case study analysis of failure

Case Studies in Product Failure and Failure Analysis

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As we discussed in Chapter 4, failures occur when the applied loads on the system exceed the strength of the components, producing failure. The applied loads are any system load that include mechanical, electrical and chemical loads that produce the necessary stresses to drive failure processes. The applied loads and the strength of any component must be recognized as random variables. The potential for failure of a component is then related to the overlap of the load and strength distribution; this applies to overstress or wear out failures. However, in the later case we expect the degradation in strength to force greater overlap as time progresses. Overlapping distributions are illustrated in Figure 9.1. Greater overlap means greater probability of failure. In terms of field use of a product, such as a consumer appliance, this means more failures, potentially greater costs and loss of name brand recognition when early failures occur.

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Carter, A.D.S., Mechanical Reliability, MacMillan, 1986.

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Evans, J. W., Evans, J. Y and Ryu, D.S., ‘Product Integrity in Design and Development of Consumer Electronics: Advancing the TankTM Concept for World Class Competitiveness’, ADVANCE, Institute for Advanced Engineering Journal, March, 1997.

Evans, J.W. and Wagner, S., ‘Deterioration of ZnO/SiO2 Diode Packages in High Humidity’, ASM International Symposium for Testing and Failure Analysis, Los Angeles, CA, November, 1987.

Fuchs, H.O., and Stevens, R.I., Metal Fatigue in Engineering, John Wiley and Sons, 1980. Uhlig, H. H., Corrosion and Corrosion Control, John Wiley and Sons, 1971.

Shigley, J.E. and Mitchell, L.D. Mechanical Engineering Design, McGraw-Hill, 1983. Smith, W.F., Structure and properties of Engineering Alloys, McGraw-Hill, 1981

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Evans, J.W., Evans, J.Y. (2001). Case Studies in Product Failure and Failure Analysis. In: Evans, J.W., Evans, J.Y. (eds) Product Integrity and Reliability in Design. Springer, London. https://doi.org/10.1007/978-1-4471-0253-3_9

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Home > Books > Pipeline Engineering - Design, Failure, and Management

Failure Analysis of Pipelines in the Oil and Gas Industry

Submitted: 01 September 2022 Reviewed: 16 September 2022 Published: 13 November 2022

DOI: 10.5772/intechopen.108140

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The term “failure” can be defined as the inability of a part or assembly to perform its intended function. Despite the significant technological advances, failure incidents frequently occur, thus, causing human and financial consequences. The failure analysis is a crucial engineering tool. It aims to avoid similar cases in the future, thereby preventing accidents, reducing economic losses due to stopping plant production and keeping the environment safe. Furthermore, the failure analysis contributes to redesign, solve manufacturing drawbacks, save money and time, and in some cases, prevents fatality and saves lives. Conversely, failures can also improve engineering practices; indeed, through analyzing failures and implementing preventive measures, significant advances have been obtained in the quality of products and systems. Moreover, a beneficial outcome of failure analysis has been improved codes and specifications governing materials, for instance, API, ASTM, and ASME. In the current chapter, the failure analysis methodology will be discussed in detail with practical examples to know how to perform analysis for any failure cases, particularly in the oil and gas industry.

• failure analysis
• oil & gas industry

Author Information

Mohamed mohamed azzam *.

• Department of Metallurgical Engineering, Faculty of Engineering, Cairo University, Giza, Egypt

*Address all correspondence to: [email protected]

1. Introduction

The term “failure” can be defined as the inability of a part or assembly to perform its intended function [ 1 ]. Based on the simple definition of failure, we can understand that the part of the component is considered failed if it cannot perform its function perfectly for any reason, for instance, a change in dimensions, corrosion, fracture, and so on. Sometimes unspecialized think the part to fail must be broken or fractured, but this is not the case. In other words, each fracture is considered a failure; however, not every failure is considered a fracture. A fracture separates parts into two or more species in response to the applied or residual stresses.

The pipeline can expose to thinning due to erosion-corrosion damage; however, it is still in service; thus, the pipeline can be considered to have failed, although it is still in service without leakage. The thinning mechanism is a failure since the pipeline has lost service life. In other words, the pipeline was designed to serve a specific period; however, the thinning damage has shortened its lifetime, which means the pipeline lost some of its lifetime. The high-pressure gas (HPG) pipeline has been subjected to internal corrosion, which led to a localized metal loss. Thus, the HPG pipeline has been converted to transfer oil or low-pressure gas due to the fitness for service, which revealed the remaining thickness cannot withstand the high pressure; thus, the pipeline has lost its function to transfer the high-pressure gas.

Material failure can be divided into four types: distortion or plastic deformation, fracture, corrosion, and wear [ 1 ]. It is worth noting that two or more physical failures can occur in the same failed part. The root causes of the failure can be divided into three levels; physical roots, human roots, and latent roots. The physical roots can be divided into four categories: design deficiencies, material defects, manufacturing or installation defects, and service life anomalies [ 2 ]. The human roots include inadequate inspection and improper equipment installed. The latent roots are the cultural or organizational rules that lead to the human cause; it is not direct roots. The inadequate inspector training is an example of the latent root, where some companies consider the training courses as additional costs that need to be reduced. These companies fail to recognize that this reduction is reflected in the ability of individuals, leading to catastrophic events due to incompetent persons.

The poor design can play a significant role in some failure cases; for example, the pipeline can be designed with a low spot that accumulates the water and causes corrosion. Also, poor design can create a crevice location which accelerates corrosion in the form of crevice corrosion due to the different concentrations of oxygen inside and outside the crevice. Additionally, material selection can be the root cause of some failure cases, using inappropriate material to serve in a harsh environment.

For instance, of inefficient material selection, using 304 austenitic stainless steel in chloride containing environment can lead to severe pitting corrosion or stress corrosion cracking [ 3 ]. Moreover, the manufacturing defects in most failure cases play a significant role in the failure. Thus, these defects act as the origin of catastrophic damage. For example, the lack of fusion of manufacturing defects can be a location for crack initiation or a stress concentration.

Furthermore, environmental change can cause premature or unexpected failure before its lifetime. For example, increasing the fluid velocity inside the pipeline accelerates the corrosion rate through erosion damage. Also, if the pipeline is designed according to a specific value (i.e., max limit) of hydrogen sulfide (H 2 S) and carbon dioxide (CO 2 ), the increase of this limit would lead to anticipated failure mechanisms such as Sulphide stress corrosion cracking and CO 2 corrosion, especially in high-pressure gas (HPG) pipelines. In addition, the change in operating conditions may play a crucial role in the failure of pipelines. For example, increasing the operating pressure beyond the design pressure can lead to overloading damage or corrosion by increasing the partial pressure of the corrosive species such as Oxygen (O 2 ), hydrogen sulfide (H 2 S), and carbon dioxide (CO 2 ) [ 4 ]. Also, the inadequate inspection may lead to failure; for example, performing the visual examination without nondestructive examination (NDE) may skip and ignore fine cracks or internal defects that the visual inspection disables to detect. Moreover, the absence of monitoring has a crucial role in some corrosion cases, where different monitoring methods are used to monitor the corrosion rate in the pipeline, such as the corrosion coupon, sand probe, and bio-probe. Without the monitoring method, assessing the operating condition, especially the fluid corrosivity, is not feasible.

Moreover, human error can play a critical role in failure cases through incompetent persons. For example, after conducting the hydro test for repaired tanks or vessels, and during the drainage of the used water, the responsible person can cause collapse due to rapid drain rate or due to the closing of the vent. Also, the non-drain of the water (i.e., Missing to drain) used in the hydro test can cause catastrophic failure, mainly if the pipeline is not used directly after the hydro test and is left for some time. The hydro test water inside the pipeline with stagnation condition will be suitable for SRB colonies to grow and cause corrosion damage, called microbiological induced corrosion (MIC) [ 5 ]. Therefore, the water used in the hydro test must be flushed and entirely drained if the pipeline will be used directly after the hydro test. However, suppose the pipeline will not be used directly after the hydro test; in that case, the pipeline must be mothballed through injection of multifunction chemical which contains a mixture of oxygen scavenger, corrosion inhibitor, and biocide.

