U.S. patent application number 11/061630 was filed with the patent office on 2006-08-24 for systems, methods and apparatus for non-disruptive and non-destructive inspection of metallurgical furnaces and similar vessels.
Invention is credited to Afshin Sadri.
Application Number | 20060186585 11/061630 |
Document ID | / |
Family ID | 36911842 |
Filed Date | 2006-08-24 |
United States Patent
Application |
20060186585 |
Kind Code |
A1 |
Sadri; Afshin |
August 24, 2006 |
Systems, methods and apparatus for non-disruptive and
non-destructive inspection of metallurgical furnaces and similar
vessels
Abstract
Some embodiments of the present invention provide systems,
methods and apparatus for more accurately determining the thickness
of a refractory lining included in an operating metallurgical
furnace. Specifically, in some embodiments a transient propagated
stress wave is used to determine the condition of a refractory
lining, and additionally, provide a systematic way to include the
affect that temperature has on the velocity of a compressive wave
through a heated refractory material and/or accretions. As
identified in aspects of the present invention, and contrary to the
common understanding in the art, the velocity of a stress wave, at
each frequency and in a refractory material, is not necessarily
constant over a temperature range. In accordance with aspects of
some specific embodiments of the invention, a scaling factor a can
be calculated for each refractory material to adjust for the
presumed velocity of the stress wave through each refractory
material.
Inventors: |
Sadri; Afshin; (Woodbridge,
CA) |
Correspondence
Address: |
BERESKIN AND PARR
40 KING STREET WEST
BOX 401
TORONTO
ON
M5H 3Y2
CA
|
Family ID: |
36911842 |
Appl. No.: |
11/061630 |
Filed: |
February 22, 2005 |
Current U.S.
Class: |
266/78 |
Current CPC
Class: |
F27D 21/0021 20130101;
F27D 21/04 20130101; F27D 19/00 20130101 |
Class at
Publication: |
266/078 |
International
Class: |
C21D 11/00 20060101
C21D011/00 |
Claims
1. A system for inspecting a metallurgical furnace wall comprising:
a stress wave generator for generating a stress wave that
propagates into a metallurgical furnace wall; a stress wave sensor
for sensing reflections of the stress wave; and a processor having
computer readable program code means embodied thereon for (i)
recording time domain data about the reflections of the stress wave
sensed by the stress wave sensor, (ii) converting the time domain
data into frequency domain data, and (iii) producing a
determination of the condition of the metallurgical furnace wall by
combining time domain data, the frequency domain data and a
temperature-dependent scaling factor which compensates for the
change in velocity of the stress wave and the reflections of the
stress wave through a refractory material included in the
metallurgical furnace wall.
2. A system according to claim 1, wherein the temperature-dependent
scaling factor is calculated as a function of a relative change in
the modulus of elasticity over a temperature range corresponding to
a temperature gradient through the refractory material within an
operating metallurgical furnace.
3. A system according to claim 1, wherein producing the
determination of the condition of the metallurgical furnace wall
includes determining the thickness of the metallurgical furnace
wall.
4. A system according to claim 1, wherein producing the
determination of the condition of the metallurgical furnace wall
includes determining the thickness of a refractory lining in the
metallurgical furnace wall.
5. A system according to claim 1, wherein producing the
determination of the condition of the metallurgical furnace wall
includes determining the presence or absence of defects including
delaminations, accretions, cracks and bubbles.
6. A system according to claim 5, wherein producing the
determination of the condition of the metallurgical furnace wall
also includes determining the position of defects including
delaminations, accretions, cracks and bubbles.
7. A system according to claim 1, wherein the stress wave is a
compressive P-wave.
8. A system according to claim 1, wherein the stress wave sensor is
one of a vertical displacement transducer and an accelerometer.
9. A system according to claim 1, wherein the stress wave generator
is an impactor having a spherical impact point.
10. A system according to claim 1 further comprising a
pre-amplifier coupled between the stress wave sensor and the
processor.
11. A system according to claim 1, wherein the processor further
comprises computer readable program code means embodied thereon for
including a geometry-dependent velocity scaling-factor in the
determination of the condition of the metallurgical furnace
wall.
12. A system according to claim 11, wherein the refractory material
included in the metallurgical furnace is provided in brick form,
and the geometry-dependent scaling factor is calculated as a
function of the relative dimensions of the refractory bricks.
13. A system according to claim 1, wherein the metallurgical
furnace wall under inspection is known to include a refractory
lining having a plurality of layers, each composed of one type of
refractory material, and wherein the processor further includes
computer readable program code means embodied thereon for producing
a determination of the condition the metallurgical furnace wall
using a plurality of temperature-dependent scaling factors, each
temperature-dependent scaling factor corresponding to a respective
one type of refractory material in the refractory lining.
14. A system according to claim 13, wherein each of the plurality
of temperature-dependent scaling factors is calculated as a
function of a relative change in the modulus of elasticity over a
temperature range corresponding to a temperature gradient through
the corresponding refractory material.
15. A system according to claim 13, wherein the processor further
comprises computer readable program code means embodied thereon for
including a geometry-dependent velocity scaling-factor in the
determination of the condition of the metallurgical furnace
wall.
16. A system according to claim 15, wherein each layer of the
refractory lining is known to include refractory bricks of one type
of refractory material and each of the plurality of
geometry-dependent scaling factors is calculated as a function of
the relative dimensions of the refractory bricks in a respective
layer.
17. An apparatus for inspecting a metallurgical furnace wall
comprising: a plurality of stress wave generator-sensor pairs, each
pair for generating a stress wave and sensing reflections of the
stress wave at point on a metallurgical furnace; and a processor
having computer readable program code means embodied thereon for
producing a determination of the condition of the metallurgical
furnace wall from a combination of time domain data collected by at
least one sensor, frequency domain data derived from the time
domain data, and a temperature-dependent scaling factor to correct
for the change in velocity of the stress wave and the reflections
of the stress wave through a refractory material included in the
metallurgical furnace wall.
18. An apparatus according to claim 17, wherein the
temperature-dependent scaling factor is calculated as a function of
a relative change in the modulus of elasticity over a temperature
range corresponding to a temperature gradient through the
refractory material within an operating metallurgical.
19. An apparatus according to claim 17, wherein the determination
of the condition of the metallurgical furnace wall includes
determining the thickness of the metallurgical furnace wall.
20. An apparatus according to claim 17, wherein the determination
of the condition of the metallurgical furnace wall includes
determining the thickness of a refractory lining in the
metallurgical furnace wall.
21. A system according to claim 1, wherein the determination of the
condition of the metallurgical furnace wall includes determining
the presence or absence of defects including delaminations,
accretions, cracks and bubbles.
