U.S. patent application number 10/834955 was filed with the patent office on 2005-11-03 for method and devices to limit a creep of mechanical fasteners.
Invention is credited to Efremov, Anatoly.
Application Number | 20050244245 10/834955 |
Document ID | / |
Family ID | 35187261 |
Filed Date | 2005-11-03 |
United States Patent
Application |
20050244245 |
Kind Code |
A1 |
Efremov, Anatoly |
November 3, 2005 |
Method and devices to limit a creep of mechanical fasteners
Abstract
A method and devices to limit or to exclude operating creep of
mechanical fasteners is disclosed. The method consists in use of
mechanical fasteners such as bolts, gaskets, screws, washers and
other power elements manufactured from shape memory alloys having
temperature interval of martensitic phase transformations
corresponding to the operating temperature of industrial equipment.
The power elements are previously shape-memorized either to tension
or to compression, flexion, torsion, or to their combinations under
temperature of martensite state with suitable quantity of conserved
residual shape-memorized deformation obtained during
loading-unloading of the power elements. Further constrained
recovery of shape-memorized deformation under operating temperature
generates reactive shape-recovering forces having direction inverse
to the direction of operating creep. The process of creep
limitation is called "Method of "negative creep".
Inventors: |
Efremov, Anatoly; (Los
Alamos, NM) |
Correspondence
Address: |
ANATOLY Efremov
9923 Osuna Rd NE
Albuquerque
NM
87111
US
|
Family ID: |
35187261 |
Appl. No.: |
10/834955 |
Filed: |
April 30, 2004 |
Current U.S.
Class: |
411/82.5 |
Current CPC
Class: |
F16B 2200/506 20180801;
Y10S 411/909 20130101; Y10T 403/21 20150115; F16B 33/006 20130101;
F16B 1/0014 20130101; Y10T 403/217 20150115; F16B 43/00 20130101;
F16L 23/20 20130101 |
Class at
Publication: |
411/082.5 |
International
Class: |
F16B 001/00; F02F
011/00 |
Claims
What I claim as my invention is:
1. A method to provide an active behavior of mechanical fasteners
to limit or to exclude their operating creep due to external and/or
internal loadings and elevated operating temperature of industrial
equipment.
2. A method according to claim 1 wherein said mechanical fasteners
are the bolts, gaskets, screws, washers or other fastening power
elements.
3. A method according to claim 2 wherein said bolts, gaskets or
other fastening power elements are manufactured from shape memory
alloys having temperature interval of martensitic phase
transformations corresponding to interval of operating temperatures
of industrial equipment.
4. A method according to claim 3 wherein said bolts, gaskets or
other fastening power elements are previously shape-memorized
either to the tension or to compression, flexion, torsion, or to
their combinations obtaining conserved residual shape-memorized
deformations under temperatures of martensite state during
loading-unloading.
5. A method according to claim 1 wherein said mechanical fasteners
interact with adjacent rigid component parts of said industrial
equipment under temperatures of martensitic phase transformation to
provide a constrained recovery of conserved residual
shape-memorized deformation that generates a reactive
shape-recovering forces having direction inverse to the direction
of operating creep of said mechanical fasteners.
6. A method according to claim 1 that is called the "Method of
"negative creep".
7. A device to limit or to exclude operating creep of mechanical
fasteners including bolts manufactured from shape memory alloy and
previously shape-memorized to the compression.
8. A device according to claim 7 including the gasket manufactured
from shape memory alloy and previously shape-memorized to the
tension.
9. A device according to claim 7 including the gasket manufactured
from typically used material.
10. A device including the bolts manufactured from typically used
structural steel and gasket manufactured from shape memory alloy
and previously shape-memorized to the tension.
11. A device according to claim 10 wherein the bolts have internal
axial hollow channel adapted to place and to fix firmly a shank
manufactured from shape memory alloy and previously shape-memorized
to the compression.
12. A device according to claim 11 wherein the gasket is
manufactured from typically used material.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] Not Applicable
FEDERALLY SPONSORED RESEARCH
[0002] Not Applicable
SEQUENCE LISTING OR PROGRAM
[0003] Not Applicable
BACKGROUND OF THE INVENTION--FIELD OF INVENTION
[0004] This invention relates to mechanical fasteners, specifically
to bolted flanged connections with gaskets that have to provide a
tight and durable joint between component parts of pressure
vessels, piping systems, and other industrial facilities under
external and/or internal loadings and operating elevated
temperatures.
