Field welding of Weld Neck flanges to Line Pipe
has occurred for years and as long as the joined assemblies of pipe
and flanges has service pressure well below flange rated pressure,
the assemblies give little trouble. As the oilfield has matured and
higher pressures have become a prominent issue, all potentially
pressurized assemblies should now receive pressure tests to 1.5
times working pressure when first weld assembled, and to full rated
working pressure with each movement of the assembly.
API Flange Specifications prescribe strength of
material and chemistry limits for flanges, but leave the operators
choice of pipe strength unspecified.
API Specification 5L specifies pipe of various
sizes and wall thicknesses, many of which will match up to
Flange Weld Necks, and this line
pipe has many strength grades (see
API 5L Line Pipe Physical
Properties) but API Spec 5L does not designate working pressures
for any sizes or strength grades.
WOODCO USA uses a formula consistent with API
Spec 6A 20th Edition, Para. 126.96.36.199 Distortion energy theory. Our
formula makes no allowance for defects in material, variation in
wall thickness, etc. You can use the calculator below, inputing your
pipe wall and yield strength for the pipe selected. Users will have
to determine the safety factors they want to use for the variation
they expect to encounter in practice including considerations for
corrosion, internal erosion, and welding variation.
provided below, will allow users to estimate the working pressure of
selected sizes and strength grades of pipe, (see
Carbon Steel Pipe Dimensions and Weights
for Pipe O.D.'s, I.D.'s, and wall Thicknesses).