Following the delivery of a Valmet Sensodec 6S condition monitoring system, remote diagnostic support provided by Valmet has proved to be an invaluable aid to predictive maintenance.
Situated in southwest Finland, the Norilsk Nickel Harjavalta operation produces nickel metals and chemicals from raw materials that come from as far as Australia and Brazil as well as Finland. Commissioned in 1959 and expanded in 1995 and 2002, today the plant is the seventh largest nickel refinery in the world with an annual capacity of 65,000 tonnes of nickel. As part of the productivity, machine availability and maintenance development activities the plant invested in a Valmet Sensodec 6S for continuous condition monitoring of key process machinery. Today the system monitors 4 ball mills, 3 nickel briquetting machines and two large process fans.
An important part of the condition monitoring analysis is a monthly report prepared by Valmet specialist, Aarno Keränen, using data from the Sensodec system he acquires via a secure remote link. According to Jere Nurmi, Norilsk Nickel Harjavalta maintenance engineer, the monthly report gives him a condensed view of machine conditions and expert analysis of vibration signals. “With Aarno’s additional input we can then follow slowly developing faults and be early enough to schedule repairs to the most convenient times, during shutdowns or together with other maintenance actions.” Recently, the monthly report alerted Jere to a bearing problem on one of the briquetting machines (Figures 1 & 2), although still below the alarm limit the warning was timely. The bearing problem was tracked on-site for four months allowing plenty of time to schedule the necessary spare parts and downtime to repair the machine. Vibration sensors on the briquetting machine motor and gearbox have also given valuable insight to other problems. “We used to repair gearboxes on average once per year, costing about 30,000 Euros a time. With Sensodec monitoring we saw strange vibration peaks that matched the timing of the once per shift compressed air gun cleaning of the machine, contamination was being blown into the machine leading to premature gearbox failure. We changed the cleaning procedure and it has now been three years since the last gearbox replacement,” says Jere.
Using the secure VPN connection, Aarno spends several hours a month looking for trends or any changes in the vibration spectra measured by the Sensodec system. Once or twice a year he also makes a detailed analysis of all the Sensodec signals for anything out of the ordinary or not easily noticed. “My specialty is to be able to concentrate on small details from the comfort of my own office,” says Aarno. His monthly report to Norilsk Nickel Harjavalta contains his expert analysis and suggestions as to what might be wrong, allowing Jere Nurmi to concentrate on day to day maintenance issues. “There are many things we can do better if we have advance warning,” says Jere. “Challenging working conditions in the field make it always preferable to remove machinery to the workshop for repair rather than rushed maintenance at the machine. Of course faults can develop very quickly and Sensodec alerts us to those as well. Ball mills are one of the key machines in the process, and close monitoring of the pinion/ring gear drive is very important. If the mounting comes loose, and it happens occasionally, severe damage can result within only a few hours.”
With the benefit of Valmet’s monthly report there have been many other occasions where catastrophic failure has been avoided. “Aarno’s input gives very valuable background information to use,” says Jere. “Our view to condition monitoring is very much just at the surface and the monthly report goes much deeper. I am able to alert the right department with the right information before problems become too severe.” A recent fault with one of the two enormous process air fans in the reduction plant is a case in point; the monthly report identified a bearing problem which was disputed by the fan manufacturer as being a problem. Based on vibration analysis, the fan bearing was disassembled and sure enough a magnet picked up metal cuttings in the bearing. Undetected, this fault would have put the fan out of operation for two weeks affecting production significantly, whereas with sufficient warning, the repair could be made in two days.
The monthly report service also picks up any problems with Sensodec itself or with the many transducers connected to it, ensuring the plant of maximum system uptime as well as production availability. “Sensodec 6S is very reliable,” says Jere, “and I think our production operations would be at a severe disadvantage without it, or the advice from the monthly reports that I have come to rely on a great deal.”
Norilsk Nickel Harjavalta Oy manufactures top-class high-technology nickel products designed according to customer needs. The principal market areas are Europe, Asia and the United States. The raw materials used are mainly nickel concentrates and nickel mattes. Production at Harjavalta is divided into four departments: Leaching, Nickel reduction, Nickel electrowinning and the chemical plant. Nickel produced at Harjavalta is highly esteemed for its excellent chemical purity and physical quality. The extensive product range is also a key asset. The majority of production consists of metallic nickel, with nickel chemicals accounting for approximately 10% of production.