7/28/2019 Alumn Block

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Standard / Test samples 1:  Quench cracked aluminium block : These blocks are made of ASTM B209, SB 211 or 2024 - T3 aluminum approximately 2" wide X 3" long X3/8’’ thick pieces. The blocks are heated and quenched to produce anoverall circular crack pattern. A groove is machined in the middle of theblock to separate the cracks into two zones. Since the cracks areuncontrolled, the blocks are used for comparing the performance of penetrants only and not for absolute evaluations. At the center of the face, an area approximately 1 inch in diameter shall be marked with 950 0 F temperature indicating crayon or paint. Themarked area shall be heated with a blow torch to a temperaturebetween 950 0 and 975 0 F. The area should be heated within 4 minutesto produce a temperature difference within the block. The block is thenimmediately quenched in cold water which produces a network of relatively tight and uniform crack pattern on the face. The block shallthen be dried by heating to approximately 300 0 F.It is because of tight crack pattern, that color contrast penetrants are

not normally checked with this block. These penetrants are not assensitive as fluorescent penetrants. The cracking will be symmetrical oneither side of the separation groove but the depth and the width of thecracks produced is uncontrolled and unknown. For the color contrast penetrants comparison only, the

950 0 F cracked block is heated a second time to 800 0 F and quenchedagain to open the cracks wider.

New and used penetrants or different brands of penetrants can beprocessed and then compared side by side. A penetrant in use can be checked for its crack detection ability andindicating brightness against fresh penetrant samples. One half of theblock is processed with the used penetrant and the other half with thefresh penetrant. The whole plate is then processed to completion in therelevant way. The indications from each half can be tested under identical illumination on the same alloy with the same surface condition,resulting in a true comparison of relative sensitivity. The slight potentialfor error with this device arises with the requirement that thediscontinuities in both halves be as identical as possible. If cracksdetected on the used penetrant side is not as complete as the freshpenetrant side, the used penetrant is considered contaminated andshould be discarded. If the brightness of the used penetrant indications

appear to be below 90 % of the brightness of the fresh penetrantindications, the used penetrant is discarded. Use of penetrant outside their normal operating temperature range

[ 16 0 to 52 0 C ] can be qualified using these blocks. Two separateblocks are processed. One block is heated or cooled to the proposedexamination temperature and maintained at that temperature throughoutthe processing cycle. The other block is processed within the normaloperational temperature of the penetrant. If the indications obtained under the proposed conditions are essentially the same as obtained with thenormal conditions, the proposed technique shall be considered to bequalified for use.  These blocks can be reused by careful cleaning.A 30 minutes soak in isopropyl alcohol clears the induced cracks

of residual penetrant.System performance check / KDS Panels :System performance checks involve processing a test specimen withknown defects to determine if the process will reveal discontinuities of the size required. The purpose of the known defect Standard is not toverify the sensitivity level of the penterant, but to monitor the performanceof the entire penetrant examination system.Further, The specimen must be processed following the same procedureused to process production parts. A system performance check istypically required daily, at the reactivation of a system after maintenanceor repairs, or any time the system is suspected of being out of control.  As with penetrant inspection, results  are directly dependent on the skillof the operator, therefore each operator should process a panel.Known Discontinuity Standards [ KDS panels ] : The panels come in

pairs having known discontinuities in known locations. Two KDS panelsare produced simultaneously from a single sheet of stainless steel, so

they are precisely matched as to plating thickness, crack size, andsurface roughness. The center section is grit blasted to specificationroughness. This rough section is used to compare washability of differenttypes of penetrant.

Compiled by K. Chatterjee, 75643  Center for NDT P 00 Rv 04 Self study material.

The two outer edges have 25 mm wide stripsof brittle chrome plating of 0.1 mm thickness.Five controlled induced cracks of varyingdimensions are produced in pairs. The sheet is

sheared into two equal sections and they arevirtual twins. Both the sections are processedfor side by side comparison.