What is the material for Turbine coupling bolts?

[Ayden]

Last December our Refinery had a major failure on one of our turbine-generators. We want to make new coupling bolts and would like to know what material is best to use for coupling bolts. (material chemical composition)
Turbine and generator are solid coupled.
Can any one assist me on this?

Thanks in advance.

 

[byrdj]

I would recomend you looked for the studs availabilty from a non OEM supplied?

 

[unclesyd]

More information please.

What failed?
What was the mode of failure?
What is the power of the turbine?
What is the type and size of the coupling?

This and any other information you have will help you get sound advice and hopefully the proper direction.

 

[diamondjim]

What were the tightening specs for the
bolts supplied. It may indicate the
strength of fastener needed.

 

[Ayden]

The turbine rotor broke just under the thrust collar and travelled towards the generator. The turbine is a 11 MW machine.
It is also a Solid coupled arrangement meaning no coupling between "hubs".
The vibration levels on the BN panel were jumping out of proportion before tripping the machine.
Because of this extensive failure we don't want to use the same bolts.

Thanks,

Jp

 

[metengr]

Agree totally with unclesyd's request for information. If the failure of the T/G was unrelated to the coupling bolts, obtain several of the coupling bolts from the failed machine, and have a reputable machine shop reverse engineer them. I would send two of the coupling bolts to a metallurgical lab to type the material. Main items to consider;

- material chemical composition
- macro hardness to establish approximate strength level
- microstructure evaluation to establish heat treatment of the coupling bolts


Make sure that you receive all material test reports and nondestructive testing reports for the reverse engineered coupling bolts.

If the coupling bolts cased the failure, you need to investigate the root cause.

 

[unclesyd]

I agree that the coupling bolts should be changed out (best) following the above recommendations or a thorough gaging performed along with a competent NDT evaluation made if necessary to reuse.

Being a solid coupling were the bolts fitted or have an interference fit?
If either of the above make sure you check the coupling bolt holes.

Have the coupling bolts ever been changed out?

What axis/direction was your first indication of high vibrations?

Expedite the metallurgical evaluation of the shaft fracture.

 

[Ayden]

Unclsyd would you know what the clearances should be on a solid coupling? How many thousands?

We made every provision with broken shaft (sent to metallurgical lab)

 

[unclesyd]

I assume you are asking about the bolt hole clearance?

Without a lot more information it would be impossible to give any specific information.

The information should be in the operating manual or you should be able to contact the manufacturer or his represenetive. The name of the manufacturer should be on the coupling or in the operating literature.

Come back with the specific clearances you are concerned with.

 

[rorschach]

Is this a steam turbine or a gas turbine? I'd be willing to bet that the bolts were an exotic like TiAl4V or a nickel based alloy like 718, but they could be more mundane like 17-4 or A286 too. there is a lot more to bolt failure than material. intallation technique has a huge effect on the longevity.

I think the best advice you've recieved so far is to ask the manufacturer and use what he supplies. anything else and you'll regret it proabably.

 

[Romefu12]

Ayden
I agree with many of these posts however you should approach this event as carefully and as scientifically as possible to find the correct "Root Cause" of this costly failure in order not to "reverse engineer" the same event at a future date. Coupling bolt design is based on many factors including type of coupling, fit tolerances, alignment toleances, fastener style, (taper sleeve, hammer tight, etc) bolting material characteristics, applied torque, inertia, thread type, operating enviroment etc.

Before attempting to have a third party "reverse engineer" anything I would gather as much information as possible and find the failure mode and root cause of the failure before moving forward.

Regards
Romefu12