Liquid-penetrant technique

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. 

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. 

Liquid Penetrant Examination. All accessible surfaces of the main load carrying components of the equipment shall be examined by a liquid penetrant examination or technique conforming to the requirements of ASTM E165 Recommended Practice for the Liquid Penetrant Examination Method. Acceptance limits shall be as agreed upon by the manufacturer and the purchaser. 

The achievements in optical detection techniques and the interest in the sol-gel process for creation of new materials, are leading to developing of various sensors. The majority of reported sensors developments have concentrated on the use of thin films. There are many reasons for this. The important one is the susceptibility of monoliths to cracking due to internal stresses, particularly when exposed to liquid penetration. More attractive are... 

Caitz, L. Nondestructive Testing Radiography, Ultrasonics, Liquid Penetrant, Magnetic Particle. Eddy Current, ASM International, Materials Park. OH, 1995 Cornua, R.D. Problem-Solving Surface Analysis Techniques. Advanced Materials Processes, 16 (December 1992). 

By comparison with other NDC methods, such as liquid penetrant examination, magnetic particle, eddy current testing, and radiography, the ultrasonic method is the only technique that is applicable to a wide range of materials. 

In many applications, powders come into contact with a liquid and we would like to quantify their wetting behavior. The usual way to do this is by the capillary rise method [233,234], In a capillary rise measurement the powder is pressed into a tube of typically 1 cm diameter (Fig. 7.7). This porous material is then treated as a bundle of thin capillaries with a certain effective radius [235-237], In order to measure this effective radius, first a completely wetting liquid is used. Either the speed of the liquid rise is measured (this technique is sometimes referred to as the capillary penetration technique [238]) or the pressure required to keep the liquid out of the porous material, is determined. This backpressure is equal to the... 

The choice of the nondestructive technique used in the examination of the sample on hand also depends upon the complexity of the shape of the sample. The following order of the methods is in progressively increasing complexity of the shape of the sample to be examined acoustic microscopy, microwave method, eddy current, magnetic particle, X-ray radiography, ultrasonics, liquid penetrant and visual methods. 

Various gas and liquid adsorption techniques are used to determine the porosity of a specimen. They are mostly based on the Brunauer-Emmett-Teller method (BET) [14]. Atoms or molecules penetrate into a sample through interconnected pores with links to the sample surface. The adsorbed volume and temperature and pressure dependent data are used to quantify the porosity and surface to volume ratios, which contain information about the pore size distribution [15]. A recent review is published by Schneider [11], Care must be taken that the used probe (gas or liquid) does not react with the sample. When pores become too small, the probe may not penetrate into them. Pores or interconnected pores are not detected, when no connection to the sample surface exists. For example, thin capping layers would close all pores and render the technique useless, even though the pores may be totally interconnected below the cap. 

General corrosion control, prevention, and monitoring should be planned for from the onset. To detect and monitor corrosion, various methods must be used, while corrosion protection would be done by the addition of inhibition and use of protection coatings [5]. Visual examination, laser methods, the replication microscopy liquid penetration testing method, magnetic particles testing, the eddy current inspection method, acoustic emission technique, thermal methods of inspection, and nondestructive methods are the various methods to be adopted when monitoring pipeline corrosion [5]. 

Examinations will include liquid penetrant or magnetic particle techniques when surface examination is specified, ultrasonic or radiographic techniques when volumetric examination is specified, and visual inspection techniques will be used to determine surface condition of components and for evidence of leakage. Specific techniques, procedures and equipment, including any special techniques or equipment will be in accordance with the requirements of IWA-22 00 of ASME Section XI and will be defined in the in-service inspection program. 

Pol5uner-billet geometry is defined by SSE scheme. In Figure 2, there are some variants of billets for the plunger (a-f) and hydrostatic (a, b) extrusion to be used in the described SSE techniques. The hydrostatic extrusion is of a lesser potential application as it is necessary to protect the compacted powder from liquid penetration and to seal the billet in the die to prevent liquid from leakage under pressure rise (coextrusion). 

While the new liquid is pumped into the drop through the inner tube, its bulk is pumped out via the outer tube. Due to the liquid flow, the drop volume is permanently mixed. In this way, the drop volume is completely exchanged when an amount of more than 250% of the drop volume has been pumped through. This experimental procedure has the only drawback that it is difficult to control the spread amount very accurately. On the other hand, it has quite a number of advantages when compared to other penetration techniques, in particular, the easy temperature control and the easy applicability to liquid/liquid interfaces. 

The diverse nature of different NDE processes results in different sources of variance and possible impact on detection output capabilities. For example, a manually applied liquid penetrant process is dominated by the skill of the operator in process application and interpretation. An automated eddy current process is dominated by calibration, instrument, and procedure variances. It is important to recognize the source of variance in each NDE process and to take the nature of the variance and process control (Table 6.11) into accoimt in applying margins to the NDE processes. NDE methods and procedures are selected using a variety of practical implementation criteria, such as the relative ratings presented in Table 6.12. The lowest-cost method that produces the required result is usually the method of choice. Table 6.13 presents a general overview of the procedural steps required for the main NDE techniques considered here. 

Liquid penetrant inspection. The liquid penetrant NDE method is apphed to detection of faults that have a capillary opening to the test object surface. The nature of this NDE method demands that attention be given to material type, surface condition, and rigor of cleaning. Liquid penetrant inspection can be performed with little capital expenditure, and the materials used are low in cost per use. This technique is applicable to complex shapes and is widely used for general product assurance. 

However, it appears that none of the non-destructive tests currently employed directly correlate with any critical failure property. Most industrial test techniques such as through-transmission and pulse-echo ultrasonics, sonic vibration techniques. X-ray radiography, thermal inspection methods, holography, liquid penetrants, etc. basically attempt to find defects in the joint. Such defects may arise from several sources. Some defects arise from porosity, cracks or voids in the adhesive layer or at the interface and are typically filled with air they will simply be referred to as voids in the present discussions. However, during the service life of the joint such voids may fill with water which makes them far more difficult to detect since, for example, water has a much higher acoustic, impedance than air. Also, zero-volume voids, or debonds, may occur when the adhesive and substrate are in contact but no... 

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