Title:
RADIOGRAPHIC INSPECTION TECHNIQUE
United States Patent 3704370
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
Application Number:
05/132821
Publication Date:
11/28/1972
Filing Date:
04/09/1971
Assignee:
AIR FORCE USA
Primary Class:
Other Classes:
378/58, 378/62
International Classes:
G01N23/18; G03B42/02; (IPC1-7): G03B41/16
Field of Search:
250/65R,18R
View Patent Images:
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:

2. 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

3. X-raying the article.

4. A method according to claim 1 wherein the article is contacted with the tetrabromoethane by immersing said article in the tetrabromoethane.

5. A method according to claim 2 wherein said immersion is carried out for about 6 to 10 hours.

6. A method according to claim 1 wherein the tetrabromoethane is 1,1,2,2-tetrabromoethane.

7. 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°C to about 130°C under a pressure of from about 4 mm of mercury to about 15 mm of mercury.

8. A method according to claim 5 wherein said article is a rocket nozzle insert.

9. A method according to claim 6 wherein said insert is a multidirectional insert.

10. 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°C under a pressure of 4 mm of mercury. It vaporizes at 120°C under 15 mm of mercury. Thus, heating an impregnated article for a few minutes at a temperature in the range of from 90°C to about 120°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°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°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°C and a pressure of about 10 mm of mercury for about 1 hour.