Steam Turbine Manufacturing

I have been wondering why steam turbine casings are always cast? Can anyone share experience on fabricated turbine casings and may be also welded rotors. With advancement in welding technology, I think one can fabricate turbine casings to the exact needs.

Reply to
turboteam123
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For the same reason engine blocks, metal working machines etc. are made of cast. This material provides vibration dampening and is the least expensive way to manufacture the shape required.

karl

Reply to
Karl Townsend

At work we have some rather large steam turbines coupled to turbine compressors, on the order of 40,000 hp for the biggest. While the compressor cases are cast, (there are three coupled end to end), the turbine case is a weldment. The compressors are one make, the steam turbine is made by somebody else. Both names escape me at this time.

Paul

Reply to
Paul

It won't be long before ceramic crystal turbines are GROWN as a single crystal.

Reply to
Tom Gardner

Thanks Paul. There I see a ray of hope. I am also told by a friend that Hydro Turbine casings are usually fabricated and not cast. I am very keen to get some inputs on this. I have my own idea / drawings / plans for a 2 and 3 MW Condensing Turbine. But, I cannot afford to get a pattern made for the casting to begin with. Instead I intend to explore fabrication which could involve may be pressing (cold forming) some shapes or may be forging and then welding together a complete casing.

Reply to
turboteam123

Reply to
Robert Swinney

==================== The "Fiddler on the Roof" song "Tradition!" may explain most of it.

When turbines were being developed [Charlie Parson - 1884] about the only way to manufacture the housing with its compound curves and internal passages was to cast them, and about the only suitable material was cast iron.

see

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for a whole bunch more google on for 127k hits

Unka' George [George McDuffee] ============ Merchants have no country. The mere spot they stand on does not constitute so strong an attachment as that from which they draw their gains.

Thomas Jefferson (1743-1826), U.S. president. Letter, 17 March 1814.

Reply to
F. George McDuffee

Thanx George. Of course I haven't read all of the excellent links you provided. But it would seem that casting is still the best way to make turbine housings.

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and for a whole bunch more

Reply to
Robert Swinney

In the case of engine blocks, not really. Large industrial (marine and locomotive) diesel engine blocks are usually weldments. A weldment doesn't need to be seasoned like a CI block does, so A) they can be built to order and B) the manufacturer doesn't have a huge amount of cash rusting away in the seasoning yard.

-Carl

Reply to
Carl Byrns

Carl, Are you sure about steam turbine casements specifically ? I think there might be tolerance problems where the case must be a very close fit over the blades. I can see whrere large engine blocks might be ok with weldments but steam turbines ?

Reply to
Robert Swinney

I'm certainly no expert on turbine construction, but I did quite a lot of tool design for GE's medium steam turbine division 15 or 20 years ago and got pretty familiar with specific components. My recollection is that the sealing surfaces for the rotors were on faces of the diaphragms - the stationary partitions between the rotor stages. The diaphragms are inserted into the case and are split along the same surface as the case. I think you can see the parting surface of the diaphragm between the first two stages in this photo.

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Here's a pic of a diaphragm...
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The diaphragms I worked on were incredibly complex and accurate weldments. I had very little exposure to the cases, but I believe those I saw were hybrid weldments/castings, as the one in that photo appears to be. The machines I worked on were about the size of the turbine in the first photo.

Ned Simmons

Reply to
Ned Simmons

I apologize for any confusion- I was refering to cast-vs- weldment of piston engine blocks only.

-Carl

Reply to
Carl Byrns

Thanx, Ned ! Who'd a thought there would be replaceable stators, esp. in weldment-based cases ? And check out the size and spacing of those studs. It seems turbine design has come a long ways since they were housed in cast iron cases. Thanks again.

Bob Swinney

Reply to
Robert Swinney

HP and IP turbine cylinders are normally cast and LP cylinders have been fabrications since the mid seventies.

In an HP cylinder you are dealing with inlet conditions of about 2300psia and

1100F. The cylinders are cast from heat resisting chrome iron rather than graphite containing cast iron. In an LP cylinder, you are only dealing with saturated steam at about 60psia.

Generally there will be an inner cylinder that holds the diaphragms and takes the torque loading and an outer cylinder that carries the load from the pressure. This allows the inner cylinder to be of a much lighter construction (1" thicknesses rather than 5" thicknesses). This means that distortion during startup is more easily manageable.

As stated by Ned, the diaphragms will often (can't vouch for other manufacturers) have the machined blades placed into the rough machined inner and outer rings of the diaphragm with disposable moulds to define the inside and outside edges of the steam passages. Then the blades will be welded in to the rings using submerged arc wire welding until the inner and outer rings are, effectively, solid metal of the same alloy as the blades. After that, the rings are split and a final light cut is taken on a boring mill to size the rings and remove distortion.

Mark Rand RTFM

Reply to
Mark Rand

On Wed, 16 May 2007 08:36:06 -0500, with neither quill nor qualm, "Robert Swinney" quickly quoth:

I'm sure that Mr. Chaos likes the nice eddies built up by any welds and non-curved sections in the housing interior, too.

-------------------------------------------------------- Murphy was an Optimist ----------------------------

Reply to
Larry Jaques

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Reply to
eryvan

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