BACKGROUND OF THE INVENTION
[0005] One of the most typically used means to obtain the tight and
durable joint between component parts of industrial facilities is
to connect their pieces with bolted fasteners. These connections
have a wide applicability in petrochemical, chemical, aerospace,
fossil fuel and nuclear power industries, and others.
[0006] There are millions of bolts in critical facilities of cited
industries, and the problem of structural durability and plant
leakage reduction is very complex and involves many areas of
applied mechanics and technological findings.
[0007] Safe design of bolted flanged connections from structural
durability point of view has been, on the whole, solved and
standardized, but the plant leakage remains a principal cause of
bolt damages and failure that are attributed to the high level of
corrosion which is combined with high level of stresses and
deformations due to alternating conditions of internal pressure,
external loading, elevated temperatures, flow-induced vibrations,
integral flow of neutrons, and other critical factors. Hence, the
leak tightness has a greater influence on the service life of the
bolted flanged connections, and highest priority in plant
reliability programs is to limit or to exclude the early leakage,
thus protecting critical engineering facilities from untimely
degradation and failure.
[0008] Statistic data show that, for example, piping system
leakages conservatively cost each process industry hundreds of
millions of dollars annually in lost profits as a result of plant
shutdowns, production penalties, maintenance rework activities, and
equipment repair or replacement.
[0009] Early plant leakage is closely connected with operating
creep of the fasteners and gaskets. Generally, creep is
accompanying by stress relaxation, and elongation of bolted
fasteners along with contraction of gaskets due to creep-relaxation
is a very serious problem because it leads to bolt load and gasket
compression losses that, in turn, increase the leakage rate.
[0010] It is found that creep-relaxation of bolted fasteners and
gaskets is increased with elevated temperature and load-induced
stresses, although room temperature creep-relaxation can be also
significant even at relatively light loads. A plant maintenance
practice includes periodical retightening or replacement of the
bolts and gaskets subjected to creep-relaxation to prevent
leakages, and, having in mind the great quantity of bolts used in
process industries, the procedure involves an expensive
time-consuming process and provides only temporary effect of leak
tightness because the creep-relaxation increases gradually after
additional retightening, and risk of leakage event relatively
increases. Nevertheless, during the development of must design
procedure, little consideration has been given to the
creep-relaxation of bolted fasteners and gaskets, and similar
situation is observed with patent documents.
[0011] U.S. Pat. No. 6,199,453 to Steinbock, entitled "High
temperature bolting system", offers a sophisticated apparatus for
maintaining a clamping force between component parts of a steam
turbine while operating at a temperatures of 800 DEG. F to 1200
DEG. F. However, the disclosed elongated stepped fastener shank
manufactured from superalloy Inconel 718, having a thermal
expansion coefficient similar to flange material and creep strength
which is several times greater than creep strength of flanged
material, can not stop a creep-relaxation process and protect
proposed bolting system from creep-relaxation that is an increase
of elongation and decrease of stress with time. Moreover, the high
level of stresses and operating temperatures induce the high level
of creep-relaxation of the fasteners.
[0012] EP Pat. No. 352608 discloses a method of fabrication of
reinforced polytetrafluoro-ethylene (PTFE) gasketing materials
"characterized by high strength, excellent recovery and superior
creep-relaxation resistance". However, these super characteristics
did not exclude the creep-relaxation from 20% to 30% depending on
thicknesses of proposed tested materials. Moreover, the tests were
carried out under standard procedure during only 22 hours at only
212 DEG. F. Thus, the proposed gasketing materials demonstrate
"superior" physical and functional properties when compared to
previous PTFE gasketing materials described in prior art. The most
important failing, however, is the fact that proposed gasketing
materials copy a typically used approach to the fabrication of
sealing elements based on traditional "passive" behavior under
operating conditions of all known today gasketing materials
excepting those described in U.S. Pat. No. 5,226,683 to Julien et
al. and U.S. Pat. No. 6,435,519 to White. These two patent
documents are the first attempts to introduce the new gasketing
material fabricated from NiTi (Nitinol) shape memory alloy.
[0013] U.S. Pat. No. 5,226,683 discloses a method to use a gasket
of Nitinol shape memory alloy under martensite state to fill the
space between the hard flange faces having microscopic surface
irregularities that can prevent the fluid leakage between the faces
und will allow further to reuse the gasket.
