The facility, an affiliate of Wessex Water, a water supply and sewerage utility company serving an area of Southwest England, employed the help of Belzona, a polymeric repair composites and coatings manufacturer, to address the corrosion problem occurring at the vapor interface level, which limited the client to only operate the buffer tank at a reduced capacity of 65 percent.
Wessex Water uses anaerobic digestion to process sewage sludge. As such, the buffer tank, fabricated from glass fused to steel (GFS), consists of bacteria that help break down organic material in sludge. This process, however, produces a mix of methane, carbon dioxide and hydrogen sulfide -- all of which contribute to the corrosion of the structure.
Accordingly, water treatment tanks are highly susceptible to corrosion due to handling aggressive chemicals on a daily basis. In the presence of moisture in the presence of vapor, the biological conversion of hydrogen sulfide gas to sulfuric acid can occur. Hydrogen sulfide gas can directly attack metals such as copper, iron and steel; this leads to metal losses where through-wall defects can develop.
|The sludge buffer tank before and after the repair (Photo credit: Belzona)
The repair was completed by a team of two from Belzona Technosol, Belzona's application division, in September, 2013. Steel plates were prefabricated to cover the leak areas, and the surface was prepared by hand abrasion to ensure good mechanical adhesion. Belzona surface-tolerant epoxies and repair plates pre-coated with Belzona 5831 (ST-Barrier) and wetted with Belzona 1831 (Super UW-Metal) were also selected to ensure full contact and excellent adhesion.
Tank maintenance can present multiple challenges where the shutdown of operations is expensive and the handling of live or hot equipment is risky. These issues prompted the implementation of Belzona's application, which took less than two days to complete with minimal disruption to activity and was accomplished without hot work or the use of mechanical equipment.
Cold-bonding technology was first introduced to tackle health and safety issues presented by welding, given that application and cure occur at ambient temperatures. Additionally, businesses now require minimal operation disruption and expedient completion from most maintenance work.
About Wessex Water
Wessex Water is a regional water and sewage treatment business serving an area of Southwest England, covering 10,000 square kilometres including Dorset, Somerset, Bristol, most of Wiltshire, and parts of Gloucestershire and Hampshire. The treatment site deals with various types of domestic and industrial effluent, which is treated at the sewage treatment works before being safely returned to the environment. For more information, visit www.wessexwater.co.uk.
Belzona is a product manufacturer that provides a complete supply and apply package through its Global Distribution Network. This network was created to provide clients with direct access to the company's products, specialist application and inspection/supervision and training services. It is Belzona's mission to meet specialist repair and maintenance needs in its target industries and markets worldwide. For more information, visit www.belzona.com.