Indeed, failure analysis aims to determine the causes or factors that have led to an undesired loss of functionality; this considers the failure analysis’s direct benefit. Also, failure analysis is an engineering tool for enhancing product quality and failure prevention; this considers the failure analysis’s indirect benefit [ 2 ]. Furthermore, the failure analysis contributes to redesign, to solve the drawbacks of manufacture, saving money, saving time, and in some cases preventing fatality and saving lives [ 6 ].

The failure analysis must be performed based on a scientific base and a standard methodology to identify the damage mechanism and determine the significant root causes; otherwise, the analysis outcome will be unexpressed about the actual root causes. Also, the wrong root causes may accuse factors that are far from playing any role in the failure, thus, taking unsuitable recommendations which can accelerate the failure. The false root causes due to poor and inefficient failure analysis methodology can be likened to accusing an innocent person of murder; however, the real killer is free.

From my point of view, failure analysis in the oil and gas industry, specifically in the offshore environment, is considered a crucial case for the failure analysis society. Since these cases enrich the knowledge and information, thus, saving the marine environment against the consequences of failure and causing disasters such as pollution and marine life death in addition to economic loss. In April 2010, in one of the most significant pipelines containment failure accidents, that is, Deepwater Horizon, it was reported that approximately 3.19 million barrels of oil spilled into the ocean [ 7 ] and polluted at least 11,200 km 2 of seawater [ 8 ], which was catastrophic to both the economy and environment.

The crude oil at offshore platforms is transferred to the processing plants onshore through pipelines, which are considered one of the safest and most effective ways to transport oil and gas, security and reliability of the transmission pipeline [ 9 ]. There are three types of pipelines: gathering lines, transmission lines, and distribution lines. Gas or crude oil gathering lines exist between a well and a treatment plant or collection point [ 2 ]. The offshore pipelines are much more critical due to their operational condition, inspection, repair difficulties, and environmental issue [ 10 ]. These pipelines are manufactured from carbon steel. The consequences of pipeline rupture could lead to loss of life, injury, fire, explosion, environmental pollution, economic loss, decreasing capacity, and increasing maintenance difficulty [ 11 ].

2. Failure analysis methodology

Collection of background data

Preliminary examination of the failed part

Chemical analysis (Sludge–Water-Liquid)

Nondestructive testing

Mechanical testing

Chemical analysis of the material

Selection, identification, preservation, and cleaning of specimens

Macroscopic examination and analysis

Microscopic examination and analysis (electron microscopy may be necessary)

Selection and preparation of metallographic sections

Examination and analysis of metallographic specimens

Analysis of fracture mechanics

Determination of failure mechanism

Testing under simulated service conditions (special tests)

Analysis of all the evidence, formulation of conclusions, and writing the report (including recommendations).

It is worth pointing out that the above methodology steps can be applied to most components in the oil and gas industry, such as storage tanks, pressure vessels, and pipelines. In other words, the above steps can be considered a generic methodology for most facilities in the oil and gas industry. However, in the further discussion for each step, most examples of the practical cases of failure incidents will be confined primarily to the pipelines, whether liquid or gas services, since the book’s topic is mainly concerned with the pipelines. Therefore, it will be helpful to give examples of pipelines specifically.

2.1 Collection of background data

The failure analysis methodology’s first step is collecting the background data. The failure investigation should include gaining an acquaintance with all pertinent details relating to the failure. In this step, the failure analyst acts as the detective who investigates a crime case by collecting all available data since the useless information, according to the operators of the failed part, is considered very important to the failure analyst and can contribute to solving the case. The failure analyst only who can judge the importance of the data.

Preparing a checklist containing all the essential required data and questions you need to ask is recommended to do not to forget anything. The list can include: the drawing or the as-built, history of the anomalies for the failed portion, repair history, history of the service environment (i.e., oil/water/gas/multiphase), pigging schedule, type of pig, whether BIDI or foam pig, water analysis reports, gas analysis reports, and scale analysis reports, in addition to the interview with the persons who are responsible for the operating of the failed portion.

It is worth noting that the failure analyst must be decent and non-offensive during the interview with the persons responsible for the failed part in the field and not accuse or blame anyone; otherwise, most of these persons vanish the important data fearing the blame or the accusation.

2.2 Preliminary examination

The preliminary examination can be divided into two stages; the first is performing a site visit to the incident location before retrieving the failed portion. The site visit to the incident location aims to figure out the actual situation of the whole location (i.e., the platform or the plant), not only the failed portion. In some cases, the preliminary site visit to the failure location of the failed part was the clue. Sometimes, the site visit to the failure location revealed simultaneous works implemented at the moment of the incident; consequently, the root causes are highly believed to be external causes due to these operational activities, not the failed part’s environment. This indicates that the analyst must enlarge the investigation area around the failed part. Gradually narrow it, especially when the damage is external, such as a dent, gouge, and scratch.

The second stage in the preliminary examination is a visual examination of the failed part that depicts the actual condition after the incident without any change. The visual inspection aims to detect abnormal features such as damage morphology, plastic deformation, cracks, thinning, erosion, dents, dimensions change, and scratches. During the visual examination, a magnifying glass can be used [ 12 ] to enlarge some significant features of the failed part, such as the origin of the crack, damage morphology, and crack arrest location. Using a ruler or measure tap is recommended to determine the aspects of the failure, mainly in the cracking or rupture incident before movement or cutting the failed part, as shown in Figure 1 , which shows the crack’s measurement process dimensions for rupture of 24-inch water injection pipeline.

Measuring the dimensions of the rupture of 24-inch water injection.

Figure 2 shows a failed 2-inch bleeding valve disconnected from the main line of high-pressure gas (i.e., 1200 psi), and the short nipple connection between the valve and the main line was found in a bent shape. On-site inspection indicated scaffolding had been installed around the failure due to concurrent work to replace an 8-inch water injection line directly above the failed valve. This means that the main reason for a defective valve to bend is that a mechanical tool fell and hit the valve, whereas the failed valve is a free end with no support. This failure case is an ideal example of the importance of on-site inspections at the fault location. Without on-site inspections, investigators will come up with unclear root causes and thus make incorrect recommendations.

Failed 2-inch bleeding valve due to drop of a mechanical tool.

The visual examination of the failed part must include determining the origin from which the crack or the corrosion started. The origin can be manifested as a bulge, such as the overloading failures, or stress concentration location, such as the sharp edges and weldment. For example, Figure 3 shows the origin of the rupture, which occurred in an 18-inch gas pipeline, where the origin appeared in a bulge shape; the spout-like form (bulge) is indicative of an overloading incident. Eventually, during a visual inspection, failure analysts can use failure morphologies to brainstorm and imagine expected failure cause scenarios.

Illustrates the origin (bulge) of fast-running ductile rupture of 18-inch oil pipeline.

2.3 Chemical analysis (sludge: water-liquid)

It is a crucial step to obtain a sample from the failed portion directly after the incident. The collected sample can be sludge or liquid. The sludge sample will be analyzed to determine the predominant components, especially in the corrosion failure cases. The scale analysis can provide us with informative data about the damage mechanism. Additionally, samples from debris and water are obtained to perform sulfate-reducing bacteria (SRB) testing to determine the count of sessile and planktonic bacteria in the fluid.

If the predominant compound in the analysis is iron carbonate, the expected damage mechanism is CO2 corrosion. If the iron sulfide (FeS) is the dominant compound, the predicted damage mechanism is microbiologically induced corrosion (MIC) due to the microorganism activity of the sulfate-reducing bacteria (SRB) [ 13 ]. If the predominant component is the sand, the expected damage mechanism is erosion damage due to the abrasive particles of the sand. If the main compound is iron oxide, the anticipated damage mechanism will be Oxygen corrosion.

The complete water analysis, iron content, H 2 S dissolved, Oxygen dissolved, and CO 2 dissolved are significant parameters in most failure cases, indicating how the environment can be harsh. Chlorides have a detrimental effect on the passive layer, destroying the protection formed by the corrosion inhibitor. Oxygen is one of the corrosive species in any corrosion reactions, which accelerates the corrosion rate; therefore, it is recommended to control the Oxygen dissolved to levels of 10 to 50 ppb (part per billion). With increasing the partial pressure of CO 2 , the dissolved concentration in the water increase, thus, lowering the pH and increasing the corrosion rate [ 14 ]. Figure 4 illustrates the scale sample collection from a failed 24-inch oil pipeline.

