Tata Steel fast-tracks bearings replacement project

Port Talbot, UK - Tata Steel engineers saved several days of costly downtime and dissasembly work as they replaced the main trunnion bearings on a BOS (basic oxygen steelmaking) plant at their Port Talbot site.

The project involved replacing the drive-side trunnion bearings with split-rolling bearings. This option saved five days of work that would have been needed to disassemble the main drive unit for the BOS plant vessel if solid bearings had been used.

The Port Talbot plant operates two BOS steel-making vessels (V1 and V2). The original vessel was installed in the late 1960s by Ashmore, Benson, Pease & Co. and subsequently upgraded in 1991/1992 by Mannesmann Demag, including a replacement of the trunnion bearings.

In July 2011, engineers at the BOS Plant reported a sudden bearing failure on the non-drive side (NDS) of the V2 BOS plant vessel. Each vessel has a steel-making capacity of 330 tonnes, so loss of operation of a BOS vessel would result in significant lost revenue for Tata Steel.

In response, the company engaged engineers from Schaeffler Germany to visit the Port Talbot site and help draw up an action plan to replace the trunnion bearings. A method statement document was drawn up by Schaeffler UK, which specified the sequence and method to replace the bearings.

The document included a detailed tooling list and a step-by-step procedure for the dismounting and mounting of the drive-side (DS) & non drive-side (NDS) bearings, according to Dave Wall, senior applications engineer at Schaeffler UK.

According to the engineer, the standard ‘solid’ bearing on the DS was replaced by a special FAG split spherical roller bearing [SSRB]. This is the recommended replacement spare, as this reduces the amount of downtime when installing the replacement bearing.

“The NDS bearing was to be replaced with a similar solid bearing. In addition, various surrounding components also required replacing, once the secondary damage caused by the bearing failure had been identified,” Wall added.

The cutting away of the existing bearing took a total of 36 hours. The distance between the trunnion spacers was measured in order to determine the thickness required for two special, TATA designed, split ‘dovetail’ spacers. These were required to ensure that the new split bearing would be correctly secured in place.

The split SRB inner ring halves with clamping rings, outer ring half and bottom roller cage halves, were fitted without any problems.

The original bearing on the NDS had failed during operation, which had caused the BOS converter to drop down. It was now resting on the bearing housing and the housing covers.

After lifting, parts of the damaged bearings were removed, including cage pieces; outer and inner ring fragments and rolling elements. All the components were sent for forensic examination to Tata Steel’s central engineering metallurgy & inspection department.

The housing back cover, bearing pressure plate and sleeve spacer were found to be seriously damaged. New replacements had to be urgently manufactured by Tata Steel’s central engineering shops (CES).

The bearing inner ring had disintegrated and the sleeve had to be cut off due to its deformed shape.

After removing the damaged bearing, it was also discovered that the trunnion back spacer was in need of repair. Again, machining work was urgently carried out by CES.

Due to the subsequent damage to the bearing housing, Schaeffler was required to manually repair this surface to restore it back to an acceptable condition.

During the dismounting process the NDS ladder expansion bearing rollers had to be replaced. To facilitate the replacement and installation of a Tata-manufactured solid inner bearing housing cover, the bottom half of the housing had to be moved away from the journal using specially manufactured crossbeams.

The new bearing was first pre-mounted to determine the correct sleeve spacer width. The bottom half of the housing was then moved back into position and the crossbeam construction removed.

Mounting of the new bearing was challenging, as the collapse of the original bearing had caused the vessel to move out of alignment.

The lowering of the converter was also a challenge as the vessel had to be moved sideways by 40mm to achieve the correct installation position. Side shifting was initially a problem for the vessel lifting contractor but the problem was overcome.

For the DS bearing, the remaining roller cage and outer ring halves were installed. For both bearings, the housing caps were fitted and each bearing was 100% filled with grease, including the surrounding free space.

The housing covers were bolted in position and new seals, with their tensioning devices, were fitted - so that the work was completed in under two weeks.

After the bearings were installed, Schaeffler UK prepared a recommended practical maintenance schedule list and forwarded this to the BOS engineers. In addition, customer “as built” cross-sectional drawings were updated to show the actual parts now in place at V2.