Abrasion can create one of the most arduous service environments, and it remains a major challenge for mining operators, starting from mineral extraction to metal refining.
by Cassia Sanada and Chloe Hirst*
Abrasion is one of the most common problems and can lead to premature failure causing long downtime and significant loss of revenue.
Hyper-abrasive environment for sludge pumps: sludge pumps are one of the most sensitive equipment subjected to abrasion wear throughout the entire production process in a mine. Due to difficult operating environments, very hard aggregates and underground mining processes, premature failure of sludge pumps used in the transport of abrasive solids in large volumes is a common problem. When a mixing pump stops unexpectedly, a large mine can lose up to US$100,000 per hour in revenue.
Although in recent years there has been significant progress regarding the mechanical design of sludge pumps, they are still plagued by erosion and abrasion problems, these effects are considered as the main threat to their longevity and performance. The manufacturing design of this equipment, commonly consider a high resistance to erosion, with exotic alloys such as Inconel, Monel, duplex, superduplex and Nickel-hard; however, these characteristics of having the ability to handle rocks, gravel and mud, mud pumps continue to fail on a large scale due to the high rate of abrasion.
Depending on the properties of abrasive particles, i.e. the size of solids, solids concentration, hardness and temperature, as well as operating conditions and process parameters, i.e. flow rate and input rate of particles; the parts of the pump exposed to the mixture can be greatly impacted.
The components of the impeller, housing and suction coating can be significantly worn within a few hours and therefore the need to be replaced at regular intervals is generated. This sets the financial loss of downtime and replacement at very high levels, as the costs of purchasing a mixing pump have a much higher cost, if we compare it with a standard water pump.
As a result, the use of a protective layer that decreases the abrasion process in the pump is of utmost importance. Specification of coating materials for sludge pumping applications is not a standard procedure and must take into account all variables, such as the type and speed of the pump and the nature of the solids. Although handling abrasive fluids presents a huge challenge for any protective material, a carefully selected abrasion-resistant coating can reduce the effects of impact wear , extend pump life, and optimize the overall performance of the pumping process.
Hazelton VDS Sludge Pump Repair
An Australian market leader in the production and marketing of nickel and cobalt, it has been constantly on the lookout for a reliable solution to repair and restore the efficiency of vertical centrifugal sludge pumps.
At a mineral refinery that processes nickel and laterite-cobalt ore that is purchased from other mines in New Caledonia, Indonesia and the Philippines. The nickel ore is dried, ground and leached into an ammonia solution to extract the nickel and cobalt in the processing plant. Nickel and cobalt are then separated and continue their refining in the area of metal refining.
One of the refinery's most critical pumps is the "Hazelton VDS 12 blend pump" used to extract and transport the ore from the tailings sink and distribute it to the refining process units. The suspended mixture contains about 60% solids by volume and has a temperature of 70°C-80°C (158°F-176°F).
Since the pump is continuously operating 24 hours a day and due to extreme wear and tear, a second pump is required to be constantly on-site as a replacement unit. To ensure this, a third pump is used as a spare unit, always available. After 2,500 hours of continuous operation, the operating unit that has been operating will be replaced by the second unit. This second backup unit will be replaced by the third spare pump and the removed pump will be disassembled for maintenance inspection.
Using the Belzona repair system, Rezitech Services PTY LTD, our authorized Belzona Distributor in Australia, undertook the restoration of the eroded unit, even if the pump has been severely damaged. "An uncoated volute was put into service in 2013, and it was almost irreparable after 5,000 hours," explains Levi Boyd, North Queensland Director at Rezitech PTY LTD Services. "The unit should have been scrapped, but since replacement would have taken up to four months to arrive, it was decided to make the repair."
Products specified for applications
In order to provide a comprehensive repair on the housing of the Hazelton mixing pump, which commonly suffers extreme wear on both water cuts, making it unsuitable for use, polymeric compounds must offer long-term erosion protection. The materials have to be highly durable, meet the need for high abrasion resistance in high temperature immersion conditions and provide excellent mechanical strength.
