Nov 11
17
Protective Coatings
Protective coatings are the most commonly used method of corrosion control. Protective coatings can be metallic, such as the galvanized steel shown below, or they can be applied as a liquid “paint.” Most of the research and testing of protective coatings at the Kennedy Space Center is related to paint-like protective coatings.
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 (Courtesy of www.corrosion-doctors.org) |
Filiform corrosion occurs underneath protective coatings. The air conditioner on the left is starting to show rust stains due to problems with protective coating. The same types of problems are starting to appear on the aluminum airplane wing shown on the right.
Source: http://corrosion.ksc.nasa.gov/microbial.htm
Nov 11
17
Materials Selection
Most large metal structures are made from carbon steel-the world’s most useful structural material. Carbon steel is inexpensive, readily available in a variety of forms, and can be machined, welded, and formed into many shapes.
This large statue by Pablo Picasso in front of the Chicago city hall is made from a special form of carbon steel known as weathering steel. Weathering steel does not need painting in many boldly exposed environments. Unfortunately, weathering steel has been misused in many circumstances where it could not drain and form a protective rust film. This has given the alloy a mixed reputation in the construction industry.
Nov 11
17
What is MIG Welding?
MIG welding is an abbreviation for Metal Inert Gas Welding. It is a process developed in the 1940’s, and is considered semi-automated. This means that the welder still requires skill, but that the MIG welding machine will continuously keep filling the joint being welded.
MIG welders consist of a handle with a trigger controlling a wire feed, feeding the wire from a spool to the weld joint. The wire is similar to an endless bicycle brake cable. The wire runs through the liner, which also has a gas feeding through the same cable to the point of arc, which protects the weld from the air.
MIG welding is most commonly used in fabrication shops where production is high, and the possibility of wind blowing away your gas shielding is unlikely.
FACT OR MYTH?
“Small animals eating steel” is a myth. It is however a fact that local corrosion, occurring at very high rates and typically looking like clusters of pits, can be caused by chemical processes initiated by bacterial activity, i.e. bacterial corrosion exists. This phenomenon is sometimes described as “microbial corrosion” indicating that types of microbes other than bacteria may be involved in the process. The accepted technical term is “microbially influenced corrosion”. Bacterial corrosion most frequently occurs on cargo oil tank bottom plating. It occurs also in water ballast tanks, primarily on up-facing, horizontal surfaces.
By David Smith & John Demusz
An expansion joint and a pipe loop are two methods employed to safely absorb thermal expansion or contraction in piping systems due to thermal temperature changes. When design conditions exist, where an expansion joint or a pipe loop can be utilized, the major advantages of using an expansion joint are as follows:
- Space is inadequate for a pipe loop with sufficient flexibility.
- A minimum pressure drop throughout the pipe line is required and the absence of flow turbulence from the elbows and piping is required by process flow conditions.
Jan 11
7
What Is a Seismic Survey?
A seismic survey is used to investigate Earth’s subterranean structure and is mainly used for oil and gas exploration. This method uses the
principles of reflective seismology to acquire and interpret seismic data, which permits the estimation of the Earth’s composition. The technique is similar to that used by computerized axial tomography (CAT) scans, involving the analysis of seismic waves that travel through the Earth.