Free guide to bearings for petrochemical applications

Few working environments can compete with the potent mix of production demands and pressures routinely encountered in chemical and petrochemical processing.

Numerous rotating machines are required to successfully complete processes and deliver products on time. The use of bearings in such applications provides many technical challenges. NSK has deployed its global knowledge of the petrochemical market and its technical innovation to produce a range of bearings designed to address the economic and environmental issues facing the petrochemical industry.

Centrifugal pumps test bearing designs

As the primary equipment type used in petrochemical applications, centrifugal pumps continually test the endurance and integrity of rolling bearing designs. The problems of handling difficult-to-pump corrosive liquids, the continuous operating regimes, and the critical nature of the applications themselves, mean that the pumps and their associated bearings are always under the maximum pressure to perform reliably and consistently over long periods.

NSK has responded to this challenge with a system based upon its EW/ET/EM series of cylindrical roller bearings, and paired BMPC series of angular contact bearings with 40deg contact angles. All of these bearings are designed to extend the periods between pump failures.

Bearings achieve longer service life

BMPC series bearings exceed the API (American Petroleum Institute) 610 specification with what is claimed to be the strongest machined brass cage in the industry, providing superior reliability in the harshest of applications. They also achieve longer service life through smoother running, reduced levels of friction and lower temperature rise; the latter as a result of the better heat dissipation of the brass cage material.

The BMPC series design is an amalgam of high strength materials technology, ABEC3 (P6) manufacturing tolerances and pump-specific axial internal clearances. It delivers higher running accuracy, plus optimum levels of bearing stiffness, shaft positioning accuracy, load sharing and cooler running.

In addition, the combination of super finished raceways, lowest inner-ring run-out and tight tolerance ball grade, all contribute to reduced levels of ball skidding and hence, smoother operation.

The BMPC bearings are manufactured with 40deg contact angles to support both the axial and radial loading of pumps. They also have universally ground faces, allowing mounting versatility on a wide range of shaft sizes from 20mm OD to 150mm OD.

Cylindrical Roller Bearings (CRB)

The NSK 'E' series of cylindrical roller bearings (CRBs) are used in conjunction with the BMPC angular contact bearings. EW/EM series CRBs are capable of carrying particularly large radial loads and are also suitable for high-speed applications.

Whereas the EW series features a pressed steel cage, the EM series has a one-piece machined brass cage. Both of these cage designs offer higher load ratings compared to standard size bearings (30 per cent for EM; 20 per cent for EW), giving a longer operating life, approximately twice that of conventional CRBs.

Another feature of the EW and EM cage designs is that the cage pockets are extremely precise, leading to enhanced accuracy in the roller position, which provides greater control over the rollers and helps to minimise excess vibration. With the EW series, the reduction is between 30 to 50 per cent; while that for the EM series is greater still, at 50 to 60 per cent.

Other equipment

In addition to centrifugal pumps, the EM and EW series CRBs are used on equipment such as displacement blowers and also on electric motors used to drive all types of prime movers. In displacement blowers the EM and EW series bearings carry radial loads, while the axial loads generated by synchronisation gears are carried either by the NSK double-row ball bearings or by pairs of tapered roller bearings.

As regards electric motors, the EW series bearings are especially suitable for high temperature conditions experienced in smaller sized electric motors, where conventional designs of CRB cannot meet the application needs. The EM series bearings are more suitable for medium and large motors where low running noise is required. They are also suitable for use in speed reducers and vibration equipment where harsh operating conditions are the norm.

SPACEA bearings

While comprehensive, the range of BMPC, EM, EW and angular contact bearings is not the total extent of NSK's offering to the chemical and petrochemical markets. Supporting the latter products is the SPACEA series, a range of bearings that provides high performance and reliability under all types of demanding operating conditions: super-clean, vacuum, non-magnetic, corrosive, high/low temperature and high speed.

SPACEA bearings meet the widest range of technical requirements with a programme of high-performance materials, surface finishes and specially developed lubricants, including solid types. Depending upon the application, SPACEA bearings can be manufactured from Martensitic and Austenitic stainless steels for corrosive environments, ceramics, or a combination of both. Hybrid SPACEA types can have any combination of ceramic inner/outer rings or balls; however, the range also includes all-ceramic bearings for use in highly corrosive and high-temperature environments.

For a free copy of the NSK petrochemical bearing publication, please contact the NSK marketing department on telephone number +44 (0)1636 605123.