MSS SP-83 2018 includes forged carbon steel, alloy steel, stainless steel, and nickel alloy pipe unions with socket weld and threaded ends, along with packaging, basic dimensions, surface treatments, tolerances, tests, markings, materials, and minimum performance requirements.
History of MSS SP-83
- 1976: The standard was first introduced, establishing industry guidelines for Class 3000 carbon steel unions, primarily used in high-pressure industrial, oil, and petrochemical sectors. It also included metric units and standard conversion factors.
- 1987: Austenitic stainless steel grades 304/304L and 316/316L were added to the unions, suitable for the chemical, pharmaceutical, power, and other industries with higher corrosion resistance requirements.
- 1995: Adjustments were made to the dimensions of socket welding unions, aligning the socket diameter, socket wall thickness, and union “flow” hole with the ASME B16.11 Class 3000 fitting dimensions. The use of metric conversions as reference units was removed.
- 2001: Improvements were made to the flow path design for threaded unions to accommodate larger diameter drilling for National Pipe Thread (NPT) type threads, consistent with the use of threaded fittings in the same pipeline system.
- 2006: The standard was essentially confirmed, with minor editorial modifications.
Important Changes in the 2014 Revision of MSS SP-83
- Substantive Revisions: The 2014 revision brought significant updates to the SP-83 standard.
- Pressure-Temperature Ratings Confirmation and Updates: The committee reviewed and confirmed the foundation for pressure-temperature ratings in the original standard. The pressure-temperature tables were also updated, meaning that the standard reassessed and revised the capacity of fittings under different pressure and temperature conditions.
- Inclusion of New Materials: Based on formulas, testing, and practical applications, the standard added coverage for various alloy steels, stainless steels, and nickel alloys.
- Introduction of Class 6000 Unions: Based on the above analysis, the standard added requirements for Class 6000 socket weld and threaded unions, including their dimensions, materials, and pressure-temperature ratings.
- Improvement of the Standard: These revisions made the 2014 version more robust and comprehensive, suitable for various pipeline connection requirements in commercial and industrial applications.
Updates in the 2018 Revision of MSS SP-83
- Material Updates: New materials were added in Tables 4 and 5, including A350 LF2, A420-WPL6, and B462-N08020. These materials are typically used in low-temperature, corrosion-resistant, and high-pressure pipeline applications.
- Dimension and Service Marking Requirements: Updates were made to the size and service designation/pressure marking requirements for union nuts. This means further standardization of markings to ensure that unions clearly display their specifications and pressure ratings when in use.
- Appendix A Citation Updates: Citations in Appendix A were updated to ensure accuracy and alignment with the latest standards.
- Editorial and Formatting Adjustments: In addition to the substantial changes, there were also editorial and formatting adjustments to make the document clearer and easier to read.
- Reintroduction of Metric Units: It is noteworthy that metric units (ST) are planned for reintroduction in the next version, alongside existing U.S. customary units as an independent and equivalent standard. This indicates that future standards will include metric units, making them more universally applicable in international contexts.
Pressure Ratings & Size
2.1 These unions shall be designated as Class 3000 or Class 6000, socket welding or threaded, and shall carry ratings shown in Table 4 for Class 3000 or Table 5 for Class 6000.
2.2 Class designations of these unions are correlated with ASME B36.10 Pipe Schedule Thicknesses as shown in Table 1.
2.3 Since ASME B36.10 does not include Schedule 160 thickness for NPS 1/8, 1/4, and 3/8, the values in Table 2 shall be used as the nominal wall thicknesses of the pipe.
SIZE
3.1 The size of the union is identified by the nominal pipe size (NPS).
Table 1
Correlation of Class Designation with Pipe Schedule
| Class Designation of Union | Pipe Used in Wall Thickness Calculations(a) |
| 3000 | Schedule 80 |
| 6000 | Schedule 160 |
Note: (a) This table is not intended to restrict the use of pipe with thinner or thicker walls with unions. The pipe actually used may be thinner or thicker in nominal wall than that shown in this table. The rating of the pipe, or the rating of the union as shown in Tables 4 or 5, whichever is less, may govern the rating of the system.