Collection of scale sample from failed 24-inch oil pipeline.

2.4 Nondestructive testing

Nondestructive testing is a helpful and essential tool in most failure cases. Ultrasonic testing (UT) is often used to measure the remaining wall thickness to calculate the maximum pressure that can be applied. Also, UT is used to detect internal defects, whether base metal or weldment, like porosity, cracks, and laminations. Additionally, UT can give the location and size of the defects [ 12 ] and measure the remaining wall thickness, as shown in Figure 5 .

UT Technique (a) calibration of the UT device, and (b) Conducting of UT examination.

The dye penetrant test (PT) is often used to detect the surface cracks and clearly show the damage’s extent, as shown in Figure 6 shows a fine crack in the fillet weld of the 2-inch line of the High-pressure gas. The magnetic particles test (MT) also performs the same function as the PT, detecting surface cracks.

Crack detected in the fillet weld of 2-Inch HPG line by dye penetrant test (PT).

2.5 Mechanical testing

It is a crucial step among the steps of the analysis to confirm the desired mechanical properties of the failed part according to the specification to facilitate the subsequent steps, especially the stress analysis step. Thus, the tensile test determines the yield strength, ultimate tensile strength, and elongation. Additionally, hardness testing is the simplest of mechanical tests; it can be used to assist in evaluating heat treatment [ 6 ]. Furthermore, the impact test is used to measure the toughness of the failed parts in the overloading cases and fracture when the notch or point of stress concentration is experienced in the failure case [ 15 ]. The impact test is Mainly used when the failed part operates at low temperature or a mechanical tool hit or falls on it, as shown in Figure 7 . It can be concluded that the mechanical tests are considered a verification that the material of the failed part was convenient to the applied stresses or the environment during the in-service period or not, according to the specification and the design criteria.

Performing impact test for specimen cut from an 18-inch offshore pipeline.

2.6 Chemical analysis of the material

In failure analysis cases, routine chemical composition analysis is highly recommended [ 6 ]. The chemical analysis of the material is used to determine the failed part’s chemical composition, the same as the mechanical testing. The alloying elements in the cast alloys are rarely distributed uniformly. Thus, the chemical analysis is considered a verification tool by ensuring that the chemical composition does not deviate from the nominal composition according to specification. The chemical analysis is conducted in the laboratory using the optical emission spectrometer. The deviation from the nominal composition at a specific location of the failed part is called segregation [ 2 ]. Table 1 illustrates the deviation of the chemical composition of 2205 duplex stainless steel pipe using X-Ray Fluorescence (i.e., XRF) device as shown in Figure 8 , which caused a premature failure and gas release [ 16 ].

Chemical composition of 2205 Duplex stainless steel pipe.

Performing chemical analysis for the weldment using XRF.

In some cases, it is difficult to perform the chemical analysis in the laboratory; therefore, positive material identification (PMI) is a prompt tool that can be used in the field to identify the material with the chemical compositions of the alloying element. The PMI is a portable device used to determine the chemical composition of the material without needing to transfer the sample to the laboratory. For example, Figure 9 shows embrittlement in the flare of low-pressure gas, where the burner’s designed material is 310 stainless steel; however, the PMI analysis revealed that the material is 384 stainless steel. This case shows the importance of the PMI and how it can facilitate determining the clue in the field without needing the laboratory.

Embrittlement of flare due to unsuitable material.

2.7 Selection, sectioning, preservation and/or cleaning of specimens

In my view, the steps of selection, cleaning, and preservation are very critical and crucial since any fault can destroy the fracture surface, thus, making the failure analysis process difficult, and the root causes may not be present in the actual failure. The significant and valuable portion of the failed part is the origin, whether it is cracking or corrosion damage. The origin (i.e., the start point of the failure) is the clue of most failure cases since it would contain a defect, and the damage starts. Figure 10 shows the locations to be cut for examination (i.e., mechanical testing, chemical testing, macro examination, and micro examination). The proficiency of the failure analyst is shown in the selection of what specific portions are to be studied. Since the whole failed part is not used in the analysis, small selected specimens, such as the origin, are expressed and valuable.

Selection of location to be cut and studied.

Furthermore, the sectioning step of the selected portion must be performed far enough from the failure’s origin to prevent destroying it, which could lead to false conclusions [ 2 ]. During the sectioning process, it must be considered the sample size to be suitable for macro and micro examination and optical and scanning electron microscopes, respectively. It is recommended to use cold cutting techniques for sectioning the samples, like the wire cut and the abrasive blade cutting, which do not introduce any heat to the failed portion, thus, preventing any alteration to the actual condition, as shown in Figure 11 .

Cutting machine with cooling system.

Moreover, handling the selected portion of the failed part is a significant step. Therefore, the selected samples are stored in special boxes made from plastic to avoid friction between the specimens and the container. It is recommended to coat the pieces with grease or apply a removable coating of oil or plastic compound to prevent further interaction between the cut samples and the surrounding environment [ 12 ]. The surrounding environment causes corrosion and oxidation to the specimens and confuses whether the source of this corrosion is due to an in-service environment or not.

The cleaning process of the specimens is a crucial step since improper cleaning can destroy the fracture surface. The cleaning process aims to remove corrosion products, debris, and grease from the fracture surface. The cleaning process is an inevitable step in the microscopic examination, particularly when the scanning electron microscope is used. The cleaning program must be started with soft tools and gradually increase to aggressive cleaning tools based on the surface condition. Many cleaning methods can be used in the preparation of the samples. For instance, using the soft hair artist’s brush as a preliminary step, and then using one or more methods from the following: using inorganic solvents, either by immersion or by jet, acetone or alcohol, cellulose acetate tape, replica, and use the ultrasonic cleaning bath. The ultrasonic bath is very useful in accelerating the cleaning process, as shown in Figure 12 .

Ultrasonic cleaning for specimen before examination by SEM.

2.8 Macroscopic examination and analysis

The macro examination step is performed after the excellent cleaning of the sample in which the fracture surface becomes clear and free of corrosion products, dirt, grease, and residual species. The stereoscope is the most helpful tool in this step. The stereoscopic viewing has the same scope as visual inspection but is more detailed as typical stereoscopes allow 10X to 70X magnification [ 17 ]. The macroscopic examination does not require the fracture surface to be extremely smooth. The cleaning only is sufficient to perform a macroscopic analysis, unlike the microscopic examination (i.e., Optical microscope), which needs a polished surface to produce high contrast between the microstructural constituents.

The macroscopic examination can provide the failure analyst with beneficial information, for instance, the origin of the fatigue crack and secondary cracks, especially the fine cracks that could not be observed during the visual examination. Furthermore, the macroscopic shows a comprehensive view of the failure location compared to that of microscopic examination, thus, helping the failure analyst to imagine the scenario of what happened during the incident. Figure 13 shows a cross-section macrograph of the failed pipe at the seam weld side. The joint configuration of the seam longitudinal weld is a double-V groove weld. A fusion welding process produces the seam weld. It is most likely a SAW process was used due to the considerable penetration depth in one pass (the filling pass). It is also evident that the crack propagated along the HAZ, HAZ/base metal boundary, or the base metal.

Macrographs across the fracture surface at about 40 cm from the burst origin.

2.9 Microscopic examination and analysis

The microscopic examination is the clue in most failure cases, especially for metallurgical investigation, and is typically performed by the scanning electron microscope (SEM), as shown in Figure 14 . The scanning electron microscope is an effective and helpful tool to know what happened during the incident; it looks like a recorded camera of the events of the failure. The scan electron microscope can provide a large magnification ranging from 5000 to 10,000X [ 6 ].

Scanning electron microscope (SEM).

