New HP-/IP-Blades With Protective Coating for High Temperature Steam Application

Abstract

Today’s challenging requirements on thermal power plant cycle efficiency favor plants with steam temperatures up to 630°C. Cost competition, however, confines the application of particularly cost-intensive materials causing high manufacturing effort such as Ni-based alloys. Alternatives are martensitic steels containing less than 10% Cr. Due to the low Chromium content, these materials are less oxidation-resistant compared to 12% Cr-steels. Increased load-cycling requirements resulting from varying renewable energy production may result in decreased plant efficiency due to increased scaling and spallation of oxide layers during thermal transients. Hence, it is beneficial to protect such components against oxidation using coatings. Investigations on various coating systems for their potential to serve as oxidation protection are described in this paper. These investigations consisted of a short-term screening program to identify the most promising coatings followed by an extensive test program including long-term steam exposure at high temperatures, thermal cycling, solid particle erosion tests as well as tests under operating conditions on samples and blades. The test program revealed which coatings appeared to be the most promising solution for power plant applications, showing excellent oxidation protection capability of the base material in steam at high temperatures, structural stability upon thermal cycling and good solid-particle erosion protection. Tests under operational conditions have proven the functionality and stability of the coatings.