Table 2
Nominal Wall Thickness of Schedule 160 Pipe
| NPS of Union | Schedule 160 Nominal Wall Thickness |
| 1/8 | 0.124 |
| 1/4 | 0.145 |
| 3/8 | 0.158 |
DESCRIPTION
4.1 Parts of the Union: The complete union shall consist of three parts: the male end, the female end, and the nut. Equivalent terms for these parts are listed in Table 3.
4.2 Joint Design and Specifications
The seating surfaces of the joint shall be integral metal-to-metal, with a ball-to-cone design. The male and female ends shall be machined with sockets for socket welding or threaded with internal National Pipe Thread (NPT) type pipe threads, in accordance with ASME B1.20.1. The male and female ends, as well as the nuts, may be round, polygonal, or modified polygonal with rounded corners, based on the manufacturer’s option. The length of the union ends shall be sufficient to provide a suitable wrenching surface.
TABLE 3: Terminology of Parts
| Preferred Term | Equivalent Terms |
| Male | Male seat-end, Tail Piece, Nut Piece, Coupling, Ball End |
| Female | Female seal-end, Thread Piece, Body, Head, Cone End |
| Nut | Union Coupling Nut, Swivel, Ring |
MARKING
5.1 Marking Requirements
Each union part shall be permanently marked in accordance with MSS SP-25. The marking shall include (but is not limited to) the following:
a) Manufacturer’s name or trademark.
b) Material grade identification, in accordance with the requirements of the applicable ASTM specifications listed in Tables 4 or 5.
Note: Multiple material markings are allowed as covered in the ASTM material specifications listed in Tables 4 or 5.
c) Material lot or heat number for traceability.
d) Service designation: 3000 or 3M, or 6000 or 6M (M to designate units of 1000). See Section 5.4.
e) The nominal pipe size. See Section 5.4.
5.2 Marking for Compliance
All three parts of a union, in compliance with all requirements of this SP, shall be marked “SP83.”
5.3 Multiple Specification Marking
Unions manufactured from materials meeting all the ASTM material specification requirements for more than one specification, class, or grade may, at the manufacturer’s option, be marked with more than one specification, class, or grade designation, such as F304/304L and F316/316L, or A105/A234 WPB.
5.4 Optional Marking for Union Nut
The union nut marking of Service Designation (Section 5.1(d)) and Nominal Pipe Size (Section 5.1(e)) are at the option of the manufacturer.
MATERIAL
6.1 Conformance to Material Specifications
Unions shall conform to the requirements of the material specifications, grades, and classes listed in Tables 4 and 5.
TABLE4
Pressure-Temperature Service Rating, Class 3000 Pipe Unions-Socket Welding and Threaded Ends （pdf Click here）
TABLE5
Pressure-Temperature Service Rating, Class 6000 Pipe Unions-Socket Welding and Threaded Ends
6.2 Uniform Material Requirements
The three parts of a union assembly (assy.) shall be manufactured from materials that have the same requirements for chemical composition, mechanical properties, and applicable heat treatment.
6.3 Manufacturing Process
Union parts may be forged, seamlessly formed, or made from wrought bars, all conforming to the requirements for the grades and classes of the ASTM material specifications listed in Tables 4 and 5.
6.4 Use of Other Materials
Unions may be made from other wrought seamless materials by agreement between the manufacturer and the purchaser, but shall not be marked “SP83.”
DESIGN AND DIMENSIONS
8.1 Socket Wall Thickness for Socket Welding Unions: The socket wall thickness must meet or exceed the values shown in Tables 7 and 8.
8.2 Minimum Body Wall Thickness for Socket Welding Unions: The minimum body wall thickness (excluding the socket wall) should be at least equal to the nominal wall thickness of Schedule 80 pipe for Class 3000 or Schedule 160 pipe for Class 6000 as per ASME B36.10M.
8.3 Minimum Wall Thickness for Threaded Unions: The wall thickness at the root of the pipe thread at the wrench tight plane should meet or exceed the nominal wall thickness for Schedule 80 pipe for Class 3000 or Schedule 160 pipe for Class 6000, as shown in Tables 9 and 10.
