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Corrosion
Innovation in corrosion resistant materials technology: Glass-lined steel tubes in heat exchanger design
Glass-lined steel is a groundbreaking material that combines the strength and durability of steel with the exceptional corrosion resistance of glass. Originally developed nearly 150 years ago, advancements in manufacturing techniques have refined this composite material, making it an ideal choice for applications requiring chemical resistance, thermal efficiency, and longevity. From pharmaceutical production to industrial heat recovery, glass-lined steel is proving to be a cost-effective and environmentally friendly alternative to traditional alloys, revolutionizing industries that demand both performance and sustainability.
By Tom Patnaik, Vice President, Sales & Service, THALETEC USA Inc., with contribution from Christian Stentzel, Head of Research & Development, THALETEC GmbH
The strength of steel is well known, as well as the corrosion-resistant properties of glass. Combining the two to produce a glass-lined steel surface( often referred to in the industry as‘ glass-lined steel’) creates material that is both strong and corrosion resistant, but the engineering challenges to produce this material were considerable. While glass has poor conductivity, steel is just the opposite. The two could be combined in a manner where the impact of glass on the overall heat transfer is minimized while taking advantage of its very high chemical resistance and ease of cleaning. But at the same time, using steel to provide structural strength, durability, and cost savings results in a construction material that has the best of both worlds. This challenge of bonding glass to steel was overcome almost 150 years ago. The technology has been further improved and refined in the 21st century to overcome a wide range of process, operational, and cost issues.
What is glass-lined steel? Glass-lined steel is a composite material of glass particles( or frits) fused to a steel substrate. Glass is applied to steel in two ways: 1) either as a glass particulate slurry sprayed on the steel in six 0.25 mm layers with each layer followed by high temperature fusing in a furnace, or 2) as two layers of electrostatically charged glass particles applied to a specially treated steel pipe, with each application followed by firing in a furnace at high temperature. Each layer is approximately 10 mil( 0.25 mm) thick. As such, the wet method yields a glass thickness of 39 to 87mils( or 1.0 to 2.2 mm) thick, whereas the dry electrostatic method yields glass thickness of just 20 mil( or 0.5 mm) thick. The wet method is usually applied to the inside of cylindrical vessels( such as chemical
Installation of large glass-lined heat exchangers in a 500 mW power plant unit, improving the thermal efficiency by up to 12 %.
reactors or storage vessels) where the glass layers are under compression due to the larger coefficient of thermal expansion / contraction of the steel substrate. This compressive force and a chemical reaction between glass and carbon steel produces an extremely strong bond capable of absorbing significant impact. As such, glass-lined steel is very strong and durable and can handle an operating pressure of-1 /+ 10 bar and temperatures of-29 /+ 230 ° C for standard applications( higher with some special design considerations). In the wet slurry method of glass application, the first two layers comprise a‘ ground’ coat that provides the adhesion and transition from steel to glass, which is then applied in 3-5 cover coats. The ground coats are usually applied at a higher temperature( 900 ° C) and the cover coats at about 850 ° C. The ground coats provide:
• adherence to the steel
• transition from the high thermal expansion of steel to the lesser expansion of glass
• suitable bubble structure( porosity) for outgassing during firing
The cover coats provide:
• the corrosion-resistance properties of glass
• the release properties( smooth surface) required by many pharma-chemical processes
26 Heat Exchanger World June 2025 www. heat-exchanger-world. com