Probe - Vol. 15, No. 1, First Issue 2008
Who Says It's a Recession?
Corrosion can creep up on you
Estimates reveal that corrosion is costing the U.S. economy $300 billion per year in sectors such as utilities, transportation, infrastructure and manufacturing. Much of this corrosion occurs over time when the presence of moisture results in the general recession (loss of material) of metal components. Rusting iron alloys are perhaps the most well-known example of corrosion. In many instances iron corrosion is visible to the naked eye and can be monitored over time so repairs or replacements can be made when the component becomes unsafe or loses functionality.
There are, however, more insidious forms of corrosion that can go undetected, eventually resulting in an unexpected and potentially catastrophic failure. These forms usually involve the elevated stress in a component in the presence of a corrosive liquid or gas. In the design of a load-bearing component engineers usually consider the loads, or stresses, to which a component will be subjected, as well as the strength of the alloy, and then apply a factor of safety.
Although this methodology generally results in low overall stresses in the component, it sometimes cannot account for geometric effects that can locally cause the stress to rise above acceptable limits, such as a sharp corner radius, crevice, weld and other sharp features such as threaded holes. These geometric crack-like features can also occur via flaws inherent to the alloy itself, such as non-metallic inclusions and porosity that can be flattened into sharp crack-like defects through normal rolling and forging processes.
The combined effect of these highly localized stresses and a corrosive environment can produce preferential corrosion in these locations, leading to cracks that slowly, but continuously, grow over time. Once these cracks reach a critical length and stress state, the fracture toughness of the material will be exceeded, and the component may fail catastrophically. This generic description of stress-induced environmental cracking manifests itself in many materials under a wide variety of operating conditions. High-temperature, highstrength nickel superalloys used in gas turbines operating at temperatures approaching 1,200 degrees F have, in certain instances, shown a susceptibility to cracking in the presence of oxygen (i.e. air). Other examples include the cracking of nickel and stainless steel alloys in the presence of hydrogen sulfide and the cracking of aluminum and stainless steel alloys in aqueous solutions containing chlorides.
Crane Engineering regularly encounters varied examples of these failures, especially involving stainless steel products, such as those used in the food and dairy industry, as well as stainless steel and brass plumbing fixtures used in the home. Our stateof- the-art metallurgy and microscopy laboratory and decades of materials expertise enable the swift and dependable investigation, identification and mitigation solutions for these and other types of corrosion.
Jeff Pfaendtner, P.E., Ph.D.
Materials Scientist
All Fired Up
Ignitable liquid residue analysis yields answers
What is seemingly unimportant to the untrained eye might be just what fire scene investigators are looking for. Their primary role – a challenging one, to be sure – is to identify the origin and cause of a fire, whether accidental or incendiary. At the scene they use their knowledge of the principles of combustion and fire behavior to reconstruct the events of a fire and collect physical artifacts for detailed testing. The fire investigator then calls on the expertise of laboratory specialists to conduct a chemical analysis for the presence of ignitable liquid residues (ILRs) in the fire debris evidence.
The American Society for Testing and Materials (ASTM) has established a series of test methods, guides and practices that are adhered to by reputable laboratories and analysts. Using these guidelines, laboratory technicians extract fire debris evidence utilizing passive headspace adsorption and then analyze it using gas chromatography/ mass spectroscopy (GC/MS).
Using ignitable liquid standard comparisons as well as reference samples, the resulting chromatogram is evaluated for patterns characteristically seen in petroleum products. It may seem this would be obvious, but it is not, as petroleum products are used in a vast amount of consumer products such as copy paper, newspaper print, solvents in glues, and adhesives used in floor coverings and footwear. Since these products are often found at the scene of a fire, they can contribute foreign ignitable liquid residues to a sample. As a result, the simple presence of an ILR is not conclusive evidence. Instead it takes a trained analyst to identify specific ILR patterns and rule out extraneous components as well as pyrolysis and combustion products. Once an ignitable liquid residue had been identified it is placed into the appropriate ASTM class, and the investigator is notified of the results so the case can be resolved.
Crane Engineering now provides free ILR sampling kits, which come complete with detailed instructions (click here for a PDF) on how to collect the evidence. Please contact me to obtain a kit and ask any questions you may have.
Kerri Schnell
Chemistry Technician
Engineers Without Borders
Making a difference around the world
You've probably heard of Doctors Without Borders. Occasionally they appear on the television news providing much-needed medical treatment in remote locations. Maybe you haven't heard, however, about Engineers Without Borders USA (EWB), a non-profit humanitarian organization that was established in 2000 to partner with developing communities worldwide to improve their quality of life. This partnership involves the implementation of sustainable engineering projects, while engaging and training internationally responsible engineers and engineering students.
Engineering students at the University of Minnesota have an opportunity to share their skills and gain valuable knowledge through involvement in EWB's University of Minnesota Chapter (EWB-UMN). Recent projects include clean water supply, hygienic sanitation, plastic waste re-processing and solar panel installation. In the past two years the group has fundraised and completed a solar-powered well pump at a school in Amponsah, Ghana, and a sustainable agriculture park in Chuwi Tinamit, Guatemala. New projects in Uganda, Guatemala, and Haiti are currently in the design and fundraising stages.
EWB-UMN projects require creative and critical thinking that lead to elegant and appropriate design solutions, advanced communication skills, and the ability to work as an efficient team in extreme environments. These experiences are more relevant today than ever before as engineering students are entering into a rapidly changing global environment where sustainability, integrated engineering, and global teamwork are essential.
EWB-UMN is always looking for professional mentors, equipment and financial support. Other student chapters in the Upper Midwest include North Dakota State University; South Dakota State University; South Dakota School of Mines and Technology; Marquette University; Milwaukee School of Engineering; and the University of Wisconsin – Madison, Milwaukee and Platteville.
Crane Engineering recently provided financial support to the University of Minnesota chapter and encourages others to find out more and consider doing the same. More details, including donor information, is available at www.tc.umn.edu/~ewb/.
Nate Knutson
Public Relations Chair
Engineers Without Borders - University of Minnesota
Cross Sections
| Expanding our knowledge. Kerri Schnell, chemistry technician, is attending the International Symposium on Fire Investigation in May 2008. This is a conference dedicated solely to fire investigation science, research, technology and methodology. | Expanding the team. Crane Engineering is seeking to add a mechanical engineer to its consulting team. If you would like more information, please visit our news section or contact Robin Krier, robink@CraneEngineering.com. | EVEN SHARPER, EVEN CLEARER, EVEN MORE PRECISE. Crane Engineering is pleased to announce that it has added a Keyence Digital Microscope VHX-600 to its laboratory. The microscope offers an incredibly fine 3-D image displayed on a UXGA high-resolution LCD monitor, giving clients an even more comprehensive view of the object in question. The microscope is compact, flexible and mobile – it can actually be taken off site to view large, immobile objects that can't easily be brought to the laboratory. It features the world's first 54 million-pixel 3CCD handheld camera and has a graphic engine that enables observation of profiles not possible using conventional systems. To find out more about this exciting new piece of equipment and how it could benefit your next project, contact Jeff Pfaendtner. |