8.4 Other Dimensions: Additional dimensions for socket welding and threaded unions are listed in Tables 7, 8, 9, and 10.
8.5 Interchangeability of Union Parts: Union parts from different manufacturers are not functionally interchangeable. Combining parts from different manufacturers is not recommended.
| NPS | Pipe End (min.) | Socket Bore Dia. | Socket Wall (min.) | Water Way Bore (a) | Laying Length | Male Flange (min.) | Nut (min.) | Threads per Inch | Bearing (min.) | Depth of Socket (min.) | Length of Assy. (nominal) | Clear Assy. Nut |
| A | B | C | D | E | F | G | H | J | K | L | N | |
| 1/8 | 0.86 | 0.440 0.420 | 0.125 | 0.299 0.239 | 0.88 0.75 | 0.125 | 0.125 | 16 | 0.049 | 0.38 | 1.63 | 2.0 |
| 1/4 | 0.86 | 0.575 0.555 | 0.130 | 0.394 0.334 | 0.88 0.75 | 0.125 | 0.125 | 16 | 0.049 | 0.38 | 1.63 | 2.0 |
| 3/8 | 1.02 | 0.710 0.690 | 0.138 | 0.523 0.463 | 1.06 0.81 | 0.135 | 0.135 | 14 | 0.054 | 0.38 | 1.81 | 2.2 |
| 1/2 | 1.23 | 0.875 0.855 | 0.161 | 0.652 0.592 | 1.06 0.81 | 0.145 | 0.145 | 14 | 0.059 | 0.38 | 1.93 | 2.3 |
| 3/4 | 1.46 | 1.085 1.065 | 0.168 | 0.854 0.794 | 1.25 1.00 | 0.160 | 0.160 | 11 | 0.066 | 0.50 | 2.24 | 2.6 |
| 1 | 1.79 | 1.350 1.330 | 0.196 | 1.079 1.019 | 1.35 1.03 | 0.180 | 0.175 | 1 | 0.073 | 0.50 | 2.44 | 3.1 |
| 1-1/4 | 2.16 | 1.695 1.675 | 0.208 | 1.410 1.350 | 1.60 1.28 | 0.210 | 0.205 | 10 | 0.084 | 0.50 | 2.80 | 3.7 |
| 1-1/2 | 2.42 | 1.935 1.915 | 0.218 | 1.640 1.580 | 1.66 1.34 | 0.230 | 0.220 | 10 | 0.091 | 0.50 | 3.01 | 4.4 |
| 2 | 2.96 | 2.426 2.406 | 0.238 | 2.097 2.037 | 1.79 1.47 | 0.260 | 0.250 | 10 | 0.106 | 0.62 | 3.39 | 5.2 |
| 2-1/2 | 3.61 | 2.931 2.906 | 0.302 | 2.529 2.409 | 2.43 2.05 | 0.295 | 0.280 | 8 | 0.121 | 0.62 | 4.03 | 5.9 |
| 3 | 4.30 | 3.560 3.535 | 0.327 | 3.128 3.008 | 2.51 2.11 | 0.325 | 0.315 | 8 | 0.139 | 0.62 | 4.29 | 6.9 |
Note: (a) The contact diameter of the male/female end is affected by the waterway bore (Column D). The manufacturer should consider the relationship between the contact point and the waterway diameter in the design.
