1、Designation: E 1312 99 (Reapproved 2004)e1Standard Practice forElectromagnetic (Eddy-Current) Examination ofFerromagnetic Cylindrical Bar Product Above the CurieTemperature1This standard is issued under the fixed designation E 1312; the number immediately following the designation indicates the year
2、 oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.e1NOTEEditorial changes were made to provide consistent terminology
3、, where applicable in May 2004.1. Scope1.1 This practice covers procedures for eddy-current exami-nation of hot ferromagnetic bars above the Curie temperaturewhere the product is essentially nonmagnetic, but below2100F 1149C.1.2 This practice is intended for use on bar products havingdiameters of12
4、in. 12.7 mm to 8 in. 203 mm at linearthroughput speeds up to 1200 ft/min 366 m/min. Larger orsmaller diameters may be examined by agreement between theusing parties.1.3 The purpose of this practice is to provide a procedure forin-line eddy-current examination of bars during processing forthe detecti
5、on of major or gross surface discontinuities.1.3.1 The types of discontinuities capable of being detectedare commonly referred to as: slivers, laps, seams, roll-ins(scale, dross, and so forth), and mechanical damage such asscratches, scores, or indentations.1.4 This practice does not establish accep
6、tance criteria.They must be specified by agreement between the usingparties.1.5 This practice does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this practice to establish appro-priate safety and health practices and determi
7、ne the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 543 Practice for Evaluating Agencies Performing Nonde-structive TestingE 1316 Terminology for Nondestructive Examinations2.2 Other Documents:SNT-TC-1A Recommended Practice for Personnel Qualifi-
8、cation and Certification in Nondestructive Testing3ANSI/ASNT-CP-189 Standard for Qualification and Certi-fication of NDT Personnel32.3 AIA Standard:NAS 410 Certification and Qualification of NondestructiveTesting Personnel43. Terminology3.1 DefinitionsTerminology E 1316 shall apply to theterms used
9、in this practice.4. Summary of Practice4.1 PrincipleThe major advantage of examining ferro-magnetic bar product above the Curie temperature with eddycurrents is the enhanced signal-to-noise ratio obtained withoutthe need for magnetic saturation.4.2 SensorsThis examination may be performed withvariou
10、s types or designs of encircling coils or with probe coilsthat are fixed or rotating.4.2.1 One or more exciter or sensor coils is used to encirclethe bar through which the product to be examined is passed.When the hot bar is in close proximity to the sensing andexciting coils, eddy currents are indu
11、ced in the hot product byan alternating current. The sensing coil detects the electromag-netic flux related to these currents. Changes or disruptions inthe normal flux pattern indicate the presence of discontinuities.This technique is capable of examining the entire circumfer-ence without contacting
12、 the product.4.2.2 The surface can also be examined with probe coilshaving one or more exciters and sensors which are spaced inclose proximity to the product surface. The probe is usuallysmall and does not encircle the product, making it necessary torotate either the probes or the product to obtain
13、100 % coverage1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-structive Testing and is the direct responsibility of Subcommittee E7.07 onElectromagnetic Method.Current edition approved May 1, 2004. Published June 2004. Originallyapproved in 1989. Last previous edition approve
14、d in 1999 as E 1312 - 99.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from The American Society
15、 for Nondestructive Testing (ASNT), P.O.Box 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518.4Available from the Aerospace Industries Association of America, Inc., 1250Eye Street, N.W., Washington, DC 20005.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19
