1、Designation: E1814 14Standard Practice forComputed Tomographic (CT) Examination of Castings1This standard is issued under the fixed designation E1814; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A num
2、ber in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This practice covers a uniform procedure for the exami-nation of castings by the computed tomography (CT) tech-nique. The requirements ex
3、pressed in this practice are intendedto control the quality of the nondestructive examination by CTand are not intended for controlling the acceptability or qualityof the castings. This practice implicitly suggests the use ofpenetrating radiation, specifically X rays and gamma rays.1.2 This practice
4、 provides a uniform procedure for a CTexamination of castings for one or more of the followingpurposes:1.2.1 Examining for discontinuities, such as porosity,inclusions, cracks, and shrink;1.2.2 Performing metrological measurements and determin-ing dimensional conformance; and1.2.3 Determining revers
5、e engineering data, that is, creatingcomputer-aided design (CAD) data files.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determi
6、ne the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E543 Specification for Agencies Performing NondestructiveTestingE1316 Terminology for Nondestructive ExaminationsE1441 Guide for Computed Tomography (CT) ImagingE1570 Practice for Computed Tomogra
7、phic (CT) Examina-tionE1672 Guide for Computed Tomography (CT) System Se-lectionE1695 Test Method for Measurement of Computed Tomog-raphy (CT) System PerformanceE1935 Test Method for Calibrating and Measuring CTDensityE2339 Practice for Digital Imaging and Communication inNondestructive Evaluation (
8、DICONDE)E2767 Practice for Digital Imaging and Communication inNondestructive Evaluation (DICONDE) for X-ray Com-puted Tomography (CT) Test Methods2.2 ASNT Documents:3SNT-TC-1A Recommended Practice for Personnel Qualifi-cation and Certification in Nondestructive TestingANSI/ASNT CP-189 Standard for
9、Personnel Qualificationand Certification of Nondestructive Testing Personnel2.3 Military Standards:4NAS 410 Certification and Qualification of NondestructiveTest Personnel3. Terminology3.1 DefinitionsDefinitions of terms applicable to thispractice may be found in Terminology E1316 and GuideE1441.3.2
10、 Definitions of Terms Specific to This Standard:3.2.1 fixturingthe mounting hardware used to place theobject in the CT system.3.2.2 scan planscan locations and the system configura-tion parameters for a specific part examination.4. Significance and Use4.1 CT may be performed on an object when it is
11、in theas-cast, intermediate, or final machined condition. A CTexamination can be used as a design tool to improve wax formsand moldings, establish process parameters, randomly checkprocess control, perform final quality control (QC) examina-tion for the acceptance or rejection of parts, and analyzef
12、ailures and extend component lifetimes.4.2 The most common applications of CT for castings arefor the following: locating and characterizing discontinuities,1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-structive Testing and is the direct responsibility of Subcommittee E07.
13、01 onRadiology (X and Gamma) Method.Current edition approved June 1, 2014. Published June 2014. Originallyapproved in 1996. Last previous edition approved in 2007 as E1814 - 96(2007).DOI: 10.1520/E1814-14.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer S
14、ervice at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available fromAmerican Society for Nondestructive Testing (ASNT), P.O. Box28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http:/www.asnt.org.4Available
15、 from Standardization Documents Order Desk, DODSSP, Bldg. 4,Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098, http:/assist.daps.dla.mil.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 194
16、28-2959. United States1such as porosity, inclusions, cracks, and shrink; measuringas-cast part dimensions for comparison with design dimen-sions; and extracting dimensional measurements for reverseengineering.4.3 The extent to which a CT image reproduces an object ora feature within an object is dic
17、tated largely by the competinginfluences of spatial resolution, contrast discrimination, thespecific geometry and material of the object itself, and artifactsof the imaging system. Operating parameters strike an overallbalance between image quality, examination time, and cost.4.4 Artifacts are often
18、 the limiting factor in CT imagequality. (See Practice E1570 for an in-depth discussion ofartifacts.) Artifacts are reproducible features in an image thatare not related to actual features in the object. Artifacts can beconsidered correlated noise because they form repeatable fixedpatterns under giv
