Material Selection & Process Selection for Rotor Steam Turbine

[Kryptex]

Hi

I need to perform a material selection case on the rotor of a steam turbine. Both material selection as process selection have to be made.
Since my background is rather chemical than mechanical or material engineering I've encountered some difficulties. I hope you can help me with them.

For the material selection part I considered the yield strength, fracture toughness and maximal service temperature as most important properties to maximize the output per unit mass. By using CES EduPack I became a selection of 5 materials, including low alloy steels, which seem to me as most plausible. Any comments on that?

Further on, for the process selection part, I'm somewhat troubled. I miss some specifications.
First of all: is a rotor usually solid or hollow? Cause I found some contradicting answers to that question. And can its section be considered circular or should I include something to anchor the blades?
Next I assumed following dimensions for a 250MW turbine: 5m length, section radius of about 0.2 m. Is that acceptable?
And to conclude: which processes are common to produce rotors? Forging? Sand casting?

I thank you! It would be a great help!

(to moderators: I posted this in Materials section because of the material selection part, but if you think it should be in a mechanical section because of the subject of study, that's fine.)

 

[Astronuc]

These might be of interest:

http://www.energy.siemens.com/us/po...bines-power-plants/3_Design_and_Materials.pdf

http://www.siemens.com/innovation/en/publikationen/publications_pof/pof_spring_2008/energy/effiziente_kraftwerke.htm

http://www.fujielectric.com/company/tech/pdf/r51-3/05.pdf

 

[Kryptex]

Hi

The design and materials link I've already got in my references :).
The other two are also nice reference materials, thank you for that. Especially the one from fujielectric. Still a quick diagonal reading doesn't get met precise numbers on the rotor. But maybe I can deduce them from the length of the blades and the technical drawings. I'll have to look upon that later this evening after study.

I also mailed Alstom and Siemens, hopefully they're able and willing to help me with my issues. I don't know whether they answer such questions.

Anyway thanks for your response.

 

[Astronuc]

The key details of turbine design are generally proprietary. I was focussing more on the materials, the composition of which the citations indicate depend on temperature (and amount of superheat or dampness) and fluid (steam) chemistry.

There are also high pressure and low pressure turbines. In between, there is a moisture separator, if the exit of the HP stage has a quality less than unity, i.e., there is no superheat.

Both HP and LP turbines are designed to optimize the number of stages, and the stages are optimized on change in fluid kinetic energy, which is determined by blade geometry (height, width or chord length, curavture, . . . ) and root diameter. The root and hub diameter influence the rotor diameter, and they are balanced with the thermomechanical constraints, i.e., stresses, strains and fatigue/IGSCC resistance, . . . .

Turbine design is an art based upon experience. It demands good knowledge of mechanical design as well as materials science.

 

[AlephZero]

And can its section be considered circular or should I include something to anchor the blades?

I wouldn't worry too much about how the blades are fixed to the rotor, but if you are selecting materials based on stress criteria you need to take account of the radial loads (mr\omega^2) that the blades apply to the rotor. The radial acceleration on the blades will be of the order of thousands of g so a blade with a mass of 1kg will exert a force of a few tonnes on the rotor.

 

[Kryptex]

Turbine design is an art based upon experience. It demands good knowledge of mechanical design as well as materials science.

And accidentally I've got to figure it all out in one week, cause of the exams that are coming up. If they could've only given us the assignment a little earlier...

you need to take account of the radial loads (mr\omega^2) that the blades apply to the rotor

Thanks for that, I don't know why I didn't account for that earlier. Just forgot it, I suppose. Shame on me...

Thanks again for the answers AlephZero and Astronuc, I'll be examining them further tomorrow. Cause there's too much Christmas eve 'OH-spirit' in my vains at the moment. ;)

Best wishes to both of you!

 

[Kryptex]

Hi, I like to get back to this, cause I'm still struggling with the assignement.

Does any of you know which production process is commonly used for rotors of steam turbines?
Cause with the software I use, I find out it should be sand casting. But I'm not convinced by that. Especially for larger masses even sand casting isn't an option. So I thought that maybe welding smaller parts together is an option. The parts could then be produced by forging or sand casting I suppose.

Can anyone help me on that matter?
Much obliged!