After six years in service, the worn pump components were still in good condition.
Regardless of the pulping methods, paper mill pumps are put under immense strain due to the transfer of viscous material throughout the pulping process. Together, the sludge and slurries combine a high solids content, copious amounts of entrained air and often processing chemicals, used to extract the cellulose from the wood fibre.
This resulting combination can cause issues associated with erosion, corrosion, and chemical attack, and the subsequent impact of these damage mechanisms can truly affect the pump’s efficiency. Initially, damage will lead to rough and pitted surfaces, which will increase friction and lead to a drop in the efficiency of the system, as well as increased running costs.
Pumps in Anguish
If not tackled in time, corrosion-erosion problems may jeopardise the integrity of the component, ultimately causing failure of the equipment. This can be to the detriment of the pulping process and the operation of the paper mill.
In 2010, an Italian paper mill was suffering from particular problems relating to these effects. The casing and internal components of a cast iron, submersible sludge pump were being troubled by immersion in chemically saturated slurries and the pumping of the erosive materials. In fact, the stresses were taking a significant toll on the pump, which was barely lasting a maximum of two years in service before requiring major overhaul and replacement.
While replacement might be an obvious solution, this was costly. Not only in terms of replacing the equipment, but also the downtime that was associated with dismantling and installation of new pump components. In addition, replacement usually involves long lead times of weeks or months. These periods of limited processing power made it necessary that the paper mill reduced output, an expensive problem when taking into consideration the regularity of the pump’s deterioration.
The components were recoated with a polymer to create a barrier against chemicals used in the paper pulping process.
Why Replace What Is Not Broken?
More importantly, replacement did not address the underlying problem. Unsatisfied with their current approach and in search of an alternative, the paper mill contacted Belzona’s representative in Italy, BS srl, looking for a viable solution for its consistently failing pumps. After careful selection, a combination of erosion-corrosion resistant systems was chosen to complete the application. Initially rebuilding the metal loss in the pump using Belzona 1311 (Ceramic R-Metal), the pump was internally coated with Belzona 1321 (Ceramic S-Metal). These coatings form a durable protective barrier for metal repair and erosion and corrosion protection. They also demonstrate chemical resistance in continuous immersion situations.
Finally, the pump was coated externally using Belzona 5811 (Immersion Grade), designed to preserve equipment operating under immersed conditions. This created an essential barrier against the chemicals used in the pulping process.
Return to Palatable Pulping
Overall, this solution aimed to eliminate the need for replacement, reducing the much-maligned downtime associated with regular overhaul. Originally coated in 2010, six years later, the customer opened the pump for mechanical maintenance. Throughout its service life, the pump faced zero downtime due to Belzona erosion-corrosion protection and the coating was found to be in excellent condition.
However, the mill refreshed the coatings to prepare the pump for more years of service in sludge; the original coatings were roughened before applying a new layer on top. Not only did this continue to extend the pump’s service life, saving the company replacement costs, but ensured the equipment was protected in the long term against the dangers of erosion and corrosion.
“This type of application is one that we complete frequently on small, medium and large scale components,” said Enzo Arrabito, CEO of BS srl. “The pump in question was suffering immensely from erosion-corrosion damage; therefore, the client expressed their satisfaction that the lifespan of the pump could be extended significantly through the use of a polymeric solution.
“At the same time, this reduced their maintenance costs and allowed them to achieve greater efficiency from their equipment. Its immediate effects on performance will be maintained over a long period, reducing power consumption and saving on operating costs.”