Manufacturers Standardization Society (MSS)

Manufacturers Standardization Society

High-Strength, Wrought, Butt-Welding Fittings

This Standard Practice covers factory-made, seamless and electric welded carbon and low-alloy steel, butt-welding fittings for use in high pressure gas and oil transmission and distribution systems; including pipelines, compressor stations, metering and regulating stations, and mains.

This Standard Practice governs dimensions, tolerances, ratings, testing, materials, chemical and tensile properties, heat treatment, notch toughness properties, manufacture, inspection, certification, and marking for high-strength, butt-welding fittings NPS 60 and smaller.

With respect to minimum yield strength, MSS SP-75 pipe fittings can be further classified into 7 classes: WPHY-42, WPHY-46, WPHY-52, WPHY-56, WPHY-60, WPHY-65 and WPHY-70.

WP is the abbreviation for "wrought pipe" or "wrought plate" while HY stands for "high yield".

These WPHY pipe fittings can be supplied as long radius elbows, 3R elbows, straight tees, reducing tees, caps and reducers. They are typically used to connect to API 5L pipes or ASTM A694 forged pipe flanges.

MSS SP-75 Grade WPHY 60, 65, and 70 are used a lot in the high pressure oil and gas pipeline fittings, for WPHY-42, 46, 52 and 56, they are working in a medium-high pressure pipelines, so mostly client may choose with ASTM A234 WPB or WPC instead.


The raw material for MSS SP 75 pipe fittings is fully killed steel manufactured by the open-hearth, basic oxygen or electric-furnace process. It consists of blooms, billets, slabs, forging grade bar, plate, seamless or fusion-welded pipes. Welding processes are performed in accordance with Section IX of the ASME Boiler and Pressure Vessel Code, or related ASTM and API specifications.

Heat treatment after welding shall be in accordance with the requirements of Section VIII, Division 1 of the ASME Boiler and Pressure Vessel Code. The weld ends (bevels) of the fitting shall be different in wall thickness.

The MSS SP 75 WPHY pipe fittings can be readily fabricated by forging, hammering, pressing, piercing, rolling, extruding, stamping, welding or a combination of these processes. The finished products must be free of harmful defects or weld repairs. Some customers may require surface defects to be machined and ground.

Chemical Composition
MSS SP-75 Fittings

Elements Value, %
Carbon (C) ≤0.30
Manganese (Mn) ≤1.60
Phosphorus (P) ≤0.035
Sulfur (S) ≤0.035
Copper (Cu) ≤0.50
Nickel (Ni) ≤0.50
Silicon (Si) ≤0.50
Chromium (Cr) ≤0.25
Molybdenum (Mo) ≤0.13
Vanadium (V) ≤0.13
Columbium (Cb) ≤0.10
Titanium(Ti) ≤0.05

Mechanical Properties
MSS SP-75 Fittings

MSS SP 75 Class Yield Strength Tensile Strength Elongation
Min. psi Min. psi min. %
WPHY-42 42000 60000 25
WPHY-46 46000 63000 25
WPHY-52 52000 66000 25
WPHY-56 56000 71000 20
WPHY-60 60000 75000 20
WPHY-65 65000 77000 20
WPHY-70 70000 82000 18

Heat Treatment
Fittings for piping manufactured according to MSS SP-75 shall be supplied in heat-treated condition. Heat treated fittings shall be cooled below the lowest critical temperature prior to heat treatment. Fittings shall be heat treated by one or more of the following procedures: annealing (stress relieving), normalizing, normalizing and tempering, quenching and tempering.

Tests and examinations
Tests and examinations available for WPHY fittings include hydrostatic test (pressure test), tensile tests, PMI (spectrum), Charpy test, radiographic examination (X-ray, RT), magnetic particle inspection (MPI), ultrasonic examination (UT), liquid penetration examination (LPE), etc.

Dimensions and tolerances
MSS SP 75 specifies dimensions and tolerances only for pipe fittings from NPS 16 (DN 400) to NPS 60 (DN 1500). Size specifications for NPS 14 and smaller are given by reference to ASME B 16.9. Tolerances can be found on each fitting dimensions page.

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