MSS SP-95-2018 is a standard practice document issued by the Manufacturers Standardization Society (MSS), which provides detailed specifications for the design, manufacture, and inspection of swaged nipples and bull plugs.
This Standard Practice covers the dimensions, finish, tolerances, marking, and material for carbon steel and alloy steel Swaged Nipples (male-end reducing fittings) from NPS 1/8 to NPS 12 (DN 6 to DN 300) and Bull Plugs (hollow or solid male closures) from NPS 1/8 to NPS 12 (DN 6 to DN 300).
These fittings have ends that may be threaded, beveled, square cut, grooved, or any combination of these. Both concentric and eccentric Swaged Nipples are included.
Fittings with special dimensions and non-standard materials may be designed and manufactured by agreement between the manufacturer and purchaser, provided they are marked as partial compliance fittings in accordance with Section 4.1(c).
PRESSURE RATINGS
2.1 The allowable working pressure for fittings designed under this Standard Practice is to be calculated as for straight seamless pipe with equal end preparation, following the applicable sections of ASME B31.1 (Power Piping) or ASME B31.3 (Process Piping). The pipe wall thickness and material type will correspond to the ordered fittings, and fittings shall be identified by pipe wall thickness and material grade instead of pressure rating.
2.2 Fitting designs can be based on mathematical analysis from nationally recognized pressure vessel or piping codes, or by proof testing at the manufacturer’s discretion in accordance with Section 9. Records of designs or successful proof tests shall be available for inspection at the manufacturer’s facility. For Bull Plugs, the minimum head thickness must be at least 1.5 times the thickness of the corresponding pipe schedule. If drilled and tapped, the head thickness must be increased to meet the minimum L2 thread length as specified in ASME B1.20.1.
SIZE
Each fitting shall be marked as per MSS SP-25 to show the following:
a) Manufacturer’s name or trademark
b) “CR” followed by the material identification symbol established for the respective grade in the appropriate ASTM specifications or AISI/SAE designations
c) Manufacturer’s heat number/identification number|
d) Schedule number or nominal wall thickness designation
e) Size
Where the size of the fittings does not permit complete marking, Sections 5.1(a) and (c) are mandatory. The other marking and identification marks may be omitted in the sequence, as specified in MSS SP-25.
The required markings shall be made by any suitable method that is not injurious to the fitting.
| NPS | DN | NPS | DN | NPS | DN |
| 1/8 | 6 | 1 1/4 | 32 | 4 | 100 |
| 1/4 | 8 | 1 1/2 | 40 | 5 | 125 |
| 3/8 | 10 | 2 | 50 | 6 | 150 |
| 1/2 | 15 | 2 1/2 | 65 | 8 | 200 |
| 3/4 | 20 | 3 | 80 | 10 | 250 |
| 1 | 25 | 3 1/2 | 90 | 12 | 300 |
MARKING
4.1 Each fitting shall be marked with the following prescribed information using raised lettering, electro-etching, vibro-etching, laser etching, or other permanent methods that do not cause harmful contamination or sharp discontinuities:
- a) Manufacturer’s name or trademark.
- b) Material Identification:
- Fittings shall be marked with the material grade according to the applicable ASTM Fittings Specifications, such as A234/A234M, A403/A403M, A420/A420M, A815/A815M, or A858/A858M (e.g., WPB, WP304, WPL6).
The material lot or heat number, traceable to the material, must be included as part of the material identification.
- c) Schedule number or nominal wall thickness designation of Swaged Nipple or Bull Plug.
- For combination schedules: large-end x small-end of Swaged Nipples.
Example: Sch. 80 x Sch. 40. - d) Size:
- Nominal pipe size (NPS or DN) of Bull Plug.
Nominal pipe size (NPS or DN) for Swaged Nipples, with large end size listed first and small end size second.
Example: 2 x 1 (50 x 25). - e) Product Conformance:
- Fittings must be marked with the symbol “SP95” to denote full conformance with this Standard Practice. Partial compliance fittings (as covered in Section 1.2) shall not be marked “SP95.” If marked with an ASTM designation, the marking shall be followed by the symbol “S58” as required by the “Supplementary Requirements” for Special Fittings in ASTM A960/A960M.
4.2 If the size and shape of the fitting do not permit all the above markings, they may be omitted in reverse order as listed above.
4.3 The minimum permanent marking includes the manufacturer’s name or trademark, material grade, heat number, and schedule number or nominal wall thickness.
4.4 When steel stamps are used, care must be taken to ensure that the marking is not deep enough to reduce the wall thickness of the fitting below the minimum allowed.
4.5 Additional marking may be required as per MSS SP-25.
MATERIALS
5.1 The steel used for Swaged Nipples and Bull Plugs shall consist of forgings, extrusions, round or hex bars, or seamless pipe or tube, and must conform to the requirements of ASTM A234/A234M, A403/A403M, A420/A420M, A815/A815M, A858/A858M, or the corresponding ASME Specification.
When Swaged Nipples and Bull Plugs are made from materials other than those referenced in this Standard Practice, they should be appropriately marked as agreed upon between the manufacturer and purchaser.
Dimensions
6.1 The dimensions of Swaged Nipples shall conform to Table 1 or Table 1M, and Bull Plugs shall conform to Table 2 or Table 2M. Tolerances for Swaged Nipples and Bull Plugs shall conform to Table 3 (U.S. customary units) or Table 3M (SI metric units).
End Preparation
7.1 Pipe ends may be threaded, beveled for butt-welding, square cut (plain) for socket welding, grooved, or any combination thereof.
7.2 Threaded ends shall conform to ASME B1.20.1. Threads shall be chamfered at the ends of the fitting to protect the first thread. The reference point for gauging threads is the last thread scratch on the chamfer cone.
7.3 Butt-welding ends shall conform to ASME B16.25.
7.4 Grooved ends shall be agreed upon between the manufacturer and purchaser.
Surface Quality
8.1 Fittings supplied under this specification shall comply with the surface quality requirements of ASTM A960/A960M.
ANNEX A Referenced Standards and Applicable Dates
| Standard Name | Description |
| ASME;ANSI/ASME | |
| B1.20.1-2013 | Pipe Threads,General Purpose(Inch) |
| B16.25-2017 | Buttwelding Ends |
| B31.1-2016 | Power Piping |
| B31.3-2016 | Process Piping |
| ASTM | Standard Specification for: |
| A234/A234M-18 | Pipe Fittings of Wrought Carbon Steel and Alloy Steel for Moderate and High Temperature Service |
| A403/A403M-18 | Wrought Austenitic Stainless Steel Piping Fittings |
| A420/A420M-16 | Pipe Fitting of Wrought Carbon Steel and Alloy Steel for Low-Temperature Service |
| A815/A815M-17 | Wrought Ferritic,Fermitic/Austenitic,and Martensitic Stainless Steel Piping Fittings |
| A858/A858M-14 | Heat-Treated Carbon Steel Fittings for Low-Temperature and Corrosive Service |
| A960/A960M-16a | Common Requirements for Wrought Steel Piping Fittings |
| SP-25-2018Ss | 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 ANSI-accredited Standards Developer:
ANSI/MSS SP-25: Standard Marking System for Valves, Fittings, Flanges, and Unions
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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