Oct. 3, _1944.
c. M. scuDDER
2,359,446
.METHOD 0F GONSTRUCTING MULTI-«LAYER PRESSURE VESSELS
Filed Dec. 8, 1941
Charles MScudder
INVENTOR.
ATTORNEY
2.359,44@
Patented 'oec a, 1944
- UNITED STATE sVassautPATENT
Mn'rnon or ooNs'r-nuc'rmo MUL'rniAYER
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massima vassnrs
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- charles M. scudder, wsuwitbú.- wie., mienn- to
A. 0. Smith Corporation,
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_corporation of New York` A .
`’siilliiicinipu December s. 1e4i,¿.f_serm ne. 42am x _ „
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comms. ' (clica-¿nazi
This invention relates to a method of construct
ing multi-layer pressure vessels _andmore par-. .
ticularly tothe pre-stressing ofthe 'cylindrical'
walls oi avessel duringfabrication. A
_
v
"
erable thickness or it may be relativelythin and
be backed up by internal fluid` pressure to sup
port the innermost vlayers of the vessel wall dur
- ing fabrication. It preferably comprises a form
It has been known that in the construction
of multi-layer pressure vessels in accordance with
.
the Stresau Patent No; 1,925,118, and with cer
tain improvements thereon,l it is possible-to pre
`stress the cylindrical wall oi’ the vessel to corn-I
pensate for the different rates of stress increase 10
in thevmetal of the inner and outer section oi the
vessel under working load. This pre-stressing
is accomplished by squeezing the structure dur-l '
ing the welding of each-layer to an extent pro
ducing elastic ilow of vthe metal oi the layers,
ot collapsible mandrel and has an outer circum
ference which is‘capable oi.'v absorbing consider
able ~compression stress in a circumferential di
rection as well as radially.
l
v
The inner 'structure l constitutes a foundation
upon which th'e innermost layer 2 of the vessel
is wrapped _and tensioned. This tensioning is ac
complished~ by applying tightening bands 3 en
rcircling the‘layer- and pulled tightly thereon by
hydraulic. cylinders- I .which exert forces suiii
resulting in_ initial residual compression stresses
cient to cause the bands to actually squeeze the
structure beneath to a smaller diameter, within
the limit for elastic return of the metal.
in the inner section of the cylindrical wali‘of the _
'
The layer 2 is then welded along its longi
vessel and initial residual tension stresses in the
tudinal seam while the bands are tensioned. Up
outer section oi the wall. In carrying out this
oriv release of the bands the inner structure I
process it- has been found that there _isa tend 20 which has been compressed will tend to expand
ency for the innermost layer or layers to be ex
outwardly and place the ’inner‘layer 2` under
cessively compressed so that' the over-al1 e?l- ,
_
tension.
ciency of the vessel may be less than desired, In
-As subsequent layers are applied in the same
other words, the stress has aI tendency to ac 25. manner the neutral axis between the compres
cumulate or concentrate in the innermost lay
sive stresses and tensile stresses moves outward
ers. as subsequent layers are successively applied
ly, and the inner layer 2 should have its stress
to the structure.
A
changed from tensile stress to compressive stress.
Various methods have been proposed for remov
This may occur when the fifth layer 5 is applied
ing> the concentration oi Streß or evening out
depending upon the amount of compression and
the stress distribution in the structure. Most of
« elastic return in the inner supporting structure l.
these methods require additional and expensive>
.The inner structure l is removed after the
cylinder is completely fabricated, although it may
’be removed beforel all of the layers are applied,
where a very thick wall is being built up. This
takes away the support for the inner layer 2
The principal object of the present invention
isto provide a process for preventing the exces
sive concentration oi compressive stress in the 35
innermost layers of the -structure when fabricat-l -. and the latter is immediately compressed an
ed ln the manner described. '
Y «
amount depending upon the tension of the outer`
The accompanying drawing illustrates a meth
The final cylinder will have the inner
' layers.
od »of carrying out the invention and the views
layers under residual compressive stress and the
therein are as follows: ‘
-f
'
outer layers under residual tension .stress The
Figure l is a-perspective view showing dia
` neutral axis of pre-stress will be nearer the cen
grammatically the application of the tlfth layer
ter of the wall than would be the case if the
.40
of the cylinder; and
'
-
Fig. 2 is a transverse section through a com
pleted cylinder with the inner supporting struc
ture removed.
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45
inner structure were not used".
