MIL-STD-1622B(SH)
volumes that cannot be bypassed, but can either be locally cleaned as specified in 5.13.4 or the configuration of the volume will not collect separated oil during the final flush, such as an in-line vertically oriented flask, a preclean flush is not required.
5.6.4 Leak-check. The flush boundary shall be leak-checked to the anticipated flush pressure with air, nitrogen, or grade C water for general or grade B water for critical applications. This will eliminate the time consuming clean-up of spilled or leaked cleaner. Where a clean system interfaces with a flush boundary, using air or nitrogen for the leak check is recommended. Any air or nitrogen leakage into a clean system will not cause loss of cleanliness.
5.6.5 Preflush. For new systems or systems with extensive modifications, a preflush as follows is recommended:
(a)Perform forward and backward preflush at a minimum of 3 ft/sec using grade C water for general applications or grade B water for critical applications. The preflush water temperature may be elevated to not greater than 180oF. The higher temperatures will increase the effectiveness of the preflush and preheat the system minimizing the pipe line cleaning time.
(b)Outlets should be opened one at a time to help clean valve bodies and other probable pocketing areas. The flush should continue until there is no visual evidence of debris.
5.6.6 Hydrostatic test. Hydrostatic testing as specified in 5.10 should normally be accomplished after the preflush, if applicable, and before the final flush.
5.6.7 Final flush/pipe line cleaning. For general applications using a low foaming cleaner selected as specified in 4.3, flush the system with the cleaner in accordance with the process determined as specified in 4.4. Final pipe line cleaning with NOC or TSP shall be accomplished as follows:
(a)Flush the system with NOC at 150 to 170oF or TSP at 160 to 180oF at the flow rate as specified in 5.6.7(b). The temperature of the NOC at the outlet of the system being cleaned shall be maintained at no less than 140oF. If TSP is used, the system shall be preheated by flushing once-through with hot grade B water until the desired temperature is attained. In order to prevent precipitation of the TSP, the TSP shall not be allowed to cool or remain uncirculated prior to rinsing as specified in 5.6.8. If NOC is used, it may be recirculated in the system cold and heated in place. For NOC or TSP, the flush starts when the outlet temperature reaches 140oF.
(b)The fluid velocity shall be no less than 3 ft/sec. The flow rate in gallons per minute equivalent to 3 ft/sec can be determined by multiplying the square of the pipe or tube inside diameter in inches by 7.4, as follows:
GPM at 3 ft/sec = (ID-inches)2(7.4)
(c)The requirements for a back flush and the flush durations and temperatures for various applications are given in 5.6.7(a) and Table V.
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