Bearings help to improve MTBF rates in petrochemical industry
08 November 2010
The bearing solutions provided by NSK for use in petrochemical applications are designed to address the demanding and hostile environments where pumps and compressors are used, and are routinely exposed to heat, chemicals, oils and gases, including refrigerants and ammonia gas.
The ranges available include the EM/EW cylindrical roller and HPS series of angular contact bearings. The bearings are designed to provide support for the helical rotors used in gas and air compressors, offering higher levels of heat tolerance, chemical stability and increased load carrying capacity.
In both types of bearings, substantial improvements in load capacity have been achieved. Basic dynamic load rating has been improved on the cylindrical roller bearings by as much as 30%, and on the HPS angular contact bearings by a maximum of 20% - when compared to conventional bearing types. The result is said to be an improvement in fatigue life for both types of bearings, enabling users to benefit from longer trouble-free operation and extended intervals between overhauls.
Substantial performance improvements are also provided on centrifugal pumps with the company’s HR series of high-capacity deep-groove ball bearings. The bearings feature an internal design which allows for larger rolling elements than standard deep-groove ball bearings; at the same time retaining standard external dimensions to ISO standards. This new design enables the HR bearings to deliver increased dynamic load ratings, by 7% to 19% (depending on size), resulting in a 22% to 68% increase in ISO life.
As a result, the HR series helps to improve the operating life of pumps, minimising downtime without involving the pump operator in any costly changes to standard bearing dimensions.
Also designed to enhance pump performance without cost fitment issues are NSK’s Anti-Creep bearings. The bearing can be fitted without the need for any special machining of housings, and are said to offer an effective solution to the problem of creep, which is the result of loads becoming excessively high on the driving shaft of a pump. If not addressed, creep causes excessive shaft vibration, which can trigger abnormal oscillation and lead to impeller damage.
Common measures against creep include an interference fit between bearing and housing. For pumps, however, a tight fit is not practical, as it makes pump assembly more difficult and does not allow for additional loading caused by an increase in the shaft length due to heat generation. A better solution, provided by the Anti-creep bearings, is to install O-rings into the two grooves on the bearing outer ring. With this design, the frictional force of the O-rings helps to prevent the occurrence of creep and subsequent damage to the shaft of the pump upon which the bearings are fitted.
In addition to delivering improved MTBF in standard pumping and compression applications, NSK’s petrochemical bearing package also addresses demanding and arduous pumping tasks. The SPACEA LNG series bearings are designed for use in pumping liquid nitrogen gas (LNG) and have been developed to operate at speeds of up to 3,600rpm while immersed in the gas, at -162 degrees C, with lubrication provided by the cryogenic agent itself.
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