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A-7 DA097 936 ARMY MATERIALS AND MECHANICS RESEARCH CENTER WATERTOWN MA F/A 14/5
I COMPOSITE SCREENS USED AS A RADIOGRAPHIC AIO.I(i)I AR I S DERSOGHOSIAN ,A J COATES
UNCLASSIFIED AMMR .TR1-11 NL.
AMVMRC TR 81-11 LJi 1
COMPOSITE SCREENS USED("CJC " AS A RADIOGRAPHIC AID
SATRAK DerBOGHOSIAN and ALBERT J. COATESMATERIALS TESTING TECHNOLOGY DIVISION ,
March 1981
>Approved for public release; distribution unlimited.
_ ARMY MATERIALS AND MECHANICS RESEARCH CENTERSWatertown, Massachusetts 02172
81 4 17 043
The findings in this report are not to be construed as an officialDepartment of the Army position, unless so designated by otherauthorized documents.
( Mention of any trade names or manufacturers in this reportshall not be construed as advertising nor as an official
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REPORT DOCUMENTATION PAGE BFRE ICOMPUTINORM
I' A MRCTR-1-1'?/2 GOVT ACCESSION NO. 3RE IPIENT'S CATALOG NUMBER
4. TITLE (and S~btiI.o) 6 T %7 a L 0CVRED
( COMPOSITE SCREENS USED AS A RADIOGRAPHIC AID.) Final Xepmt I ____
__________________________________________________________________ _____________NUMBER____
7. AUTHOR(&) S. CONTRACT OR GRANT NUMBER($)
// SatrakX erBoghosian an~d Albert J./Coates.
9PERFORtMING ORGANIZATION NAME AND ADDRESS 10eaies . PROGRtAM ELEMENT, PROJECT, TASK(
Arm Mteias ndMechanics Research Center D/A Project: M6350WaetwMsahsts02172 kCMS Code: 5397OM6350
71CONTROLLING OFFICE NAME AND ADDRESS 12 OI1"'1
Ui. S. Army Materiel Development and RaiesMrt 91
Command, Alexandria, Virginia 22333T3svne&F
14 MONITORING AGENCY NAME 4 AP04Skif dillon an- Controllin~g Ofbe..I IS SECURITY CLASS. tot this report)
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Approved for public release; distribution unlimited.
17 DISTRIBUTION STATEMENT (oftheN abstract entered In Stock 20. if different from, Repot)
IS SUPPLEMENTARY NOTES
This project has been accomplished as part of the U.S. Army Materials Testing Technology Program,which has for its objective the timely establishment of testing techniques, procedures or prototypeequipment (in mechanical, chemical, or nondestructive testing) to insure efficient inspection methodsfor materiel /material procured or maintained byDARCOM.___________KI EY WORDS (Confirn, on a s.. -wo.,do If ce artf W dervofy~ b block .. ost)
Nondestructive tests4 Composite screensIRadiography
_______
20 ABSTRACT (Cotlet.0 t on ,ls. .,do it n.-0-Y end Ident.Iy by' block ncuffbo,l
(SEE REVERSE SIDE)
DD 'YI1473 1 EDITION OP 'NO -0 'IS OBSOLETE INCLASS I FI F /11sE EcURT-yLASSI FicIC OP 40N--T..iS PAC.E - lt.1.....
UNCIASSIFIEDI8t 1TV CLAUIPICATION OF lW1$ PA@9MlIM 0a* be1I )
Block No. 20
ABSTRACT
Tests evaluating fluorometallic or composite X-ray intensifyingscreens have shown that these screens can be valuable and useful acces-
sories in the field of industrial radiography. In many applications,they can increase inspection efficiency by reducing exposure times and
possibly lowering the kilovoltages which are required when using con-
ventional lead screens.
The radiographic tests were performed using steel plates ranging
in thickness from 0.250 to 4.0 inches in the 150 kV to 2.5 MeV radiation
quality range with ASTM film classes 1 and 2. Image resolution assess-
ment was based upon penetrameter requirements (2-2T) set forth inMIL-STD-453, Inspection, Radiographic. The resultant radiographs usingthese screens attained at least the 2-2T quality required by most codes.
The high speed screen appears to offer more advantages than the highdefinition screen.