Some fracture modes can be identified according to the microscopic characteristics, where the dimpled morphology indicates ductile fracture due to overloading, and cleavage facets refer to brittle fracture. The striations are the most characteristic microscopic evidence of fatigue fracture. Figure 15 shows cleavage facets at the origin of an 18-inch gas pipeline crack ruptured due to a welding defect. Figure 16 illustrates the quasi cleavage of a fracture surface of an 18-inch oil pipeline, which ruptures in the form of rapid ductile fracture.

Shows cleavage facets.

Shows quasi cleavage.

2.10 Selection and preparation of metallographic sections

The metallographic selection and preparation are crucial steps in metallurgical investigation cases. The selected region of the failed part must be chosen to present unique features of the failed part, which are selected for the characterization process. The selection of the samples which would be examined must be carried out carefully since these samples shall be near the edge of the fracture (i.e., around the origin). In other words, the significant sample which provides valuable information is the sample of the failure location. The sectioning of the metallographic specimens should be perpendicular to the fracture surface in edge view. Furthermore, selecting pieces far from the failure region (i.e., undamaged location) is helpful.

The selected specimens for the metallographic examination should be cut with cold manners. The cold cut prevents alteration of the specimens’ microstructure, high precision cut, and deformation-free cutting for various workpiece sizes. Thus, the wire cut machine or the abrasive cut-off wheels are the standard practical methods for cutting the specimens examined in metallography. The samples are cut into small sizes to facilitate the handling and examination processes; these samples are ground using silicon carbide (SiC) foil and paper to produce a smooth surface before polishing.

2.11 Examination and analysis of metallographic specimens

Metallography is defined as the scientific discipline of examining and determining the constitution and the underlying structure of (or spatial relationships between) the constituents in metals, alloys, and materials (sometimes called materialography) [ 18 ]. The most common tool in the metallography examination is the optical or light microscope, with magnifications ranging from ~50 to 1000×, as shown in Figure 17 . The optical microscope is used to identify the phases, constituents, and precipitations and determine the size and shape of the grains. The high contrast between microstructural constituents in light microscopy mainly depends on the quality of the specimen preparation process. The metallographic examination is also a verification of the heat treatment where the grains sizes are an indication of the heat treatment quality.

The optical microscope for metallography.

In Figure 18 , it is evident that the HAZ at both sides of the joint contains coarse ferrite grains. In addition to the coarse ferrite grains, grain boundary austenite (GBA) has been observed along the grain boundaries of the coarse ferrite. It is believed that the excessive heat input of the welding process resulted in coarse-grained HAZ, which played a role in the degradation of HAZ zones.

Coarse grain HAZ of 2205 duplex stainless steel pipe.

2.12 Analysis of fracture mechanics (stress analysis)

It is sometimes quite apparent that excessive loading plays a detrimental role in the failure. Noticeable plastic deformation is observed at the failed pipeline due to the overloading, which causes a change in the pipeline configuration from circle to oval shape. Additionally, the stress analysis is performed based on the specifications, standards, and codes, for instance, ASME B31.8, API 579, and ASME 31G.

For the components with very complex shapes and high thermal gradients, a finite-element analysis (FEA) may be performed to estimate the most likely stress level in the failed part. These analyses can stand alone or can be used to help select critical locations for strain gauge attachment. Finite-element calculations can be time-consuming and expensive, but they are necessary for accurately assessing stress levels in areas of the complex geometry of some components. This analysis is almost essential for determining stresses caused by thermal gradients such as those found in welding [ 6 ].

Figure 19 shows an offshore pipeline ruptured due to overloading, where the outer surface of the ruptured wall is bowing out, indicating that the pipeline was highly inflated before it bursts. After failure, the surface is still bowing out, meaning that the deformation of the pipe wall was plastic deformation, and the level of stress encountered was very high.

Shows the topography of the ruptured wall and the wall bow-out.

2.13 Determination of failure mechanism

Determining the failure mechanism is almost the last step in the failure analysis methodology. The failure mechanism is determined based on the main finding of the visual examination, chemical analysis, mechanical testing, macro examination, and micro examination. It is believed that identifying the failure mechanism is easier and faster than determining the root causes of this failure damage. Since in most failure cases, the visual examination is preliminary and sufficient to figure out the failure damage.

Figure 20 shows a failed 4-inch control valve, and from the visual examination, it is clear that the expected damage is erosion-corrosion damage. Figure 21 illustrates scattered pitting at the 30-inch oil discharge header. Based on the damage morphology and operating condition, it is believed that the microbiological induced corrosion (i.e., MIC) is the anticipated damage mechanism due to bacterial activity (i.e., SRB) and according to the cup-shaped damage.

Erosion at the 4-inch control valve of discharge line.

Microbiological induced corrosion (MIC) at 30-inch discharge header.

Figure 22 shows a rupture of the 24-inch water injection pipe, where the observed bumps indicate an overload event; visual inspection shows severe thinning due to corrosion damage; therefore, with a working pressure of 1600 psi, the anticipated failure mechanism is Stress corrosion cracking. The corrosion cracking mechanism combines the stress and the corrosive environment [ 5 ]. Also, Figure 23 shows a fracture in the 6-inch well flowline, and site visits to the platform show that the tubing is undergoing significant movement; therefore, the damage mechanism is believed to be fatigue damage due to cyclic loading.

Stress corrosion cracking (SCC) at 24-inch water injection pipeline.

Crack due to fatigue at 6-inch flow line of oil well.

2.14 Determination testing under simulated service conditions (special tests)

In some cases, simulation of operating conditions or special testing is strongly recommended to understand the effect of the environment on the same material of the failed component. It is important to note that most simulation tests are not feasible or practical because service conditions cannot be achieved, especially in the case of corrosion failure, which is not feasible in the laboratory. In addition, running simulations requires safety considerations, especially in the event of failures that occur under catastrophic conditions, such as overloading high-pressure gas lines. Figure 24 shows pitting and crevice corrosion testing of an undamaged specimen cut from a defective 2205 duplex stainless steel weldment. This test is designed to determine the effect of the chloride (i.e., high salinity) on welded joints operating in harsh high salinity environments. The results show that preferential corrosion of the specimen occurs in the heat-affected zone and near the weld, as shown in Figure 25 .

Pitting and crevice corrosion testing according to STM G-48.

The specimen after conducting the pitting and crevice corrosion testing.

2.15 Determination analysis of all the evidence, formulation of conclusions, and writing the report

This step is the outcome of all stages in the failure analysis methodology. The main findings depict every step and are discussed and analyzed intellectually and scientifically to prove the damage mechanism and support the believed root causes. Also, all evidence is collected together during the investigation steps to complete the correct scenario about what has occurred.

The analyst’s competence is also reflected in the preparation of the report, especially in the discussion and conclusion. Suppose the inspector has access to extensive laboratory facilities. In that case, best efforts should be made to analyze and discuss the results of mechanical testing, chemical analysis, fracture, and microscopy before formulating any preliminary conclusions [ 6 ]. Eventually, in investigations where the cause of failure is particularly elusive, searching for reports of similar cases may help identify possible root causes. Some references to other similar issues are suggested to support the discussion during the discussion.

