MIL-STD-1330D(SH)
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c. Order for mixing: In order to yield a more stable solution which will extend the life of the cleaner, water should be added to NOC rather than adding NOC to water.
4.3.1.7 Use of NOC in previously used equipment. For cleaning equipment previously used with other than NOC, the following actions should be taken to minimize and evaluate for the possibility of the NOC reacting with the residue left behind.
a. Fill the cleaning equipment with NOC diluted 25 to 50 percent with Grade B water. b. Operate the cleaning equipment covered for 4 hours at 140 to 160 °F.
c. Visually inspect the NOC for foam and precipitate. Visually inspect the equipment for milky white deposits. Some white deposits at the fluid-air boundary are acceptable.
d. If precipitate is visible in the NOC, the NOC foams, or milky white deposits are visible on the equipment in areas continuously wetted with NOC, discard the NOC solution, remove the deposits as specified in 4.3.1.7(e), and repeat the process.
e. Deposits can be removed by soaking in hot water, or soaking and scrubbing with commercial white vinegar or a warm (up to 110 °F) 10 to 16 percent citric acid solution followed by a water rinse. A 10 to 16 percent citric acid solution can be prepared by adding 12 to 20 ounces of powdered citric acid (CAS No. 77-92-9) to one gallon of water.
4.3.1.8 Use for extended periods. Extended use of NOC should be in covered equipment to minimize evaporation. NOC can be recycled using filtration, and continuously used or reused, provided the following conditions are satisfied:
a. A shake test as specified in 5.13.2.2 reveals no excessive foam.
b. A visual inspection as specified in 5.13.3.2 reveals no particulate, fiber, or oil.
c. A hydrocarbon or NVR inspection as specified in 5.13.2 reveals less than 5 parts per million (ppm) above baseline.
d. An alkalinity test as specified in 5.13.5 indicates a satisfactory result. As the alkalinity of NOC is depleted in use, the volume of NOC required to obtain the blue end-point specified in 5.13.5 increases. When the alkalinity test measures 35 to 40 milliliters (mL) of NOC, the NOC is at risk of developing an insoluble precipitate. The NOC should either be replaced, or a portion of the low alkalinity NOC removed and replaced with fresh NOC to restore alkalinity. If evaporation concentrates the NOC causing the alkalinity test to measure less than 10 mL of NOC, the NOC should be diluted with water as specified in 4.3.1.6 to restore the alkalinity to a nominal measured range of 15 to 30 mL of NOC. Do not attempt to adjust the alkalinity of 50 to 100 percent concentrated NOC by adding acid; an immediate gel or precipitate will develop. Alkalinity of NOC in use or stored in cleaning equipment should be checked weekly until the alkalinity test measures about 30 mL of NOC. Then, more frequent analysis should be performed to ensure an insoluble precipitate does not form.
4.3.1.9 Filtration. For long term use in cleaning equipment such as large ultrasonic tanks or parts washers, a filter sized at about 1-micrometer nominal should be installed. For use in a flushing rig, a 5-micrometer nominal or finer filter shall be installed, and it is recommended that a filter sized at about 1-micrometer nominal be installed. A
5-micrometer filter prevents introducing significant contamination back into the system. A 1-micrometer filter allows recycling and extending the use of NOC. It is also recommended that for flushing applications, a strainer be installed upstream of the filter to remove large debris that can prematurely clog the filter. Filters used for the first time shall be checked for extractable organic material by recirculating with clean NOC at 140 to 160 °F for not less than 1 hour and then verifying organic cleanliness as specified in 5.13.2. Checking for extractable organic material of filters is not required for filters from the same vendor and of the same material that previously tested satisfactorily. A suitable filter material is thermally bonded, pleated polypropylene containing no plasticizer or adhesive. The major advantage of disposable polypropylene filter cartridges is ease of use. Cleaning stainless steel reusable filters can be difficult and time consuming. The large soil holding capacity of disposable filter cartridges can often balance the cost of using smaller soil holding capacity stainless steel filters requiring frequent cleaning. Filter housings should be configured with a vent on the top of the housing to allow removing oil that has separated from the NOC. Verify with the manufacturer that the temperature, pressure, and flow ratings of any filters are adequate for the intended application. Disposal of used filters or separated oil shall be in accordance with local, state, and federal regulations.
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