Turbine material details

 

The Turbine is operated in hi temperature, pressure ,speed and erosion environment. So materials need are for Cr, Ni and Mo, V-based alloys for operation at 537 to 600°C with (i) adequate creep rupture strength; (ii) ability to cast them into the required size and shape, and to inspect for defects; and (iii) ability to perform initial fabrication welding (on cast or wrought forms, including dissimilar metal welds), and to make repair welds on aged material. It is observed that percentage of Cr and Ni are increased to improve the quality of steel for the different parts of the turbine.

 

Component	566°C	620°C	700°C	760°C
Casings/Shells	CrMoV (cast)	9-10%Cr(W)	CF8C-Plus	CCA617
(valves; steam	10CrMoVNb	12CrW(Co)	CCA617	Inconel 740
chests; nozzle box;		CrMoWVNbN	Inconel 625	CF8C-Plus (?)
cylinders)			IN 718 Nimonic 263
Bolting	422	9-12%CrMoV	Nimonic 105	U700
	9-12%CrMoV	A286	Nimonic 115	U710
	Nimonic 80A	IN718	Waspaloy	U720
	IN718		IN718 Allvac718Plus	Nimonic 105 Nimonic 115
Rotors/Discs	1CrMoV	9-12%CrWCo	CCA617	CCA617
	12CrMoVNbN	12CrMoWVNbN	Inconel 625	Inconel 740
	26NiCrMoV115		Haynes 230 Inconel 740
Vanes/Blades	422	9-12%CrWCo	Wrought Ni-	Wrought Ni-
	10CrMoVNbN		base	base
Piping	P22	P92	CCA617	Inconel 740

 

Material for casing has complex structure , It should have been hi steam oxidation resistance, castability or forged still be heat-treated and tempered to produce the best combination of high temperature strength and ductile-to-brittle transition temperature (DBTT) behaviour at low temperature.

The choice of blading material will depend on (i) the-temperature-of-the rotor, hence on the thermal expansion characteristics of the component material, and (ii) the size and shape of the blade, which will be designed using computational fluid dynamics modeling.

The main issues for rotors/discs concern manufacturing, especially the capability to produce large castings and forgings. With modern secondary steel making practices, such as ladle furnaces, electroslag remelting to control freezing segregation, and control of the sulfur and phosphorus levels in the alloy, very large rotors now can be produced, but experience is related mostly to Cr-Mo-V alloys (used in current 541-566°C plants), and for 12 Cr alloys (needed for advanced steam cycles to 620°C).

 

 

This is the material plan for different parts of the turbine for super critical steam turbine HP and IP section.

 

Usage of higher grade of steel for 700-760degC and design data points are not available. Major issues are forging and casting procedure, weldability and costing of the materials and manufacturing.