Economic pressure is forcing power plant operators to increase their effectiveness by increasing temperature and steam pressure to provide energy at the lowest prices possible.
For current power stations, the characteristic steam temperature at the turbine intake is between 540°C – 565°C, although in the last few years, there has been an increase of the working medium to go above 565°C. In some cases, the water vapour is used with a temperature of up to 600°C. In the case of using the steam in the state of supercritical parameters (610°C/30MPa), compared to the current water vapour parameters (540°C/18MPa) it is possible to achieve an increase of effectiveness of energy devices by up to 8% at the current decrease of CO2 emissions by up to 20%.
Železiarne Podbrezová is adapting to the requirements of the segment. Today it is offering its customers seamless tubes destined for the critical parameters of above 600°C usage. This is provided by the steel grade P91 and T91 or X10CrMoVNb9-1 and corresponding equivalents.
P91 grade – key factors
P91 grade is ferrite-martensitic steel (9% chromium, 1% molybdenum) microalloyed with vanadium, niobium and with controlled content of nitrogen. Tubes made out of P91 grade are destined for boiler superheaters, power plant tube heaters, headers and duct pipes for high-temperature applications, and eventually for furnace ductwork in petrochemical assembly.
P91 grade – advantages
- Significantly improved strength and material creeping behaviour at higher temperatures
- Improved material corrosion resistance compared to other boiler type grades
- Decrease of tube weight and subsequently tube components and boilers alone
- Increased material resistance against thermal fatigue
- Good heat transfer and low expansion coefficient compared to austenitic steel grades
In 1983, the ASTM/ASME approved the T/P91 tubes and since then they have been approved by many national standards.
- A213/T91: seamless ferritic and austenitic alloy-steel boiler, superheater and heat exchanger tubes
- A335/P91: seamless ferritic alloy-steel pipe for high-temperature service
- A234/WP91: piping fitting of wrought carbon steel and alloy steel for moderate and high-temperature service
- A200/T91: seamless ferritic, alloyed tubes to be used in the refinery field
- NF A 49213/TUZ 10CDVNb 09-01: steel tubes; seamless unalloyed and Mo and Cr-Mo alloyed steel tubes for use at high temperatures
- DIN 17175/X10CrMoVNb9-1: seamless steel tubes for elevated temperatures
- BS 3604-2/P91: steel pipes and tubes for pressure purposes: ferritic alloy steel with specified elevated temperature properties
- BS 3059-2/P91: specification for carbon, alloy and austenitic steel tubes with specified elevated temperature properties
- EN 10216–2/X10CrMoVNb9-1: seamless steel tubes for pressure purposes. Part 2 – Non-alloy and alloy steel tubes with specified elevated temperature properties
Tubes for power suppliers from Železiarne Podbrezová
Železiarne Podbrezová is the leading manufacturer of seamless tubes and pipes to be used in boiler production, especially in Central Europe but also worldwide. Two production plants (in Slovakia and Spain) are served by the steel from its own production.
- OD (outside diameter) from 12.7mm to 139.7mm
- WT (wall thickness) from 0.89mm to 12.50mm
- Tubes made up to 21.3mm diameter are produced by the cold drawing process
Basic facts and numbers:
- Revenues: €216m
- Number of employees: 3,200
- Production capacity: 110,000 ton seamless steel tubes