22. An apparatus according to claim 21, wherein the determination
of the condition of the metallurgical furnace wall also includes
determining the position of defects including delaminations,
accretions, cracks and bubbles.
23. An apparatus according to claim 17 further comprising a
respective plurality of pre-amplifiers coupled between the
plurality of stress wave generator-sensor pairs and the
processor.
24. An apparatus according to 17 further comprising a stress wave
generator control box coupled between the processor and the
plurality of stress wave generator-sensor pairs.
25. An apparatus according to claim 17, wherein the processor
further comprises computer readable program code means embodied
thereon for including a geometry-dependent velocity scaling-factor
in the determination of the condition of the metallurgical furnace
wall.
26. An apparatus according to claim 25, wherein the refractory
material included in the metallurgical furnace is provided in brick
form, and the geometry-dependent scaling factor is calculated as a
function of the relative dimensions of the refractory bricks.
27. An apparatus according to claim 17, wherein the metallurgical
furnace wall under inspection is known to include a refractory
lining having a plurality of layers, each composed of one type of
refractory material, and wherein the processor further includes
computer readable program code means embodied thereon for producing
a determination of the condition of the metallurgical furnace wall
using a plurality of temperature-dependent scaling factors, each
temperature-dependent scaling factor corresponding to a respective
one type of refractory material in the refractory lining.
28. An apparatus according to claim 27, wherein each of the
plurality of temperature-dependent scaling factors is calculated as
a function of a relative change in the modulus of elasticity over a
temperature range corresponding to a temperature gradient through
the corresponding refractory material.
29. An apparatus according to claim 27, wherein the processor
further comprises computer readable program code means embodied
thereon for including a geometry-dependent velocity scaling-factor
in the determination of the condition of the metallurgical furnace
wall.
30. An apparatus according to claim 29, wherein each layer of the
refractory lining is known to include refractory bricks of one type
of refractory material and each of the plurality of
geometry-dependent scaling factors is calculated as a function of
the relative dimensions of the refractory bricks in a respective
layer.
31. A method of inspecting a metallurgical furnace wall comprising:
introducing a stress wave into a metallurgical furnace wall at a
point; sensing one or more reflections of the stress wave near the
point of introduction of the stress wave into the metallurgical
furnace wall; and processing the reflections in the time and
frequency domain in combination with a temperature-dependent
scaling factor to correct for the change in velocity of the stress
wave and the reflections of the stress wave through a refractory
material included in the metallurgical furnace wall.
32. A method according to claim 31, wherein the
temperature-dependent scaling factor is calculated as a function of
a relative change in the modulus of elasticity over a temperature
range corresponding to a temperature gradient through the
refractory material within an operating metallurgical furnace.
33. A method according to claim 31 further comprising determining
the thickness of the metallurgical furnace wall.
34. A method according to claim 31 further comprising determining
the thickness of a refractory lining in the metallurgical furnace
wall.
35. A method according to claim 31 further comprising determining
the presence or absence of defects including delaminations,
accretions, cracks and bubbles.
36. A system according to claim 35 further comprising determining
the position of defects present in the metallurgical furnace
wall.
37. A method according to claim 31 further comprising amplifying
sensed reflections before processing.
38. A method according to claim 31 further comprising including a
geometry-dependent velocity scaling-factor in the determination of
the condition of the metallurgical furnace wall.
Description
FIELD OF THE INVENTION
[0001] The invention relates to ways of inspecting metallurgical
furnaces and the like, and, in particular to systems, methods and
apparatus, for non-disruptive and non-destructive inspection of
metallurgical furnaces and similar vessels.
BACKGROUND OF THE INVENTION
[0002] A typical metallurgical furnace is a container having
sidewalls with a multi-layer construction. The outer layer is
typically a steel shell provided for structural support. The inner
layer includes a refractory lining, constructed from one or more
layers of refractory bricks, that is provided to shield the outer
steel shell from molten materials and aggressive chemicals inside
the furnace. In some furnaces, a cooling layer is also provided
between the outer steel shell and the refractory lining to prevent
excessive heat transfer from the refractory lining to the outer
steel shell. In some furnace designs, the layers of brick and/or
cooling elements are set in place with a soft sand-like material
that solidifies during the operation of the furnace.
[0003] During the operation of a metallurgical furnace, the
refractory lining is deteriorated by mechanical and thermal stress
in addition to chemical corrosion resulting in a loss of overall
refractory lining thickness. As the refractory lining deteriorates
molten materials and aggressive chemicals penetrate into widening
spaces in and/or between refractory bricks leading to delamination
(i.e. separation) of the layers in the refractory lining.
Deterioration of the refractory lining ultimately leads to
structural failures that may cause the outer steel shell to be
exposed to molten materials and aggressive chemicals inside the
furnace. Moreover, if the molten materials and aggressive chemicals
reach the outer steel shell there is an imminent risk of severe
injury to personnel working near the furnace, because the outer
steel shell is not capable of reliably holding back the molten
materials and aggressive chemicals from inside the furnace. Loss of
heat transferability and conductivity are also known to occur as
results of the deterioration of the refractory lining.
[0004] Another mode of refractory lining deterioration, common in
furnaces that include water-cooled elements, is hydration of the
refractory lining. Under certain temperatures, water that has
leaked from a cooling element can react with the refractory bricks
causing expedited deterioration of the refractory lining. In
particular, magnesium (MgO) based refractory bricks are susceptible
to this mode of failure.
[0005] It is desirable to regularly check the thickness of the
refractory lining, as well as inspect the refractory lining for
defects such as cracking, delaminations, accretions and other
build-up. Making a reliable and accurate assessment of the
refractory lining thickness is difficult to do without first
emptying the furnace and shutting down the industrial process in
which the furnace is involved. Shutting down a metallurgical
furnace for routine inspection is costly and operators try to make
use of inspection methods that can be employed while the furnace is
operating. However, the hostile working-environment, that the
furnaces are included in, skews the measurements made. For example,
extremely high temperatures in the furnaces, vibrations, ambient
noise, dust, and electrical and mechanical hazards are known to
distort the thickness measurements generated by the previously
known inspection methods. A systematic method of taking such
sources of error into account has not been developed to improve
previous inspection methods. As a result, operators are forced to
shut down and cool furnaces in order to check the refractory lining
from time-to-time.
SUMMARY OF THE INVENTION
[0006] According to an aspect of an embodiment of the invention
there is provided a system for inspecting a metallurgical furnace
wall having: a stress wave generator for generating a stress wave
that propagates into a metallurgical furnace wall; a stress wave
sensor for sensing reflections of the stress wave; and a processor
having computer readable program code means embodied thereon for
(i) recording time domain data about the reflections of the stress
wave sensed by the stress wave sensor, (ii) converting the time
domain data into frequency domain data, and (iii) producing a
determination of the condition of the metallurgical furnace wall by
combining time domain data, the frequency domain data and a
temperature-dependent scaling factor which compensates for the
change in velocity of the stress wave and the reflections of the
stress wave through a refractory material included in the
metallurgical furnace wall.
