outer metal ring, the gasket will not be crushed and an
problems. Most piping systems have installed pipe
adequate preload is imparted on the gasket. After
hangers or supports that can be adjusted to properly
aligning the joint, inserting the gasket, and installing the
support the pipe. Adjust the hangers by loosening up on
bolts as previously discussed, you are ready to tighten
the supports and then adjusting them to carry their share
the joint. Tighten the bolts in sequence according to the
of the load. By adjusting pipe hangers and supports, you
applicable technical documentation until you bring the
should be able to align piping sections so that flange
flanges in contact with the gasket's outer ring. After
bolts may be inserted freely without forcing.
flange contact is made, you should torque the bolts to
Plain Flange Makeup.--This section will address
the required tension. An alternate technique would be
the makeup of plain flanges using flexible gasket
to measure the thickness of the outer ring of the gasket.
material. After you have aligned the flanges, choose the
You should then tighten the joint until the distance
proper gasket material for the job at hand. When
between the flanges is equal to the ring thickness plus
choosing gasket thickness, keep the following factors
0.003 inch. Check this dimension with a feeler gauge at
in mind:
four points, 90 degrees apart. Remember to tighten all
joints evenly and maintain proper alignment.
The thinner the gasket material the better the
joint, especially in high-pressure joints.
Bolt-Stud Stress.-- To ensure that the gasket has
been compressed the correct amount and that the
If the flanges are too far apart to be brought
bolt-stud has not been overstressed, measure the
together, use a spacer and two thin gaskets
elongation of each bolt stud. The bolt-stud stress
(except for spiral wound, buna, and cork gaskets)
required for proper compression of gaskets is shown in
rather than one that is thicker than l/16 inch.
table 16-3. These bolt-stud stresses have been selected
With the use of thinner gaskets, you may have to
to provide a reasonable factor of safety based on the
use stronger bolts to obtain required gasket
yield point of the material and to ensure a tight joint.
compression.
After obtaining the correct gasket material, you
Table 16-3.--Bolt-Stud Stress Required for Correct Com-
pression of Metallic-Asbestos Spiral-Wound Gaskets
imperfections before installation. Replace bolts and
nuts that show signs of corrosion, damage, or other
Size of Pipe or Bolt-Stud Stress
Operating
Type
imperfections. Before inserting the gasket between the
Pressure
Tubing
(psi) (based on
Gasket
flanges, you should coat one side of the gasket with
cross-sectional
(psi)
graphite. By coating one side of the gasket with
area at root
graphite, you will lessen the danger of tearing the gasket
diameter of
when the joint is broken. After installing the gasket,
thread)
insert all the bolts and nuts and tighten as required.
All
MIL-G-
150
30,000 10%
Buna and Cork Gaskets.--These gaskets require
16265
special precautions when making up flanged joints.
l/4″ to 1″ IPS
Buna and cork gaskets should be compressed between
300
25,000 10%
and 16″ OD
20 and 30 percent of the original thickness but never
more than 70 percent. If you compress the gasket more
400
than 70 percent, you could cause excessive side flow,
1-1/4 ″ to 12″
600
30,000 10%
permanent set, or loss of resiliency. After you assemble
IPS and 14″ to
a buna- or cork-gasketed joint, tighten setup nuts in
15″ OD
approximately 180- and 90-degree sequence from the
starting point. After final seating of the gasket, you
1/4″ to 1″ IPS
MIL-G-
150
25,000 10%
should use feeler gauges at 90-degree intervals to
300
21032
measure gasket compression.
400
1-1/4″ IPS and
600
30,000 10%
Raised Face Flange Makeup.--Raised face
900
larger
flanges are designed for use in high-pressure and
1500
temperature systems using spiral-wound metallic
gaskets. Spiral-wound metallic gaskets are designed so
2500
All
25,000 10%
that when the mating flanges are brought up against the
16-20