Laser Precision vs. Tradition: How CENTRALIGN® Transformed a 550 MW Steam Turbine Overhaul 

Summary

A leading turbine manufacturer’s service team and Pruftechnik specialists used CENTRALIGN® to align a 550 MW steam turbine, cutting assembly time in half while achieving precision within ±0.03 mm.

• The project was completed in just 10 days instead of the usual 20.
• Eliminating the need for dummy shafts allowed real-time adjustments during alignment.
• Accuracy reached ±0.03 mm, meeting the manufacturer’s strict standards.

What would happen if a service team from one of the world’s leading manufacturers of turbines confronted turbine specialists from Pruftechnik? What with “dummy shaft or piano string technology” or “laser beam technology”, the competition would be bound to be intense. 

Exactly the opposite proved to be the case when the two teams met in Andalusia. The working relationship between them as they spent a fortnight together in Carnoberas near Almeria, where a 550 MW steam turbine, the property of ENDESA power station, had to be completely overhauled, could only be described as most friendly and congenial. 

The overhaul work included the alignment of internal fittings of a high and medium pressure stage and two low pressure stages. The stages were enclosed in a 30 m long housing. 

Alignment was carried out using CENTRALIGN®. This optical laser alignment system uses a laser beam and its inherent high precision as its reference as opposed to the often employed conventional method that utilizes a dummy shaft or piano strings. 

CENTRALIGN® can measure diaphragms, bearings, bearing seals, deflectors, oil guards, circular housings and packings with diameters ranging from 150 mm to 6000 mm with a resolution of 0.01 mm. 

Before measurement began, the actual position of all the fittings, i.e. bearing bores, stuffing boxes, seals, packing and housing bores, with the top half removed (TopsOff), was established. The process was repeated with the top half in place (TopsOn). 

As would naturally be expected, the two positions were not identical. Due to the massive weight of the top diaphragms and the top half, the turbine centre line changed. Using the two observed positions, the CENTRALIGN® program was employed to calculate a static alignment configuration for the entire turbine which was then used to carry out the actual alignment. 

The results of the measurements taken and the required corrections were discussed and agreed upon by both teams of experts.

A major advantage in using CENTRALIGN® became evident during the alignment process. Using the conventional method, the dummy shaft must be lifted from the turbine before a fitting that requires alignment is removed. Using CENTRALIGN®, the fitting can be measured and moved simultaneously. The Move function shows the actual position of the fitting within the turbine. These characteristics and the capabilities available in CENTRALIGN® enable a drastic reduction in assembly time. 

Although already familiar with CENTRALIGN®, the turbine manufacturer engineers found the sensor holder, also referred to as a large bore bracket, awesome. They were fascinated with the holding device and its ability to be applied comfortably on the 3 m bores in the low pressure housing. Its flexibility was impressive.

The entire work, which included three TopsOff and three TopsOn measurements and the alignment of 42 diaphragms and nine stuffing boxes, was completed within ten days – use of the conventional method would have required twice as much time. And the alignment was to within the turbine manufacturer’s standards. In this particular instance, an accuracy of ±0.03 mm of the reference line was attained.

To the joy of both teams of experts, the alignment parameters at recommissioning were exactly the same as those determined by the CENTRALIGN® alignment system. This gratifying situation speaks volumes for the working together of the two teams in future turbine overhauls.