Deep in the Wuling Mountain range, at an altitude of 1,800 meters, lies a mirror-like body of water that reflects the sky and clouds above. As visitors approach, they are astonished to discover a remarkable fact hidden beneath the surface of what’s known as Wuling Mountain Tianchi: the lakebed and sidewalls are fully lined with 3 mm thick 304 stainless steel. In total, 656.76 tons of stainless steel were used, with a welded surface area equivalent to four standard football fields.
This is not a modern art installation or a piece of futuristic architecture—it is an engineering marvel created by Chinese engineers to overcome the challenges of the karst landscape.
Wuling Mountain is characterized by a typical karst topography, riddled with caves and highly fractured bedrock, resulting in extremely poor natural water retention. The Tianchi basin spans about 27,683 square meters and is designed to store up to 150,000 cubic meters of water. Previously, the natural reservoir continuously leaked due to underground fissures, severely limiting its capacity. Traditional waterproofing solutions—such as concrete sealing and geomembranes—failed repeatedly under geological movement and hydrostatic pressure.
Ultimately, engineers turned to a complete lining of 3 mm thick 304 stainless steel, welded seamlessly to create a fully sealed, leak-proof barrier. Completed in 2017, the project dramatically increased the lake’s storage capacity and has withstood multiple droughts. Its service life is projected to exceed 50 years.
304 stainless steel contains 18–20% chromium and 8–10% nickel. Its surface naturally forms a dense chromium oxide passive film that protects against rust by blocking water and oxygen penetration. The low carbon content (≤0.08%) minimizes the risk of localized corrosion, especially after welding.
It also meets food-grade standards—commonly used in kitchenware, thermos bottles, and water tanks—conforming to national safety regulations (GB 4806.9-2016). This ensures no harmful heavy metals leach into the water, making it safe for drinking.
Engineering Suitability
The 3 mm thick stainless steel plates offer excellent weldability and flexibility, allowing them to adapt to subtle geological shifts in the karst environment without cracking. While ultra-low carbon 304L stainless steel offers even better weldability, it has lower strength and higher cost, making it less advantageous for large-scale infrastructure projects.
304 stainless steel costs only 60–70% of 316 stainless steel, which contains molybdenum for enhanced resistance to seawater corrosion. Since Tianchi is a freshwater reservoir, the superior corrosion resistance of 316 is unnecessary—304 provides a more cost-effective solution without compromising performance.
Tianchi is not only a scenic attraction but also serves as a critical freshwater source for drinking water and forest fire prevention. The use of 304 stainless steel not only solved the long-standing leakage problem but also improved water storage stability, supporting both tourism and agricultural irrigation needs in the region.
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