3. Conclusion

Collection of background data (i.e., Drawing, anomalies, repair history, environment, pigging activities, water analysis reports, gas analysis, and scale analysis)

Preliminary examination of the failed part (i.e., a site visit to the failure location and visual examination)

Nondestructive testing (i.e., UT, MT, PT, & RT)

Mechanical testing (i.e., Tensile test, impact test, & hardness test)

Chemical analysis of the material (Using the optical emission spectrometer &PMI)

Selection, identification, preservation, and cleaning of specimens (i.e., specimens’ selection, wire cut, abrasive blade cutting, and ultrasonic cleaning)

Macroscopic examination and analysis (i.e., using of stereoscope)

Microscopic examination and analysis (i.e., Using of SEM)

Selection and preparation of metallographic sections (i.e., grinding, polishing, and etching of the samples)

Examination and analysis of metallographic specimens (i.e., optical microscope)

Analysis of fracture mechanics (i.e., stress analysis and finite element)

Determination of failure mechanism (i.e., identify the damage mechanism)

Testing under simulated service conditions (i.e., special tests)

• 1. Wulpi DJ. Understanding How Components Fail. Second Edition. Materials Park, Ohio, USA: ASM International; 1999
• 2. ASM International. ASM International. In: ASM Handbook. Failure Analysis and Prevention. Vol. 11. Materials Park, OH; 2005
• 3. Davis JR. Corrosion of weldments. In: Chapter 3: Corrosion of Austenitic Stainless-Steel Weldments. Materials Park, Ohio, USA: ASM International; Dec 2006. pp. 43-75
• 4. Bahadori A. Corrosion and Materials Selection. Chichester, West Sussex, United Kingdom: John Wiley & Sons, Ltd; 2014
• 5. Winston Revie R. UHLIG’s Corrosion Handbook. Hoboken, New Jersey: John Wiley & Sons, Inc; 2011
• 6. Dennies DP. How to Organize and Run a Failure Investigation. ASM International; 2005
• 7. United States of America v. BP Exploration & Production, Inc. et al. Findings of fact and conclusions of law: Phase two trial. In: RE: Oil Spill by the Oil Rig “Deepwater Horizon” in the Gulf of Mexico, on April 20, 2010. U.S. District Court for the Eastern District of Louisiana; 2015
• 8. DWH-NRDA, Deepwater Horizon Natural Resource Damage Assessment (NRDA) – DRAFT. 2015 – section 4, injury to natural resources, DWH-NRDA. 2015. p. 685
• 9. Han CJ, Zhang H, Zhang J. Failure pressure analysis of the pipe with inner corrosion defects by FEM.International Journal of Electrochemical Science. 2016; 11 :5046-5062
• 10. Cheng YF. Stress Corrosion Cracking of Pipelines. Hoboken, New Jersey: John Wiley & Sons; 2013
• 11. HSE. Guidelines for Pipeline Operators on Pipeline Anchor Hazards. Aberdeen: Health and Safety Executive; 2009
• 12. McEvily AJ. Metal Failures Mechanisms, Analysis, Prevention. Hoboken, New Jersey: John Wiley & Sons, Inc.; 2013
• 13. Javaherdashti R. Microbiologically Influenced Corrosion. London Limited: Springer-Verlag; 2008. pp. 49-100
• 14. Palacios CA. Corrosion and Asset integrity Management for Upstream Installations in the Oil/Gas industry, CreateSpace Scotts Valley, California, 1st ed. 2016
• 15. Callister WD Jr. Materials Science and Engineering-An Introduction. John Wiley & Sons, Inc.; 1985; 1985
• 16. Azzam M, Khalifa W. Investigation of duplex stainless steel flow line failure, engineering failure analysis (under review). 2022
• 17. González-Velázquez JL. Fractography and Failure Analysis. Mexico: Springer International Publishing AG, part of Springer Nature; 2018
• 18. ASM International. ASM Handbook. Metallography and Microstructures. Vol. 9. ASM International: Materials Park, OH; 2004

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3.0 License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Case Study: Failure Analysis of Functional Shmoo Hole with Laser Voltage Probing

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S.H. Lee , Y.W. Lee , K.T. Lee , C.Y. Choi , H.W. Shin , Yin S. Ng , T.R. Lundquist; November 15–19, 2009. "Case Study: Failure Analysis of Functional Shmoo Hole with Laser Voltage Probing." Proceedings of the ISTFA 2009 . ISTFA 2009: Conference Proceedings from the 35th International Symposium for Testing and Failure Analysis . San Jose, California, USA. (pp. pp. 193-197). ASM. https://doi.org/10.31399/asm.cp.istfa2009p0193

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Innovations in semiconductor fabrication processes have driven process shrinks partly to fulfill the need for low power, system-on-chip (SOC) devices. As the process is innovated, it influences the related design debug and failure analysis which have gone through many changes. Historically for signal probing, engineers analyzed signals from metal layers by using e-beam probing methods [1]. But due to the increased number of metal layers and the introduction of flip chip packages, new signal probing systems were developed which used time resolved photon emission (TRE) to measure signals through the backside. However, as the fabrication process technology continues to shrink, the operating voltage drops as well. When the operating voltage drops below 1.0V, signal probing systems using TRE find it harder to detect the signals [2]. Fortunately, Laser Voltage Probing (LVP) technology [3] is capable of probing beyond this limitation of TRE. In this paper, we used an LVP system to analyze and identify a functional shmoo hole failure. We also proposed the design change to prevent its reoccurrence.

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• Bridge Failure Cases
• Dam Failure Cases
• Building Failure Cases
• Other Failure Cases

There is a documented need for failure awareness in the undergraduate engineering curriculum.  Engineering students can learn a lot from failures, and failures play an important role in engineering design.  This need has been expressed in a number of papers and at a number of conferences over the past two decades.  This book is a specific response to that need and will provide (1) much needed access to examples, and (2) a heightened appreciation of the role failure analysis knowledge can play in higher education and public safety.

Many of the key technical principles that civil engineering students should learn can be illustrated through case studies.  For example, the author has discussed the Hyatt Regency walkway collapse, the Tacoma Narrows Bridge failure, and other well-known cases with students in Statics, Mechanics of Materials, and other courses.  These cases help students:

• Grasp difficult technical concepts and begin to acquire an intuitive feel for the behavior of systems and structures,
• Understand how engineering science changes over time as structural performance is observed and lessons are learned,
• Analyze the impacts of engineering decisions on society, and
• Appreciate the importance of ethical considerations in the engineering decision making process.

The main obstacle to integrating case studies and lessons learned from failures into existing courses has been that many faculties does not have time to research and prepare case studies.  Although there are many references available, they are difficult to translate into classroom lectures without considerable added effort on the part of the instructor.

There are three ways to introduce failure analysis and failure case studies into civil engineering education.  A small number of colleges and universities, probably only a few percent, offer courses in forensic engineering or failure case studies. Often, these are at institutions such as the University of Texas, Mississippi State University, or the University of Colorado at Denver that have practicing forensic engineers on the faculty (Delatte and Rens, 2002).  Clearly, this approach depends on the availability of qualified and interested faculty.

Another method is to use case studies in capstone (Senior) design projects (Delatte and Rens, 2002).   This is also dependent on the interested and qualified faculty, as well as on the availability of appropriate projects (which must be sufficiently free of liability concerns).

These two approaches offer great depth in the topic, but due to their inherent limitations, their application is likely to remain limited.  As a result, even at colleges and universities where courses are offered in this area, few undergraduates are likely to be able to take them.  While some might argue for a required stand-alone course in failure analysis for all undergraduate civil engineering students, the argument is likely to fall on deaf ears as programs shrink their credit hour requirements.  However, this book would be an excellent text for a civil engineering failure analysis course.

A more promising approach is to integrate failure case studies into courses throughout the curriculum.  Many professors have done this on an informal basis for years.  The author used this approach at the United States Military Academy (USMA) while teaching two courses in engineering mechanics, Statics and Dynamics and Mechanics of Materials (Delatte, 1997).  He continued the approach in engineering mechanics and civil engineering courses at the University of Alabama at Birmingham (UAB) (Delatte, 2000, Delatte and Rens, 2002, Delatte, 2003) and at Cleveland State University.

Why Study Failures?

In a survey conducted by the ASCE Technical Council on Forensic Engineering (TCFE) Education Committee in December 1989, about a third of the 87 civil engineering schools responding indicated a need for detailed well-documented case studies.  The University of Arizona said ASCE should provide such materials for educational purposes and Swarthmore College suggested ASCE should provide funds for creating monographs on failures that have occurred in the past (Rendon 1993a).

The ASCE TCFE conducted a second survey in 1998, which was sent to all Accreditation Board for Engineering and Technology (ABET) accredited engineering schools throughout the United States (Rens et al, 2000a).  Similar to the 1989 survey, the lack of instructional materials was cited as a reason that failure analysis topics were not being taught.  One of the unprompted written comments in that survey was a selected bibliography is needed on the topic, which could be accessed via the Internet.

