Earth’s harshest natural environments.
With the long-duration mission, researchers generated rare real-world data on how different materials behave after prolonged exposure to one of the harshest environments on Earth.
The achievement also marks a major step forward in China’s deep-sea in-situ testing capabilities. The project was announced by the China State Shipbuilding Corporation (CSSC) on Saturday.
Unlike laboratory simulations, in-situ testing involves placing instruments and materials directly into the natural deep-sea environment, allowing researchers to study corrosion, pressure resistance, and material degradation under authentic ultra-deep-sea conditions.
Testing materials at 6.8 miles
The 537-day mission focused on evaluating corrosion resistance in ultra-deep-sea conditions. Researchers deployed multiple categories of materials, including ferrous and non-ferrous metals, functional coatings, sacrificial anode materials, and non-metallic buoyancy materials.
After recovery, scientists observed major differences in how the materials performed.
“This is a sample we retrieved after conducting tests for 537 days at a depth of 11,000 meters on the seabed. These are all coating-protection experiments. Based on the current condition of this sample, we can see that many materials have very poor corrosion resistance in the deep sea,” said Sun Mingxian, deputy chief engineer and researcher of the CSSC’s 725 Research Institute.
“A lot of the coatings have already started to peel off, while some others still remain intact. We’ll conduct further in-depth analysis in the lab to draw more definitive conclusions,” he continued.
The test was designed to evaluate the long-term corrosion resistance of materials and coatings in the 10,000-meter deep-sea environment.
According to Liao Zhiqian, deputy director of CSSC’s 725 Research Institute, the recovered specimens provide rare long-term empirical data from real 10,000-meter deep-sea environments.
The record-setting test was conducted under extremely harsh deep-sea conditions, including intense pressure, low temperatures, high salinity, and extremely low dissolved oxygen levels, according to CSSC.
Data could improve subsea engineering
Researchers believe the findings could help improve the durability and lifecycle prediction of future subsea infrastructure.
Liao explained that the environmental data collected during the mission will support more accurate corrosion-resistant designs for deep-sea equipment operating under extreme conditions.
The project also resulted in the development of several new protective coating formulations designed for deep-sea oil extraction and mining systems.
Such technologies are becoming increasingly important as countries and companies push further into deep-sea exploration for energy resources and mineral extraction.
Simulation system refined using mission data
The 725 Research Institute also used the mission data to upgrade its self-developed deep-sea simulation system.
Operating at depths of over 10,000 meters exposes materials to pressures exceeding 1,000 times atmospheric pressure, making real-world testing extremely difficult and expensive.
The 537-day experiment represents a major step in China’s broader ambitions involving deep-sea exploration, underwater mining, and offshore oil and gas development.