| NPS | Pipe End (min.) | Socket Bore Dia. | Socket Wall (min.) | Water Way Bore (a) | Laying Length | Male Flange (min.) | Nut (min.) | Threads per Inch | Bearing (min.) | Depth of Socket (min.) | Length of Assy. (nominal) | Clear Assy. Nut |
| A | B | C | D | E | F | G | H | J | K | L | N | |
| 1/8 | 0.86 | 0.440 0.420 | 0.135 | 0.189 0.126 | 0.88 0.75 | 0.125 | 0.125 | 16 | 0.049 | 0.38 | 1.63 | 2.0 |
| 1/4 | 1.02 | 0.575 0.555 | 0.158 | 0.280 0.220 | 1.06 0.81 | 0.135 | 0.135 | 14 | 0.054 | 0.38 | 1.81 | 2.2 |
| 3/8 | 1.23 | 0.710 0.690 | 0.172 | 0.389 0.329 | 1.06 0.81 | 0.145 | 0.145 | 14 | 0.059 | 0.38 | 1.93 | 2.3 |
| 1/2 | 1.46 | 0.875 0.855 | 0.204 | 0.494 0.434 | 1.25 1.00 | 0.160 | 0.160 | 11 | 0.066 | 0.38 | 2.24 | 2.6 |
| 3/4 | 1.79 | 1.085 1.065 | 0.238 | 0.642 0.582 | 1.35 1.03 | 0.180 | 0.175 | 11 | 0.073 | 0.50 | 2.44 | 3.1 |
| 1 | 2.16 | 1.350 1.330 | 0.273 | 0.845 0.785 | 1.60 1.28 | 0.210 | 0.205 | 10 | 0.084 | 0.50 | 2.80 | 3.7 |
| 1-1/4 | 2.42 | 1.695 1.675 | 0.273 | 1.190 1.130 | 1.66 1.34 | 0.230 | 0.220 | 10 | 0.091 | 0.50 | 3.01 | 4.4 |
| 1-1/2 | 2.96 | 1.935 1.915 | 0.307 | 1.368 1.308 | 1.79 1.47 | 0.260 | 0.250 | 10 | 0.106 | 0.50 | 3.39 | 5.2 |
| 2 | 3.61 | 2.426 2.406 | 0.374 | 1.717 1.657 | 2.43 2.05 | 0.295 | 0.280 | 8 | 0.121 | 0.62 | 4.03 | 5.9 |
| 2-1/2 | 4.30 | 2.931 2.906 | 0.409 | 2.155 2.095 | 2.51 2.11 | 0.325 | 0.315 | 8 | 0.139 | 0.62 | 4.29 | 6.9 |
Note: (a) The contact diameter of the male/female end is affected by the waterway bore (Column D). The manufacturer should consider the relationship between the contact point and the waterway diameter in the design.
| NPS | Pipe End (min.) | Wall (min.) | Water Way Bore (a) | Male Flange (min.) | Nut (min.) | Threads per Inch | Bearing (min.) | Length of Assy. (nominal) | Clear Assy. Nut |
| A | C | D | F | G | H | J | L | N | |
| 1/8 | 0.58 | 0.095 | 0.332 0.253 | 0.125 | 0.125 | 16 | 0.049 | 1.63 | 2.0 |
| 1/4 | 0.75 | 0.119 | 0.438 0.372 | 0.125 | 0.125 | 16 | 0.049 | 1.63 | 2.0 |
| 3/8 | 0.90 | 0.126 | 0.562 0.532 | 0.135 | 0.135 | 14 | 0.054 | 1.81 | 2.2 |
| 1/2 | 1.09 | 0.147 | 0.703 0.672 | 0.145 | 0.145 | 14 | 0.059 | 1.93 | 2.3 |
| 3/4 | 1.32 | 0.154 | 0.906 0.842 | 0.160 | 0.160 | 11 | 0.066 | 2.24 | 2.6 |
| 1 | 1.63 | 0.179 | 1.141 1.092 | 0.180 | 0.175 | 11 | 0.073 | 2.44 | 3.1 |
| 1-1/4 | 1.99 | 0.191 | 1.484 1.392 | 0.210 | 0.205 | 10 | 0.084 | 2.80 | 3.7 |
| 1-1/2 | 2.25 | 0.200 | 1.714 1.622 | 0.230 | 0.220 | 10 | 0.091 | 3.01 | 4.4 |
| 2 | 2.76 | 0.218 | 2.188 2.052 | 0.260 | 0.250 | 10 | 0.106 | 3.39 | 5.2 |
| 2-1/2 | 3.36 | 0.276 | 2.609 2.532 | 0.295 | 0.280 | 8 | 0.121 | 4.03 | 5.9 |
| 3 | 4.03 | 0.300 | 3.250 3.042 | 0.325 | 0.315 | 8 | 0.139 | 4.29 | 6.9 |
Note: (a) The contact diameter of the male/female end is affected by the waterway bore (Column D). The manufacturer should consider the relationship between the contact point and the waterway diameter in the design.
