Boilers are often classified based on the maximum operating temperature and pressure for which they are designed. Classifications, in ascending order, are subcritical, supercritical, ultra-supercritical, and to advanced ultra-supercritical. At each higher operating point comes greater efficiency, as well as greater demand on construction materials. This chapter discusses the primary requirements for boiler tube materials, including oxidation and corrosion resistance, fatigue strength, thermal conductivity, and the ability to resist creep and rupture. It also provides information on various steels and alloys, covering cost, engineering specifications, and ease of use.

Black liquor recovery boilers are an integral part of the kraft pulping process used in paper mills. Besides recovering chemicals for reuse, they also produce process steam. High operating temperatures and exposure to process chemicals and combustion byproducts make recovery boilers susceptible to corrosion. This chapter describes some of the problems that the pulp and paper industry has solved as well as ongoing issues and concerns. It includes an in-depth review of 304L cladding failures involving coextruded composite tubes used as floor tunes in the lower furnace, as superheater tubes, and for other purposes such as smelt openings. It provides detailed images showing cracks on the outer surfaces of the tubes and explains where the tubes were used and how they were operated.

A turbine blade in an aircraft engine failed, fracturing at the root above the fir tree region. Fractography indicated that a fatigue crack initiated at the trailing edge of the blade and the final fracture occurred when the crack reached critical length. Although the exact cause of crack initiation could not be established, material defects, improper root loading, and high operating temperatures were ruled out. This chapter describes how investigators came to their conclusions and what they learned through visual and SEM examination and qualitative elemental analysis. It includes images of the microstructure and fracture surfaces and explains what some of the details reveal about the failure.

This chapter discusses the progress that has been made in the development of superalloy operating temperatures, properties, and performance. It also provides forward-looking projections based on advances in process modeling, alloying, and production techniques.

Superalloys, although not strictly defined, are generally regarded as high-performance alloys based on group VIII elements (nickel, cobalt, or iron, with a high percentage of nickel) to which a multiplicity of alloying elements have been added. The defining feature of a superalloy is its combination of relatively high mechanical strength and surface stability at high operating temperatures. This chapter provides a brief history of the development of superalloys and discusses their use in the gas turbine engines.

High-pressure cold spray repair process has been used on a number of different applications in the defense industry. This chapter describes various applications for cold spray systems that have operating pressures greater than 2.4 MPa (350 psi) and operating temperatures greater than 500 deg C (930 deg F).

This chapter describes the molecular structures and chemical reactions associated with the production of thermoset and thermoplastic components. It compares and contrasts the mechanical properties of engineering plastics with those of metals, and explains how fillers and reinforcements affect impact and tensile strength, shrinkage, thermal expansion, and thermal conductivity. It examines the relationship between tensile modulus and temperature, provides thermal property data for selected plastics, and discusses the effect of chemical exposure, operating temperature, and residual stress. The chapter also includes a section on the uses of thermoplastic and thermosetting resins and provides information on fabrication processes and fastening and joining methods.