19、en conditions yet carry no object informa-tion. For castings, it is imperative to recognize what is and isnot an artifact since an artifact can obscure or masquerade as adiscontinuity.Artifacts are most prevalent in castings with longstraight edges or complex geometries, or both.5. Basis of Applicat
20、ion5.1 The following items shall be agreed upon between thepurchaser and the supplier and specified in the contract or joborder:5.1.1 Nondestructive Testing Agency EvaluationThe useof a nondestructive testing (NDT) agency, as defined inPractice E543. If a systematic assessment of the capability ofth
21、e agency is specified, a documented procedure, such as thatdescribed in Practice E543, should be used as the basis forevaluation.5.1.2 Personnel QualificationsAll CT examination per-sonnel shall be qualified and certified in accordance with awritten procedure conforming to ANSI/ASNT CP-189, SNT-TC-1
22、A, NAS 410, or a similar document. The written proce-dure shall include training that addresses CT issues specifically.5.1.3 General RequirementsGeneral requirements shall bespecified in accordance with Section 8:(1) written procedure,8.1; and (2) CT system validation measurements, 8.3.5.1.3.1 Speci
23、fic requirements regarding preparation and ap-proval of the written procedures should be agreed upon inadvance by the purchaser and the supplier.5.1.4 FixturingThe object fixturing shall be determinedby agreement between the purchaser and the supplier inaccordance with 9.2.5.1.5 Image ProcessingImag
24、e processing routines used inanalysis of the CT data shall be specified in accordance with6.2:(1) dimensional measurements, 6.2.1; and (2) discontinuitycharacterization, 6.2.2.5.1.6 Discontinuity TypesA listing of the expected kindsof discontinuities shall be provided or referenced, and theacceptanc
25、e and rejection criteria shall be stipulated.5.1.7 RecordsRecords requirements shall be specified inaccordance with Section 10.6. Apparatus6.1 The success of the CT application depends on theoverall system configuration and the selection of appropriatesubsystem components. Guidance on the selection
26、of sub-system components and the overall system configuration isprovided in Guide E1672. Guidance on the initial systemperformance evaluation for baseline and periodic system per-formance check of the CT system is provided in Test MethodE1695. Guidance on calibrating and measuring CT densitymeasurem
27、ents is provided in Test Method E1935. The suitabil-ity of the CT system shall be demonstrated by attainment of therequired image quality and compliance with all other require-ments stipulated herein.6.2 Computer/Image Processing SoftwareImage process-ing software may be used for image enhancement o
28、perationsthat will facilitate dimensional measurements and discontinuitydetection or characterization.6.2.1 Dimensional measurements, with tolerance, can beobtained from the CT image. There is a degree of blurring inthe CT image that makes sharp boundaries indistinct. Acommon approach for on-screen
29、dimensional measurements isto generate a density profile along a straight line between thepoints in the image representing the distance to be measured.The end points of the measurement are generally taken to bethe density profile values located at the half maximum valuepoint on each slope. This is c
30、alled the full-width-at-half-maximum (FWHM) method. This method or various othertechniques, that is, the area under the curve or determiningcontours for CAD output, can be generalized for wallthickness, hole diameter, and crack width measurements.6.2.2 Each dimensional measurement technique has its
31、ownprecision, and for its determination, the creation of the CTimage must be understood thoroughly. A point-like object willnot appear in an image as a sharp point. Instead, the “true”image will be convolved with a Gaussian distribution-likefunction called the point spread function (PSF). Therefore,
32、when looking at a density profile along a line in a CT image,an abrupt density change (that is, from material to air) will notappear as a step but as a curve. See Guide E1441 and Sections5, 8, and 9 for further discussion.6.2.3 Some tools require the availability of an object thatcan be scanned and
33、then dissected (destructive evaluation) forcomparison with actual dimensional measurements. The CTsystem can be “spatially calibrated” (determine the voxel sizefor dimensional measurements) for a specific object from thiscomparison data.6.2.4 Various types of density analysis tools may be neededfor
34、discontinuity characterization, such as tools for measuringlow-density indications, missing mass, area, and shape.6.3 Purchasers are cautioned to test thoroughly, or haveprior experience with, the proposed image processing param-eters before authorizing routine use. For example, some spatialfilter f
