Examination visual

Examination of a ftuoropolymer surface visually shows the following t5q)es of degradation. They are based on visual manifestations only and do not refer to the underlying degradation mechanism. Underlying degradation mechanisms are covered in the failure analysis section (Ch. 10). 

This method is the simplest of all the methods and is capable of detecting surface flaws such as corrosion, contamination, surface finish and surface discontinuities on joints.47 The discontinuities on joints such as welds, seals, solder connections and adhesive bonds can be detected. General corrosion, qualitative pitting corrosion, stress-corrosion cracking, weld-heat-affected zone attack, erosion corrosion and other type of degradation can be observed by visual examination aided by microscopes with sufficient magnification. Degradation of plastics can also be detected by visual examination. Visual examination is also used in conjunction with other techniques, such as powerful microscopes. 

Holographic imaging can also lead to detection of defects and has been used in detection of defects in automobile clutch plates, brake drums, gas pipelines, high-pressure tanks and turbine blades. 

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Traditionally, least-squares methods have been used to refine protein crystal structures. In this method, a set of simultaneous equations is set up whose solutions correspond to a minimum of the R factor with respect to each of the atomic coordinates. Least-squares refinement requires an N x N matrix to be inverted, where N is the number of parameters. It is usually necessary to examine an evolving model visually every few cycles of the refinement to check that the structure looks reasonable. During visual examination it may be necessary to alter a model to give a better fit to the electron density and prevent the refinement falling into an incorrect local minimum. X-ray refinement is time consuming, requires substantial human involvement and is a skill which usually takes several years to acquire. 

Mercury thermometers are subject to separation of the mercury column or to inclusion of bubbles of the fiU gas. These may result from shipping and handling and cause a scale offset which can usually be seen upon visual examination, and they are always recogni2ed by a 0°C verification check. Manufacturers will suggest means by which these temporary defects may be cured. 

Inflated Diaphragm Method (ASTM D3886). This method is appHcable both to woven and knitted fabrics. The specimen is abraded by mbbing either unidirectionally or multidirectionally against an abradant having specified surface characteristics. The specimen is supported by an inflated mbber diaphragm under a constant pressure. Evaluation of abrasion resistance can be either by determination of the number of cycles required to wear through the center of the fabric completely or by visual examination of the specimens after a specified number of cycles. 

Phenol Coefficient Test. The first important attempt at standardizing testing methods was known as the phenol coefficient test (96). It has been modified several times, and is an official AO AC screening test recognized by EPA and PDA. The phenol coefficient test compares the activity of disinfectants to that of phenol, under specific conditions, to give a number that measures the activity of the chemical tested with respect to that of phenol, ie, the phenol coefficient. The AO AC method employs visual examination of bacterial growth in a nutrient medium. The Kelsey-Sykes test (1969) is a modified method popular in British circles. 

Visual Examination This consists of observation of the portion of components, joints, and other piping elements that are or can be... 

In-process examination. In-process examination comprises visual examination of the following as apphcable ... 

Testing Upon completion of shop fabrication and also during maintenance operations it is desirable hydrostatically to test the shell side of tubular exchangers so that visual examination of tube ends can be made. Leaking tubes can be readily located and serviced. When leaks are determined without access to the tube ends, it is necessaiy to reroll or reweld all the tube-to-tube-sheet joints with possible damage to the satisfactoiy joints. 

Close visual examination of internal surfaces using a low-power stereomicroscope revealed a coating of reddish iron oxides on the internal surface. A population of small, knoblike mounds of corrosion product resembling tubercles was present on the surface (Fig. 5.16). 

Visual examination of external surfaces revealed grooves and general metal loss (Figs. 7.24 and 7.25). Metal loss was caused by erosion-corrosion. However, the corrosive loss was more important than erosive loss, since metal loss was also substantial in low-flow regions. 

The unit was shut down, drained, and visually examined. Numerous branched cracks of the type shown in Fig. 9.21 were observed. Cracks were oriented longitudinally. 