| NPS | Pipe End (min.) | Wall (min.) | Water Way Bore (a) | Male Flange (min.) | Nut (min.) | Threads per Inch | Bearing (min.) | Length of Assy. (nominal) | Clear Assy. Nut |
| A | C | D | F | G | H | J | L | N | |
| 1/8 | 0.65 | 0.124 | 0.332 0.126 | 0.125 | 0.125 | 16 | 0.049 | 1.63 | 2.0 |
| 1/4 | 0.83 | 0.145 | 0.438 0.220 | 0.135 | 0.135 | 14 | 0.054 | 1.81 | 2.2 |
| 3/8 | 0.99 | 0.158 | 0.562 0.329 | 0.145 | 0.145 | 14 | 0.059 | L.93 | 2.3 |
| 1/2 | 1.22 | 0.188 | 0.703 0.434 | 0.160 | 0.160 | 11 | 0.066 | 2.24 | 2.6 |
| 3/4 | 1.49 | 0.219 | 0.906 0.582 | 0.180 | 0.175 | 11 | 0.073 | 2.44 | 3.1 |
| 1 | 1.82 | 0.250 | 1.141 0.785 | 0.210 | 0.205 | 10 | 0.084 | 2.80 | 3.7 |
| 1-1/4 | 2.16 | 0.250 | 1.484 1.130 | 0.230 | 0.220 | 10 | 0.091 | 3.01 | 4.4 |
| 1-1/2 | 2.46 | 0.281 | 1.714 1.308 | 0.260 | 0.250 | 10 | 0.106 | 3.39 | 5.2 |
| 2 | 3.06 | 0.344 | 2.188 1.657 | 0.295 | 0.280 | 8 | 0.121 | 4.03 | 5.9 |
| 2-1/2 | 3.63 | 0.375 | 2.609 2.095 | 0.325 | 0.315 | 8 | 0.139 | 4.29 | 6.9 |
| 2-1/2 | 4.38 | 0.438 | 3.250 2.594 | 0.401 | 0.401 | 8 | 0.160 | 7.50 | 7.9 |
Note: (a) The contact diameter of the male/female end is affected by the waterway bore (Column D). The manufacturer should consider the relationship between the contact point and the waterway diameter in the design.
SOCKET WELDING UNIONS
9.1 Assembly Uniformity: Union ends should be faced at right angles to the axis to ensure a flat welding surface. The socket should be counter-bored or machined for uniform depth and circularity.
9.2 Installation Recommendations: To minimize cracking of fillet welds, it is recommended to withdraw the connecting pipe about 0.06 inches away from the union socket bore before welding (refer to Figure 1).
Figure 1-Welding Gap
THREADED UNIONS
10.1 Dimensions: Threaded union dimensions are specified in Tables 9 and 10. Internal NPT pipe threads must comply with ASME B1.20.1, and gaging procedures should follow Section 3.1 of ASME B1.20.1.
NUT THREADS
11.1 Thread Form: Internal threads of the nut and external threads of the female part (thread piece) must follow the American National Thread form, according to ASME B1.1, Unified and American Screw Threads, with Class 2A external and 2B internal tolerances and clearances.
11.2 Modifications: Manufacturers may alter values in Column “H” of Tables 7 through 10, provided that ASME B1.1 and all other standard requirements are met.
FINISH
12.1: Surfaces must be free of sharp burrs and have a workmanlike finish.
TOLERANCES
13.1 General Tolerances: These are listed in Tables 7, 8, 9, and 10.
13.2 Concentricity: The socket must be concentric with the waterway bore within a tolerance of ±0.03 inches for all sizes.
13.3 Coincidence of Axis: The alignment of the threaded pipe ends should not vary by more than 0.19 inches per foot. Figure 2 shows a method for checking alignment. Minimum nut tightening torque values for checking axis coincidence are listed in Table 6.
Figure 2
Recommended Method for Checking Coincidence of Axis on Threaded Unions (For Illustration Only)
Table 6
Minimum Recommended Nut Tightening Torque for Checking Coincidence of Axis
| NPS | 1/8 | 1/4 | 3/8 | 1/2 | 3/4 | 1 | 1-1/4 | 1-1/2 | 2 | 2-1/2 | 3 |
| Foot-Pounds (ft-lbs) (Minimum) | 85 | 85 | 100 | 100 | 120 | 120 | 130 | 130 | 130 | 150 | 150 |
Note: Torque can also be expressed as foot-pound (ft-lb) or pound-force-foot (lbf-ft), often shortened to lb-ft.
