MIL-DTL-18182F
3.8.1.2.1 Insert material. Insert seats, when used, shall be any of the listed materials for the union
pressure specified (see 6.2):
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2,000 lb/in - Bronze or stainless steel.
2
3,000 lb/in - Bronze, molybdenum steel or stainless steel.
2
6,000 lb/in - Stainless steel.
3.8.2 Contact surfaces. The surfaces of all unions subjected to contact pressure in tightening shall be
grounded or machined to ensure proper and leakproof seating.
3.9 Pressure. The unions shall be capable of withstanding a hydrostatic test pressure equal to 1.5 times
the specified (see 6.2) rating pressure without impairing the serviceability of the union.
3.10 Union coupling nut.
3.10.1 Union coupling nut threads. Union coupling nut threads shall be the manufacturer's commercial
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standard except, if specified (see 6.2), 3,000 lb/in rated unions shall have modified ACME threads (see
6.4).
3.10.2 Coupling nut. The union coupling nut shall have parallel-sided polygon flats except the
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3,000 lb/in unions with modified ACME threads may have hammer (handle bar) style coupling nuts.
When the union is closed, not less than four full threads shall be engaged by the nut.
3.10.3 Tensile breaking strength. The tensile breaking strengths of the unions shall be not less than
those listed in table I.
TABLE I. Minimum tensile strength of unions.
Minimum ultimate breaking loads (pounds)
Size
Style A
Style B
(inches)
Class 1
Class 2
Class 3
Class 1
Class 2
0.125
4,000
6,000
-
2,400
3,600
0.25
6,000
8,500
12,000
3,400
5,200
0.375
8,000
11,500
16,000
4,900
7,900
0.5
10,000
14,000
20,000
6,700
10,500
0.75
14,000
20,000
28,000
9,500
15,000
1
18,000
26,000
36,000
13,000
21,500
1.25
23,000
33,500
46,000
19,000
31,800
1.5
28,000
41,500
56,000
23,000
39,400
2
40,000
50,000
80,000
32,500
55,000
2.5
55,000
75,000
-
48,500
75,000
3
75,000
80,000
-
68,000
80,000
3.11 Ends.
3.11.1 Pipe connection. Threads for the end connections shall be in accordance with
ASME/ANSI B1.20.1, NPT designation. Wall thickness shall be in accordance with the dimensional
requirements of ASME/ANSI B36.10M for the pipe identification required (see table II).
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