UNCLASSIFIED
SECURIT CL ASSPIC ATION OP THIS PA6GVWhP e Date f.,ro,.-)
CONT ENTS P g
INTRODUCTION. .. .......... ............. 1
RADIOGRAPHIC INTENSIFYING SCREENS .. ............. 1
Lead Screens .. ............ ......... 1
Fluorescent Screens. .. ............ ..... 2
Composite Screens. .. ........... ....... 2
GENERAL DISCUSSION. .. .......... .......... 3
TEST PARAMETERS .. ........... ........... 4
TESTS PERFORMED .. .......... ............ 5
PRACTICAL APPLICATIONS. .. ........... ....... 7
CONCLUSIONS .. ........... ............. 8
(RECOMMENDATIONS .. ........... ........... 9
BIBLIOGRAPHY. .. .......... ............. 9
p~ccesiO'For
ork
Distriblt 1 es
A_3t v / o de011
INJTRODUCTIONJ
In the field of industrial radiography, the absorption by the film of the trains-nutted radiation energy may Oc less than one percent. Because of this, intensifyingscreens are used as amplification devices to make more efficient use of the radiationreceived by the film.
The relatively recent introduction of composite or fluoronetallic intensifyingscreens represents an interesting development which merits further investigation intotheir effect on radiographic efficiency and economy.
The object of this report is to examine essential aspects of these screens by eval-uating their sensitivity and resolving capabilities utilizing various parameters.First, however, it would be helpful to briefly review intensifying screens in generaluse.
RADIOGR~APHIC INTENSIFYING SCREENS
Radiographic intensifying screens are used to reduce exposure time and to improvethe quality of the radiograph. This is done by the intensification action of the,creeps which more effectively utilizes the radiation absorbed by the film. Any de-vice, tl'erefore, which can enhance or improve the energy-absorbing process by thefilm contributes to the X-ray examination process.
At the present time, there are three kinds of screens which are generally beingused in the field of industrial radiography; namely, lead, fluorescent, and composite.
Lead intensifying screens are used almost exclusively in the industrial radio-giaphic field. Most codes do not allow the use of fluorescent screens or only by spe-cial permission if absolutely necessary. This study will attempt to identify someareas of applications where the fluorometallic or composite screen can be utilized tomeet or improve radiographic quality requirements.
Lead Screens
Lead is by far the most common screen material utilized and is available for thispurpose in the form of foil mounted on thin cardboard or plastic, or as an oxide ap-plied to a thin base in she'et form with film sandwiched between these sheets. Thistype of film-screen combination is convenient to use in many applications and is com-mercially available. What makes lead a desirable screen material is its ability torelease photoelectrons and scatter radiation when struck by X-rays. These photoelec-trons have enough energy to cause photochemical action in the film emulsion which, inturn, produces film blackening or density. The amount of photoelecLrons produced bythe X-ray beam determines the intensification effect of the screens.
Generally, lead screens are used in most radiography conducted above 125 kV and* are used as front and back screens with the film, of course, in between. The effec-
tiveness of the screen on the film density is called the intensification factor (I.F.)and is determined by dividing the exposure used to produce a given radiographic densitywith no screens by the exposure required to yield the same density with screens, As
* stated previously, lead screens are used in pairs with the film in intimate contactwith both front and back screep surfaces. Front screen thicknesses range from 0.004to 0.006 inch with back screens in the 0.010- to 0.01.5-3 ncii range. However, at volt-ages between 140 to 250 kV, the maximum intensification fac~tor for the front screen
i
occurs at about 0.001-inch lead thickness. Adding much more than a few thousandths oflead thickness only on the front screen reduces the intensification effect because ofprimary beam and scattered radiation absorption. The back screen is usually thicker inorder to absorb backscattered radiation.
Care must be taken to prevent damage, discoloration, scratches, or impurities inthe lead screen since these conditions cause artifacts in the finished radiograph.
In summary, lead causes the following effects when in close contact with a photo-
graphic emulsion:
1. The photochemical action on the film is increased because of electrons emittedand by the generation of scattered radiation.