[0007] In some embodiments, the temperature-dependent scaling
factor is calculated as a function of a relative change in the
modulus of elasticity over a temperature range corresponding to a
temperature gradient through the refractory material within an
operating metallurgical furnace.
[0008] In some embodiments, producing the determination of the
condition of the metallurgical furnace wall includes determining
the thickness of the metallurgical furnace wall.
[0009] In some embodiments, producing the determination of the
condition of the metallurgical furnace wall includes determining
the thickness of a refractory lining in the metallurgical furnace
wall.
[0010] In some embodiments, producing the determination of the
condition of the metallurgical furnace wall includes determining
the presence or absence of defects including delaminations,
accretions, cracks and bubbles. In some such embodiments, producing
the determination of the condition of the metallurgical furnace
wall also includes determining the position of defects including
delaminations, accretions, cracks and bubbles.
[0011] In some embodiments, the processor further comprises
computer readable program code means embodied thereon for including
a geometry-dependent velocity scaling-factor in the determination
of the condition of the metallurgical furnace wall. In some such
embodiments, the refractory material included in the metallurgical
furnace is provided in brick form, and the geometry-dependent
scaling factor is calculated as a function of the relative
dimensions of the refractory bricks.
[0012] In some embodiments, the metallurgical furnace wall under
inspection is known to include a refractory lining having a
plurality of layers, each composed of one type of refractory
material, and wherein the processor further includes computer
readable program code means embodied thereon for producing a
determination of the condition the metallurgical furnace wall using
a plurality of temperature-dependent scaling factors, each
temperature-dependent scaling factor corresponding to a respective
one type of refractory material in the refractory lining. In some
such embodiments, each of the plurality of temperature-dependent
scaling factors is calculated as a function of a relative change in
the modulus of elasticity over a temperature range corresponding to
a temperature gradient through the corresponding refractory
material. In other embodiments, the processor further comprises
computer readable program code means embodied thereon for including
a geometry-dependent velocity scaling-factor in the determination
of the condition of the metallurgical furnace wall. In very
specific embodiments, each layer of the refractory lining is known
to include refractory bricks of one type of refractory material and
each of the plurality of geometry-dependent scaling factors is
calculated as a function of the relative dimensions of the
refractory bricks in a respective layer.
[0013] According to an aspect of an embodiment of the invention
there is provided an apparatus for inspecting a metallurgical
furnace wall having: a plurality of stress wave generator-sensor
pairs, each pair for generating a stress wave and sensing
reflections of the stress wave at point on a metallurgical furnace;
and a processor having computer readable program code means
embodied thereon for producing a determination of the condition of
the metallurgical furnace wall from a combination of time domain
data collected by at least one sensor, frequency domain data
derived from the time domain data, and a temperature-dependent
scaling factor to correct for the change in velocity of the stress
wave and the reflections of the stress wave through a refractory
material included in the metallurgical furnace wall.
[0014] In some embodiments, the temperature-dependent scaling
factor is calculated as a function of a relative change in the
modulus of elasticity over a temperature range corresponding to a
temperature gradient through the refractory material within an
operating metallurgical.
[0015] In some embodiments, the determination of the condition of
the metallurgical furnace wall includes determining the thickness
of the metallurgical furnace wall.
[0016] In some embodiments, the determination of the condition of
the metallurgical furnace wall includes determining the thickness
of a refractory lining in the metallurgical furnace wall.
[0017] In some embodiments, the determination of the condition of
the metallurgical furnace wall includes determining the presence or
absence of defects including delaminations, accretions, cracks and
bubbles. In some such embodiments, the determination of the
condition of the metallurgical furnace wall also includes
determining the position of defects including delaminations,
accretions, cracks and bubbles.
[0018] In some embodiments, the processor further comprises
computer readable program code means embodied thereon for including
a geometry-dependent velocity scaling-factor in the determination
of the condition of the metallurgical furnace wall. In some such
embodiments, the refractory material included in the metallurgical
furnace is provided in brick form, and the geometry-dependent
scaling factor is calculated as a function of the relative
dimensions of the refractory bricks.
[0019] In some embodiments, the metallurgical furnace wall under
inspection is known to include a refractory lining having a
plurality of layers, each composed of one type of refractory
material, and wherein the processor further includes computer
readable program code means embodied thereon for producing a
determination of the condition of the metallurgical furnace wall
using a plurality of temperature-dependent scaling factors, each
temperature-dependent scaling factor corresponding to a respective
one type of refractory material in the refractory lining. In some
such embodiments, each of the plurality of temperature-dependent
scaling factors is calculated as a function of a relative change in
the modulus of elasticity over a temperature range corresponding to
a temperature gradient through the corresponding refractory
material. In other embodiments, the processor further comprises
computer readable program code means embodied thereon for including
a geometry-dependent velocity scaling-factor in the determination
of the condition of the metallurgical furnace wall. In very
specific examples, each layer of the refractory lining is known to
include refractory bricks of one type of refractory material and
each of the plurality of geometry-dependent scaling factors is
calculated as a function of the relative dimensions of the
refractory bricks in a respective layer.
[0020] According to an aspect of an embodiment of the invention
there is provided a method of inspecting a metallurgical furnace
wall including introducing a stress wave into a metallurgical
furnace wall at a point; sensing one or more reflections of the
stress wave near the point of introduction of the stress wave into
the metallurgical furnace wall; and processing the reflections in
the time and frequency domain in combination with a
temperature-dependent scaling factor to correct for the change in
velocity of the stress wave and the reflections of the stress wave
through a refractory material included in the metallurgical furnace
wall.
[0021] In some embodiments, the temperature-dependent scaling
factor is calculated as a function of a relative change in the
modulus of elasticity over a temperature range corresponding to a
temperature gradient through the refractory material within an
operating metallurgical furnace.
[0022] In some embodiments, the method further includes determining
the thickness of the metallurgical furnace wall.
[0023] In some embodiments, the method further includes determining
the thickness of a refractory lining in the metallurgical furnace
wall.
[0024] In some embodiments, the method also includes determining
the presence or absence of defects including delaminations,
accretions, cracks and bubbles. In more specific embodiments, the
method may also include determining the position of defects present
in the metallurgical furnace wall.
[0025] In some embodiments, the method also includes including a
geometry-dependent velocity scaling-factor in the determination of
the condition of the metallurgical furnace wall.
