This chapter provides a detailed overview of the creep behavior of metals and how to account for it when determining the remaining service life of components. It begins with a review of creep curves, explaining how they are plotted and what they reveal about the operating history, damage mechanisms, and structural integrity of the test sample. In the sections that follow, it discusses the effects of stress and temperature on creep rate, the difference between diffusional and dislocation creep, and the use of time-temperature-stress parameters for data extrapolation. It explains how to deal with time dependent deformation in design, how to estimate cumulative damage under changing conditions, and how to assess the effect of multiaxial stress based on uniaxial test data. It also includes information on rupture ductility, creep fracture, and creep-crack growth and their effect on component life and performance.

Elevated-temperature failures are the most complex type of failure because all of the modes of failures can occur at elevated temperatures (with the obvious exception of low-temperature brittle fracture). Elevated-temperature problems are real concerns in industrial applications. The principal types of elevated-temperature failure mechanisms discussed in this chapter are creep, stress rupture, overheating failure, elevated-temperature fatigue, thermal fatigue, metallurgical instabilities, and environmentally induced failure. The causes, features, and effects of these failures are discussed. The cooling techniques for preventing elevated-temperature failures are also covered.

Creep occurs in any metal or alloy at a temperature where atoms become sufficiently mobile to allow the time-dependent rearrangement of structure. This chapter begins with a section on creep curves, covering the three distinct stages: primary, secondary, and tertiary. It then provides information on the stress-rupture test used to measure the time it takes for a metal to fail at a given stress at elevated temperature. The major classes of creep mechanism, namely Nabarro-Herring creep and Coble creep, are then covered. The chapter also provides information on three primary modes of elevated fracture, namely, rupture, transgranular fracture, and intergranular fracture. The next section focuses on some of the metallurgical instabilities caused by overaging, intermetallic phase precipitation, and carbide reactions. Subsequent sections address creep life prediction and creep-fatigue interaction and the approaches to design against creep.

This chapter compares and contrasts the high-temperature behaviors of metals and composites. It describes the use of creep curves and stress-rupture testing along with the underlying mechanisms in creep deformation and elevated-temperature fracture. It also discusses creep-life prediction and related design methods and some of the factors involved in high-temperature fatigue, including creep-fatigue interaction and thermomechanical damage.

Depending on the operating environment and the nature of the applied loading, a structure can fail by a number of different modes, including brittle fracture, ductile fracture, plastic collapse, fatigue, creep, corrosion, and buckling. These failure modes can be broken down into the categories of fracture, fatigue, environmental cracking, and high-temperature creep. This article discusses each of these categories, as well as the benefits of a fitness-for-service approach.

This chapter compares and contrasts empirical approaches for partitioning hysteresis loops and predicting creep-fatigue life. The first part of the chapter presents experimental partitioning methods, explaining how they can be used to partition any loading cycle into its basic strain-range components. The methods covered include rapid cycling between peak stress extremes, half-cycle rapid loading and unloading, and variations of the incremental step-stress approach. The methods are then compared based on their ability to predict creep-fatigue life. The chapter goes on from there to describe how fatigue life can be estimated from ductility measurements when cyclic data are unavailable or are likely to change. It also explains how cyclic life is influenced by the time-dependent nature of creep-plasticity and the physical and metallurgical effects of environmental exposure.

This chapter provides an outline of the failure modes and mechanisms associated with most boiler tube failures in coal-fired power plants. Primary categories include stress rupture failures, water-side corrosion, fire-side corrosion, fire-side erosion, fatigue, operation failures, and insufficient quality control.

Large-scale yielding at the crack tip and time-dependent crack growth mechanisms, such as stress relaxation due to creep, are nonlinear behaviors requiring nonlinear analysis methods. This chapter presents two such methods, one based on elastic-plastic fracture mechanics, the other on time-dependent fracture mechanics. It also introduces two new fracture indices, the J-integral for handling large-scale yielding and the C*-integral for creep crack growth, providing close-form and handbook solutions for each.

Boiler tubes operating at high temperatures under significant pressure are vulnerable to stress rupture failures. This chapter examines the cause, effect, and appearance of such failures. It discusses the conditions and mechanisms that either lead to or are associated with stress rupture, including overheating, high-temperature creep, graphitization, and dissimilar metal welds. It explains how to determine which mechanisms are in play by interpreting fracture patterns and microstructural details. It also describes the investigation of several carbon and low-alloy steel tubes that failed due to stress rupture.

This chapter focuses on creep-rupture failure, or more precisely, the time required for such a failure to occur at a given stress and temperature. It begins with a review of creep-rupture phenomena and the various ways creep-rupture data are presented and analyzed. It then examines a large collection of creep-rupture data corresponding to different alloy designations and heat treatments, identifying key relationships, similarities, and differences. It also presents a test method developed by the authors in which twelve materials are tested over a range of temperature, stress, and time in order to determine multiheat constants that are then used to fit multiheat data from other materials and thus estimate rupture times.

This chapter examines the phenomena of deformation and fracture in metals, providing readers with an understanding of why it occurs and how it can be prevented. It begins with a detailed review of tension and compression stress-strain curves, explaining how they are produced and what they reveal about the load-carrying characteristics of engineering materials. It then discusses the use of failure criteria and the determination of yielding and fracture limits. It goes on to describe the mechanisms and appearances of brittle and ductile fractures and stress rupture, providing detailed images, diagrams, and explanations. It discusses the various factors that influence strength and ductility, including grain size, loading rate, and temperature. It also provides information on the origin of residual stresses, the concept of toughness, and the damage mechanisms associated with creep and stress rupture, stress corrosion, and hydrogen embrittlement.

This chapter familiarizes readers with the mechanisms involved in creep and how they are related to fatigue behavior. It explains that what we observe as creep deformation is the gradual displacement of atoms in the direction of an applied stress aided by diffusion, dislocation movement, and grain boundary sliding. It describes these mechanisms in qualitative terms, explaining how they are driven by thermal energy and how they can be analyzed using creep curves and deformation maps. In addition, it examines the types of damage associated with creep, presents a number of creep strain and strain rate equations, explains how to determine creep constants, and reviews the findings of several studies on cyclic loading. It also discusses the development of a novel test that measures the cyclic creep-rupture resistance of materials in tension and compression.

Durability is a generic term used to describe the performance of a material or a component made from that material in a given application. In order to be durable, a material must resist failure by wear, corrosion, fracture, fatigue, deformation, and exposure to a range of service temperatures. This chapter covers several types of component and material failure associated with wear, temperature effects, and crack growth. It examines temperature-induced, brittle, ductile, and fatigue failures as well as failures due to abrasive, erosive, adhesive, and fretting wear and cavitation fatigue. It also discusses preventative measures.

This article describes the general aspects of and practical problems of failure analysis of creep, stress relaxation, and yielding for homogeneous polymers. The effect of temperature and strain rate on the relationship between yield point and elastic modulus and the aging effect that polymers often undergo at room temperature are also discussed.