2. The lead'absorbs the long wavelength scattered radiation more readily than theshorter primary wavelengths.
3. The primary radiation is intensified more than the scattered radiation.
Fluorescent Screens
Fluorescent intensifying screens emit light rays when subjected to X-rays. The
light emitted is directly proportional to the radiation intensity. Calcium tungstateand barium lead sulphate are the two most commonly used compounds for fluorescentscreen manufacture since they exhibit the above characteristics. The screens are madeby coating a cardbcard support with either of the above compounds. Like lead screens,the film is sandwiched between a pair of these screens and placed in a suitable filmholder or cassette. The exposure or film blackening is caused by a combination of theX-rays and the light emitted by the screens.
Even though fluorescent screens are widely used in medical radiography, the), areused sparingly in industrial radiography and then only under special circumstances,such as attempting to avoid unduly long exposure times with limited equipment or exces-sive thicknesses. The two main reasons for this are the loss of image quality becauseof a spreading of the light emitted by the screens and, secondly, by screen mottlewhich appears to be affected by the amount of absorbed X-ray quanta.
Fluorescent screens require more care than lead screens in that they must be peri-odically examined for film-screen contact and screen surfaces must be protected fromsoiling, finger contact, dust, etc. Suffice it to say that fluorescent screens arerarely used and then only in very unusual situations.
Composite Screens
The composite or fluorometallic intensifying screen (Figure 1) is a relativelyrecent introduction which attempts to combine the best qualities of lead and fluores-cent screens into a practical accessory for use in the improvement of radiographic ef-ficiency. This is accomplished by utilizing the luminescence of the fluorescent layer(calcium tungstate) and the secondary electrons from the lead layer. These mechanismsmake more efficient use of the radiation striking the film and account for most of theresulting film density.
The composite screens require as nuch care as fluorescent screens and must be freeof any surface soil or scratches.
2
X-RAY
I X-RAYSPECIMEN
\ - SCATTERED RADIATION
LEAD LAYESECONDARY ELECTRON
FLUORFLUORESCENCE
,FI F ELM LY FLUORESCENCE
V FLN LSECONDARY ELECTRON
LEAD LAYER
/-C SCATTERED RADIATION
Figure 1. The fluorometallic intensifying screen and composition.
GENERAL DISCUSSION
The composite screens are manufactured in two categories of high speed and high
definition which represent the general areas of application. These categories, in
turn, are subdivided into three energy levels ranging from 80 kV to 35 MeV. Table 1
shows the various codes selected for each type of screen, the voltages used which are
within the range for each type; and the films and their designations utilized for each
screen.
Table 1. CODES
a. Screen Designations (X-Ray Source)
Screen Type Voltage
18 High Definition 150 kV38 High Speed 150 kV13 High Definition 300 kV33 High Speed 300 kV11 High Definition 2.5 MeV31 High Speed 2.5 MeV
b. Film Designations
Film ASTM Type E94 RelativeIden. Description Speed
A 1 - Extra-Fine Grain 30B 2 - Fine Grain 100
3
TEST PARAMETERS
The composite screens consist of the six types listed in Table la, which cover arange of radiation quality from 150 kV to 2.5 MeV even though the screens are manufac-tured for use in the 80-kV to 30-MeV range. The screens are further divided into twocategories of high speed (1t1) and high definition (1i)), depending upon the application.Two of the most common industrial X-ray films were utilized with the above compositescreens and are described in Table lb. They are the ASTM E94 type 1 and 2 classeswhich account for the greater majority of industrial radiographic applications. Thescreens are made to radiograph thin and thick steels using a given radiation qualityrange.
For purposes of this investigation, the thicknesses for thin steel ranged from1/4 to 3/4 inch utilizing 150-kV X-rays which fall within the recommended 80- to200-kV range. Screens lID 18 and [IS 38 were used at these thicknesses in 1/4-inchincrements. Screens 1i1) 13 and HS 33 were used for intermediate thicknesses, begin-ning with 1 inch and up to 1-1/2 inches in 1/4-inch increments, utilizing 300-kV X-rayswhich fall within the recommended 200-kV to 0.66-MeV range. Screens HiD 11 and hIS 31were used for thicker steels, beginning with 2 inches and up to 4 inches in 1-inch in-crements, utilizing 2.5-MeV X-rays which are closer to the recommended lower range of3 to 35 MeV.
