Brittle fractures of pressure vessels can be both catastrophic and costly. The intent of this article is to provide guidance in avoiding such failures by identifying some of the causes for cold embrittlement hazards and brittle fracture in pressure vessels. Selected examples will help illustrate the main factors that contribute to brittle fracture, through identifying brittle fracture features, and demonstrating the importance of coordination of materials and potential operating condition. This article also discusses how to assess existing equipment pressure vessels subject to cold conditions and brittle fracture concerns using the guidelines of API 579-1/ASME FFS-1, Part 3.

In the aircraft engine industry, as in others, fracture surfaces are mined as a rich source of information. When present, fatigue striations can be used to judge the cracking mode, measure the crack growth rate, and estimate the number of propagation and initiation cycles. With training and practice, a failure analyst can learn to measure striations on fracture surfaces. Each individual striation is not counted, because there are thousands on a typical fracture and that would not be practical. Striations are measured from photographs taken in several locations across a fracture and their locations are recorded. It is best to start photographing selected areas at the deepest part of the fracture and work back toward the origin. Striations are usually much easier to see at the end of a fatigue zone due to several factors. The density of the striations (cycles per in. or lines per in.) is plotted as a function of crack depth. This data is fitted with a curve. The area under the striations/in. versus crack depth plot is an estimate of the total number of cycles the crack has propagated. Once the number of crack propagating cycles has been estimated, this data can be used to determine the number of cycles for crack initiation if the number of total cycles on the part is known.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

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This article addresses the effects of damage to equipment and structures due to explosions (blast), fire, and heat as well as the methodologies that are used by investigating teams to assess the damage and remaining life of the equipment. It discusses the steps involved in preliminary data collection and preparation. Before discussing the identification, evaluation, and use of explosion damage indicators, the article describes some of the more common events that are considered in incident investigations. The range of scenarios that can occur during explosions and the characteristics of each are also covered. In addition, the article primarily discusses level 1 and level 2 of fire and heat damage assessment and provides information on level 3 assessment.