16、428-2959, United States.of the circumference. This is essentially a contact techniquebecause the coil is fixtured in a device that rides on thecircumference to maintain a fixed distance between the coil andproduct surface.4.2.3 Discontinuities cause either a change in phase orsignal amplitude when d
17、etected by the sensing coil. Thesesignals are amplified and processed to activate marking orrecording devices, or both. Relative severity of the imperfec-tion can be indicated by the signal amplitude generated by theflux change or the degree of change in phase.4.2.4 Caution must be exercised in esta
18、blishing referencestandards because flux changes caused by natural discontinui-ties might differ significantly from those generated by artificialdiscontinuities.5. Significance and Use5.1 The purpose of this practice is to describe a procedurefor in-line-eddy-current examination of hot cylindrical b
19、ars inthe range of diameters listed in 1.2 for large and repetitivediscontinuities that may form during processing.5.2 The discontinuities in bar product capable of beingdetected by the electromagnetic method are listed in 1.3.1. Themethod is capable of detecting surface and some subsurfacediscontin
20、uities that are typically in the order of 0.030 in. 0.75mm and deeper, but some shallower discontinuities might alsobe found.5.3 Discontinuities that are narrow and deep, but short inlength, are readily detectable by both probe and encircling coilsbecause they cause abrupt flux changes. Surface and
21、subsur-face discontinuities (if the electromagnetic frequency providessufficient effective depth of penetration) can be detected by thismethod.5.3.1 Discontinuities such as scratches or seams that arecontinuous and uniform for the full length of cut length bars orextend for extensive linear distance
22、s in coiled product may notalways be detected when encircling coils are used. These aremore detectable with probe coils by intercepting the disconti-nuity in their rotation around the circumference.5.3.2 The orientation and type of coil are important param-eters in coil design because they influence
23、 the detectability ofdiscontinuities.5.4 The eddy current method is sensitive to metallurgicalvariations that occur as a result of processing, thus all receivedsignals above the alarm level are not necessarily indicative ofdefective product.6. Basis of Application6.1 Personnel QualificationIf specif
24、ied in the contractualagreement, personnel performing examinations to this practiceshall be qualified in accordance with a nationally recognizednondestructive testing (NDT) personnel qualification practiceor standard such as ANSI/ASNT-CP-189, SNT-TC-1A, NAS-410, or a similar document and certified b
25、y the employer orcertifying agency, as applicable. The practice or standard usedand its applicable revision shall be identified in the contractualagreement between the using parties.6.2 Qualification of Nondestructive AgenciesIf specifiedin the contractual agreement, NDT agencies shall be qualifieda
26、nd evaluated as described in Practice E 543. The applicableedition of Practice E 543 shall be specified in the contractualagreement.6.3 Acceptance CriteriaSince acceptance criteria are notspecified in this practice, they shall be specified in thecontractual agreement.7. Apparatus7.1 Electronic Appar
27、atus, should be capable of energizingthe test coils or probes with alternating current at selectablefrequencies from 400 Hz to 100 kHz. Either manual orremotely operated switches can be used for frequency selec-tion. The equipment should include a detector display (CRT,meters), phase discriminator,
28、filters, modulators, recorders, andalarming/marking devices required for particular applications.7.2 Sensors, whether probe or encircling coils, should op-erate through a frequency range from 400 Hz to 100 kHz.7.2.1 The sensor windings must be cooled (such as waterjackets) to control the sensor oper
29、ating temperature and pre-vent thermal damage to the sensors.7.2.2 Magnetic or electrostatic shields might be necessary tosuppress extraneous electrical transient noise. Electrostaticshields usually float above ground at the sensor and areconnected to a cable and then to the preamplifier shield.7.2.