[0026] Other aspects and features of the present invention will
become apparent, to those ordinarily skilled in the art, upon
review of the following description of the specific embodiments of
the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] For a better understanding of the present invention, and to
show more clearly how it may be carried into effect, reference will
now be made, by way of example, to the accompanying drawings, which
illustrate aspects of embodiments of the present invention and in
which:
[0028] FIG. 1 is a cross-sectional drawing of a simplified example
metallurgical furnace;
[0029] FIG. 2A is a first example graph showing that an elasticity
of a refractory material included in the metallurgical furnace of
FIG. 1 is temperature dependent;
[0030] FIG. 2B is a second example graph showing that an elasticity
of another refractory material included in the metallurgical
furnace of FIG. 1 is temperature dependent;
[0031] FIG. 3 is a simplified illustration showing a
Single-Impactor Single-Sensor (SISS) inspection system according to
an embodiment of the invention in combination with the
metallurgical furnace shown in FIG. 1;
[0032] FIG. 4 is a simplified perspective view of a segment through
the metallurgical furnace wall directly under an impactor and
sensor of the SISS inspection system shown in FIG. 3;
[0033] FIG. 5 is a flow chart illustrating one very specific
example method according to an embodiment of the invention for use
with the SISS inspection system shown in FIG. 3;
[0034] FIG. 6 is a simplified illustration showing a
Single-Impactor Multiple-Sensor (SIMS) inspection system according
to another embodiment of the invention in combination with the
metallurgical furnace shown in FIG. 1; and
[0035] FIG. 7 is a simplified schematic drawing of a
Multiple-Impactor Multiple-Sensor (MIMS) inspection system
according to yet another embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0036] Inspecting the refractory lining of a metallurgical furnace
is a challenging procedure that typically requires emptying,
shutting down and cooling the furnace to reliably evaluate the
condition of the refractory lining. Shutting down a furnace can
cost operators significant amounts in lost revenue, man-hours, and
other expenses. In some instances, repetitive cycles of cooling and
re-heating, required for routinely shutting down a furnace for
inspection, leads to faster deterioration of the refractory
lining.
[0037] Unfortunately, previously known methods of determining the
current condition of a refractory lining, while a metallurgical
furnace is running, provide flawed results. The results are flawed
because previously known inspection methods rely on quantitative
models that are based on unrealistic assumptions about the state of
the refractory materials in the furnace. For example, the models
previously relied upon do not take into consideration the effects
of extremely high temperatures on the refractory material
properties. Consequently, thickness measurements have been seen to
be off by as much as 30% to 100% using these previously known
methods. Thus, in order to avoid expensive and dangerous accidents
operators of such furnaces have been forced to routinely shut down
their furnaces to reliably evaluate the condition of the refractory
lining.
[0038] By contrast, some embodiments of the present invention
provide systems, methods and apparatus for more accurately
determining the thickness of a refractory lining included in an
operating metallurgical furnace. In some embodiments a transient
propagated stress wave, such as a compressive (i.e. longitudinal,
primary, etc.) stress wave, is used to determine the condition of a
refractory lining. The reflections of the stress wave are evaluated
to identify the presence and position of defects such as, for
example, cracks, delaminations and bubbles in the refractory lining
in addition to the overall remaining thickness of the refractory
lining. In some embodiments, the transient propagated stress wave
includes frequencies ranging from the acoustic (i.e. audible) to
the ultrasonic (i.e. non-audible). For example, a stress wave
generated according to an embodiment of the invention may have a
frequency range of 100 Hz to 80 kHz. This range of frequencies can
be advantageous in many scenarios since ultrasonic stress waves
alone typically lack sufficient energy to pass through thick
refractory linings and generally experience rapid attenuation
through solid heterogeneous masses.
[0039] Additionally, some embodiments of the present invention
provide a systematic way to include the affect that temperature has
on the velocity of a compressive stress wave through a heated
refractory material and/or accretions. As identified in aspects of
the present invention, and contrary to the common understanding in
the art, the velocity of a stress wave, at each frequency and in a
refractory material, is not necessarily constant over a temperature
range. In accordance with aspects of some specific embodiments of
the invention, a scaling factor .alpha. can be calculated for each
refractory material to adjust for the presumed velocity of the
stress wave through each refractory material. The scaling factor
.alpha. for a particular refractory material is a function of the
modulus of elasticity and the temperature and/or temperature
gradient through that refractory material. In some very specific
embodiments, the scaling factor .alpha. is calculated as a function
of the relative change in the modulus of elasticity over a
temperature range corresponding to the temperature gradient through
a layer of one type of refractory material. As will be described in
more detail below this is a significant departure from what is
known in the art, since a change in the modulus of elasticity and
the corresponding affect on the velocity of a stress wave through a
particular refractory material were previously assumed to be
non-existent.
[0040] The modulus of elasticity for a material is a quantitative
relationship between stress and strain in that material. For metals
(e.g. steel, lead, copper, etc.) it is commonly understood that as
the temperature increases the deformation behavior of a metal
changes from elastic to plastic. Consequently, it is generally
considered easier to deform a metal at higher temperatures than at
lower temperatures. In other words, less stress induces the same or
greater strains within a metal at higher temperatures as compared
to at lower temperatures. This relationship between stress and
strain is often quantified as the modulus of elasticity , which is
commonly calculated as a ratio of stress to strain. The change in
the deformation behavior (from elastic to plastic) is due to the
weakening of a metal lattice structure at higher temperatures that
in turn allows metal atoms to flow more easily. Eventually, the
melting point temperature is reached and a solid metal changes to a
liquid. For steel the melting point is approximately 1500.degree.
C.
[0041] Refractory materials have a very strong lattice structure
and high temperatures do not generally cause a refractory material
to melt and/or behave in a way that can be categorized as plastic.
Refractory materials also tend to be far more brittle than metals.
As a result, the melting and deformation characteristics of metals
described above are not found in refractory materials. By contrast,
refractory materials simply tend to break, crack and/or
disintegrate into a powder while remaining in the elastic
regime.
[0042] In quantitative terms, the modulus of elasticity of a
refractory material does not change significantly as a function of
temperature in a way that is comparable to the change observed in
metals. In fact, the modulus of elasticity for a particular
refractory material is typically considered to be a constant.
Seemingly negligible changes in a modulus of elasticity were
previously not considered to be of importance when considering
properties of a refractory material in relation to the intended
uses for that refractory material. Despite not having a significant
impact on the structural and insulating properties of a refractory
material, a relative change in the modulus of elasticity , as
identified as an aspect of the present invention, may have a
significant impact on the velocity of a stress wave in the
refractory material.
[0043] Returning again to the use of stress waves, a shock or
impulse disturbance to a solid induces a number of linear and
angular displacements within that solid. Specifically, in a
refractory material the applied shock or impulse disturbance
generates various types of stress waves. Stress waves may be
categorized as either body or surface waves. Body waves travel
through a solid, whereas surface waves travel primarily along the
surface of the solid.
