Rock Products

FEB 2018

Rock Products is the aggregates industry's leading source for market analysis and technology solutions, delivering critical content focusing on aggregates-processing equipment; operational efficiencies; management best practices; comprehensive market

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34 • ROCK products • February 2018 www.rockproducts.com I ndustrial processes such as aggre- gates operations across the globe require pumps to operate reliably and efficiently. The latest pump designs and coating technologies offer signif- icant improvements in the long-term performance of industrial pumps. By minimizing the effects of corrosion and erosion, users can enhance productivity and reduce running costs. Continued research into the processes that degrade pump performance is being matched by the development of better application techniques for pro- tective coatings. By gaining a better understanding of both the pumping process and the factors that affect it, end users can make significant improvements in their maintenance strategies. Affected Applications Almost every industrial process involv- ing liquids will include a pump at some point. From deep sea oil and gas to DNA sequencing, pumps are required to per- form a vast range of tasks. However, no matter what the design or the size of the pump, central to every application is reliability and efficiency – minimizing down time and running costs is essen- tial to modern industry. For those working with large industrial pumps, such as aggregates operations – often operating in harsh environmental conditions – maintaining pump perfor- mance in the face of a continuous threat from corrosion and erosion can be a particular challenge. With increased knowledge of these processes and the techniques used to tackle them, it is possible to implement a more cost-ef- fective pump refurbishment program. Corrosion – Corrosion is commonly defined as a chemical reaction between the component surface and the react- ing fluid passing through a pump. In general a distinction is drawn between general or uniform corrosion and local- ized corrosion like pitting and crevice corrosion. Non-stainless materials suffer mainly from uniform corrosion whereas metals forming oxide layers that adhere to and passivate the surface are prone to localized corrosion. Flow Accelerated Corrosion – Flow accelerated corrosion (FAC) describes the removal of the protective oxide layer on a metal. The speed of this pro- cess is affected by the oxygen content, the flow velocity and, to some extent, the chloride content. The formation of a calcareous layer due to high carbonate hardness of the water reduces or even prevents FAC. The influence of oxygen can be seen in the following example: Water with an oxygen content of less than 20 ppb (parts per billion) and a flow veloc- ity around 15 m/s will typically see a corrosion rate around 0.01 mm/year. However, increased oxygen content can see the corrosion rate rise to several mm/year, which will present a signif- icant challenge to the process. Fortunately, FAC only poses a real issue for low carbon steels and cast iron. Increasing the chromium con- tent or using stainless steel will largely eliminate the vulnerability to flow accelerated corrosion. Erosion – Pumps that are used to transfer fluids containing abrasive sub- stances, such as sand, can experience significant levels of erosion, especially in areas with high flow velocities. This can be seen in the oil and gas industry where injection pumps are employed to force water back into the oil field and thus maintain the pressure which is needed to lift the oil to the surface. The entrained sand particles act as an abrasive and the high working pres- sures only serve to compound the issue. From a pure design standpoint, pump manufacturers in this field effectively have two options to minimize the erosion: •  Reduce the flow velocities in every part of the pump. •  Design the pump in such a way that the flow velocities through the close-running clearances are low. However, in most cases the specifica- tions required for the application will prevent either of these solutions from being implemented. Coatings with high erosion resistance in selected areas of the pump are a proven solution in these applications. Erosion-Corrosion – In operating conditions where both erosion and corrosion are present, the degradation mechanism can become very complex A Cost-Effective Pump Solution Maximizing Pump Efficiency Through Reduced Corrosion and Erosion. By Mark S.Kuhar PUMP EFFICIENCY Coating technologies offer improved performance and durability. In situations where erosion-corro- sion is evident, specialized coatings may be the best solution.

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