U.S. patent number 3,704,370 [Application Number 05/132,821] was granted by the patent office on 1972-11-28 for radiographic inspection technique.
Invention is credited to William L. Shelton.
United States Patent |
3,704,370 |
Shelton |
November 28, 1972 |
RADIOGRAPHIC INSPECTION TECHNIQUE
Abstract
A contrast enhancement technique for use in radiography involves
impregnating material to be inspected by nondestructive
radiographic techniques with a tetrabromoethane prior to carrying
out the actual radiographic inspection and then removing the
tetrabromoethane.
Inventors: |
Shelton; William L.
(Springfield, OH) |
Assignee: |
|
Family
ID: |
22455756 |
Appl.
No.: |
05/132,821 |
Filed: |
April 9, 1971 |
Current U.S.
Class: |
250/302; 378/62;
378/58 |
Current CPC
Class: |
G01N
23/083 (20130101); G01N 23/18 (20130101); G03B
42/028 (20130101) |
Current International
Class: |
G01N
23/18 (20060101); G01N 23/02 (20060101); G03B
42/02 (20060101); G03b 041/16 () |
Field of
Search: |
;250/65R,18R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lindquist; William F.
Claims
I CLAIM:
1. A method for detecting cracks and flaws in a composite article,
said method comprising the steps of:
1. contacting the article with a tetrabromoethane for a period of
time sufficient to allow the tetrabromoethane to impregnate any
cracks or flaws in the article; and
2. X-raying the article.
2. A method according to claim 1 wherein the article is contacted
with the tetrabromoethane by immersing said article in the
tetrabromoethane.
3. A method according to claim 2 wherein said immersion is carried
out for about 6 to 10 hours.
4. A method according to claim 1 wherein the tetrabromoethane is
1,1,2,2-tetrabromoethane.
5. A method according to claim 4 wherein said
1,1,2,2-tetrabromoethane is removed, after the article is X-rayed,
by heating the impregnated article to a temperature in the range of
from about 90.degree.C to about 130.degree.C under a pressure of
from about 4 mm of mercury to about 15 mm of mercury.
6. A method according to claim 5 wherein said article is a rocket
nozzle insert.
7. A method according to claim 6 wherein said insert is a
multidirectional insert.
8. A method according to claim 5 wherein said article is a rocket
nose tip.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the use of materials to enhance the
contrast of photographs obtained in nondestructive radiographic
inspection techniques.
2. Description of the Prior Art
The use of radiographic nondestructive inspection techniques is
well known. One example of such a technique resides in the
inspection of the visceral organs of a patient by a medical doctor.
When a doctor wishes to inspect a patient for an ailment, such as
reflux peptic esophagitis, the doctor has the patient ingest an
aqueous suspension of barium sulfate which has been acidified by
hydrochloric acid. X-rays are then made of specific portions of the
patient's anatomy. The acidified aqueous suspension of barium
sulfate acts as an X-ray contrast medium and permits the doctor to
obtain good X-ray photographs of the patients internal organs
without resorting to complex and painful procedures. After such a
procedure, the contrast medium is removed by the natural functions
of the patient's body.
Another example of radiographic nondestructive inspection
techniques resides in the X-ray inspection of steel girders and
beams prior to their use in building construction. Steel building
parts are routinely inspected by X-ray techniques in order to
insure that they do not contain cracks or flaws which may result in
the eventual collapse of the building in which they are used. When
steel building parts are X-rayed, a contrast medium is not used
because many cracks or flaws which might be present will generally
be so minute that any contrast medium, such as an acidic aqueous
suspension of barium sulfate, cannot penetrate the flaws. Also, if
a contrast medium such as barium sulfate is used, it must be
acidified and the acid would have a corrosive effect on the
steel.
Still another example of radiographic nondestructive inspection
resides in the X-ray inspection of articles such as rocket nozzle
inserts and rocket nose tips. A rocket nozzle insert obviously must
not contain cracks or flaws or else it will fail under the extreme
conditions of temperature and pressure to which it is subjected
during flight of the rocket. The same conditions apply to rocket
nose tips.
In the prior art, articles such as rocket nozzle inserts and rocket
nose tips have been X-rayed without the benefit of a contrast
medium because no suitable medium has been available. When such
articles have been X-rayed the pictures obtained have exhibited
generally poor resolution and even large cracks and flaws have been
difficult to detect.
A suitable contrast medium must have three qualities. Firstly, it
must penetrate into any cracks or flaws present in the material
being X-rayed. Secondly, once it has penetrated it must provide
contrast (absorb X-rays) when it is X-rayed. Thirdly, after the
X-ray process has been completed, it must be easily removable from
the material into which it has penetrated.
Acidic aqueous suspensions of barium sulfate have been found to be
of no use as contrast mediums in the X-ray inspection of rocket
nozzle inserts and rocket nose tips. Barium sulfate suspensions,
because they are suspensions, will not penetrate into minute cracks
and flaws. Furthermore, barium sulfate suspensions, even if they
would penetrate into cracks or flaws of a rocket part, could not be
easily removed after the X-ray process was completed. Still
further, the hydrochloric acid or other acid which must be present
in the formulations would have a deleterious effect on most rocket
parts.
Other contrast mediums have been tried in attempts to obtain
clearer X-ray photographs of rocket parts. One such contrast medium
is lead perchlorate. Lead perchlorate will penetrate into minute
cracks and flaws of rocket parts and provide excellent contrast.
