flexible coupling misalignment limit - steam turbine

I can't help you. You are your own worst enemy:

"They were in a hurry and did not make the run out measurement "

"Our customer did not have such measurements, as well..."

"There was not enough time to correct it and we shipped rotor to power plant."

Good luck.

Remember, when there's never enough time to do it right the first time, you can always re-do it when it fails prematurely.

I dont have experience in power generation plants, but, WOW man! 0.045mm runout in a 46000 kg rotor? Sounds pretty fine!

I recall once being watched a presentation about the measurement of vibration at a large hydro-electric power plant. They had huge equipment like you mention. They measured vibration with micrometers... while the rotor was turning. The natural elastic movement of the rotor was much more than the values you are mentioning.

But... I agree with my colleague here. Didnt have time to do it right in the first time? Will need time to rebuild it later. Are you able to access it and make something about it in the installed equipment?

Or, even better, have you already contacted the original manufacturer of the flexible coupling at least to have the actual allowable misalignment and runout?

You should even contract a specialist because this information can cost you a lot of money, and, if I am not wrong, even the health and continuity of your business...

Squpek,

I certainly wouldn't want to be in your shoes. If the spec said .030mm runout but you provided the assembly with .045mm, you're going to get nailed with fault for anything that goes wrong with the unit, whether it's due to excessive misalignment or not.

Discuss it with the Plant Manager. If you're lucky, he'll tell you not to worry about it. If you're unlucky, you may have to pull the rotor and properly address this mess. It's better to do it now rather than later as the cause of a forced outage.

has the rotor been balanced ? (It is not on the same topic though, but is equally critical) at our place even smaller ones are vaccum balanced (obviously you can not let it run in air)

But 0.045mm R/O is a bit too high. I don't have any idea about the re-conditioned rotors, but the new ones have the limit set at 20 microns. But then, it all depends on the design of course.

RADIAL LIMIT=0.05 MM OR 0.10 MM TIR

ANGULAR MISALIGNMENT LIMIT=0.025MM

REGARDS

IRSHAD

Hi,

radial limit is offset or run out?

Thank you for you comments even if some of them are out of subject .

Let me give you more info. What we left is 0.045 mm of the offset - distance between LP rotor axis center and FXC axis center. The measured run out is 0.09 mm.

The another info which I did not write earlier is that this FXC coupling is equipped with bushes installed inside the coupling bores using hydraulic cylinder , then the coupling bolts are put and the right oil pressure is applied (using hydraulic cylinder) to get the bolt tighten with the right force and the nut is screwed by hand. I have not dealt with such coupling design, so far. However, I think that this design should make alignment easy and quick, as it is one of the main advantage of such solutions, only to pay attention to the bolts tight sequence (cross tightening, I mean). If nothing has been changed - the same buses, bolts, FXC, the right tightening sequence should fix the FXC in the same position like it was before. Yes, we do not know like it was before ... . Correct me if I am wrong.

The customer will be informed, it is obvious. If they decide to correct it, we are ready to do it. There is enough time to correct this alignment on site. They did not provided proper data but in this conditions, it will be necessary to know the acceptable limit

0.001 inch/inch of span between coupling hubs for a flexible coupling.

On a 225 MW turbine there should not be any flexible couplings. They are all flanged, so I am a bit confused by your referring to a flexible coupling on such a machine. This cannot be.

Ahhh, you're using Hydraulic Coupling Bolts.

Yes, the use of these bolts do help to quickly and easily re-establish coupling concentricity. They will not necessarily solve your present dilemma. Please read on:

Hydraulic Coupling Bolts are installed into the bores as clearance bolts but then, become fitted bolts.

Fully fitted bolts prevent coupling movement because they act as "drive pins". However, traditional "fitted" bolts are a misnomer: As soon as they are tightened, their diameter reduces. Thus, the coupling can conceivably shift under unexpected load such as may be encountered during a synchronisation error or a system fault. Hydraulic Coupling Bolts, on the other hand, are and will always be fully fitted.

For those who aren't familiar with them, they consist of two primary components:

• a bolt with a tapered shank
  
• a sleeve with a matching taper on its ID but with a parallel OD

To install , the sleeve is dropped over the bolt's shank. The assembly is then inserted into the bore where, by use of a setting bridge, the sleeve is expanded to fully fill the bore*. This step also sets the proper axial location of the assembly.

Next, the nuts are installed onto either end of the bolt. A hydraulic tensioning head is then attached via a puller to a tapered ID thread in the bolt. This is pressurized and, the nut is able to be hand-turned until it no longer moves. The pressure is then released and the bolt is not only fitted but, also fully tightened. Very simple, very fast and very effective.

However, in order to provide these benefits, proper initial preparations are absolutely critical. Central to this is close-toleranced line boring of the two havles of each coupling bolt hole. This had to have been done when the rotors were temporarily connected with properly alignment and concentricity. If the two haves were sized by honing, the hole will likely be mishappen ( a hone indeed opens up a hole but it cannot straighten a hole since it follows the axis of the non-concentric mating halves. When expanding a Hydraulic Coupling Bolt in such a hole, the sleeve will react on the 'high' and "low" areas of the bore. This will "crank" the holes and change the coupling's concentricy. In properly bored holes, the expansion is straight and no movement would take place. In fact, when properly installed using the proper steps (there are too many details learned through years of experience with these systems to include in this post), Hydraulic Coupling Bolts will always bring the coupling's orientation back to exactly where it was during the initial line boring exercise.

If the holes were honed, you may be chasing your tail during final runout checks. If there has been any movement at all of the coupling flanges relative to their initial position you'll be encountering major headaches

Good luck.

Thank you for such detailed info. As I wrote only disassembly and assembly operations took place. However it could be true that during some earlier overhauls the coupling holes were honed, we do not know it. It is clear that prior to FXC disassembly, its run out measurement is essential. The run out results would give us the info if something was done or was not

Squpek,

Please do not be offended; I am sure that you and your crew are very experienced in turbine overhauls. However, if you should encounter difficulties or require further details when installing the Hydraulic Coupling Bolts, please don't hesitate to contact me personally. Although we are often contracted to provide on-site TFA when such couplings are assembled or disassembled, I'd be happy to provide simple advice by phone and at no charge - if not abused