Failure analysis methodology is applied to the principal mechanisms by which boiler tubes fail during service. Several important factors often associated with component failures are deficiency in design, fabrication, operating conditions, unsuitable materials selection, and expended useful life. These factors are of primary consideration. The failure analysis procedure, or methodology for evaluation, is provided in a step by step approach. This includes justification for conducting a failure analysis investigation, developing a logical plan for the investigation to follow, collection of background information, sample removal techniques, on-site inspection, laboratory testing and analysis, and the formulation of final report based on relevant data, analysis, and recommendations. Among the case histories discussed are: fatigue, erosion, short-term overheating, and hydrogen damage.
Failure analysis, and the principal mechanisms by which boiler tubes fail in service, will be examined in this introductory survey. As this is an introductory survey, the reader is referred to two excellent reference texts covering the field of boiler failures for more detailed information. These are the texts authored by French1 and by Port and Herro2. Deficiencies in design, fabrication, operating conditions, unsuitable materials selection, and expended useful life are important factors to consider not only for boiler tubes, but operational components in general. Thus, the failure analyst must consider them of primary importance when a failure occurs in a boiler. If identified early, potential failures or accidents can often be prevented, and as a result costly repair expenses, lost revenue, and legal expenses may be avoided.
To investigate a failure, and analyze the conditions that promoted the failure, important information must be collected on the failed component. Background information on the make and model of the boiler and the tube, specifications, the service history, and physical evidence of the failed part are necessary components to determine why, how, when, and where a failure may have occurred. If these answers are provided during the course of the investigation, future failures may be better understood or possibly prevented.
The conditions that promoted the failure are essential in identifying the underlying factors that may have initiated the failure. Other elements that may not be readily acknowledged in failure analysis, yet are no less important, are common sense, a critical and unbiased mode of thinking, experience, knowledge, and experimental observation.
Provided in this survey is a step by step approach to failure analysis investigation. The accepted theories and mechanisms, which cause boiler components to fail, will be explored in this paper.
A failure analysis investigation is much like the work of a detective. Clues or relevant facts pertaining to the investigation must be gathered, analyzed, explored, and studied to make a knowledgeable determination. As in the case of a good detective, first hand field experience is of the utmost importance, yet academic studies are also essential.
A background and thorough understanding of materials used in construction, physical and mechanical properties of materials and their production, fabrication and performance characteristics of the materials, as well as a working knowledge concerning machinery and structural design, and the application and distribution of stresses resulting from service loads as they relate to the properties of materials are vital to fully develop as a successful failure investigator.