[0044] Two significant types of body waves are Primary-waves (i.e.
P-waves, longitudinal, compressive waves, etc.) and Secondary-waves
(i.e. S-waves, shear waves, etc.). P-waves induce particle motion
in the same direction as the path of travel of the wave front. That
is, as a P-wave passes through a solid, particles vibrate about an
equilibrium position, in the same direction as the P-wave is
traveling. P-waves also cause compression and rarefaction, but not
rotation of a refractory material. On the other hand, S-waves
induce particle motion perpendicular to the path of travel to the
wave front. That is, as an S-wave travels through a body, particle
displacement is perpendicular to the direction of propagation of
the S-wave. S-waves also cause shearing and rotation, but no volume
changes of a refractory material.
[0045] In many embodiments according to the invention, P-waves and
reflections of P-waves are evaluated to determine the condition of
a refractory lining of an operating metallurgical furnace. P-waves
are generally considered to be the fastest of the stress waves and
are known to travel through solids, liquids, and gases.
Accordingly, measurements relating to the thickness of a refractory
lining and the presence and position of accretions and defects in
the refractory lining can be determined using data collected about
the propagation of P-waves through the walls of an operating
metallurgical furnace irrespective of the state of the matter at
any point within the walls. As noted above some embodiments of the
invention provide a method by which the effect of temperature on
P-wave velocity, through a refractory material included in a
furnace wall, can be more accurately considered.
[0046] It is generally accepted that the fundamental wave equation
(1) is suitable to relate velocity V.sub.p of a P-wave to the
frequency f and wavelength .lamda. of the P-wave. The velocity
V.sub.p of a P-wave in a particular refractory material and the
density .rho. of the refractory material can be multiplied together
to determine the acoustic impedance Z for that refractory material,
as shown in equation (2). The acoustic impedance Z provides a value
that is useful in estimating how much energy is reflected from an
interface between two materials. V.sub.p=f.times..lamda. (1)
Z=.rho..times.V.sub.p (2)
[0047] However, when used to analyze an operating furnace,
equations (1) and (2) produce inaccurate results stemming from
assumptions made about the wavelength .lamda. and frequency f of a
P-wave in a heated refractory material. The extremely high
temperatures inside an operating furnace result in non-linear
changes in the wavelength .lamda. and frequency f of a P-wave,
which are not accurately observable or observable at all given the
hostile working-environment the furnaces are included in. As a
result, significant errors are encountered when using previously
known methods of inspecting operating metallurgical furnaces.
[0048] Alternatively, and in accordance with some embodiments of
the invention, the velocity V.sub.p of a P-wave in a refractory
material can also be determined from the density .rho. and the
modulus of elasticity .sub.d of the refractory material. For
example, the velocity V.sub.p of a P-wave through an infinite
isotropic elastic refractory solid, with homogeneous composition,
can be determined with equation (3). In contrast, equation (4)
provides the velocity V.sub.p of a P-wave through refractory
rod-shaped structures, where the diameter of the rod is much
smaller than the length (i.e. d<<L). V p = E d .function. ( 1
- .upsilon. ) ( 1 + .upsilon. ) .times. ( 1 - 2 .times. .upsilon. )
.times. .times. .rho. ( 3 ) V p = E d .rho. ( 4 ) ##EQU1## In
equations (3) and (4), .upsilon. is Poisson's ratio, .rho. is again
the density and .sub.d is Young's (dynamic) modulus of elasticity
for the refractory material.
[0049] The velocity of a P-wave through a rod-shaped structure, as
given by equation (4), will be less than the velocity of the P-wave
through an infinite isotropic solid, as given by (3). Taken
together, equations (3) and (4) define respective upper and lower
end points for a range of P-wave velocities in homogenous
refractory solid structures that fall somewhere between the
extremes of a infinite solid mass and a very skinny rod. Although
both equations (3) and (4) relate elasticity of a material to
velocity, neither take into consideration the temperature of the
material.
[0050] Some embodiments of the invention provide a velocity
scaling-factor .alpha. that can be used to correct the velocity of
a P-wave in a refractory material in which the modulus of
elasticity changes due to extreme heating. In some specific
embodiments, the velocity scaling-factor .alpha. is calculated as a
function of the relative change in the modulus of elasticity .sub.d
over a temperature range corresponding to a temperature gradient
through a layer of one type of refractory material. Accordingly,
velocity equations (3) and (4) can be re-written as corrected
equations (5) and (6), respectively. V p ' = .alpha. .times.
.times. V p = E d .function. ( 1 - .upsilon. ) ( 1 + .upsilon. )
.times. ( 1 - 2 .times. .upsilon. ) .times. .times. .rho. .times.
.alpha. ( 5 ) V p ' = .alpha. .times. .times. V p = E d .rho.
.times. .alpha. ( 6 ) ##EQU2##
[0051] In one very specific example, if the change in elasticity is
linear over a continuous temperature range, the velocity
scaling-factor .alpha. is given by equation (7). .alpha. = 1 + (
.intg. T 1 T .times. E .times. .times. ( T ) .times. d T E o ) = (
1 + .DELTA. .times. .times. E d E o ) = ( 1 + E d .times. .times. 2
- E d .times. .times. 1 E o ) ( 7 ) ##EQU3## The terms .sub.d2 and
.sub.d1 correspond to the elasticity of the refractory material at
respective first and second temperatures (e.g. on a hot face and
cooler face, respectively, of a refractory brick), whereas .sub.o
corresponds to the elasticity used to first calculate the
uncorrected velocity V.sub.p, which is likely the room temperature
value of .sub.d available from the manufacturers of refractory
materials.
[0052] For many refractory materials, the change in elasticity as a
function of temperature is generally non-linear and not always
easily characterized in an equation as simple as equation (7). In
such instances, advanced curve fitting techniques can be used to
derive numbers for the integral, shown in equation (7), as required
for each type of refractory material. In general, each type of
refractory material used in a furnace wall will have a
corresponding velocity scaling-factor .alpha.. Moreover, many
manufacturers do not have accurate elasticity data for refractory
materials at high temperatures, since elasticity in such materials
is normally assumed to be relatively constant. Accordingly, in many
cases testing has to be done to determine elasticity at elevated
temperatures in the range of those found in metallurgical furnaces.
The tests involve heating the refractory material and measuring
either the static or dynamic modulus of elasticity.
[0053] Turning to FIG. 1, shown is a cross-sectional drawing of a
simplified example metallurgical furnace 30. The metallurgical
furnace 30 includes an outer steel shell 31, a first layer of
refractory bricks 33 and a second layer of refractory bricks 35.
