MSS SP-75 WPHY Pipe Fittings

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.

the standard specifies the dimensions, tolerances, ratings, materials, chemical composition and tensile properties, heat treatment, notch toughness, manufacturing and marking of quality butt welded pipe fittings for nps 60 and smaller. normally for nps14 and smaller butt weld pipe fittings referred to asme b16.9.

pressure ratings

the allowable internal pressure ratings for straight seamless steel pipe (or welded steel pipe with a joint coefficient of 1.0) of equivalent grades and diameters and wall thicknesses shall be calculated in accordance with the rules established in the applicable section of asme b31 and in accordance with the fittings designed in this standard specification.

 according to mss sp-75, all fittings made shall be designed to support the field hydrostatic pressure test at a pressure level . this pressure level is equivalent to the pressure level required to form an hoop stress. based on the barlow formula, the hoop stress is equal to the specified minimum yield strength for pipe of equivalent grade and wall thickness under the condition of no damage, leakage or failure.

barlow's formula

it is defined as:

p = 2st/ d

where:

p= internal design pressure, psig;

s= specified minimum yield strength of the pipe, psi;

t= nominal wall thickness of the pipe, inches;

d= outside diameter of the pipe, inches.

size

the nominal size of the pipe fitting is shown in the nominal outside diameter of the pipe to which it is connected.

 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%.

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