MIL-DTL-16356E
4.7.7.3 Glass set sampling. A random sample of glass sets (glasses, gaskets, spacers, and mica shields, as
applicable) shall be selected in accordance with ASQ H1331 at Inspection Level III (S-3 for thermal shock, fracture,
and service test). Each of the sample sets or units shall be subjected to the conformance inspection shown in
4.7.7.4 Visual and dimensional examination. Each of the sample glasses, gaskets, spacers, and mica shields
selected as specified in 4.5.2 shall be visually and dimensionally examined to verify compliance with the
requirements of this specification not involving tests. Any items in the sample containing one or more visual and
dimensional defects shall be rejected, and likewise, the lot represented by the sample shall be rejected.
4.7.7.5 Thermal shock test. The glasses shall be placed on edge in a wire rack which has been wrapped with
insulation to prevent glass-to-metal contact. The glasses shall be placed in the rack with care taken to ensure there is
no glass-to-glass contact of the samples. The glasses shall be placed in the tack as specified herein and heated in a
furnace (preheated to 500 °F) for a period of 25 minutes. The glasses shall then be quickly immersed in a cold water
bath maintained at a temperature of 40±5 °F. The glasses shall then be examined to determine conformance to
4.7.7.6 Fracture test. Glasses shall be mounted in a water gauge frame and impacted with a pointed tool, such
as a center punch, at the midpoint of the outer face to produce fracture. The glass shall be examined to determine
conformance to 3.12.3.2.1.
4.7.7.7 Bend test. The bend test shall be in accordance with DIN 7081 requirements using the sampling
requirements of 4.7.7.3. The bend test shall only be accomplished when simulative service testing in accordance
with 4.7.7.9 is not required.
4.7.7.8 Polariscopic examination. A polariscope such as specified in ASTM F218 shall be used to examine the
glasses sampled by 4.7.7.3 qualitatively for the rings or strain pattern specified in ASTM F218. Each sample shall
show clear isochromatic lines running parallel to the edges.
4.7.7.9 Simulative service test for glass set. Type A glass sets (glass, mica, and gaskets) shall be installed in
the applicable water level gauge frame which shall be mounted on a boiler steam drum or test facility (simulating
boiler conditions) and operated at a steam gauge pressure of approximately 1500 psig. Class IV glass sets shall be
hydrostatically tested to 2500 psig. Gauge assembly shall be in accordance with instructions of the gauge
manufacturer. Minimum requirements of simulative service test shall be as follows:
a. Assembled water level gauges shall be operated continuously for a minimum of 100 hours at design
pressure.
b.
Water level shall be maintained at the visible range centerline.
c. Water level gauge shall be blown down a minimum of five times during each working day in accordance
with the following procedure:
(1)
Open water level gauge drain line stop valve.
(2)
Shut water level gauge top cut out valve.
(3)
Crack open water level gauge drain valve and blow down gauge, clearing it of all water.
(4)
Shut water level gauge drain valve.
(5)
Open water level gauge top cut out valve.
(6)
Shut water level gauge bottom cut out valve.
(7)
Crack open water level gauge drain valve and blow down gauge for 20 seconds.
(8)
Shut water level gauge drain valve.
(9)
Open water level gauge bottom cut out valve. Ensure water level returns to visible range centerline.
(10) Shut water level gauge drain line stop valve.
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