5
alternative is to increase the size of the flange while keeping
the pipe size, for example, using a 3” flange on a 2” pipe.
However, this strategy has certain disadvantages:
• Project costs increase due to the procurement of
more expensive flanges and potential equipment
adapted to the revised drilling pattern/size.
• The unavailability of mating equipment compatible
with the new drilling pattern/size may pose addi-
tional complications
FRP FLANGE FABRICATION
Similar to the design of FRP flanges, the fabrication of the
flanges is not a straightforward process. Here is a summary
of some common practices in the fabrication of hand lay-
up (HLU) flanges.
There are two main fabrication methods for FRP HLU
flanges, integral flanges and flanges on pipe. In the flange-
on-pipe method, a premade pipe will be used as a starting
point and the rest of the flange will be laminated onto the
pipe. In the integral method, there is no premade part and
the whole flange will be made from starch.
The flange-on-pipe type is usually less expensive
because long lengths of pipe can be made on a mandrel, cut
into pieces, and then used for flanges, reducing the time
required for flange fabrication. On the other hand, inte-
gral flanges offer superior structural integrity as all layers
including pipe layers are interconnected to the flange face.
It should be noted that regardless of the type of fabrica-
tion the flanges are designed adequately for the operating
conditions.
FRP flanges are typically made using the reinforcement
shapes shown in Figure 2.
• Skirts are rectangular fabrics with cuts on one side.
This fabric is wrapped around the flange stub, with
the cut pieces extending onto the flange face. The
skirts increase the thickness of the stub, hub, and
flange.
• Rings are circular fabrics with a hole in the middle
with the size of the hub. The rings increase the flange
thickness without altering the hub or stub thickness.
• Stars are similar to rings with smaller holes in the
middle and some cuts. By applying stars on the
flange face, the cut portion of the star extends onto
the hub. Stars contribute to the flange thickness and
depending on the dimensions could contribute to
the hub thickness. Stars are not as common as rings
in the industry.
There is no standard method of fabrication and typi-
cally each manufacturer uses a different method based on
their experience, tooling availability, and comfort. The
complexity of fabrication typically arises from the follow-
ing factors:
• Different ways to achieve the specified thicknesses do
not necessarily lead to the same flange quality.
– The interdependency of thicknesses of different
sections.
• Strict tolerances, especially in the case of LJ flanges
and FF flanges with backing rings.
• The geometry makes it more challenging to apply
and roll the reinforcement.
Due to these challenges, proper fabrication planning is
as important as proper design in achieving a high-quality
FRP flange.
Another major contributing factor in the fabrication of
high-quality flanges is the number and distribution of the
layers that connect the flange face to the hub, i.e., skirts and
stars (with proper dimensions). Since the flange thickness
is usually larger than the hub thickness some ring layers
are required to build up the flange. However, stacking large
numbers of rings without having some interspersed skirts
could lead to flange with lower structural integrity. There
is no hard-and-fast rule for the number of rings allowed
Figure 2. Typical laminate shapes used in the fabrication of FRP flange (a) skirt (b) ring (c) star
alternative is to increase the size of the flange while keeping
the pipe size, for example, using a 3” flange on a 2” pipe.
However, this strategy has certain disadvantages:
• Project costs increase due to the procurement of
more expensive flanges and potential equipment
adapted to the revised drilling pattern/size.
• The unavailability of mating equipment compatible
with the new drilling pattern/size may pose addi-
tional complications
FRP FLANGE FABRICATION
Similar to the design of FRP flanges, the fabrication of the
flanges is not a straightforward process. Here is a summary
of some common practices in the fabrication of hand lay-
up (HLU) flanges.
There are two main fabrication methods for FRP HLU
flanges, integral flanges and flanges on pipe. In the flange-
on-pipe method, a premade pipe will be used as a starting
point and the rest of the flange will be laminated onto the
pipe. In the integral method, there is no premade part and
the whole flange will be made from starch.
The flange-on-pipe type is usually less expensive
because long lengths of pipe can be made on a mandrel, cut
into pieces, and then used for flanges, reducing the time
required for flange fabrication. On the other hand, inte-
gral flanges offer superior structural integrity as all layers
including pipe layers are interconnected to the flange face.
It should be noted that regardless of the type of fabrica-
tion the flanges are designed adequately for the operating
conditions.
FRP flanges are typically made using the reinforcement
shapes shown in Figure 2.
• Skirts are rectangular fabrics with cuts on one side.
This fabric is wrapped around the flange stub, with
the cut pieces extending onto the flange face. The
skirts increase the thickness of the stub, hub, and
flange.
• Rings are circular fabrics with a hole in the middle
with the size of the hub. The rings increase the flange
thickness without altering the hub or stub thickness.
• Stars are similar to rings with smaller holes in the
middle and some cuts. By applying stars on the
flange face, the cut portion of the star extends onto
the hub. Stars contribute to the flange thickness and
depending on the dimensions could contribute to
the hub thickness. Stars are not as common as rings
in the industry.
There is no standard method of fabrication and typi-
cally each manufacturer uses a different method based on
their experience, tooling availability, and comfort. The
complexity of fabrication typically arises from the follow-
ing factors:
• Different ways to achieve the specified thicknesses do
not necessarily lead to the same flange quality.
– The interdependency of thicknesses of different
sections.
• Strict tolerances, especially in the case of LJ flanges
and FF flanges with backing rings.
• The geometry makes it more challenging to apply
and roll the reinforcement.
Due to these challenges, proper fabrication planning is
as important as proper design in achieving a high-quality
FRP flange.
Another major contributing factor in the fabrication of
high-quality flanges is the number and distribution of the
layers that connect the flange face to the hub, i.e., skirts and
stars (with proper dimensions). Since the flange thickness
is usually larger than the hub thickness some ring layers
are required to build up the flange. However, stacking large
numbers of rings without having some interspersed skirts
could lead to flange with lower structural integrity. There
is no hard-and-fast rule for the number of rings allowed
Figure 2. Typical laminate shapes used in the fabrication of FRP flange (a) skirt (b) ring (c) star