MSS SP 75 is the standard specification for high-test, wrought, butt-welding fittings which covers factory-made seamless and electric fusion-welded carbon and low-alloy steel butt-welding pipe fittings for use in high-pressure oil and gas transmission and distribution systems, including pipelines, compressor stations, metering and regulating stations, and mains. In term of minimum yield strength, MSS SP 75 pipe fittings can be further categorized 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 furnished as long-radius elbows, 3R elbows, straight tees, reducing tees, caps and reducers. They are usually used for the joint with API 5L pipes or ASTM A694 forged pipe flanges.

 1. Chemical Composition Requirements of MSS SP 75

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

*1. The sum of Cu, Ni, Cr and Mo shall not exceed 1%.
*2. Carbon equivalent C.E.=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15 shall not exceed 0.45%.

2. Mechanical Properties of MSS SP 75 Pipe Fittings

MSS SP 75 Class	Yield Strength	Tensile Strength	Elongation	Charpy Test
	Min. psi	Min. psi	min. %	Ave. Energy absorbed @ 20°F
WPHY-42	42000	60000	25	≥20ft*lbs
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

3. Material, Welding & Manufacture

The raw material of MSS SP 75 pipe fittings shall be fully killed steels made by either open hearth, basic oxygen, or electric furnace process. It consists of blooms, billets, slabs, forging quality bar, plate, seamless or fusion-welded pipes. The welding processes shall be conducted in accordance with Section IX of ASME Boiler and Pressure Vessel Code, or related ASTM & API specifications. Post-weld heat treatment shall be taken in accordance with the requirements of Section VIII, Division 1 of ASME Boiler and Pressure Vessel Code. The welding ends (bevels) of the fitting shall be furnished differently in terms of wall thickness.

The MSS SP 75 WPHY pipe fittings may be readily manufactured by forging, hammering, pressing, piercing, rolling, extruding, upsetting, welding, or by a combination of these processes. Finished products shall be free of injurious defect or welding-repair. Machining and grinding of surface defects may be required by some clients.

4. Heat Treatment

Pipe fittings manufactured to MSS SP 75  shall be furnished in the heat treated condition. Hot formed fittings shall be cooled below the lower 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.

5. Tests and Examinations

The tests and examinations available for WPHY fittings includes hydrostatic test(proof test), tensile tests, PMI(spectrum), Charpy test, radiographic examination(X-Rays, RT), magnetic particles inspection(MPI), ultrasonic examination(UT), Liquid Penetration Examination(LPE), etc.

6. Dimensions and Tolerances

MSS SP 75 only specifies the dimensions and tolerances for pipe fittings sized from NPS 16 (DN 400) through NPS 60 (DN 1500). Dimensional requirements for NPS 14 and smaller are provided by reference to ASME B 16.9.

Dimensions of MSS SP 75 Butt-welding Pipe Fittings
Long-Radius Elbows	3R Elbows	Straight Tees
Reducing Tees	Caps	Reducers

*Click to see the tolerances for dimensions of MSS SP 75 WPHY pipe fittings.

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