Vacuum, damage

Lees (Loss Prevention in the Process Industries, 2d ed., Butter-worths, London, 1996), BP (Hazards of Trapped Pressure and Vacuum, 2003), and Kletz (What Went Wrong —Case Histories of Process Plant Disaster, Gulf Publishing Company, 1989) include additional case histories providing valuable lessons about how equipment failures and human errors can combine to inflict vacuum damage. 

Water has the unique ability to expand 1570 times when changing from a liquid to a vapor, and to contract 1570 times when it is condensing. To visualize this dramatic contraction, just think that a typical rail tank car filled with steam at atmospheric pressure could condense to the volume of 10 or 11 gallons of water. [1] These properties can result in destructive vacuum damage as just shown. The explosive expansion from water to steam can result in a catastrophic incident as the next case history graphically demonstrates. 

Typically, PIXE measurements are perfonned in a vacuum of around 10 Pa, although they can be perfonned in air with some limitations. Ion currents needed are typically a few nanoamperes and current is nonnally not a limiting factor in applying the teclmique with a particle accelerator. This beam current also nonnally leads to no significant damage to samples in the process of analysis, offering a non-destmctive analytical method sensitive to trace element concentration levels. 

Special drying methods, such as superheated steam, solvent, vacuum, infrared radiation, and high frequency dielectric and microwave heating, are occasionally employed when accelerated drying is desired and the species being dried can withstand severe conditions without damage. None of these methods is of significant commercial importance. 

Hand and power tool cleaning is used on ships mostly for spot repair of damaged areas. Hand tools include scrapers, wire bmshes, and sanders. Electric and pneumatic power tools, which include grinders and needle guns, clean faster and more thoroughly than hand tools. Most power tools have vacuum lines coimected to collect paint debris. 

Cavitation Formation of transient voids or vacuum bubbles in a liquid stream passing over a surface is called cavitation. This is often encountered arouna propellers, rudders, and struts and in pumps. When these bubbles collapse on a metal surface, there is a severe impact or explosive effec t that can cause considerable mechanical damage, and corrosion can be greatly accelerated because of the destruction of protective films. Redesign or a more resistant metal is generally required to avoid this problem. 

Note For molors thal are insulated other than by vacuum impregnation, it is recommended to rewind a damaged. stator with class F insulation, even if the original insulation was E or B. This... 

---