Double Studded Adapters and
Except for Crossover
Connections, Double Studded Adapters (DSA's) serve as the
shortest method to join flanges of different sizes or pressure
ratings. The DSA has a body resembling a flange with a different
seal size or bolt pattern on each side. The connecting bolts for
each side, called "Tap End Studs" thread into tapped holes in
the body, conforming to the same size bolts and bolt circle as
nominal for the specified flange each side shall fit. The
internal bore will not exceed that specified for the smaller
side, and if nominally different on each side, shall transcend
by a taper, (see illustration below). API specifies
no thickness requirement for DSA's. DSA's usually have a minimum
thickness equal to the thickness of a flange of equal size and
pressure to the largest and highest pressure side of the DSA,
and may have any amount of additional thickness as necessary to
satisfy design requirements or allow for lock screws.
LAYOUT, DOUBLE STUDDED ADAPTER
(To see a catalog page
DSA's shall have their bolt circles oriented so that equipment
assemblies will maintain consistent orientation throughout the
equipment stack-up. All API conventional flange bolt circles
have a number of evenly spaced holes, divisible by four. All API
equipment shall have bolt circles with two holes of each bolt
circle equally straddling a common centerline.
(To see a catalog page
In the event an equipment assembly needs a small amount of
extension, a Spacer Flange may have the appearance of a DSA yet
have the same connection geometry on both sides. Such a spacer
flange may have its bolt circle drilled through and attach
within the equipment stack using extra-long flange
bolts. Spacer flanges may have any length (thickness) not
constrained by design requirements. Studded spacer flanges must
have sufficient length (thickness) to accommodate tapped holes
that accept full thread engagement of the tap end studs.
Spacer flanges with drilled through holes may have a much
shorter length (thickness), so long as the root thickness
between opposite ring grooves remains adequate to the stresses
necessary to coin the ring gaskets to seal (the drilled through
spacer flange experiences only compression and pressure
loading). Bolts produce no stress in drilled through spacer
flanges. As a general rule, a drilled through spacer flange may
have a minimum thickness of 4 times its ring groove depth.
11" 5M x 11" 5M SPACER FLANGE
DSA's and spacer flanges may or may not have lock-down screws to
secure internal bore wear bushings or sealing devices.
DSA's having a different number of
bolts on each side may not allow enough space between tapped holes for
drilling lock-screw holes. Adding thickness to the DSA design, if
equipment stack-up height permits, may remove this limitation.
For more about DSA minimum thickness, see
Q & A 9.