The investigation was conducted by grouping the two screen types of high defini-tion and high speed so that screens of each type were evaluated together. The screenswere utilized as recommended by placing film between screens. l-ven though other ap-proaches in this regard could have been used for evaluation pul'poses, it was decidedto follow manufacturers' procedures. A film density of 2.0 ± 0.20 H&D units was ob-tained for all exposures with all other conditions held constant for each voltage range.
The effectiveness of the composite screen on film density, which in this case mayalso be called screen performance, was determined by obtaining the intensificationfactor. The intensification factor may be calculated b" obtaining the ratio of the ex-posure required to produce a film density of 2.0 H&D units using lead screens to theexposure required to produce the same density with composite screens. This may bewritten as follows:
I.F. = Exposure with lead screensExposure with composite screens.
The steel specimens radiographed throughout the tests consisted of a series ofplates 1/8, 1/4, and 1/2 inch in thickness stacked to make up the required thicknesswhich ranged from 1/4 to 4 inches. In every case, the final 1/8 inch (tube side) con-sisted of a cracked plate which was used to evaluate the effect of composite screens onimage resolution. This %as considered important from a fault-sensitivity standpoint.All the above steel plates w'ere a standard 3 x 6 inches, including the top I/8-inchcracked plate.
For this investigation, radiographic quality levels were dtermined by using thepenetrameter method for lead as well as composite screen radiographs. The penetrametermethod is generally utilized in the field of industrial radiography, hence its use herefor controlling radiographic quality. The penetrameters utilized are in accordancewith the requirements of DoD MIL-STD-453, Inspection, Radiographic, 11 November 1977.
47
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Paraoraph I1. , . ,'2:, ' '.. , t atts t hat
"Thret m iniui lual I i tv levels l isted i Table Ta nay 1vhe ass i gied oithe basis () tile percept ihi I ity ut ofne , tWO, 0" t' !--e 1101 s ill tilie"penetrameter imIa ,e on the radiograph. The quality level shall be
specified by the procuring activity. Uli) esS othler'ise sIecified,all radiographs of aeronautical componenit s sha I1 show, th(_. i a!,' Ofat least two holes (quality level 2-2') and the outer edge of thepelietrameter palnel .
"Table II - Rad iographic (,ual ity Levels
Rad i og;raph i c Mi n imuun Pert ept i 1 e Equ iva l entOualit Level Penetrameter Hole Sensitivity, %
1 2T 2.4 4T 2.8."
Quality level 1 is specified as I-IT (where I equals material thickness radio-graphed) and indicates the showing of the IT hole in a penetrameter ihose thickness isone per,-ent of the material thickness. Thi s is a special quality level and .ill beconsidered above standard for this report and will be rated as such.
Quality level 2 is specified as 2-2T and indicates the showIng of the 21 hole in apenetrameter whose thickness is two percent of the material thickness. This qualitylevel is specified as the standard radiographic quality required by most radiographicspecifications and codes including MIL-STD-453. Therefore, radiographs bearing the2T' hole will be given a standard rating.
Quality level 4 is specified as 2-4T and indicates the showing of the 4T hole ina penetrameter ,hose thickness is two percent of the material thickness. This qualitylevel will be rated as below standard. The image of the cracked plate placed on topof the plates built up for the required thickness will be evaluated based upon a stan-dard radiograph made for that thickness and will be rated as acceptable (A) or notacceptable (NA).
TESTS PERFORMED
Fhe composite screen evaluation tests were conducted with both the high speed andhigh definition screens at the appropriate kilovoltage beginning with 150 kV, 300 kV,and finally, 2.5 MeV. Test results are presented in Table 2.
a. The li) 18 screen was used in radiographing thicknesses from 0.250 to 0,750inch of steel at 150 kV. Tests at this kilovoltage indicate significant increases inradiographic speed, up to about 4.5 times faster than conventional lead screens. Imagequality appears to be somewhat better at greater thicknesses. At 150 kV, the 1.F.seems to dimoinish somewhat with increasing: plate thickness. Iven though some compositescreen mottle has been noted, it does not appear to simage quality;
in fact, penetrameter contrast sensitivity appears to be slightly enhanced. Film typesI and 2 were used for these tests w ith the faster film (type 2) showing the greatestgain in I.F.
ai
Ilate A, TM
Iiiiigkness Screen f i lm Radiographic Crackteen Rad liat ion in. ) E xposure Type Type QualIty image 1..
