THERMAL EXPANSION
The inner pipe of Models DCL, DIS PRO and DAS PRO is load bearing and its thermal
expansion is the same as that of a continuous pipe. A simplified rule for exhaust pipe
expansion estimation is that the axial growth will be approx. 1” per 100’ of pipe length
for each 100°F the flue gas temperature is above the surrounding air temperature. See
THERMAL EXPANSION CALCULATIONS in SECTION B
When assembled in any orientation, the amount of thermal expansion of the inner pipe
is directly dependent on the inner wall temperature and the length of pipe between fixed
points. Good installation practice requires that expansion greater than 1/4 inch will
be compensated for using a Bellows Joint or Adjustable Length, depending on the
maximum pressure encountered.
The flanged inner piping joints have negligible flexing capacity, and in addition, tees and
elbows are not designed to withstand bending moment forces. Because the amount
of outer casing axial movement is the same as inner casing movement, the outer
jackets of piping must slide to avoid excessive forces on tees, elbows or fixed points.
To accommodate outer casing movements, external guides along walls at floors, or in
lateral breechings, must allow for movement of pipe.
CAUTION:
When a joint of assembly is just bellow a Guide Support
(WGHD)
, a
minimum space between the top of the outer Band
(BSE)
and the Guide must be
added. This distance must be at least the value of the Thermal expansion calculated.
NOTE:
When resupporting a high rise exhaust system, Adjustable Lengths or Bellows
Joints must be used just below every support above the first to compensate for
thermal expansion. For engine and turbine exhaust systems requiring pressures to
60 inches of water column, or where the construction must be absolutely gas tight, all
welded Bellows Joints are recommended for expansion and vibrational movements
of the exhaust piping. Out-of-doors construction or low pressure systems, such as
boilers (to 6 inches of water column), can effectively use the Adjustable Length.
Spacing of guides and supports, when a thermal expansion part is used, should be not
greater than specified in
Section B
. Proper guiding and support of expansion parts often
requires closer spacing.
BELLOWS LENGTH (LB): Thermal Expansion and Positive
Pressure
For exhaust pressure to 60 inches of water column, Bellows are recommended for
expansion and vibrational movements of the piping. See
Figure 12
for an illustration of a
Bellows.
Figure 53
in the
SECTION E
illustrates the use of Bellows in a typical installation. The
use of the Lined Bellows Joints is shown to compensate for the axial expansion of the
long horizontal run.
The Bellows has a 0.035” thick or heavier straight stainless steel liner to protect the
thinner Spring material from heat and flow effects. It is used anywhere in a system for
axial and vibrational movements only and must be accurately supported and guided.
This part has limited lateral movement (1/8” max.) and lateral offsets and parallel
misalignments should be eliminated. The purpose of the liner is to minimize contact,
smooth flow, control erosion and eliminate resonance caused by exhaust gases passing
through the bellows.
The Bellows requires careful placement of piping guides to avoid interference on
thermal expansion. Bellows should not be installed with any compression, but at its full
uncompressed length in ambient state.
The joint assembly of the Bellow Length is like the standard sections. See
SECTION C
for details of Joint Assembly.
The system operating pressure of 60 inches water column (2.08 psi) is based on the
estimated capability of ceramic sealed V-Band
(BSI)
joints. The actual pressure limit of
the welded bellows will be 10 psi for 5 to 36 diameter at 1000°F.
HORIZONTAL INSTALLATION OF BELLOWS or ADJUSTABLE LENGTHS
Horizontal or sloped installations of Bellows or Adjustable Lengths use the same parts,
assembled in the same relationship, as a vertical assembly. These expansion joints, when
required may be placed anywhere between two fixed points of horizontal or sloped installation
as long as they are properly guided, properly supported; and for sloped installations in
particular, as long as bottoming out is prevented.
VERTICAL INSTALLATION OF BELLOWS or ADJUSTABLE LENGTHS
When a Bellows Joint or an Adjustable Length is installed in a vertical position between
two fixed points, such as between a AP, APL or WSHD, it should be installed immediately
below or one pipe length below the higher support. To assure proper axial alignment,
guides must be installed at the pipe section below the bellows or adjustable length (see
Figure 52 and 53
in
SECTION E
). This combination of parts will assure proper movement
of bellows and adjustable lengths and thus relieve loads due to thermal expansion. It is
desirable to install bellows and adjustable lengths near the top of a vertical section to
ensure that they do not bottom out during installation and thus become ineffective at
relieving thermal expansion loads. This arrangement of parts will also resist wind loads
on installations which run up building exterior walls.
Flue
Diameter Ø
(in)
Bellow
Outside
Diameter
Bellows
number
convolution
Material
thickness
(in)
nb of
ply
Axial
Spring
Rate
Axial
Compression
(in)
5
6 1/4
14
0.011
2
124
3
6
7 1/4
14
0.011
2
139
3
7
8 3/8
14
0.011
2
151
3
8
9 3/8
12
0.011
2
162
3
9
10 3/8
12
0.011
2
173
3
10
11 3/8
12
0.011
2
184
3
11
12 3/8
12
0.011
2
197
3
12
13 3/8
12
0.011
2
210
3
13
15
8
0.011
2
139
3
14
16
8
0.011
2
149
3
16
18
8
0.011
2
159
3
18
20
8
0.011
2
169
3
20
22
8
0.011
2
181
3
22
24
8
0.011
2
193
3
24
26
8
0.011
2
205
3
26
28
8
0.011
2
216
3
28
30
8
0.011
2
229
3
30
32
8
0.011
2
242
3
32
34
8
0.011
2
255
3
34
36
8
0.011
2
268
3
36
38
8
0.011
2
281
3
TABLE 7 -
Bellow Length Properties
Dimensions are in inches (diameter) and pound/inch (Axial Spring Rate)
10
NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.
SECTION D - COMPONENTS
EXPANSION JOINT, ODD LENGTH AND HIGH PRESSURE SYSTEM
Three different parts can be used when a system has the following
combine situation:
- Thermal Expansion and Positive Pressure System = Bellow Length
(LB)
- Positive pressure and odd length = Variable Length
(LV)
- Odd Length and Thermal Expansion = Adjustable Length
(LA)
.
See
Figure 52 and 53
in Section E
for typical installation of
LA, LV
and
LB
.
Figure 12 - Bellow Length