Those skilled in the art will appreciate that some metallurgical
furnaces also have a roof (not shown in FIG. 1) that includes an
outer steel shell and an inner refractory lining or only a singular
refractory layer.
[0054] The first layer of refractory bricks 33 is closest to the
steel shell 31 and is considered a safety layer. The second layer
of refractory bricks 35, in direct contact with the molten material
100, is considered a working layer. In a typical metallurgical
furnace the bricks in a safety layer are typically less dense than
the bricks in a working layer. However, in some furnaces the
reverse may be true or the bricks may be of the same type in each
layer. Additionally and/or alternatively, in some furnaces a safety
layer is composed of a castable material (e.g. a mixture of sand,
concrete, alumina and/or other materials), in contrast to bricks as
described above.
[0055] The thickness of each of the first and second layers of
refractory bricks 33 and 35 is partially dependent on the process
the metallurgical furnace is involved in. Generally, the more
aggressive the process the thicker the layers are. Thicknesses for
refractory linings typically range from 600 mm to 1600 mm.
[0056] As shown for illustrative purposes only, molten material 100
(e.g. molten iron ore) is inside the metallurgical furnace 30 and
the first and second layers of refractory bricks 33 and 35 have
both been deteriorated to some degree. In particular, the second
layer of refractory bricks 35 is significantly deteriorated and has
a number of defects including accretions 41, 43 and 45, a
delamination zone 47, and an area of extreme wear 49.
[0057] In the operating metallurgical furnace 30 the accretions 41,
43 and 45 are composed of impurities that have settled out of the
molten material 100. Delamination (e.g. delamination 47) occurs
when molten material 100 seeps behind bricks of one layer and
separates those bricks from the layer behind. Delaminations near
the steel shell 31 can be very dangerous, since the steel shell 31
may be exposed to the molten material 100. Areas of extreme wear
(e.g. area 49) naturally occur over time as the working layer
bricks are wasted away.
[0058] The total thickness of a furnace wall at a point is the
combination of the remaining portions of refractory brick layers at
that point in addition to any accretion on the working layer of the
refractory lining at that point plus the thickness of the outer
shell. Since deterioration is difficult, if not impossible, to
control and/or predict the thickness of the refractory lining is
expected to be different at different points. However, at each
point the same method can be used to evaluate the thickness of the
refractory lining.
[0059] According to one specific method provided by an embodiment
of the invention, a P-wave is generated by an impact applied to the
steel shell 31 of the metallurgical furnace 30. The P-wave travels
through the steel shell 31 and through the refractory brick layers
33 and 35. Reflections of the P-wave are created at material
interfaces and most notably at the interface between the second
layer of refractory bricks 35 and the molten material 100, and the
interfaces created by defects (e.g. cracks, delaminations, bubbles
and the like). In order to accurately evaluate measurements and
reflections of the P-wave a velocity scaling-factor .alpha. is
determined for each refractory material (e.g. for each refractory
brick layer 33 and 35) included in the refractory lining. This
method will be described in further detail below with reference to
FIGS. 4 and 5.
[0060] As noted earlier, the velocity scaling-factor .alpha. is
calculated as a function of the relative change in the modulus of
elasticity over a temperature gradient present in a layer of the
refractory material. In some instances, the temperature gradient
includes only a single temperature because a particular refractory
material heats evenly to the single temperature. On the other hand,
in other instances the temperature gradient corresponds to a
specific temperature gradient expected in another type of
refractory material. FIGS. 2A and 2B graphically illustrate
respective first and second examples of how elasticity in the
corresponding refractory materials in layers 33 and 35 are
temperature dependent.
[0061] Referring to FIGS. 3 and 4, and with further reference to
FIGS. 1 and 2A-2B, shown is a system for determining the condition
of a refractory lining in a metallurgical furnace, as provided by a
very specific embodiment of the invention. FIG. 3 includes the
metallurgical furnace 30 and all of the defects and patterns of
deterioration described above with reference to FIG. 1.
Accordingly, FIGS. 1 and 3 share common reference indicia for
identical features common to both figures.
[0062] The system shown in FIGS. 3 and 4 is a Single Impactor
Single Sensor (SISS) system because it includes a single impactor
70 and a single sensor 72. The impactor 70 and sensor 72 are placed
adjacent to one another. The system also includes a processor 76
and an optional pre-amplifier (Pre-Amp) 74. Those skilled in the
art will appreciate that the SISS system also includes a suitable
combination of associated structural elements, mechanical systems,
hardware, firmware and software that is employed to support the
function and operation of the SISS system. Such items may include,
without limitation, a power supply, piping, vibration sensors,
regulators, seals, insulators and electromechanical
controllers.
[0063] In some embodiments the sensor 72 is a broadband vertical
displacement transducer or a similar device suitable to operate as
a stress wave sensor. For example, in other embodiments,
accelerometers and like devices are also suitable for use as the
sensor 72.
[0064] In some embodiments, as illustrated in FIG. 3, the sensor 72
is coupled to provide a signal to the processor 76 through the
optional Pre-Amp 74. In alternative embodiments, the sensor 72 is
coupled directly to the processor 76. The Pre-Amp 74 operates to
amplify the sensor readings of the sensor 72. As described in
detail below, the processor 76 operates to evaluate sensor readings
received from the Pre-Amp 74 (or directly from the sensor 72) to
determine the condition of the refractory lining under the sensor
72. With specific reference to FIG. 4, a measure of the total
thickness T.sub.t of the furnace wall under the sensor 72 is the
combined thickness of the outer steel shell 31, the first and
second refractory brick layers 33 and 35, and the accretion 45.
[0065] In some embodiments, the processor 76 includes a computer
readable program code means embodied therein for determining a
condition of a refractory lining. In some such embodiments the
computer readable program code means includes instructions for
triggering the impactor 70 to generate a P-wave and evaluating
reflections of the P-wave.
[0066] The impactor 70 is used to generate a P-wave that is
transmitted into the wall of the metallurgical furnace 30 by first
striking a point on the outer steel shell 31. That is, the impactor
70 is a device suitable to operate as a stress wave generator. In
some embodiments, the impactor 70 is a spherical impactor.
Spherical impactors generate simple, easy to analyze spherical
P-waves in a broad range of frequencies. In alternative
embodiments, P-waves can be generated manually with a mallet (or
similar instrument), with controlled electric shocks and/or small
explosions.
[0067] The frequency range of a P-wave generated by the impactor
can be controlled by adjusting at least one of a number of
parameters, including, without limitation, the diameter of the
contact point of a spherical impactor, the surface smoothness of
the outer steel shell 31, the input force and the contact time
t.sub.c. For example, a P-wave with a relatively high frequency
range will be generated if the outer steel shell 31 is smooth,
clean and struck with a relatively small-diameter impact source.
