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Reprofiling of a Governor Valve Seat | Steam Turbine

15 Lug 2020 - Lavorazioni meccaniche

Reprofiling of a Governor Valve Seat by means of a last-gen NC lathe.

 

A Valve Seat has been perfectly restored

 

Abstract.

We have completed a complex site machining work, related to the re-profiling of a Governor Valve Seat of a 660MW conventional steam turbine.

This is located into a Power Plant owned by the most important Italian Energy Facility and the service machining work was carried out for one of the most important World Service Provider for Power Equipment. The machining operation was carried out with a numerical control portable lathe machine, equipped with a special valve kit for in-depth machining, obtaining surface finishing near to grinding. In addition, thanks to both the ergonomics of the machine and the ease of positioning and centering, the activity was completed in just 2 working shifts.

 

Challenge to be faced.

The above-mentioned Governor Valve was found in bad conditions at disassembly, as localized erosion on the seal seat was detected, cause of potential steam leaks during turbine operation.
Since the seat is overlayed into the pipe and not removable, the machining of the seat area should have been done with a special machine, in order to avoid cut and substitution of the whole piping (a very expensive and time-consuming activity).

In addition, the surface to be machined shown a double complexity: seat geometry and overlayed material hardness.
On the one hand, the geometry of the Valve seat is toroidal (curved generating line), requiring the use of a numerical control lathe machine, the only able to interpolate the profile data (coordinates) on 2 axes at the same time.
On the other hand, the seat overlayed welding material was very hard to machine (INCONEL).

Conical Valve seat is being restored

Equipment.

TD NC 2.02

A last-generation numerical control portable lathe machine was necessary to accomplish this on-site machining work. In addition, this machine is equipped with a special Valve Kit, to operate in depth, as shown in the figure.

Endoscope

Since we were dealing with an in-depth machining, we used an endoscope, in order to be able to carry out real-time checks on the progress of the machining, even during machine operation.

Scheme of Lathe Machine operating in Depth

Operation and Results.

As requested by the customer, the GV Seat reprofiling was carried out by machining almost 2 mm in depth, aiming at obtaining a spotless surface. The following contact check confirmed the extreme precision of machining work.
Further, the surface showed a good roughness, enough to avoid final lapping, resulting in additional time saving.

As previously said, the complete scope was completed in 2 work shifts.


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