The use of case studies is also supported by the latest pedagogical research.  From Analysis to Action ( Center, 1996) refers on page 2 to textbooks lacking in practical examples as an emerging weakness.  Much of this document refers specifically to the breadth of understanding, which may be achieved through case studies.  Another issue addressed (Center, 1996, p. 19) is the need to incorporate historical, social, and ethical issues into courses for engineering majors. The Committee on Undergraduate Science Education in Transforming Undergraduate Education in Science, Mathematics, Engineering, and Technology (Committee, 1999) proposes that as many undergraduate students as possible should undertake original, supervised research.  How People Learn (Bransford et al., 1999, p. 30) refers to the need to organize knowledge meaningfully, in order to aid synthesis and develop expertise.

This work raises the question of whether failure analysis is merely tangential to, or is, in fact, fundamental to, civil engineering education.  Put another way, are failure case studies simply interesting, or should they be an essential component of a civil engineering curriculum?

Failure Case Studies and Accreditation Requirements

ASCE TCFE Education Committee surveys of civil engineering departments reported in 1989 and 1998 (Rendon-Herrero, 1993a, 1993b, Bosela, 1993, Rens et al., 2000) found that many respondents indicated a need for detailed, well-documented case studies.  Some of those replying felt strongly that incorporation of failure case studies should not become part of accreditation evaluations.  However, unless something is specifically mandated by the Accreditation Board for Engineering and Technology (ABET), it is likely to be a low priority for inclusion in a curriculum.

There is certainly an argument to be made that failure analysis should be mandated by ABET.  It may also be argued that, in a sense, it already is.  Under Criterion 3, Program Outcomes and Assessment,

Engineering programs must demonstrate that their students attain:

(a) An ability to apply knowledge of mathematics, science, and engineering

(b) An ability to design and conduct experiments, as well as to analyze and interpret data

(c) An ability to design a system, component, or process to meet desired needs within realistic constraints such as economic, environmental, social, political, ethical, health and safety, manufacturability, and sustainability

(d) An ability to function on multi-disciplinary teams

(e) An ability to identify, formulate, and solve engineering problems

(f) An understanding of professional and ethical responsibility

(g) An ability to communicate effectively

(h) The broad education necessary to understand the impact of engineering solutions in a global, economic, environmental, and societal context

(I) a recognition of the need for, and an ability to engage in life-long learning

(j) A knowledge of contemporary issues

(k) An ability to use the techniques, skills, and modern engineering tools necessary for engineering practice.

Programs often struggle with how to document that their graduates understand the impact of engineering solutions in a global and societal context, engage in life-long learning and demonstrate knowledge of contemporary issues (criteria h, i, and j, respectively).  These outcomes can be difficult to demonstrate.  One method of documenting these particular outcomes is to include case studies of failed engineering works in the curriculum.  Many case studies show the direct societal impact of failures and demonstrate the need for life-long learning by highlighting the evolutionary nature of engineering design procedures.

Case studies also address the revised criterion c, design within realistic constraints.  Case studies and specifically failure case studies illuminate how economic, environmental, social, political, ethical, health and safety, manufacturability, and sustainability impact design, behavior, and performance of engineered systems.

Criteria for civil engineering programs are more specific.  Students must demonstrate an understanding of professional practice issues such as procurement of work, bidding versus quality-based selection processes, how the design professionals and the construction professions interact to construct a project, the importance of professional licensure and continuing education, and/or other professional practice issues.These professional issues are integral to many of the case studies addressed through the workshops.  As an example, some project failures may be traced to poor interaction and communications between the designers and the builders.

Failure Case Studies and the Civil Engineering Body of Knowledge

The ASCE report Civil Engineering Body of Knowledge for the 21st Century: Preparing the Civil Engineer for the Future , prepared by the Body of Knowledge Committee of the Committee on Academic Prerequisites for Professional Practice, goes beyond ABET.  The Body of Knowledge (BOK) defines 12 outcomes.  The first 11 are identical to the ABET a k. BOK outcomes 12-15 are:

• An ability to apply knowledge in a specialized area related to civil engineering.
• An understanding of the elements of project management, construction, and asset management.
• An understanding of business and public policy and administration fundamentals.
• An understanding of the role of the leader and leadership principles and attitudes.

For those failures with complex technical causes, failure case studies may be used to deepen understanding within specialized civil engineering areas (outcome 12).  Failures can expose and highlight the subtleties of structural and system behavior that are the province of the specialist.  Some specialties, such as earthquake and geotechnical engineering, have historically relied heavily on failure case studies to advance the state of the practice.

Outcomes 13, 14, and 15 may also be addressed through failure case studies.  In many failures, the technical issues involved may not be particularly complex or unusual.  Instead, breakdowns may come in the project management and construction processes or in the management of the facility by the owner (outcome 13).  Pressures of business and public interests may encourage engineers to take short cuts, with harmful consequences (outcome 14).  Some failures might have been averted with stronger leadership (outcome 15).  A more thorough discussion of the relationship between failure case studies, ABET, and BOK outcomes is provided in Delatte (2008).

Pedagogical Benefits of Case Studies

Learning that occurs in multiple learning skills domains and exercises higher level learning skills is crucial to successful engineering education.  This must, however, occur efficiently because engineering curricula are already overcrowded.  This is one reason why failure case studies should be an essential part of engineering classes.  The single activity of using a case study as part of a traditional course lesson plan simultaneously fosters learning in three different learning domains, thus making learning more efficient:

1. Affective: The failure is interesting and sometimes dramatic, thus increasing initial acquisition and permanent retention of knowledge from the learning exercise because of the emotional state of the student during the learning process.

2. Cognitive: The failure validates the science, showing that our engineering tools work and thus motivating the students to learn and retain more knowledge.

3. Social: Students discover or rediscover how engineering decisions impact individuals, communities, and society

As a result of case study inclusion, students will demonstrate an ability to process failure analysis, apply ethics in engineering, and demonstrate an understanding of the engineer’s role in and their value to society.  Students will also demonstrate a greater depth of knowledge by developing intuition about the expected behavior of engineered systems, understanding load paths, and better visualizing the interaction of components of engineered systems.  Finally, students should experience a change in attitudes about quality engineering as a result of studying failures of engineered systems.

Use of Cases

Some of the ways to use case studies and a suggested format were reviewed in Delatte and Rens (2002).  These include:

• Introductions to topics use the case to illustrate why a particular failure mode is important.  Often the importance of a particular mode of failure only became widely known after a failure examples include the wind-induced oscillations of the Tacoma Narrows Bridge and the failure of Air Force warehouses in the mid-1950’s that pointed out the need for shear reinforcement in reinforced concrete beams.
• Class discussions link technical issues to ethical and professional considerations.  Add discussions of the standard of care, responsibility, and communications to coverage of technical topics.
• Example problems and homework assignments calculate the forces acting on structural members and compare them to design criteria and accepted the practice.  This can have the added benefit of requiring students to compare design assumptions to actual behavior in the field under service loads and overloads.
• Group and individual projects have students research the cases in depth and report back on them.  This will also help build a database of cases for use in future classes.  Students gain valuable research, synthesis, and communication skills.

Common Threads

The use of case studies as common threads through the curriculum can best be illustrated through an example.  The 1907 collapse of the Quebec Bridge during construction, discussed in Chapter 3, represents a landmark of both engineering practice and forensic engineering.  The Quebec Bridge was the longest cantilever structure attempted until that time.  In its final design, it was 548.6 m (1,800 ft) long.   The bridge project was financially troubled from the beginning.  This caused many setbacks in the design and construction.   Construction began in October 1900.   In August 1907, the bridge collapsed suddenly.  Seventy-five workers were killed in the accident, and there were only eleven survivors from the 86 workers on the span.

A distinguished panel was assembled to investigate the disaster.  The panel’s report found that the main cause of the bridge’s failure was the improper design of the latticing on the compression chords.  The collapse was initiated by the buckling failure of Chord A9L, immediately followed by Chord A9R.  Theodore Cooper had been the consulting engineer for the Quebec Bridge project, and most of the blame for the disaster fell on his shoulders.  He mandated unusually high allowable stresses and failed to require recalculation of the bridge dead load when the span was lengthened.

This case study illustrates a number of important teaching points from engineering courses.