CORROSION PROTECTION
14.1: Carbon and alloy steel unions must be effectively protected against corrosion. Excess oils from forming, machining, or processing are unacceptable as corrosion protectants. Specialty protection may be agreed upon between the manufacturer and the purchaser.
ANNEX A Referenced Standards and Applicable Dates
This Annex is an integral part of this Standard Practice and is placed after the main text for convenience.
| Standard Name | Description |
| ASME B1.1-2003 (R2008) | Unified Inch Screw Threads (UN and UNR Thread Form) |
| ASME B1.20.1-2013 | Pipe Threads, General Purpose (Inch) |
| ASME B16.11-1991 | Forged Fittings, Socket-Welding and Threaded (historical) |
| ASME B36.10M-2015 | Welded and Seamless Wrought Steel Pipe |
| ASTM A105/A105M-14 | Carbon Steel Forgings for Piping Applications |
| ASTM A182/A182M-18 | Forged or Rolled Alloy and Stainless Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service |
| ASTM A234/A234M-18 | Piping Fittings of Wrought Carbon Steel and Alloy Steel for Moderate and High-Temperature Service |
| ASTM A312/A312M-17 | Seamless, Welded, and Heavily Cold Worked Austenitic Stainless Steel Pipe |
| ASTM A350/A350M-18 | Carbon and Low-Alloy Steel Forgings Requiring Notch Toughness Testing for Piping Components |
| ASTM A403/A403M-18 | Wrought Austenitic Stainless Steel Piping Fittings |
| ASTM A420/A420M-16 | Piping Fittings of Wrought Carbon Steel and Alloy Steel for Low-Temperature Service |
| ASTM B366/B366M-17 | Factory-Made Wrought Nickel and Nickel Alloy Fittings |
| ASTM B462-15 | Forged or Rolled UNS N06030, UNS N06022, UNS N06035, UNS N06200, UNS N06059, UNS N10362, UNS N06686, UNS N08020, UNS N08367, UNS N10276, UNS N10665, UNS N10675, UNS N10629, UNS N08031, UNS N06045, UNS N06025, UNS R20033 Alloy Pipe Flanges, Forged Fittings, and Valves and Parts for Corrosive High-Temperature Service |
| ASTM B564-17a | Nickel Alloy Forgings |
| MSS ANSI/MSS | |
| SP-25-2018 | Standard Marking System for Valves, Fittings, Flanges, and Unions |
| MSS Standard Practices (SPs) Related to or referenced in this publication: | |
| ANSI/MSS SP-25 | Standard Marking System for Valves, Fittings, Flanges, and Unions |
| ANSI/MSS SP-96 | Terminology for Valves,Fittings,and Their Related Components |
| American National Standards Published by MSS,an ANSl-accredited Standards Developer: | |
| ANSI/MSS SP-44 | Steel Pipeline Flanges |
| ANSI/MSS SP-55 | Quality Standard for Steel Castings for Valves, Flanges, Fittings, and Other Piping Components – Visual Method for Evaluation of Surface Irregularities |
| ANSI/MSS SP-58 | Pipe Hangers and Supports – Materials, Design, Manufacture, Selection, Application, and Installation |
| ANSI/MSS SP-96 | Terminology for Valves, Fittings, and Their Related Components |
| ANSI/MSS SP-114 | Corrosion Resistant Pipe Fittings Threaded and Socket Welding Class 150 and 1000 |
| ANSI/MSS SP-122 | Plastic Industrial Ball Valves |
| ANSI/MSS SP-134 | Valves for Cryogenic Service, including Requirements for Body/Bonnet Extensions |
| ANSI/MSS SP-135 | High Pressure Knife Gate Valves |
| ANSI/MSS SP-138 | Quality Standard Practice for Oxygen Cleaning of Valves and Fittings |
| ANSI/MSS SP-144 | Pressure Seal Bonnet Valves |
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