35、unctions produce directional results and may suppressdesired image information. Other spatial filters can introduceartifacts into the image.7. Safety7.1 The CT procedures shall comply with applicable local,state, and federal safety regulations.E1814 1428. Requirements8.1 Written ProcedureThe CT exam
36、ination should beperformed in accordance with a written procedure. The proce-dure should address all applicable portions of this practice andshould be available for review during interpretation of theimages.8.1.1 Practice E1570 (System Configuration) details a list ofthe variables that can affect th
37、e examination outcome for aselected system configuration. The values used for thesevariables should be documented in the written procedure.8.1.2 The written procedure or scan plan should also includethe following:8.1.2.1 Description of the object and engineering drawings.8.1.2.2 Fixturing requiremen
38、ts and instructions.8.1.2.3 Handling requirements and instructions.8.1.2.4 Representative Quality Indicator (RQI) to be used.8.1.2.5 Algorithms or methods to be used for measuringdimensions and discontinuities.8.1.2.6 Scan LocationsFor example, scan locations can bespecified by sketch, photograph, o
39、r drawing or determined bya digital radiograph of the object from the same CT scanner.8.2 CT System ValidationThe CT system performanceparameters must be determined initially and monitored regu-larly to ensure consistent results. The CT performance levelmay be specified in terms of one or both of th
40、e following:8.2.1 Detectability of Features in an RQIIf dimensionalmeasurements are to be made from the CT data, a CT scan ofa dimensionally known object shall be used to spatiallycalibrate the CT system. The use of an actual or simulatedobject has benefits. An RQI demonstrates that the requiredsyst
41、em performance can be achieved, in both the CT exami-nation and the interpretation and analysis.8.2.2 Performance Measurements, Using a Disk Phantom,as Outlined in Test Method E1695The performance mea-surements determined using the disk phantom are the CTsystem spatial resolution and contrast sensit
42、ivity at specifiedscan parameters. These performance measurements are re-quired to monitor the overall system performance and checkfor variations over time, as well as to determine the perfor-mance of the equipment prior to CT examination of the objects.8.3 Validation Measurement IntervalsSystem sta
43、bilityover time must be demonstrated to the purchaser. There are twoapproaches, as follows:8.3.1 System performance measurements, using the diskphantom, can be taken periodically to check the ratio of signalto noise levels at disk center, spatial resolution, and contrastresolution. These data will b
44、e made available to the purchaserfor review, upon request. Interval for performance measure-ments is as agreed between purchaser and supplier withconsideration of the CT system manufacturer recommenda-tions. At least the previous 12 months performance data shallbe available to the purchaser.8.3.2 A
45、disk phantom or RQI, or both, can be scannedbefore and after CT examination of the casting(s). If a variationexists, explanations and corrections will need to be made andvalidated.9. Procedure9.1 Handling and PreparationFollow the handling in-structions as documented in the written procedure. While
46、nosurface preparation is required for CT, the removal of surfaceblemishes and debris that could confuse the image is recom-mended.9.2 Object FixturingFixturing is typically incidental to theexamination of castings since CT will image any hardware forfixturing along with the object. However, precisio
47、n fixturingmust be used when orientation or repeatability, or both, are ofhigh importance. The fixtures usually vary from part to part andexamination to examination. If possible, the fixtures should notbe in the scan plane.9.2.1 Precision FixturingPrecision fixturing will be nec-essary if any of the
48、 following requirements pertain:9.2.1.1 Dimensional measurements in a precise location orrelative to a precise plane, or both, are specified.9.2.1.2 Dimensional measurements are to be registered withother types of measurements, such as, ultrasonic.9.2.1.3 Part to part comparisons are to be made.9.2.
49、2 Precision Fixturing ProcedureThe fixturing proce-dure will include the type and amounts of hardware, thelocations of the hardware relative to the object and the CTsystem, and how to mount and dismount the object. Theprecision fixturing should be: (1) specific to the casting to beexamined; (2) out of the scan plane, whenever possible; and (3)made of material less dense than the casting, to reduce or avoidartifacts, if in the scan plane.9.3 Data CollectionData shall be collected in accordancewith the written procedure or scan plan. A quick, qualitativeimage che