However, once lead perchlorate has impregnated a rocket part, it is
extremely difficult to remove because of its high boiling
point.
SUMMARY OF THE INVENTION
It has now been found that a tetrabromoethane such as
1,1,2,2-tetrabromoethane provides the three qualities necessary to
make it useful as a contrast medium for the radiographic
nondestructive inspection of rocket parts. It readily impregnates
into cracks and flaws in such rocket parts as nozzle inserts and
nose tips. It provides an excellent contrast medium when an
impregnated part is X-rayed. And finally, it may be easily removed
from the impregnated part once the X-ray process is completed. In
addition to the above features, the tetrabromoethane is a neutral
liquid at room temperature and causes none of the deleterious
effects which might be caused by the use of either acidic or basic
contrast mediums.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In a preferred embodiment, the present invention resides in a
method which comprises the steps of:
1. contacting, as by soaking or sponging, a piece of hardware which
is to be X-rayed, with a tetrabromoethane for a period of time
sufficient to allow the tetrabromoethane contrast medium to
penetrate into any cracks or flaws present in the piece of
hardware;
2. X-raying the impregnated piece; and
3. removing the tetrabromoethane from the piece.
The time required for impregnating the piece to be inspected, as by
soaking or sponging, depends upon the thickness and the porosity of
the material being impregnated. When thin sheets of porous material
are being impregnated, a few minutes of soaking or sponging are
sufficient to accomplish complete impregnation. On the other hand,
when relatively bulky articles such as rocket nozzle inserts are
impregnated, a time period of from about 6 to about 10 hours is
usually required.
The tetrabromoethane can be completely removed from an impregnated
article by evaporation. For example, 1,1,2,2-tetrabromoethane can
be readily removed by heating an impregnated article under reduced
pressure for a period long enough to vaporize the impregnant. The
tetrabromoethane begins vaporizing at approximately 90.degree.C
under a pressure of 4 mm of mercury. It vaporizes at 120.degree.C
under 15 mm of mercury. Thus, heating an impregnated article for a
few minutes at a temperature in the range of from 90.degree.C to
about 120.degree.C and a pressure of from 4 mm mercury to 15 mm
mercury, respectively, quickly removes the impregnant. Higher
temperatures may also be used. For example, the tetrabromoethane
boils at 151.degree.C under a pressure of 54 mm of mercury.
The invention may be more completely understood from a
consideration of the following illustrative examples which are not
intended, however, to be unduly limitative of the invention.
EXAMPLE I
Eleven multidirectional rocket nozzle inserts were X-rayed by
conventional techniques without the use of a contrast medium. The
inserts were actually three dimensional, composite, inserts which
were fabricated by laying up carbon cloth in two directions
perpendicular to each other, graphitizing the cloth, and then
inserting carbon filaments into the part in a direction
perpendicular to the plane in which the cloth was laid up. Such
inserts are commonly called carbon/carbon composites. Since the
laying up or wrapping procedures involved in fabricating a rocket
part of this type are fairly complicated, such parts often have
imperfections resulting from poor laminations and high porosity.
The X-ray photographs of the eleven nozzle inserts, taken without
the use of a contrast medium, were very fuzzy and unclear, i.e.,
they exhibited extremely poor resolution. Very few imperfections
could be detected.
The same 11 rocket nozzle inserts were immersed in
1,1,2,2-tetrabromoethane for eight hours. After soaking, the
inserts were removed from the tetrabromoethane, dried with a
lintfree cloth, and X-rayed. The X-ray photographs of the
impregnated inserts were much clearer in detail than those obtained
from the non-impregnated inserts. The X-rays obtained from the
impregnated inserts revealed the presence of cracks, flaws, and
pores not discernible when tetrabromoethane was not used. Even the
multidirectional nature of the laminated composite could be
detected.
After the impregnated inserts were X-rayed, they were placed in an
oven which was attached to a vacuum line which kept the pressure at
approximately 13 mm of mercury. The temperature of the oven was
raised to 115.degree.C and the inserts were heated for about eight
hours. They were then X-rayed again. The X-rays obtained after
heating indicated that the tetrabromoethane had been completely
removed by the application of heat under reduced pressure. That is,
the X-ray photographs appeared the same as X-ray photographs
obtained prior to the tetrabromoethane impregnation.
EXAMPLE II
A graphite nose tip which had been bonded to metal in the manner in
which nose tips are ordinarily bonded to re-entry vehicles was
X-rayed by standard techniques, i.e., without the use of a contrast
medium. Graphite nose tips of the type used are commonly called
bulk graphites. No imperfections in the bonding were detectable
from the resulting X-ray photograph. The article was then subjected
to a sponging operation in which a sponge was periodically wet with
1,1,2,2-tetrabromoethane and applied to the surface of the
graphite. The article was sponged for a few minutes until it was
completely coated with the tetrabromoethane. Then the
tetrabromoethane was allowed to penetrate for about 1 hour. After
about 1 hour, the structure was dried with a lint-free cloth and
X-rayed. The resulting X-ray, in contrast to the X-ray obtained
when no tetrabromoethane was used, showed the presence of several
areas of poor bonding between the nose tip and the re-entry
structure.
The tetrabromoethane was completely removed by subjecting the
article to a temperature of 110.degree.C and a pressure of about 10
mm of mercury for about 1 hour.
* * * * *