1) Statics truss analysis.  The bridge was a cantilever truss.  As the two arms of the bridge were built out from the pier, the moments on the truss arms increased, and the compressive stresses in the bottom chords of each arm also increased.   Both the method of joints and the method of sections, traditionally taught in statics courses, may be used to analyze the compressive strut forces at the different stages of bridge construction.  See Chapter 2.

2) Mechanics of Materials allowable stresses.  Mr. Cooper increased the allowable stresses for his bridge well beyond the limits of accepted engineering practice, without experimental justification.   He allowed compressive stresses that were considerably higher than that provided by the modern AISC code and were highly unconservative given the state of knowledge at the time.  The compression struts of the truss were too large to be tested by available machinery, so their capacity could not be precisely known.  Development of engineering codes and standards requires tradeoffs between structural safety and economy, and there must be mechanisms for resolving disputes between competing criteria.  See Chapter 3, which has this case study.

3) Mechanics of Materials structural deformation.  The bending of the critical A9L member reached 57 mm (2-inches) and was increasing at the time of the collapse.  The bending was discussed at the site and by Mr. Cooper, attempting to supervise the project from New York, but no action was taken.  In fact, the bending showed that the member was slowly buckling.

4) Mechanics of Materials buckling of columns and bars.  The critical A9L compression member failed by buckling.  It was a composite section, which meant that it required lacing to require the members to bend together.  The moment of inertia, and buckling capacity, of the composite section, may be compared to that of the individual truss members, showing the importance of the latticing system.

5)  Structural Analysis predicting, computing, and correcting dead loads.  One critical error made in the design was that the dead load was greatly underestimated.  When material invoices showed that 17-30 % more steel had gone into parts of the structure than had been planned for in the design, no attempt was made to analyze the bridge for the new loads.  See Chapter 4.

6)The design of Steel Structures analysis and design of built-up members.  This point follows from the discussion of buckling of columns and bars, above.  Many existing steel bridges use built-up members, and engineers involved in assessing and rehabilitating such structures need to know how to evaluate member capacity and likely failure modes.  See Chapter 6.

7)  Engineering Management the requirement for the engineer of record to inspect the work on the site.  Mr. Cooper attempted to supervise the construction of a bridge in Quebec from his office in New York City.  When problems arose, the problems were referred to him for a decision.  The absence of an onsite engineer with authority to stop the work meant that there was no way to head off the impending collapse.  A meeting was held to decide what to do, and the bridge collapsed just as the meeting was breaking up.

8) Engineering Ethics professional responsibility.  Mr. Cooper planned for the Quebec Bridge to be the crowning achievement of an illustrious career as a bridge engineer.  However, by this time his health was poor and he was unable to travel to the site.  He was also poorly compensated for his work.  Following the collapse, organizations such as ASCE began to define better the responsibility of the engineer of record.  Unfortunately, the collapse of the Hyatt Regency Walkways three-quarters of a century later showed that much remains to be done.

As an example, the following problem statement may be used in a structural analysis or capstone design/professionalism course, in conjunction with the Quebec Bridge collapse case study.  The problem should be assigned before the discussion of the case study, probably as an overnight homework.  Following discussion of the case study, students should be better able to identify potential problems with an unusual construction technique.

You are the engineer for a cantilever truss bridge across a major river in North America.  The bridge owner has asked you to prepare specifications, including allowable stresses, and has emphasized that they have a very shaky financial situation.   The bridge was initially intended to be 1,600 feet long to reduce the cost of the piers, they have been moved into shallower water and it will now be 1,800 feet long.  When completed, it will be the longest bridge of this type in the world.

Problem:  list all of the things you can think of that can go wrong during this bridge construction project.

Once the collapse case has been discussed, the problem may be reassigned with the additional assignment to propose communication and quality control measures to ensure against collapse.  Students should refer to the case study in formulating their answers.

The case study materials developed so far have been very well received by faculty across a wide range of civil engineering programs, as well as some other related programs.  To date, however, the benefits identified have been anecdotal (although nevertheless impressive).  There remains a need to identify, quantify, and assess the impact of case studies on teaching and learning.

Surveys have found widespread agreement that faculty consider failure case studies important and useful (Rendon-Herrero, 1993a, 1993b, Bosela, 1993, Rens et al., 2000).  Several of the faculty failure case study workshop participants have reported back that the case studies have been excellent for motivating their students to learn.  So far, the formal assessment of the impact of using case study materials in courses has been limited.  Some assessment methods and results have been published by Delatte et al. (2007, 2008).

Desired student learning outcomes are:

• Improved understanding of technical issues in civil engineering and engineering mechanics
• Improved understanding of ethical, professional, and procedural issues in civil engineering and engineering mechanics

The primary assessment question is: In what ways does the use of failure case studies improve students ability to demonstrate competencies that prepare them to be better professional civil engineers?

The assessment questions are as follows:

• Does the use of failure case studies improve student’s ability to demonstrate competencies that better prepare them as professional engineers for the 21st century?
• How does the implementation of failure case studies encourage deep learning in civil engineering students?
• What has been the time commitment and value-added experience for faculty who integrate failure case studies in the course curriculum that improves student learning of civil engineering concepts?

For Delatte’s papers published in ASEE Conference Proceedings, go the ASEE Proceedings web page, and use the “Author” search on Delatte

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May 29, 2024   |   Kevin Buda, DO ; Jay Sengupta, MD

Expert Analysis

Quick Takes

• Clinicians will increasingly encounter heart rhythm data generated from consumer-grade devices.
• Consumer-grade smartphone-paired devices and smartwatches have very high sensitivity and specificity for atrial fibrillation.
• The specificity for arrhythmias with regular R-R intervals is very poor.

As the availability of smartphone-paired devices and smartwatches increases, clinicians will increasingly encounter data generated from consumer-grade devices. This expert analysis reviews several common consumer-grade devices, their specificity for detecting atrial fibrillation (AF), and the limitations of their use.

Most consumer-grade devices for detecting arrhythmias use photoplethysmography (PPG). This technology measures volumetric changes in blood flow on the basis of the intensity of reflected light measured from the skin's surface. This signal generates peaks proportional to pulsatile blood flow, with the peak-to-peak interval proportional to the R-R interval. Given this method's ease of detecting irregularity, PPG technology has primarily been validated for detecting AF.

The broadened availability of consumer-grade devices may increase the detection of AF in the subclinical phase. With stroke as the initial manifestation of AF in almost one-quarter of cases, early AF detection may help relieve its burden as a leading cause of disability in the United States. 1

The Accuracy

• Apple Watch. The Apple Watch (Apple Inc., Cupertino, California) monitors heart rate and rhythm using PPG. Newer models can also record an on-demand single-lead electrocardiogram (ECG). The Apple Heart Study investigators enrolled >400,000 participants without AF. People who received an irregular pulse notification had telemedicine visits with a clinician and received an ambulatory ECG monitor. Of the 2,064 patients with irregular pulse notifications, the positive predictive value (PPV) for AF was 84%. 2 Notably, Apple recently received a cease-and-desist order on some Apple Watches after the United States International Trade Commission (USITC) ruled that Apple Watch technology infringes on oxygen saturation patents held by Masimo Corporation (Irvine, California). The cease-and-desist order on relevant Apple Watches is scheduled to take effect on December 26. This order may significantly reduce the number of Apple Watches that are available for purchase until patent issues have been resolved.
• Kardiamobile. Kardiamobile (AliveCor, Mountain View, California) is a small handheld device that can provide a 30-sec single-lead ECG. One study included monitoring participants three times daily and whenever they felt palpitations, with findings of a higher rate of AF detection with the Kardiamobile device than with 24-hour ECGs (9.4% vs. 2%). 3 In another study, >1,000 patients without a history of AF were randomized to standard care or twice-weekly monitoring with Kardiamobile, with findings of a 3.8% detection rate for AF in the Kardiamobile arm compared with <1% in the standard-care arm. 4
• Fitbit. Fitbit (Google, Mountain View, California) is a wrist-worn device with PPG technology with 37 million monthly users as of 2022. 5 Similar to the Apple Watch, some newer models also incorporate the ability to perform a single-lead ECG. The Fitbit Heart Study had a similar design to the Apple Heart Study; >400,000 participants enrolled. Routine ambulatory ECG monitoring occurred in patients with irregular rhythm notifications. Among 1,057 participants with an irregular heart rate notification and an analyzable confirmatory ambulatory ECG, the PPV of irregular rhythms for AF when using consumer-grade screening with reflex to medical-grade confirmation was 98.2%. 6

Overall Efficacy

The findings of two meta-analyses included high specificity (94%) and sensitivity (96%) for AF detection with smartphones and noninferiority of smartwatches compared with medical-grade devices. 7,8

Benefits Compared With Medical-Grade Monitoring

• They are more widely available. 4
• They do not require a prescription.
• They can detect arrhythmias independently of ECG checks when the patient is free of symptoms.
• They have very high sensitivity and specificity for detecting AF. 7,8
• They can help monitor patients with established asymptomatic AF to assess AF rate and burden.