30、3 Constant spacing, ranging from116 in. 1.6 mm to14in. 6.4 mm between the sensors and product surface isobtained with positioning mechanisms usually equipped withproduct guiding devices to prevent mechanical damage to thesensors.7.3 Transport MechanismA conveyor or other type ofmechanical device sho
31、uld be employed to pass the productthrough or past the sensors. It should operate at production (orsystem) speeds with a minimum vibration of the sensors orproduct, and should maintain alignment of the sensors andproduct within the specified tolerances. Some systems mayrequire the transport to rotat
32、e either the bar, the sensors, orboth.7.3.1 The mechanical tolerances for restraining the longitu-dinal centerline of the product relative to the coils are criticalto obtain an effective electromagnetic examination. Non-uniform sensitivity, the generation of erroneous signals or poorsignal-to-noise
33、ratios result when the product and encirclingcoil are not concentric or the probe coil clearance changesduring examination. Therefore, the system passline mecha-nisms must be properly designed and maintained to achieve thespatial arrangement defined in 7.2.3. Product rolling tolerances,product strai
34、ghtness, and conveyor alignment or roll wear arefactors that may influence sensor and product spatial relations.The system sensitivity profile predicated on the passlinecapabilities can be determined by utilizing the standardizationprocedure in 8.4.7.4 Reference StandardIt is impractical to use a re
35、ferencestandard heated to the same temperature as the material beingexamined because of reoxidation, furnace time, etc. Therefore,a material with nonmagnetic properties, such as 304 stainlesssteel, is substituted. It should be of the same diameter as thematerial being examined and of sufficient leng
36、th to span thetransport system rolls while passing through or past the sensorsat the same speed and under the same conditions as theE 1312 99 (2004)e12product. The standard usually has one of the following types ofartificial discontinuities on the circumference.7.4.1 Holes drilled are either partial
37、ly or completely throughthe diameter.7.4.2 Notches should be inserted on the circumference byelectric discharge machining, milling, or other methods. Theymay be either transverse or parallel to the longitudinal axis ofthe bar. Notch depths are usually given as a percentage of thediameter.7.4.3 The d
38、imensions of holes or notches (hole diameter anddepth, notch width length, depth) are either specified or agreedto between the using parties to establish sensitivity levelsand/or acceptance criteria.7.4.4 The notches or holes should be placed on the circum-ference and along the bar longitudinal axis
39、 with sufficientspacing to ensure that each is detected without interferencefrom a neighbor.8. System Standardization8.1 Fabricate the reference standard in accordance with thespecification.8.2 Pass the standard through the system at speeds andconditions simulating production examination.8.2.1 Adjus
40、t the apparatus to obtain a signal-to-noise ratiothat allows the operator to differentiate between the signalsfrom the system ambient noise and those produced by discon-tinuities. Although the minimum recommended signal-to-noiseratio is 2:1, system reliability improves as this ratio increases.8.2.2
41、The amplitude or phase may be adjusted to trigger analarm from each artificial imperfection as it passes by thesensors.8.3 After the sensitivity adjustments are completed, thestandard should be traversed through the coils or probessimulating production conditions several times.8.3.1 If the artificia
42、l discontinuities are located near one ofthe ends, the standard also should be passed through the systemby reversing the leading and trailing ends.8.3.2 The system alarm or markers, or both, should indicateevery specified artificial discontinuity during each pass.8.3.3 The electronic apparatus shoul
43、d include a suppressioncircuit to prevent system response from the ends of thestandard and cut-to-length bar product.8.4 The capability of the passline mechanism to maintainthe correct distance between the bar surface and coils can bedetermined by passing the standard through the system atproduction
44、 speeds a minimum of four times with the productrotated 90 degrees after each pass. If more passes are used, theangular rotation should be reduced accordingly. The responsesobtained from the artificial discontinuity can be used to plot asensitivity profile to determine if previously established tole
45、r-ances are satisfied.8.4.1 An alternative method is to fabricate the standard withfour or more duplicate artificial discontinuities distributedequally around the circumference and separated sufficientlyalong the longitudinal axis to produce signals without interfer-ence from a neighbor. In this cas
46、e, the standard must be passedthrough the system one time at production speeds.8.5 If acceptable by specification and/or agreement betweenthe purchaser, manufacturer or supplier, electronically gener-ated signals simulating responses from artificial discontinuitiesmay be used to adjust the sensitivi
47、ty or to standardize thesystem.9. Procedure9.1 Standardization should be performed near the start ofeach working period (or diameter, grade, and so forth, change)and rechecked at4hormore frequent intervals.9.1.1 If improper system function occurs, all material thatpassed through the system since the
48、 last satisfactory standard-ization should be re-examined. Because bar product is notreheated and recoiled, electromagnetic inspection of recoiledor cut length cold bars is the only practical method forre-examination. However, different results may be obtainedbecause of changes in metallurgical char
49、acteristics between hotand cold product with the exception of austenitic steels.9.2 Pass all the material through the system for examinationat the sensitivity levels adjusted in accordance with Section 8.9.3 Any piece with discontinuities producing responsesabove the alarm level should be marked and set aside forfurther evaluation or disposition, or both.9.4 No equipment adjustments should be made exceptduring standardization (or standardization checks) or wheneverthe apparatus is not performing correctly.10. Keywords10.1 artificial discontinuity; curie temp
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