The highest useful frequency component of a generated P-wave may be
estimated from the contact time t.sub.c according equation (8). f
max = 1.25 t c ( 8 ) ##EQU4## The contact time t.sub.c is the
duration of time that the impactor 70 connects with the steel shell
31. The contact time t.sub.c can be adjusted to control the
generated range of frequencies in a P-wave. Having a relatively
broad range of frequencies in a single P-wave is advantageous as
wave energy at each frequency is attenuated to different degrees as
a function of the materials through which the P-wave travels.
[0068] Referring specifically to FIG. 4, an impact results in the
generation of a semi-spherical P-wave 81 below the point of impact.
Surface waves and S-waves are also generated, however, more of the
energy is transmitted via the P-wave 81 directly away from the
impactor 70. The P-wave 81 propagates away from the impactor 70
until it encounters acoustic interfaces (boundaries) or fades away
due to attenuation through the furnace.
[0069] In general, when a P-wave encounters an acoustic interface,
depending on the material properties of the acoustic interface,
either the entire wave or part of the wave reflects back towards
the source of impact. If a second material has significantly lower
acoustic impedance than a first material from which a P-wave
originates (e.g. refractory to gas or refractory to liquid
interfaces), then a significant portion of the P-wave reflects back
in the direction it started from. Such an interface is called a
stress free interface. On the other hand, if the second material
has significantly higher acoustic impedance than the first
material, part of the P-wave reflects back and the other part
continues to propagate into the second material. A small portion of
the propagating P-wave in the second material refracts along the
interface and another small portion of the propagating P-wave is
converted into waveforms (e.g. surface waves and S-waves).
Reflections bounce back and forth between acoustic interfaces,
naturally attenuated as they travel through a material, until the
energy more-or-less completely fades away. If the two materials
have similar acoustic impedances then the amount of the reflection
is small and natural attenuation from the materials tends to fade
the reflection out of existence before the reflection reaches the
original impact/sensor point.
[0070] Each interface between adjacent layers (e.g. between layers
35 and 45 in FIG. 4) can be considered a respective acoustic
interface, since each layer likely has an acoustic-impedance that
is different from those of the layers adjacent to it. Despite this,
reflections from interfaces between refractory layers (e.g. 33 and
35) do not tend to produce significant reflections unless defects
are present. When the propagating P-wave 81 encounters an acoustic
interface, it goes through reflection, refraction, diffraction and
mode conversion. In many embodiments of the invention effects
stemming from refraction, diffraction and mode conversion are not
given significant consideration, whereas reflections are considered
in greater detail.
[0071] The sensor 72 is arranged to sense reflections, indicated
for example by a single semi-spherical P-wave reflection 83 in FIG.
4, as they arrive back to the impact source. The reflection
arrivals are almost periodic and relate to the velocity of the
P-wave 81 in the refractory lining and the total path length of the
P-wave 81 (and reflection 83), which is twice the total thickness
T.sub.t of the furnace wall. Moreover, the duration between two
successive reflection arrivals is an estimate of how long the
P-wave 81 and a corresponding reflection 83 took to travel through
a corresponding layer in the furnace wall. In order to simplify the
model, the velocity scaling-factor .alpha. for each layer of
refractory material is only applied to the uncorrected velocity
V.sub.p of the P-wave 81 in that particular refractory material.
Accordingly, equation (9) provides an estimate of a time during
which a P-wave travels in a given refractory layer n. t pn = 2
.times. T n V pn ( 9 ) ##EQU5## The term T.sub.n is the thickness
of a particular refractory layer n, V.sub.pn is the uncorrected
velocity, and t.sub.pn is one specific duration of time between
reflection arrivals. The time t.sub.pn can be considered as the
period between reflections 83. Given that the reciprocal of a
period is a corresponding frequency, equation (9) can be written in
terms of frequency of reflections as shown in equation (10). f pn =
V pn 2 .times. T n ( 10 ) ##EQU6##
[0072] The reflections 83, taken collectively, form a time domain
acousto-ultrasonic echo response of the furnace wall to the P-wave
81 generated by the impactor 70. The time domain acousto-ultrasonic
echo response can be converted into corresponding a frequency
domain acousto-ultrasonic echo response using a Fast Fourier
Transform (FFT) method or another (and likely less efficient)
digital signaling processing technique by the processor 76. In some
embodiments, the processor 76 has access to a computer readable
medium having instructions for carrying out an FFT method or
another digital signal processing method for converting between the
time and frequency domains. The frequency domain acousto-ultrasonic
echo response shows the effect that successive reflection arrivals
have on the surface of the outer steel shell 31.
[0073] However, before equations (9) and (10) can be used, in
accordance with a very specific embodiment of the invention, the
velocity V.sub.p of the P-wave 81 and corresponding reflection 83
in each refractory material is corrected by applying the
aforementioned velocity scaling factor .alpha..sub.n, for each
corresponding refractory material n.
[0074] The wave speed generated by the impact source is an indirect
measurement of the P-wave speed. An impact source causes multiple
reflections of the P-waves causing excitation of a particular mode
of vibration. This mode of vibration is called thickness mode of
vibration and results in alternating expansions and contractions
across the thickness of the object. Numerous finite element and
laboratory experimentations, covering a wide range of shapes and
dimensions for the solids were used to determine the first mode of
vibration generated by an impactor. This first mode of vibration or
fundamental frequency affects the P-wave speed and is called
.beta.. That is, a second geometry-dependent velocity
scaling-factor .beta..sub.n may also optionally be applied for each
refractory material n in order to improve the accuracy of the
thickness and/or defect identification measurements obtained. The
shape and dimensions of a refractory brick have an affect on the
velocity V.sub.p of a P-wave through the refractory brick. In order
to correct for these geometry-dependent effects, a second velocity
scaling-factor .beta. may be determined as a function of the
relative dimensional ratio of a typical refractory brick within
each of the refractory brick layers 33 and 35.
[0075] In one specific embodiment, .beta. is 0.96 for
length-to-width ratios over 2.0 and ranges between 0.90 and 0.96
for length-to-width ratios between 1.0 and 2.0. The precise values
for .beta. can be determined on bricks at room temperature. If a
refractory layer includes bricks of different shapes, then each
shape should be considered.
[0076] In some embodiments, the processor has access to a computer
readable medium having instructions for determining the uncorrected
velocities and scaling factors for each refractory material. In one
specific embodiment, the thickness of a refractory lining including
only one type of refractory material (i.e. one refractory layer)
can be calculated according to equation (11) as follows. T =
.alpha..beta. .times. .times. V p .times. 2 .times. f p ( 11 )
##EQU7##
[0077] Alternatively, if the refractory lining includes multiple
layers of different refractory materials (as shown in FIG. 4), the
thickness equation becomes more complex and is easier to solve in
the frequency domain. Since each refractory layer contains bricks
of different composition and thickness, the P-wave velocity through
each layer can now be taken into consideration in the overall
assessment of the furnace wall. Subsequently, equation (11) is
changed and takes the form of equation (12). f t = 1 2 .times. T 1
.times. .alpha. 1 .times. .beta. 1 .times. V p .times. .times. 1 +
2 .times. T 2 .alpha. 2 .times. .beta. 2 .times. V p .times.
