Paper 9: The Removal of Water from Low-Pressure Steam Turbine Blades by Trailing-Edge Suction Slots

This paper reports an experimental research undertaken to explore the performance of a suction slot located in the trailing edge of a representative low-pressure steam turbine fixed blade. Tests have been made on a 1-in wide section of a full-size hollow blade mounted in a single-blade test section. Typical turbine pressures were reproduced down to 3 inHg (abs.), and blade exit Mach numbers varied in the range 0·57–1·10. With round entry lips, the slot operated satisfactorily in any blade orientation, as it completely removed quantities of water that were in excess of the amount expected under operating conditions. Square entry lips gave somewhat poorer performance.

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Advanced Water Droplet Erosion Protection for Modern Low Pressure Steam Turbine Steel Blades

Volume 8: Microturbines, Turbochargers and Small Turbomachines; Steam Turbines ◽

10.1115/gt2015-43140 ◽

2015 ◽

Cited By ~ 1

Author(s):

Joerg Schuerhoff ◽

Andrei Ghicov ◽

Karsten Sattler

Keyword(s):

Steam Turbine ◽

Water Droplet ◽

Precipitation Hardening ◽

Turbine Blades ◽

Low Pressure ◽

Steam Turbines ◽

Treatment Facility ◽

Material Loss ◽

Pressure Steam ◽

Steam Turbine Blades

Blades for low pressure steam turbines operate in flows of saturated steam containing water droplets. The water droplets can impact rotating last stage blades mainly on the leading edge suction sides with relative velocities up to several hundred meters per second. Especially on large blades the high impact energy of the droplets can lead to a material loss particularly at the inlet edges close to the blade tips. This effect is well known as “water droplet erosion”. The steam turbine manufacturer use several techniques, like welding or brazing of inlays made of erosion resistant materials to reduce the material loss. Selective, local hardening of the blade leading edges is the preferred solution for new apparatus Siemens steam turbines. A high protection effect combined with high process stability can be ensured with this Siemens hardening technique. Furthermore the heat input and therewith the geometrical change potential is relatively low. The process is flexible and can be adapted to different blade sizes and the required size of the hardened zones. Siemens collected many years of positive operational experience with this protection measure. State of the art turbine blades often have to be developed with precipitation hardening steels and/or a shroud design to fulfill the high operational requirements. A controlled hardening of the inlet edges of such steam turbine blades is difficult if not impossible with conventional methods like flame hardening. The Siemens steam turbine factory in Muelheim, Germany installed a fully automated laser treatment facility equipped with two co-operating robots and two 6 kW high power diode laser to enable the in-house hardening of such blades. Several blade designs from power generation and industrial turbines were successfully laser treated within the first year in operation. This paper describes generally the setup of the laser treatment facility and the application for low pressure steam turbine blades made of precipitation hardening steels and blades with shroud design, including the post laser heat treatments.

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