a. 1 I ; 50 kV .1.250 Plb I 2I A
2 PIh 7 41 N.A3 18 1 2T A 4.04 18 2 N/A* NA 4.0
0.500 5 Pb 1 - A6
0b 7 41 NA
7 18 1 11 A 3.58 18 2 21 A 4.5
0.750 9 Pb I IT A10 Pb 2 21 A
I 1 8 I A 1.831 13 2 2T A 2.0
b. 17D 3 300 kV 1.0 13 Pb 1 13 A14 Pb 2 21 Ai5 13 I IT A 2.016 13 2 2T A 2.43
1.25 17 Pb 1 1T A28 Pb 2 IT A29 13 1 IT A 1.6720 13 2 11 A 2.33
1 .50 21 Pb 1 1T A22 Pb 2 IT A23 13 1 1 T A 1.5024 13 2 11 A 2.00
3.0 29 Pb 1 1 A
30 Pb 2 IT A27 11 1 1T A .5528 11 2 1T A 1.17
3.0 29 Pb 1 1T A30 Pb 2 iT A31 11 1 1T A 1.8032 11 2 1T A 1.4,
4.0 33 Pb 1 2T A34 Pb 2 2T A35 11 1 2T A 7.0636 11 2 2T A 3.11
.S 38 150 kV 0.250 3 Pb 1 2T A38 Pb 2 2T A39 38 1 2T A 7.540 38 2 2T A 3.00
0.500 41 Pb 1 1T A42 Pb 2 2T A43 38 7 IT A 4.8844 38 2 2T A 7.50
0.750 45 Pb I IT A46 Pb 2 2T A47 38 1 1T A 3.0748 38 2 1T A 4.71
e. HS 33 300 kV 1.0 49 Pb 1 IT A50 Pb 2 2T A51 33 1 IT A 3.6452 33 2 IT A 5.00
1.25 53 Pb 1 IT A54 Pb 2 2T A55 33 1 IT A 2.7556 33 2 IT A 4.44
1 .50 57 Pb 1 IT A58 Pb 2 IT A59 33 1 IT A 2.5060 33 2 IT A 3.00
3 HS 31 2.5 MeV 2.0 61 Pb 1 IT A62 Pb 2 IT A63 31 1 IT A 2.1464 31 2 IT A 1.17
3.0 65 Pb 1 IT A66 Pb 2 1T A67 31 1 IT A 1 .7768 31 2 IT A 2.67
4.0 69 Pb I IT A70 Pb 2 IT A
71 31 1 IT A 1.5772 31 2 IT A 2.00
*Overexposed
AL-- 'A,6
b. Ilikj II1) 1, Screen v:,W S usesd to radiograph thicliesses fron 1.() to 1 .5,( inches of
steel at i0) kV. 'lhe same pattern noted in the 150 kV tests is repeated at 300 kV inthat the intensification factor again decreased as material thickness increased, withimp rovements in image resolution. All radiographs showed at least standard quality (2'T)to above s tandard (1T).
c. T[he 111) 11 screen Ias used in radiographing thicknesses from 2.0 to 4.0 inchesof steel at 2.5 )leV. This screen produced the lowest I.F. values as a group whichagain generally decreased with increasing material thiclkness. tEven thoulh the 1.F.'Swere low, they could still be considered useful in many radiographic applications.
d. T e 1HS 38 screen, used at 150 kV to radiograph the same thicknesses as the lID18 screen, produced the highest recorded 1.F. in these tests (7.5) with a decrease in1.F. as the material thickness increased. inage quality was at least standard 21 orbetter in most cases, which indicates that, along with its superior specu, this highspeed screen is a very attractive radiographic accessory.
e. The HS 33 screen, which was used to radiograph the same thicknesses as the Ili)13 screen, shows higher 1.1. values at 300 1,V while depicting standard to above standardimage resolution. Again, the I.F. values diminish with increasing material thickness.The crack image resolution is pretty well maintained with lead as well as compositescreens. Some mottling is noted with the conposite screens which does not seem to af-fect penetrameters or crack image resolution.
f. The HS 31 screen was used at 2.5 .MeV in radiographing the same thicknesses asthe HD 11 screen. The HtS 31 screen outperforried the lID 11 screen in I.F. values eventhough the image resolution for each group is above standard. This may prove to bevery useful in the radiography of high dcnsity materials where scattering can be a prob-lem. The image resolution capacity of the 11S 31 screen appears to meet most code re-quirements for both types of films utilized. As shown in the tables, in at least halfthe exposures made at 2.5 MeV, there has been more than a 50% reduction in exposuretimes which car be significant in production radiography.