Visual examinations disclosed that the cracks originated on both the internal and external surfaces, although there were more on the internal surface. Thin coatings of deposits partially covered both the internal and external surfaces. 

Visual examinations disclosed several cracks, each very tight and difficult to see. Examinations under a low-power stereoscopic microscope revealed many short cracks running parallel to the primary crack. 

Among the available nondestructive testing techniques are ultrasonic tests, eddy-current tests, air-underwater and hydrostatic tests, and visual examinations. All of these techniques must be executed by technically qualified personnel. 

The various forms of defects on the internal surface of this tube could be overlooked in a casual, visual examination. Closer observation, however, would disclose several forms of discontinuities, such as shallow gouges (Fig. 14.7) and particles of smeared metal (Fig. 14.8). These features are prominent in a distinct longitudinal zone (Fig. 14.9). 

Identification. If the notch left by incomplete penetration emerges at a visually accessible surface, visual examination, perhaps aided by magnetic-particle or liquid-penetrant techniques, may reveal the defect. Otherwise, ultrasonics, radiography, or eddy-current techniques may have to be used. 

Identification. Defects in welds due to laminations may be difficult to identify based solely on a visual examination. Typically, cracks from welding laminated metal cause jagged, stepwise tears in the base metal. The crack may propagate into the weld itself. 

Cautions. Sensitization is a metallurgical condition. It can be identified by certain specialized nondestructive testing techniques or by destructive metallurgical examinations, but it cannot be identified by simple visual examination. It becomes visually apparent only after exposure of the sensitized metal to a sufficiently aggressive environment produces corrosion that is, weld decay. 

Anderson, R. C., Inspection of Metals, vol. I, Visual Examination, American Society for Metals, Metals Park, Ohio, 1983. 

Although it is not difficult to make injection mouldings from polystyrene which appear to be satisfactory on visual examination it is another matter to produce mouldings free from internal stresses. This problem is common to injection mouldings of all polymers but is particularly serious with such rigid amorphous thermoplastics as polystyrene. 

Test pits permit visual examination of the soil in place. Such pits also allow manual sampling of undisturbed soil samples. These samples can be taken from the side walls of the pit. 

Thickness of the filler cake is measured and reported in of an inch. Also, the cake is visually examined and its consistency reported using such notations as hard, soft, tough, rubbery, or firm. ... 

Visual examination of ignition of pilot burner and main burner ... 

Visual examination of the immersed samples showed that ZA8 suffered moderate, uniform corrosion in both tanks. ZAI2 showed extensive localised corrosion in the primary tank but slight uniform corrosion with localised corrosion at several spots in the secondary tank. ZA 27 suffered extensive localised corrosion over most of the surface in the primary tank but only slight uniform corrosion with several very small pits dispersed all over the surface in the secondary tank. 

Test methods available are the free-running test (galvanic cell), galvano-static test (constant current) and potentiostatic test (constant potential). These are always run in conjunction with visual examinations with particular emphasis on dissolution pattern. 

The extent of deterioration may be measured by one or more of the following methods visual examination, change in weight, change in tensile properties. Visual inspection was depended upon primarily in the A-5 tests... 

Where changes in appearance are of paramount interest, as in the case of metallic and organic coatings on steel or other metals, visual examination is most desirable. To facilitate ratings on such a basis, photographic standards have been employed, as, for example, in tests on chromium-plated steel undertaken by ASTM Committee B-8 on Electrodeposited Metallic Coatings . These ratings are supplemented by a shorthand description of the nature of the deterioration observed. 

Hydrocarbons. Dil 15ml of the specimen to 45ml with distd w in a Nessler tube. Visually examine for cloudiness or opalescence during 30 minutes of standing... 

The quantitative analysis procedure involves benz extr of TNT, water extr of AN, and taking of the A1 content as insol residue. Moisture content is detd by the Karl Fischer method described in ASTM Method E203-62, except that 8 to lOg samples are added to methanol. Specific gravity is detd by water displacement, and workmanship by visual examination... 

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