The invention is based on the discovery that in
constructing cylinders by the pre-stressing proc
ess there was a greater stress differential between
In carrying out the invention the compressive
stress is concentrated in a removable elastically
the ñrst few layers than-between the outer lay
_v the vessel wall, and which structure supports the
in the final structure. The diilîerence in stress
yieldablejstructure inside the innermost layer o! 50 ers, and that this stress differential was retained
layer against compression. This removable struc
' ture preferably comprises a removable inner lay
er or cylinder upon which the innermost layer
2 oi the vessel is wrapped. It may have consid
between each layer and the next previous layer
is ldependent upon the relative thickness of the
given layer and of the previous layers.
The tensile stress in the outermost layer re
2
2,359,446
suits from a tendencyto _compress the entire pre
vious structure, and the compressive stress cor
responding to it may be assumed to be distributed
said inner structure and adjacent layer to build
evenly throughout the previous layers. It is thus ,
_ divided between about fourteen layers.
On the other hand, the tensile stress in s_ay
the ilfthk layerbeing applied corresponds to a
`compressive stress divided between fourlayers.
Each timeva layer is applied'the innermost layer
2 receives some additional compressive stress.
The present invention utilizes these facts and
up a cylinder of considerable thickness and etlect
a pre-stressing of the metal of the several layers
tending to compensate for the different rates of -
stress increase therein under working load, and
subsequently removing said internal supporting
structure to redistribute the pre-stress-in the cyl
inder wall.
`
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2." The method of pre-stressing _a multi-layer
10 high pressure cylinder during fabrication to im
prove the stress distribution therein in service.
comprising providing a removable elastically
of constituting the inner layer during fabrication,
yieldable cylindrical internal supporting struc
and which is subsequently removed to eifect a re
ture capable of. resisting compression stresses in
distribution of stresses in the multi-layer eyl 15 a circumferential direction, applying a layer of
inder.
sheet metal thereon, squeezing the structure and
The innermost layer of the vessel has the posi
welding said layer to provide the innermost load
tion, during fabrication, that the third or fourth
carrying layer of the pressure cylinder. similarly
layer would have in a cylinder fabricated with
applying and welding subsequent layers under
provides an inner supporting structure capable
out an inner supporting member. The amount 20 conditions of elastic compression of said inner
of pre-stressing oi' the innermost layer will be
structure and adjacent layer to build up a cyl
determined by its position. The innermost layer,
inder of considerable thickness and effect a pre
therefore, will not receive the amount of com
stressing of the metal of the several layers tend
pression stress which is ordinarily accumulated
ing to compensate for the 'different rates of
near the inner surface of a layer structure which' 25 stress increase therein under working load, sub- .
does not have an inner support.
sequently- removing said internal supporting
After the cylindrical wall of the vessel has been
structure to redistribute the pre-stress in the
fabricated in the manner described and the inner
_cylinder wall, and thereafter completing the v
, Supporting structure removed, the remaining ves
-sel wall will have _a more evenly distributed ini
tial stress tending to compensate for the diifer
ences in rate of stressing oi' the wall under work
ing load.
Where the inner supporting structure is a
cylinder by adding subsequent layers and weld
30 ing the same thereon.
.
3. The method of pre-stressing a multi-layer
high pressure cylinder during fabrication to im
prove the stress distribution therein in service,
comprising providing aI removable elasticall'y
heavy cylinder it may be cut out after fabrica 35 yleldable cylindrical internal supporting struc
tion of the vessel wall by any suitable method to
ture capable of resisting compression stresses in
remove 'the same.
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a circumferential direction, applying a layer of
The invention is claimed as follows: .
sheet metal thereon', squeezing the structure and
1. The method of pre-stressing a multi-layer
welding said layer to provide the innermost load
high pressure cylinder during fabrication to im 40 carrying layer of the pressure cylinder, similarly
prove the stress distribution therein in service,
applying and welding subsequent layers under
comprising providing a removable elastically
conditions of elastic compression of said inner
yieldable cylindrical internal supporting struc
structure and adjacent layer to build up a cyl
turel capable of resisting compression stresses in
inder of considerable thickness and eifect a pre
a circumferential direction, applying a layer of is stressing of the metal of the several layers tend
sheet metal thereon, tensioning said layer cir
ing to compensate for the different rates of stress
oumferentially upon the structure and welding
increase therein under working load, and after
said layer to provide the innermost load carry
completion of the cylinder removing sa/id inter
ing layer of the pressure cylinder, similarly ap
nal supporting structure to redistribute the pre
plying tensioning and welding subsequent lay
ers under conditions of elastic compression of
50 stress in the cylinder wall.
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CHARLES M. SCUDDER.