Limitations Compared With Medical-Grade Devices

• They are not worn continuously and need to be removed for charging. Therefore, their sensitivity for infrequent paroxysmal arrhythmias is lower.
• The specificity for arrhythmias with regular R-R intervals is very poor. 9
• Monitoring in patients with a low pretest probability of arrhythmias increases the false-positive rate.
• There are no guideline recommendations on what to do with information from consumer-grade devices.
• The large volume of data obtained from consumer-grade devices may further contribute to an already strained clinician workforce.

Future Directions

Given the higher false-positive rate in patients with a low pretest probability of AF, future studies need to determine the patients most likely to benefit from ambulatory monitoring. Further, it is unknown whether increased AF detection on consumer-grade heart rhythm monitoring increases appropriate anticoagulation prescription or lowers cardioembolic stroke risk.

The ongoing Heartline Study will assess the impact of AF detection with the Apple Watch on clinical outcomes. The primary endpoint is the time from randomization to the detection of AF. Secondary endpoints include health resource utilization, cost-effectiveness, and a composite including stroke, heart failure hospitalization, and all-cause death. 10

• Freedman B, Potpara TS, Lip GYH. Stroke prevention in atrial fibrillation. Lancet 2016;388:806-17.
• Perez MV, Mahaffey KW, Hedlin H, et al.; Apple Heart Study Investigators. Large-scale assessment of a smartwatch to identify atrial fibrillation. N Engl J Med 2019;381:1909-17.
• Koh KT, Law WC, Zaw WM, et al. Smartphone electrocardiogram for detecting atrial fibrillation after a cerebral ischaemic event: a multicentre randomized controlled trial. Europace 2021;23:1016-23.
• Halcox JPJ, Wareham K, Cardew A, et al. Assessment of remote heart rhythm sampling using the AliveCor heart monitor to screen for atrial fibrillation: the REHEARSE-AF study. Circulation 2017;136:1784-94.
• Statista. Number of active users of Fitbit from 2012 to 2022 (in millions) (Statista website). 2023. Available at: https://www.statista.com/statistics/472600/fitbit-active-users/ . Accessed 05/15/2024.
• Lubitz SA, Faranesh AZ, Selvaggi C, et al. Detection of atrial fibrillation in a large population using wearable devices: the Fitbit Heart Study. Circulation 2022;146:1415-24.
• Prasitlumkum N, Cheungpasitporn W, Chokesuwattanaskul A, et al. Diagnostic accuracy of smart gadgets/wearable devices in detecting atrial fibrillation: a systematic review and meta-analysis. Arch Cardiovasc Dis 2021;114:4-16.
• Elbey MA, Young D, Kanuri SH, et al. Diagnostic utility of smartwatch technology for atrial fibrillation detection - a systematic analysis. J Atr Fibrillation 2021;13:[ePub ahead of print].
• Rajakariar K, Koshy AN, Sajeev JK, Nair S, Roberts L, Teh AW. Modified positioning of a smartphone based single-lead electrocardiogram device improves detection of atrial flutter. J Electrocardiol 2018;51:884-8.
• Gibson CM, Steinhubl S, Lakkireddy D, et al.; Heartline Steering Committee. Does early detection of atrial fibrillation reduce the risk of thromboembolic events? Rationale and design of the Heartline study. Am Heart J 2023;259:30-41.

Clinical Topics: Arrhythmias and Clinical EP, Atrial Fibrillation/Supraventricular Arrhythmias

Keywords: Atrial Fibrillation, Wearable Electronic Devices

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Future Cities

Shaping Tomorrow’s Cities

Fostering resilient and vibrant urban environments.

May 29, 2024 60 Minute Read

• Chapter 1 The Shape of American Cities
• Chapter 2 The Urban Renaissance
• Chapter 3 Disruption in the Pandemic Era
• Chapter 4 Building on Success
• Chapter 5 The Conversion Potential
• Chapter 6 Keys to a Thriving City
• Chapter 7 A Path Forward
• Chapter 8 SWOT Analysis: Los Angeles & New York
• Chapter 9 Case Study: Transforming Manhattan’s Financial District: The Making of a Neighborhood
• Chapter 10 Appendix: Methodology

Executive Summary

While cities have always been business and social hubs, they have undergone much evolution and oftentimes reinvention as economies advanced, technology progressed and society’s needs changed over time. American cities are much younger than those in many other parts of the world, yet would still be unrecognizable today by those who originally built them. The current evolution of American cities in response to the rise in remote working represents another waypoint in their journey.

CBRE has analyzed the real estate implications of American cities’ current evolution to help inform business and public policy choices. The study offers insights, recommendations and a case study about shaping the future of cities. We have designed a mapping tool that identifies clusters of urban characteristics across mixed-use, business and residential districts and their effect on real estate market fundamentals. This in turn offers insights about how cities can reinvent themselves.

• Super Cities: Los Angeles, New York
• Mixed Majors: Boston, Chicago, Philadelphia, San Francisco, Seattle, Washington, D.C.
• Sprawling Darlings: Atlanta, Dallas, Denver, Houston, Phoenix
• Developing Destinations: Austin, Charlotte, Miami, Nashville, Orlando, Tampa
• Suburban growth that dominated the last half of the 20th century gave way to an urban renaissance beginning in the 1990s and accelerating in the 21st century. Many baby boomers and millennials moved into urban neighborhoods in search of a walkable live-work-play environment.
• Office-using job growth contributed to the 21st-century urban renaissance and became ever more concentrated in CBDs, leading to a boom in office and residential construction. The downside was congestion and increased commute times for suburbanites, often compounded by a lack of modern infrastructure.
• Disruption by the COVID pandemic in the early 2020s brought 30 years of urban renaissance to a halt. Many city dwellers moved to the suburbs, and domestic in-migration was fastest in the suburban areas of the Sprawling Darlings and Developing Destinations. Density became a public health concern and remote work a necessity for many office-using jobs, driving out-migration that continues today as millennials age and buy homes.
• Commercial real estate has been particularly affected by these demographic shifts and new working patterns. Public safety concerns also have made workers and visitors more reluctant to return to cities, especially in the Mixed Majors. The office sector has had an unprecedented rise in vacancy that is unlikely to return to pre-pandemic levels. Higher interest rates, also a legacy of the pandemic, have exacerbated the crisis.
• Future success of cities – and the role they play in their greater markets – is not guaranteed. Clearly identifying their strengths and weaknesses is required to inspire reinvention, successfully retrofit their urban cores and maintain their economic power and competitive advantage. The ultimate goal is to attract more residents, visitors, businesses and development that will drive urban vibrancy and tax revenue.
• Much of this reinvention will come through conversions or demolition of older, underutilized real estate. In most cities, the amount of conversion activity underway is not yet enough to be fully transformative, but data shows that targeted conversion activity can be a catalyst for broader change.
• We identified six keys that help cities to thrive: economic dynamism, demographic potential, lifestyle vibrancy, distinctive identity, responsive governance and resilient infrastructure. Each of these presents an opportunity to drive change.
• Public and private stakeholders have an integral role to play in shaping American cities. By having an all-hands-on-deck approach, the collective impact of experiences and rich data will drive insights and strategies to transform our cities.

Figure 1: Population Change in Top 30 Markets – 1970-2020

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