Based on these considerations, a set of four erosion-corrosion resistant composite materials and protective repair coatings: Belzona 1812 (Ceramic Carbide FP), Belzona 1321 (Ceramic S-metal), Belzona 1311 (Ceramic R-Metal) and Belzona 1391 (Ceramic HT), has been tested to meet abrasion and resistance requirements to temperature requirements.
To measure the impact abrasion resistance of its materials, Belzona ran a sandblasting abrasion test as part of its abrasion/erosion testing program. It is an internal test method, where a test specimen consisting of a disc made by molding with set Epoxy compound is pre-weighed and placed at a certain distance from the outlet nozzle.
The sample is held at an angle, 30° or 90°, to the nozzle and then shot with angular cast iron using an air pressure of approximately 5.5 bar (80 psi). The erosion resistance of the material is determined from the associated volume loss.
When the G34 granulometry cast iron shot is released at 75 psi and at an angle of 90 °, the Belzona 1812 (Ceramic Carbide FP), an abrasion-resistant coating based on high molecular weight polymers and oligomers incorporating ceramic aggregates, exhibited a volume loss of only 8 mm3.
Application steps
Since the pump is constructed of hard nickel (a cast iron alloyed with nickel and chromium), an abrasive cleaning of the substrate is done following the Swedish Standard Sa 21/2 with aluminum oxide, a very hard and sharp ceramic aggregate, in order to achieve the necessary anchor profile on the surface and avoid contamination of the substrate.
Additionally, custom-made samples are fixed to the impeller ring and the openings of the discharge ports to serve as a mold, to restore the internal diameter and also to ensure correct alignment by allowing the applicator to achieve a uniform thickness throughout the surface coating of the repair area. Once all the arrangements have been finished and before applying with Belzona products, the areas to be treated should be thoroughly cleaned.
Extremely worn water cuts are commonly reduced by approximately 100 mm, they are repaired with Belzona 1311, a pasty grade ceramic product, epoxy, to perform repairs and reconstructions of damaged areas. Once the product is cured, the water cuts can be conformed to the required dimensions using an angle grinder.
The Belzona 1321 is an epoxy coating with ceramic filling designed to protect against moderate abrasion, applied to the entire inner part of the housing as a primer layer to improve adhesion to the hard nickel substrate. The coating exhibits adhesion to the cast iron surface and forge with no signs of shrinkage as the system is 100% solid.
Belzona 1812 is an epoxy product that has been formulated with ceramic aggregates with an extremely high hardness, in a highly concentrated polymeric binder. It is then applied to a thickness of approximately 6 mm using the previously installed templates.
A final layer of Belzona 1391, ideal for equipment operating at high temperatures and in immersion, was also applied to all the internal parts of the pump to provide additional heat resistance. Once the final layer has set, the jigs are removed, and all the extruded material is removed by grinding. The pump is then externally coated with Belzona 5891 (HT Immersion Grade) to protect it from tailings fluids at high temperatures.
Minimize downtime – Increase performance
From start to finish, the application lasted less than a week and with very simple application techniques, the customer was able to avoid equipment replacement costs that could exceed approximately US$15,000. The repair proved to be more durable than the hard nickel substrate, cost about half this amount, and provided for equipment shutdowns that could cost approximately $77,000 per hour.
The refinery has been a loyal customer to Belzona to repair more equipment at its plant, such as vacuum pumps, large filter heads and chemical containment areas since they began in 1970 and have expressed happiness with the products ever since.
*Cassia Sanada, Technical Coordinator, and Chloe Hirst, Marketing Assistant at Belzona. Cassia Sanada joined Belzona Inc. in 2011 and is a member of the Marketing Department. Cassia is a Chemical Engineer and holds a Master's Degree in Biotechnology. Chloe Hirst joined Belzona Polymerics Ltd. in 2013 and is a member of the Marketing and Public Relations Department. Chloe holds a degree in Art and Media with a major in journalism.
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