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Passive heating of nickel casings using thermal barrier coatings to improve lifetime

IP.com Disclosure Number: IPCOM000198686D
Publication Date: 2010-Aug-12
Document File: 5 page(s) / 111K

Publishing Venue

The IP.com Prior Art Database

Abstract

As a result of environmental concerns, steam turbines with higher and higher steam inlet temperatures have been developed to increase the turbine efficiency. Although steel materials have been the standard materials choice, recent development in the field of ultra super critical turbines have brought the steam inlet temperatures to the physical limits of steel materials, this temperature is approximately 620C. To achieve higher temperatures, it is necessary to select a different class of materials, and to this end Nickels alloys have been investigated extensively.

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Passive heating of nickel casings using thermal barrier coatings to improve lifetime

Abstract

As a result of environmental concerns, steam turbines with higher and higher steam inlet temperatures have been developed to increase the turbine efficiency. Although steel materials have been the standard materials choice, recent development in the field of ultra super critical turbines have brought the steam inlet temperatures to the physical limits of steel materials, this temperature is approximately 620C. To achieve higher temperatures, it is necessary to select a different class of materials, and to this end Nickels alloys have been investigated extensively.

Although Nickel alloys perform better then steels at 700C conditions, they posses two characteristics that present problems for the design engineer. Firstly they posses relative low yield strengths, and secondly they posses poor thermal conductivity.

The combination of low yield strength characteristics and low thermal conductivity means that Nickel alloys experience plastic strains at low levels of stresses when exposed to large thermal gradients. This can occurs during steady state and transient operation.

Where Nickel alloys are used for inner casing materials, large thermal gradient across the wall section, may lead high levels of plastic strain of the material and significantly reduce component life. This may become extreme in the area of the turbine inlet spiral, where the greatest temperature gradients are seen. In this scenario, the problem may be considered to be the strong cooling effects of the steam flow around the outside of the casing, rather then the high temperatures in the inlet spiral. Therefore an approach to avoid high thermal gradients would be to avoid the cooling effects of any cooler steam flow on the outside of the casing.

The basis of the concept described in this document is that thermal barrier coatings are used to prevent cooling of the outer surface of the component. Thereby avoiding the large thermal gradients that lead to plastic strain. Due to the fact that Nickel alloys have only recently been considered for use in Steam Turbines, the technology development to address the issue of life limiting material plastic strain has not been significantly addressed.

Although this concept has been developed specifically for 700C temperature turbine applications with nickel casings that suffer from high plastic strain issues, it is not limited to that application. And indeed steel turbines suffering from low lifetimes resulting from high thermal gradients could also incorporate a similar solution.

Description of the invention

A typical steam turbine consists of an inner and outer casing. High temperature steam enters via an inlet spiral, then passes through the bladed area, and then exhausts to the cavity between the inner and outer casing. The steam finally exhausts from the module through the exhaust pipe attached to the outer casing. Having passed through the turbine...