[0014] The Nitinol shape memory alloy of which the gasket of this
invention is made "remembers" the shape, which it had when it was
last formed in its austenite state. When this gasket is deformed
under temperature of martensite state it fills the irregularities
of flange faces under pressure exerted by hard clamping members of
the flanges. The shape memory effect is used when gasket resumes
its original shape after heating to austenite state during the
restoration step before reuse. Although this invention has failed a
main problem of plant leakage reduction by means of creep
limitation, it remains a turning point from leakage problem point
of view.
[0015] U.S. Pat. No. 6,435,519 represents a next attempt to use a
Nitinol shape memory alloy as a gasketing material to provide a
seal between component parts of an imaginary generalized assembly.
Unfortunately, this invention claims a well-known long time
procedure to clamp the gasket between adjacent flange faces. As for
application of gasket of shape memory alloy, this invention claims
the spring forces generated by bending of the gasket when it is in
super-elastic state. It is easily to observe that shape memory
alloy in super-elastic state displays all mechanical properties of
typical elastic material including the property of creep-relaxation
while subjecting to elevated temperature and external loading.
Meanwhile, this invention tries to open a real way to the
application of shape memory alloys as sealing materials even though
the problem of creep-relaxation remains out of consideration.
[0016] A wide range of patent documents having relation to the
present invention is dedicated to the application of shape memory
alloys, mostly of the Nitinol, in design of couplings, fasteners,
washers, plugs, springs and other structural components for such
things as pipes, oil well casings and similar shell structures.
[0017] U.S. Pat. Nos. 3,759,552, 4,001,928, 4,149,911, 4,198,081,
4,281,841, 4,450,616, 4,469,357, 4,501,058, 4,537,406, 5,791,847 as
well as GB Pat. Nos. 1554432, 1580036, SU Pat. No. 1086282 and JP
Pat. No. 62-116292 describe the means of stressing a structural
members of Nitinol shape memory alloy components that provide
stiffness to shell structures and tubular members as well as
prestressed loadings for head bolts or other prestressed fasteners.
These documents, however, did not touch the problem of
creep-relaxation of mechanical fasteners and gasketing joints.
[0018] Japanese Pat. No. 62-188764 describes a method to
manufacture a bolt of Nitinol shape memory alloy that may be easily
fastened and detached. This bolt is subjected to axial compression
and to aging treatment under specific temperatures while holding it
under compressive strain. Thus-obtained shape memory alloy bolt
reversibly repeats the elongation in a length direction at a
temperature of an initial temperature of martensite transformation
and the contraction at a temperature of an initial temperature of
inverse transformation. Owing to these characteristics, the length
of bolt is arbitrary changed, so that bolt may be firmly fastened
or easily detached.
[0019] The procedure of described bolt production relates to the
method known as constrained formation of shape memory effect by
means of fixed deformation and following aging treatment under
specific temperature above of temperature of austenite state. This
procedure is very complex and the bolt's compression under elevated
temperature increases a risk of bolt's buckling, and, moreover, the
problem of creep-relaxation is failed too.
[0020] None of the above-mentioned prior patent documents touch the
problem of creep-relaxation of mechanical fasteners and gasketing
joints from active intervention to the plant leakage reduction
point of view. Accordingly, it is an object of the present
invention to form a new approach to provide a bolt-flange-gasket
assembly wherein there is a significant limitation or exclusion of
creep-relaxation due to operating elevated temperatures and
external and/or internal loadings. This invention is the first to
introduce a new technological philosophy based on "active"
resistance of the fasteners and gaskets to the creep-relaxation
under critical operating conditions.
SUMMARY OF THE INVENTION
[0021] It is, therefore, a primary object of the present invention
to form a new idea of sealing technology based on active behavior
of the fasteners and gaskets to limit or to exclude their operating
creep while subjecting to the operating elevated temperature and
external and/or internal loadings.
[0022] It is another object of the present invention to provide a
method and devices to limit a creep-relaxation of the fasteners
and/or gaskets that are a power elements manufactured from shape
memory alloys and previously shape-memorized under temperatures of
martensite state.
[0023] Active behavior of the power elements results from
shape-recovering forces that appear during a recovery of previously
shape-memorized deformations under operating elevated temperatures.
These forces have a direction inverse to the direction of operating
creep deformations of the fasteners and/or gaskets that limits or
excludes the elongation of the fasteners and contraction of the
gaskets due to creep. This active behavior may be called "negative
creep".
[0024] The method consists in application of power elements such as
bolts, screws, washers, gaskets, and the like manufactured from
shape memory alloys and previously shape-memorized either to
tension or to compression, flexion, torsion, or to their
combinations. The shape-memorized deformations are obtained during
loading-unloading of the power elements under temperature of
martensite state when the power elements conserve the residual
shape-memorized deformations upon unloading.
