Spindle screw pumps are among the most wear-resistant pumps on the market – but still require frequent maintenance when certain fluids are pumped. ITT Bornemann now presents an innovative wear prevention concept for its pumps.
Wear of flow-impacted components presents a basic major problem in process engineering. The combination of abrasion and corrosion puts an extremely critical strain on many of the standard materials used in pump technology. Spindle screw pumps have an advantage in this respect: Since the impellers do not touch each other and the geometry of the pump chamber is constant, the technology is already relatively resistant to wear and requires little maintenance. On the basis of this technology ITT Bornemann developed its multi-phase pumps and applied for a patent in 1993, which resulted in a paradigm shift in oil production.
However the high sand content in oil production facilities in Venezuela causes extreme wear so the impellers mus be replaced every six months. “Not only the replacement parts cost money, but also the downtimes”, remarks Jens Dralle, Global Product Manager Industrial at ITT Bornemann, “so we were asked to find a solution.” The company located in Obernkirchen has been working intensively for 15 years on the subject of wear – and had an answer to the problem. At Powtech 2019 in Nuremberg, the engineers recently presented to the broad public an innovative wear prevention concept that substantially prolongs the service life of spindle screw pumps.
Focus on abrasion and erosion
“Nevertheless, it is inevitable that components wear out”, says Jens. “That is why we conducted test bench experiments to determine how a pump has to be constructed in order to minimize wear.” Since abrasive wear is eliminated due to the fact that there is no contact between the screws, the engineers focused on abrasion and erosion. “The primary cause of wear is that the particles are harder than the material of which the pump is made”, Jens ascertains. In addition, virtually no wear is to be expected if the particles are larger than the gap between the impellers. Then they cannot enter the gap in the pump, but instead are transported with the medium through the pump chambers, where they can cause no damage. If the particles are nearly identical in size to the gap, friction can result. If they are smaller than the gap, erosion is possible.
“The first step was to set up a test bench that can provide reproducible results under realistic conditions”, Jens explains. The engineer has been interested in the subject of wear since writing his thesis and followed the single steps of the development at ITT Bornemann intensively. For the problem-causing material the employees in the research department used quartz sand, which was added continuously to the material being pumped, in order to create a perfect simulation of real conditions. “First it was necessary to understand the conditions leading to wear and the parameters that affect wear: speed, differential pressure and also the pump geometry.” That is why the sand is removed from the medium after passing through the pump, after which the same amount of fresh sand is added again upstream of the pump. To create the most realistic conditions possible, no particle passes through the pump twice, which would result in its abrasion. The knowledge gained from the tests was always applied directly in the continued development of the pumps. The experts also used this knowledge for selection of the right pump: “Speed, for example, is an important factor that influences wear. Certain threshold values should generally not be exceeded. But then again there are applications in which a higher speed is advantageous, since this prevents particles from accumulating at the bottom and therefore from entering the gap.”
A good combination
Over the years, however, it has become obvious that the design of the right pump alone is not enough. The engineers started experimenting with materials, and testing hardening processes and coatings. The best solution, according to Jens, is to manufacture the entire pump geometry of ceramic or hard metal – which, however, is generally too expensive and not justifiable even with respect to life cycle costs. “A combination of surface hardening and thin-film coating of the base material, however, proved to be especially promising”, Dralle explains. At the same time, the use of austenitic materials as well as duplex materials assures resistance to corrosion. “This allows us to prolong the service life by a factor of four to five, while maintaining an attractive price with an extra charge of only 20 to 30 percent.”
The new wear prevention concept has already been tested in several field tests and in diverse potential applications. “We are pleased to report that the results of our tests can be reproduced in reality”, says Jens. While use of the concept in the Venezuelan oil field showed that the intervals for replacement were extended to more than two years, the concept has also been used convincingly in the food industry. The service life of the SLH spindle screw pump used in this application was prolonged substantially with a wear prevention concept tailored to the particular material being pumped – whether toothpaste with cleaning particles or hot chilli sauce with seeds.
Focus on TCO
The new wear prevention concept from ITT Bornemann is especially convincing with respect to the total cost of ownership (TCO) and life cycle cost (LCC). When purchasing a new pump it is always necessary to consider the overall costs – from the purchase price to the operating costs and utilization over a particular period of time. The value for the longer service life is a direct factor in the profitability calculation. Since repairs and predictable downtimes are much more expensive, the additional investment in pumps with a coating is generally much more economical.
With a sophisticated predictive maintenance concept ITT Bornemann also intends to increase the meantime between failure (MTBF). The systems equipped with a sensor are monitored by the so-called i-Alert and send data on vibrations, temperatures and operating hours. The data-collecting application already sends information as soon as suspicious machine parameters are detected. In the future the data will be used for efficient scheduling of upcoming maintenance tasks – in order to further minimize downtimes.