.times. 2 + 2 .times. T 3 .alpha. 3 .times. .beta. 3 .times. V p
.times. .times. 3 + ( 12 ) ##EQU8## where f.sub.t is the P-wave
thickness frequency of the refractory layers, V.sub.p1 is the
P-wave velocity in the material of layer 1, T.sub.1 is the
thickness of layer 1, V.sub.p2 is the P-wave velocity in the
material of layer 2, T.sub.2 is the thickness of layer 2, and so
forth.
[0078] Referring to FIG. 5, and with continued reference to FIG. 4,
a flow chart illustrating one very specific example method
according to an embodiment of the invention is provided. A number
of steps in FIG. 5 are collectively assigned a prefex "B" because
these particular steps have been provided to illustratively
describe, in simplified discrete steps, what is happening to a
P-wave as it travels through a furnace wall. These steps generally
cannot be controlled after the P-wave is created. Those skilled in
the art will appreciate that an actual sequence of events relating
to a propagating P-wave is somewhat more complex.
[0079] At step 5-1 the impactor 70 is triggered to generate the
P-wave 81 on the outer surface of the outer steel shell 31.
Consequently, at step B5-2 the P-wave 81 propagates through the
outer steel shell 31. At step B5-3, the P-wave reaches an acoustic
interface that may be representative of the first refractory layer
of bricks 33, the molten material 100 or a defect as described
above.
[0080] At step B5-4, if the material at the acoustic interface is
the molten material (no path, step B5-4), then most of the P-wave
81 is reflected backwards towards the sensor 72. The rest is lost
into the molten material 100. On the other hand, if the material at
the acoustic interface is a solid (e.g. the first refractory layer
of bricks 33), then (yes path, step B5-4) a portion of the P-wave
81 continues to propagate away from the impactor 70 at step B5-6
and another portion of the P-wave 81 reflects back towards the
impactor 70 at step B5-7. Following step B5-6 the P-wave 81
continues to repeat through steps B5-3, B5-4 and so on until the
wave energy finally completely fades away. The reflections 83
produced at steps B5-5 and B5-7 eventually reach the outer steel
shell 31, at step B5-8, after reflections, refractions,
diffractions, and mode conversions of their own.
[0081] At step 5-9, the sensor 72 senses the reflections 83 as they
arrive over time and the processor 76 records the arrival time and
magnitude of each reflection. This data forms the time domain
acousto-ultrasonic echo response of the furnace wall to the P-wave
81. After the reflections measurements have been made the processor
76 converts the time domain acousto-ultrasonic echo response to a
frequency domain acousto-ultrasonic echo response at step 5-10. The
frequency domain acousto-ultrasonic echo response is evaluated, as
in equations (9) and (12) to determine the condition of the
refractory lining, taking into consideration the uncorrected
velocities and scaling factors described above, which can be
calculated a priori.
[0082] A simplified illustration showing a Single-impactor
Multiple-Sensor (SIMS) non-destructive and non-invasive inspection
system according to another embodiment is provided in FIG. 6. The
SIMS shown in FIG. 6 is similar to the SISS shown in FIG. 3. FIG. 6
also includes the metallurgical furnace 30 and all of the defects
and patterns of deterioration described above with reference to
FIG. 1. Accordingly, FIGS. 1, 3 and 6 share common reference
indicia for identical features common to all three figures.
[0083] The SIMS system shown in FIG. 6 includes the single impactor
70 as described for the SISS system in FIG. 3. However, instead of
a single sensor and a single optional Pre-Amp, the SIMS system
includes two sensors 72a,b and two corresponding optional Pre-Amps
74a,b. That is, the two sensors 72a,b are optionally coupled to the
processor 76 through the two corresponding Pre-Amps 74a,b,
respectively The sensors 72a,b are placed adjacent to the impactor
70, and, in operation measurements obtained from the two sensors
72a,b are averaged, correlated and/or integrated together. Again,
velocity scaling-factors are advantageously employed as described
above. Those skilled in the art would appreciate that the processor
may have access to a computer readable program code means having
instructions for combining the measurements from the two sensors
72a,b.
[0084] In yet another embodiment, a simplified schematic drawing of
a Multiple-Impactor Multiple-Sensor (MIMS) non-destructive and
non-invasive inspection system is provided in FIG. 7 in combination
with a metallurgical furnace 32. The MIMS, shown in FIG. 7,
includes a number of sensor-impactor pairs, indicated for example
by 73a, 73b, 73c and 74d, that are arranged around the surface of
the metallurgical furnace 32. The MIMS system also includes an
impactor control and sensor Pre-Amp array 77 and a processor 78.
Each of the sensor-impactor pairs is coupled to the processor 78
via the impactor control and sensor Pre-Amp array 77. Specifically,
as an illustrative example the sensor-impactor pair 73d is coupled
to the impactor control and sensor Pre-Amp array 77 by a I/O line
61 that branches from a I/O bus 63 connected to the impactor
control and sensor Pre-Amp array 77.
[0085] In operation, individual impactors may be triggered one at a
time, in groups or all together. Each impactor can be arranged and
triggered to generate a respective P-wave that has a specific range
of frequencies that may or may not be different from the P-waves
generated by other impactors included in the MIMS system. Those
skilled in the art would appreciate that the impactor control and
sensor Pre-Amp array 77 and/or processor 78 may have access to a
computer program readable code means having instructions for
combining the measurements
[0086] Similarly, the individual sensors may be used to collect
P-wave data from the impactors they are paired with and/or one or
more impactors in the MIMS system. Accordingly, reflection
measurements collected from one or more of the sensors can be
averaged, correlated and/or integrated together. Again, velocity
scaling-factors are advantageously employed as described above.
Those skilled in the art would appreciate that the processor 78 may
have access to a computer program readable code means having
instructions for combining the measurements.
[0087] While the above description provides example embodiments, it
will be appreciated that the present invention is susceptible to
modification and change without departing from the fair meaning and
scope of the accompanying claims. Accordingly, what has been
described is merely illustrative of the application of aspects of
embodiments of the invention. Numerous modifications and variations
of the present invention are possible in light of the above
teachings. It is therefore to be understood that within the scope
of the appended claims, the invention may be practiced otherwise
than as specifically described herein.
* * * * *