[0025] The recovery of conserved shape-memorized deformations is
occurred after standard tightening of the fasteners and clamping of
the gasket during the operating external and/or internal loadings
and variety of elevated operating temperatures including the
temperatures of martensitic phase transformation of shape memory
alloy. The recovery of conserved shape-memorized deformations is
further stopped by rigid component parts of the assembly forming an
effect of constrained recovery event, so that reactive
shape-recovering forces are generated that leads to the stress of
fasteners and/or gaskets at the direction inverse to the direction
of creep deformations.
[0026] The shape memory alloys on a basis of Cu, Fe, Al, Ma, Ga,
Ni, Ti, In, Pd, Hf, and others have a large temperature interval of
martensitic phase transformations that corresponds to the
temperatures to recover the conserved shape-memorized deformations.
Hence, the operating temperatures of the assembly have to be in
temperature interval of martensitic phase transformations of the
power elements manufactured from suitable shape memory alloy. For
example, the operating temperatures of Fossil Fuel and Nuclear
Power Plants' equipment such as heat exchangers, piping systems,
steam generators, coolant system installations, and others vary
from dozens to hundreds degrees and remain stable enough for given
type of equipment, so that temperatures of martensitic phase
transformation of suitable shape memory alloy have to be in the
interval of operating temperatures of the assembly. The reactive
shape-recovering forces may be considerable depending on quantity
of conserved shape-memorized deformations and rigidity of opposed
component parts of the assembly.
[0027] A most important advantage of the present invention is a new
progressive approach to the sealing technology based on active
intervention in operating process by means of fasteners and gaskets
manufactured from shape memory alloys and previously
shape-memorized either to tension or to compression, flexion,
torsion, or to their combinations.
[0028] Another advantage of the present invention consists in use
of reactive shape-recovering forces generated by fasteners and/or
gaskets under operating conditions to provide a "negative creep"
and to limit or to exclude the creep-relaxation of the fasteners
and gaskets.
[0029] It is next advantage of the present invention to provide a
continuous automatic contact between flange faces and gasket under
operating conditions. Reactive shape-recovering forces having
direction inverse to the direction of the creep deformations
produce this contact.
[0030] Proposed devices provide a limitation of creep deformations
excluding simultaneously a retightening of the fasteners that
increases significantly a leak tightness of critical facilities and
extends their service life.
[0031] Further brief description of applied drawings and following
detailed description of the invention are intended to provide a
basis for understanding the nature and character of the present
invention, and to explain the principles and operation of presented
devices.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 represents schematically a physical basis of
constrained recovery when a conserved residual shape-memorized
deformation .epsilon..sub.c under temperature of martensite state
below M.sub.f tries to be recovered during the heating to
temperature A.sub.f of austenite state with appearance of reactive
shape-recovering stress .sigma..sub.r.
[0033] FIG. 2 is a bolted fastener of two component parts of a
pressure vessel having a top, base, bolts with nuts and gasket.
[0034] FIG. 3 is a similar to FIG. 2 except that the bolts have an
internal axial hollow channel adapted to place and to fix firmly a
shank manufactured from shape memory alloy and previously shape
memorized to the compression.
DETAILED DESCRIPTION OF THE INVENTION--FIG. 3 IS PREFERRED
EMBODIMENT
[0035] FIG. 1 is three-dimensional stress-strain-temperature
diagram .sigma.-.epsilon.-T showing a behavior of power element of
shape memory alloy during the formation of shape-memorized
deformation along with its constrained recovery. An initial point
"O" corresponds to temperature below M.sub.f at which the
transformation of martensite finishes. The stress-induced
martensite is obtained during loading-unloading of the power
element that is presented at the stress-strain diagram
.sigma.-.epsilon. at the rear graph in FIG. 1. The point K
corresponds to the final stress .sigma..sub.f before unloading, and
the point S corresponds to the final strain .epsilon..sub.c after
unloading.
[0036] The strain .epsilon..sub.C is a conserved residual
shape-memorized deformation of the power element of shape memory
alloy. This deformation tries to be recovered during the heating to
the temperature A.sub.f (point Q at the front graph in FIG. 1
corresponding to austenite state of the power element), but its
shape recovery is stopped by rigid component parts of the assembly
providing an effect of constrained recovery (point R at the front
graph). The constrained recovery of the shape-memorized deformation
generates reactive shape-recovering stress .sigma..sub.r that is
shown at the front graph in FIG. 1.
