It is essential when beginning a root-cause failure analysis involving metallic materials to collect and maintain the as-found physical evidence properly prior to detailed examinations. This has two objectives. In all cases collecting and protecting the evidence in its undisturbed condition provides the best opportunity to derive meaningful good results from the subsequent analyses. Secondly, in a legal proceeding lack of attention to these matters can produce the accusation of spoilation of evidence. As a minimum this will cause presentation problems for the offending party in the suit. At worst such deficiencies by that party may cause the case to be thrown out.
Aluminum alloy materials are well known for their light weight and strength-to-weight ratios. They are also susceptible to several forms of corrosion. Relative to other metals, their natural electrochemical potential places them adjacent to other very susceptible (active) metals such as magnesium (Mg) and zinc (Zn) in a traditional galvanic series in seawater. However, Al alloys naturally form a very thin, protective (passive) oxide film on their surface when exposed to oxygen. This film prevents corrosion as long as it is maintained over the surface. Pitting corrosion is a common form of attack on aluminum. This is typically caused by exposure to halide ions, chloride ions being the most common type found in corrosive media, that breakdown the passive film at discreet spots. This permits pits to initiate and grow.
Often when engineers consider mechanical fatigue they envision cyclic, reversing stresses in a spinning shaft or possibly the up and down flex of aircraft wings. Rolling contact fatigue (RCF) or the associated mechanical wear is an important, closely related process to the traditional mechanism of fatigue but with distinct differences. RCF is also often known as spalling.
This term raises some vital issues that the engineer should be aware of when using it. First several definitions are available and thus it is perceived differently by different groups and individuals. From a legal standpoint, in many states, using the term to describe a product that was involved in an incident involving an injury means that the designer or manufacturer of that product may be financially liable for the injury. Engineers sometimes use the term simply to indicate an imperfection in a product without intending its frequent legal use. Further the engineer realizes that no material and no finished product is perfect. However, these variations from perfection do not necessarily mean they were cause for failure and thus the injury that may occur in a given incident. Some product liability attorneys may not readily acknowledge or understand this distinction.
The optimal time to make decisions and take actions to minimize potential failures of equipment, facilities and components is during their design. This two-part blog post provides an overview of the types of issues involved and specific actions that can be useful to the design engineer. Archived blog posts (at www.dmme-engineering.com) that discuss specifics are provided parenthetically.
Four, tri-lobe pumps were damaged and required extensive repair during the latter stages of construction for a modification in a pharmaceutical manufacturing plant. The economic loss was significant and the general contractor for the work paid the plant's owner for the loss. The renovated units were installed and are in use. However, the general contractor then sued one of its subcontractors - a welding contractor that fabricated and completed weld joints between piping sections on the inlet side of the pumps. The general contractor claimed poor quality welds in the piping permitted loosened weld fragments to enter the pumps during the required water flow verification of the system and this caused the damage.
Most realize that damage due to corrosion of metals is costly - but what specifically is that cost and what is included in the total? A study completed in 2002 sponsored by the Federal Highway Administration (FHWA), the National Association of Corrosion Engineers (NACE International) and implemented by CC Technologies Laboratories (now part of DVN) addressed those questions.
Material selection entails picking an engineering material - either metal alloy or non-metal - that is inherently resistant to the particular corrosive environment and also meets other criteria. Variables that will affect corrosion are established along with materials that may provide suitable resistance for those conditions. Obviously other requirements such as cost and mechanical properties of the potential materials must be considered.
Pin-hole leaks from a fire-control sprinkler piping system just above the false ceiling of multiple rooms in an office building resulted in a suit against three parties involved with supplying the system. The plaintiff - a financial service organization that owned the building - had much computerized transaction data stored on magnetic tapes in several rooms damaged or destroyed by the incident. The monetary loss was major. The leaks occurred within two years after the system was installed. This period is clearly far short of the expected life of the system. Defendants in the case included the supplier of the piping used in the system, the engineering firm that designed it and the installation contractor.
A variety of low-voltage electronic devices may fail to operate properly because of exposure to certain corrosive, gaseous environments. Susceptible items include consumer products such as microwave ovens, audio equipment, TV's and personal computers as well as many types of industrial sensors and automatic control devices. Failure generally occurs because of specific application factors. These include the severity of the environment, the presence or absence of atmospheric sealing of components within the device and the metals used at critical internal locations. Frequently complete failure doesn't occur but normal operation is erratic.