High Temperature Brush Seal Development

Abstract

The industry bristle material of choice for brush seals has been the cobalt-based alloy Haynes®25 (also known as L605) for over 30 years. Haynes®25 has excellent oxidation resistance and wear properties in brush seal applications up to temperature of 620°C [1148°F]. Above this temperature creep resistance becomes undesirable for brush seal bristles and has lead to alternative sealing solutions to be implemented in these turbine locations. Nickel-based alloys have been explored as an alternative for Haynes®25 but have been shown to gall badly and wear quickly in comparison. As increases in turbine performance have resulted in an increase in operating temperatures, it has lead to a need to find a bristle material that performs at temperatures above the limitation of Haynes®25. Initial experimental data has been obtained for a new cobalt-based alloy that shows potential for use as a bristle material at temperatures above 620°C [1148°F]. Further experimental results also indicate that the material appears to have better wear characteristics than Haynes®25 and may prove to be a feasible alternative in some cases. This paper outlines a material selection process for brush seals, along with development of the alloy for use within brush seals and details of the comparative testing carried out at Cross Manufacturing Company.

Estimation of the rotordynamic characteristics of a single brush seal using least-squares and instrumental variable methods under super-heated steam environment

“…Surface friction heating due to the bristle interface was negligible (49.2°C), considering the relatively high sliding speed (265.5 m/s) and temperature of the steam (250°C). The steady-state temperature was much less than the value in the work by Kirk et al 14…”

“…Surface friction heating due to the bristle interface was negligible (49.2°C), considering the relatively high sliding speed (265.5 m/s) and temperature of the steam (250°C). The steadystate temperature was much less than the value in the work by Kirk et al 14 2. Compared to the static condition, rotation reduces the damping effect mainly because of static friction from multiple sources: bristlebristle, bristle-disk surface, and bristle-back plate.…”

“…Due to the existence of an interface between the existence of bristles and the rotor surface, heat may be generated owing to friction. 14 Considering the friction, rotation experiment with 16,900 r/min without working fluid was conducted. The operation was continued until the steady state was obtained.…”

“…12,13 However, Haynes 25 is still preferred for steam turbine brush seals where high temperature tolerance and resilient bristles are needed. 14 Heat generation effects arising from friction were investigated numerically 15 and experimentally, suggesting a theoretical heat generation model. 16 To unveil the unknown dynamic characteristics of brush seals, numerous studies on various aspects of brush seals have been conducted.…”

Study of Heat Transfer and Leakage Characteristics of Brush Seals Based on Local Temperature Non-Equilibrium Model

“…Compared to labyrinth seals, brush seals are lighter in mass and less abrasive, with a leakage rate of only 1/5th to 1/10th that of labyrinth seals [4][5][6]. In brush seals, the brush filaments are subject to thermal deformation caused by frictional heat, which in turn has a serious impact on sealing performance [7].…”