[0037] A direction of the shape-memorized deformation coincides
with direction of operating creep deformation of the fastener or
gasket, and, therefore, previously compressed gasket will be
shape-memorized to the tension because it will try to recover its
initial elongated shape during the heating that will stopped by
rigid component parts of the assembly. This constrained recovery of
the gasket generates the reactive shape-recovering forces of
tension having direction inverse to the direction of operating
creep deformation of the gasket. This effect of "negative creep"
results in active resistance of the mechanical fasteners to their
operating creep that determines a new approach to the sealing
technology.
[0038] The "negative creep" provides continuous automatic contact
between adjacent component parts of the assembly, because, for
example, gasket from shape memory alloy being previously
shape-memorized to tension will restore its initial elongated shape
during the operating process under operating temperature
corresponding to the temperature of martensitic phase
transformation of applied shape memory alloy. It will be "active"
behavior of the gasket, which will actively resist to its operating
creep.
[0039] The described process of forming of shape-memorized
deformation and constrained recovery may be obtained either for
tension or compression, flexion, torsion, or for their
combinations.
[0040] FIG. 2 is a part of the cross section of a pressure vessel
having a top 111 and base 12 with flange rings 13 and 14 connected
with bolts 15 and nuts 16, compliant gasket 17 manufactured from
typically used material being placed between adjacent flange faces.
The assembly is subjected to internal pressure "P" and operating
temperature "T".
[0041] The bolts 15 are manufactured from shape memory alloy and
previously shape-memorized to the compression under temperature of
martensite state with suitable quantity of conserved residual
shape-memorized deformation. The temperature of martensitic phase
transformation of the shape memory alloy corresponds to operating
temperature of the assembly, so that previously elongated bolts try
to recover their initial length. The recovery process is stopped by
resistance of rigid component parts of the assembly with
simultaneous generation of reactive shape-recovering forces of
compression having direction inverse to the direction of operating
creep of the bolts. The reactive forces block a development of bolt
elongation due to creep that excludes the bolt retightening and
increases the leak tightness of bolted flanged connection.
[0042] The same FIG. 2 shows second embodiment of the present
invention except the materials of the bolts and gaskets. The bolts
of second embodiment are manufactured from typically used
structural steel, and the gasket is manufactured from shape memory
alloy and previously shape-memorized to the tension with suitable
quantity of conserved residual shape-memorized deformation. The
process of generation of reactive shape-recovering forces of
tension of the gasket is similar to described above, because the
gasket tries to recover its initial thickness and, therefore,
provides a continuous contact with adjacent flange faces. The
reactive forces of the gasket have a direction inverse to the
direction of operating creep of the gasket that limits creep
development.
[0043] The same FIG. 2 relates to third embodiment of the present
invention except the materials of the bolts and gasket which are
both manufactured from shape memory alloy and previously
shape-memorized to the compression (bolts) and to the tension
(gasket). Further process is similar to the one described
above.
[0044] FIG. 3 shows the same component parts of the assembly
described in FIG. 2 except that the bolts are manufactured from
typically used structural steel and have an internal axial hollow
channel adapted to place and to fix firmly a shank 20 manufactured
from shape memory alloy and previously shape-memorized to the
compression. The gasket may be manufactured from shape memory alloy
or from typically used material. Further process is similar to the
one described above.
CONCLUSION
[0045] The present invention opens a new approach to the sealing
technology based on active intervention of the fasteners and
gaskets in operating process by means of creep limitation and plant
leakage reduction. The power elements manufactured from shape
memory alloys may be previously shape-memorized either to tension
or to compression, flexion, torsion, or to their combinations that
significantly increases applicability of presented method using the
feature of shape memory alloys to provide a "negative creep" to
limit or to exclude operating creep of the fasteners and gaskets.
The real application of the present invention in plant process
industries will allow to protect the fasteners and component parts
of technological equipment from damages due to the corrosion, and
to extend its service life.
[0046] It will be understood that various shape memory alloys may
by used for manufacturing the power elements to limit the creep of
mechanical fasteners and gaskets having temperatures of martensitic
phase transformation corresponding to operating temperatures of
technological equipment, and various changes in details, materials,
and arrangements of the parts of the fasteners and gaskets which
have been described and illustrated above in order to explain the
nature of this invention may be made by those skilled in the art
without departing from the basic principles of the present method
as recited in the applied claims.
* * * * *