PRACTICAL APPLICATIONS
Figure 2 represents radiographs of a 0.625-inch uranium section taken at 2.5 MeVusing conventional lead screens and composite screens. The left radiograph was made
/,
a. Lead b. Composite
Figure 2. Comparison of radiographs of lead and composite screens of uranium section.
.,7
using lead screens and exposed for 2 minutes and 45 seconds. The right radiograph wasmade using composite screen tS 31 which was exposed for 1 minute and 30 seconds. Allfactors were held constant with the exception of exposure time. Image details of bothradiographs appear similar, however, the composite radiograph represents a 45% reductionin exposure time, which is considerable in terms of inspection speed and X-ray tubeeconomics.
Figure 3 represents radiographs taken of a 0.625-inch steel casting at 220 kV,again comparing lead and composite screens. The left radiograph was made using leadscreens and exposed for 5 minutes. The right radiograph was made using the same com-posite screen H1S 31, and exposed for 2 minutes. As above, all test parameters were con-stant other than exposure time. The exposure time using the composite screen resultedin a 60% reduction with no apparent adverse effects upon image resolution.
High speed screens were used in the radiography of tank repair welds. Initialtests indicate a reduction of at least 25% of exposure time while extending the tfick-ness range penetrated by a 300 kV X-ray unit.
a. Lead b. Composite
Figure 3. Comparison of radiographs of lead and composite screens of steel casting.
CONCLUS I ONS
The tests conducted in this investigation have shown that fluorometallic or com-posite intensifying screens are a valuable and useful accessory in the field of indus-trial radiography. In many applications they can be used to increase radiographic in-spection efficiency by reducing exposure times and possibly lowering the kilovoltagesrequired when using conventional lead screens. Image resolution assessment was basedupon the penetrameter requirements set forth in MIL-STD-453. This document outlines theradiographic quality requirements of aeronautical components. All radiographs were madeusing steel plates ranging in thickness from 0.250 to 4.0 inches in the 150 kV to2.5 MeV radiation quality range. Two types of film, ASTH 1 and 2, were used throughoutthis investigation. It can be concluded that:
8
1 . During this investigation, the int ens i f icat ion factors ranged t'rorm 1 .0(, t u 7
2. In many applications, the composite screen can allow si gnificant reductionsin radiographic speed while reducing, in some cases, kilovoltages that would be other-wise required.
3. Shorter exposure times appear to be shortened more than longer exposure times.
4. The I.F. decreases with increasing material thicknesses.
S. Image quality is generally adequate to meet most code requirements.
6. The high speed screen appears to offer more advantages than the high definitionscreen.
7. The composite screen represents a new amplification device for theradiographer.
RECOMMENDAT IONS
It is recommended that corposite screens be utilized in appropriate applicationswhile promoting shorter exposures without loss of image resolution.
It is also recommended that, based upon the above, codes and specifications recog-
nize the usefulness of composite screens as valid radiographic accessories by allowingtheir use in many production radiographic applications.
B IBLIO0GRAPHY
ASTM Standard E94-77, "Standard Recommended Practice for Radiographic Testing," 1977.
GRAY, W. H., and JACSON, C. N., "Performance of Composite Intensifying Screens forRadiography in the Nuclear Field," Westinghouse Hanford Company, September 1973.
KYOKKO, "SMP Intensifying Screens for Industrial Use," Dai Nippon Toryo Company,Ltd., Tokyo, Japan, 1975.
MIL-STD-453, Military Standard, "Inspection, Radiographic," 11 November 1977.
PACE, A. L., "Lead Screens Mean Better Films with Less Exposure," G. E. RadiationDigest, 1958.
TAKIZAWA, T., HIRAKI, H., and MIURA, N., "Characteristics and Applications of Fluoro-metallic Intensifying Screens in Radiographic Testing," Materials Evaluation,v. 28, no. 3, 1970.
9
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