MIL-PRF-27401G
4.2.7.1 Liquid phase samples. Liquid phase samples shall be tested for each parameter in
applicable grade of Type II nitrogen. Sampling under the "continuous service" provisions can be applied.
4.2.7.2 Gas phase samples.
a. Samples shall be tested for each parameter in the applicable grade of Type I nitrogen.
Samples shall be drawn in accordance with 4.2.4 from a point immediately prior to entering the user's
system. The frequency of sampling shall not be less than once every seven days at regular intervals.
b. When specified in contract, in-line samples shall be drawn and tested with continuous
monitors for each parameter specified in contract for the applicable grade of Type I nitrogen. Each
analyzer shall be equipped with a permanent recording device. When specified in contract, an alarm
system to indicate contaminant contents in excess of specified maximum shall be provided (see 6.2).
c. After internal exposure of the pipeline to the atmosphere or other foreign materials, a sample
of gas shall be taken from the pipeline prior to delivery into the user's system at a point between the final
filter and the interface with the Government system. The sample shall be tested for each parameter in
applicable grade of Type I nitrogen. After cleaning operation, the sample shall also be tested for
contamination by vapors from the cleaning materials.
4.3 Rejection. When any sample tested in accordance with 4.4 fails to conform to the
requirements specified herein, the entire lot represented by the sample shall be rejected.
4.4 Analytical procedures. Unless otherwise specified, samples shall be analyzed according to
the procedures described in 4.4.2 (see 6.2). Calibration gas standards may be required to calibrate (zero
and span) analytical instruments used to determine the purity and impurity contents of the nitrogen. The
accuracy of the calibration gas standards is to be traceable to the National Institute of Standards and
Technology.
4.4.1 Nitrogen content. The nitrogen content in percent shall be found by determining the
aggregate impurities by the methods described in 4.4.2. The nitrogen purity is the value obtained when
the aggregate impurities, expressed as volume percent, is subtracted from 100 percent.
4.4.2 Impurities. Methods shall be selected from those of CGA G-10.1.
4.4.3 Particulate content. A filter holder assembly, (Pall Life Sciences part number 2220), or
equivalent modified as shown on Figure 1 shall be attached to the withdrawal line of the vessel to be
utilized to fill the tanks. A preweighed filter paper (47 mm glass fiber paper, type A/E or equivalent) shall
be placed on top of another filter of the same kind. The filters shall then be placed on the porous filter
support, which, in turn, shall be placed in the filter holder as shown on Figure 1. The male threads of the
filter holder shall be wrapped with thin, nonadhesive-backed polytetrafluorethylene tape A-A-58092 or
equivalent to prevent galling of the threads. The holder shall be tightened by hand as tight as possible to
prevent bypassing of the filter element. The discharge liquid from the filter housing shall be collected in a
clean, uninsulated, ambient temperature vessel marked to indicate when 5 liters of liquid have been
collected. The liquid flow shall be terminated when 5 liters of liquid have been collected. The filter holder
shall be removed from the line and permitted to reach ambient temperature. The warmup to ambient
temperature may be expedited by use of an oven or other heat source. Care shall be exercised to ensure
that any airflow which enters the unit will be directed through the inlet of the assembly to prevent
displacing any particles from the surface of the filter. Upon warmup, the other side of the holder shall be
wiped with a clean cloth and the holder then disassembled. The filter paper shall be closely inspected.
The test shall be repeated if evidence of either (a) the filter not being securely clamped by uniform
depression of its edge; (b) the filter having been cut by the holder; or (c) when dirt particles are detected
in the clamped area indicating bypassing had been encountered. The test shall also be repeated when
either the bottom filter shows any discoloration or when leakage of liquid from the filter holder is detected.
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