Nondestructive visualization

Thin-Layer Chromatography. Chiral stationary phases have been used less extensively in tic as in high performance liquid chromatography (hplc). This may, in large part, be due to lack of availability. The cost of many chiral selectors, as well as the accessibility and success of chiral additives, may have inhibited widespread commercialization. Usually, nondestructive visualization of the sample spots in tic is accomplished using iodine vapor, uv or fluorescence. However, the presence of the chiral selector in the stationary phase can mask the analyte and interfere with detection (43). 

Figure 12.3. Internal bmising affects texture and acceptability of fruits but is hardly detected by inspection of the outer surface. Nondestructive visualization of internal bruising in a single apple by MRI. Above. Sections at time 0. Below. Evolution after 10 days.

The isolation of antifungal and antimolluscicidal saponins from Serjania salzmanniana also involved the use of a silica column, but it then followed this with separation by countercurrent chromatography (Scheme 3). An interesting feature of the final preparative TLC stage was the use of water as a nondestructive visualization stain. As these compounds are so hydrophobic, this region of the plate remained white (dry), and the remainder of the plate turned dark (wet) (S). 

Nondestructive testing techniques for welded joints usually include visual, radiographic, magnetic particle, liquid penetrant, and ultrasonic testing methods. Of interest in this paper is the radiographic testing (RT) technique. 

Nondestructive Testing. Nondestmctive inspection of an explosion-welded composite is almost totally restricted to ultrasonic and visual inspection. Radiographic inspection is appHcable only to special types of composites consisting of two metals having a significant mismatch in density and a large wave pattern in the bond interface (see Nondestructive evaluation). 

Personnel performing examinations other than visual shall be qualified in accordance with applicable portions of SNT TC-IA, Recommended Practice for Nondestructive Testing Personnel Qualification and Ceitification. Procedures shall be qualified as required in Par. T-150, Art. 1, Sec. Vof the ASME Code. Limitations on imperfections shall be in accordance with the engineering design but shall at least meet the requirements of the code (see Tables 10-58 and 10-59) for the specific type of examination. Repairs shall be made as applicable. 

NOTE Nonferromagnetic (metals that cannot be magnetized, such as copper and brass) tubes that are not visually accessible can be examined nondestructively using eddy current testing. 

Most defects can be detected using one or more appropriate nondestructive testing techniques. However, in the absence of routine nondestructive testing inspections, identification of defects in installed equipment is generally limited to those that can be observed visually. Defects such as high residual stresses, microstructural defects such as sensitized welds in stainless steel, and laminations will normally remain undetected. Defects that can be detected visually have the following features ... 

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. 

Identification. If accessible, defects from burnthrough may be visually identified as fused holes in the tube wall. Various nondestructive testing techniques, such as radiography and ultrasonics, may also detect this defect. The defect generally causes leakage soon after affected equipment is placed in service. 

Identification. Slag inclusions will not be visually identifiable unless slag particles emerge at the weldment surfaces. Radiography, eddy-current testing, and ultrasonics are nondestructive testing techniques that can disclose slag inclusions. 

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. 

Identification. Weld-root cracks originate at the root of the weld and run longitudinally along the weld, perpendicularly to the base-metal surface and parallel to the axis of the weld. In general, they may be identified visually or by various nondestructive testing techniques such as radiography or ultrasonics. Failures from weld-root cracking may occur soon after start-up or after extended periods of successful service. 

Although not commonly listed as a weld defect, high-welding stress nevertheless provides an essential ingredient to stress-corrosion cracking and other failures. It differs in an important respect from other types of weld defects in that stresses cannot be visually identified or revealed by conventional nondestructive testing techniques. 

Welding stresses are not visually observable. The common nondestructive technique available for determining residual stresses is x-ray diffraction. 

Gross cracks may be visually observable. Nondestructive testing for the presence of cracks includes using dye penetrant, ultrasonics, and radiography. Determination of the cracking mechanism will require metallographic analysis. 

Visually observable breaks in surface laminations indications on nondestructive testing charts. 

Welding Defects Visual, radiographic and/or ultrasonic Indications. Any welded joints. Basic welding problem laminated steel can cause trouble. Electrode manipulation. Control of welding speeds, procedures, careful inspection and nondestructive testing to locate defects for cutting out or repair. 

These techniques include (1) vibration monitoring (2) thermography, (3) tribology, (4) process parameters, (5) visual inspection and (5) other nondestructive testing techniques. This chapter will provide a description of each of the techniques that should be included in a full capabilities predictive maintenance program for typical plants. 

In Chapter 7, approaches for visualization of zones in chromatograms are discussed, including use of nondestructive and destructive dyeing reagents, fluorescence quenching on layers with a fluorescent indicator, and densitometry. In Chapter 8, additional detection methods, such as those used for biologically active and radioactive zones, as well as the recovery of separated, detected zones by scraping and elution techniques are covered. 

The reagent used for the deteetion may be speeifie to a special functional group or specific lipids or may be a nonspecific reagent that makes all hpids visible. The most commonly used reagent that is nonspecific for any lipid group is 0.1% (w/v) 2, 7 -dichlorofuorescein in 95% methanol. This is mainly useful when the plates have been developed in acidic solvents. The lipid spots or bands can be visualized as yellow spots or bands under UV light. After the plates are developed in alkaline solvents, an aqueous solution of Rhodamine 6G (0.01%) can be used, and lipid spots can be seen as pink spots under UV. Because both these methods are nondestructive, they can be effectively used in PTLC so that the separated sample bands can be scraped off and used for further analysis. 

In a separate study, a protocol for Matrix-assisted laser desorption-ionization (MALDI) imaging mass spectrometry (IMS) has been proposed.18 This IMS technique provides a new approach to visualize spatial distribution of thousands of molecular species, including peptides, proteins, and their metabolites in two- or three-dimensional levels. This approach may also provide a straightforward method of determining the tissue distribution of multiple peptides or proteins in a quantitative manner.18 Chu et al.19 reported a nondestructive molecular extraction method to obtain proteins from a single FFPE or frozen tissue section, without destroying the tissue morphology, such... 

Macro visual examination is done with the unaided eye or low power (up to 2 OX) magnification. An item may need to be cleaned prior to examination. Fracture origins and location of samples to be removed for further analysis are determined by macro visual examination. Nondestructive evaluation methods may be necessary for more accurate determinations (see Step 4). 

---