MIL-DTL-18182F
TABLE II. Pipe identification corresponding to union class
for determination of wall thickness.
Union Class Pipe Identification
Class 1 Standard
STD (schedule No. 40)
Class 2 Extra strong
XS (Schedule No. 80)
Class 3 Double extra strong
XXS (No schedule Number)
3.11.2 Female threaded ends. The female threaded ends shall have a wall thickness of metal (between
the thread root of the female pipe thread and either the cylindrical surface described by the outside
diameter or the minimum dimension across the flats of the outer surface) not less than 87.5 percent of the
nominal wall thickness for the pipe identification on which the union will be used (see table II).
3.11.3 Male threaded ends. The wall thickness on male threaded ends, before the threads are cut, shall
be not less than the nominal wall thickness of pipe corresponding to the class of the union as listed in
table II.
3.11.4 Wrench purchase. Each union end-piece shall be provided with an external wrench grip surface
of sufficient length to permit adequate wrench purchase. The wrench grip shall either be a parallel-sided
polygon or round with lugs.
3.12 Inside diameter. The inside diameter (bore) of the union shall be no smaller than the ID of
ASME/ANSI B36.10M welded and seamless steel pipe for the pipe identification, which corresponds to
the required union class.
3.13 Surface finish. Unions shall be uncoated unless coated as specified (see 6.2).
3.13.1 Uncoated. Coupling threads may be plated for the purpose of thread lubrication. Inorganic
chemical surface treatments, such as rust inhibitors, will not disqualify uncoated unions as such.
3.13.2 Coated. Coated unions shall have zinc coating. The hot-dip process, in accordance with ASTM
A153/A153M, shall apply the zinc coating before machining the threads or by the electroplating process
either before or after machining.
3.14 Marking. The unions shall be stamped or otherwise permanently marked as specified in
MSS SP-25.
3.15 Workmanship. The quality of workmanship shall be such as to produce material that is in
accordance with the requirements of this specification. Unions shall be free from blemishes, burrs,
forging cracks, and all other visible defects.
4. VERIFICATION
4.1 Requirements cross-reference matrix. Table III provides a cross-reference matrix of section 3
requirements tested or verified in the paragraphs below.
TABLE III. Requirements cross-reference matrix.
Requirement
Verification
Requirement
Verification
3.1
4.2.2
3.9
4.3.2
3.2
4.2.2
3.10.1
4.2.2
3.3
4.2.2
3.10.2
4.2.2
3.3.1
4.2.2
3.10.3
4.3.3
5
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