1、Designation: E 309 95 (Reapproved 2006)Standard Practice forEddy-Current Examination of Steel Tubular Products UsingMagnetic Saturation1This standard is issued under the fixed designation E 309; the number immediately following the designation indicates the year oforiginal adoption or, in the case o
2、f 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.This specification has been approved for use by agencies of the Department of Defense.1. Scope1.1 This pr
3、actice2covers a procedure for applying theeddy-current method to detect discontinuities in ferromagneticpipe and tubing (Note 1) where the article being examined isrendered substantially non-magnetic by the application of aconcentrated, strong magnetic field in the region adjacent to theexamining co
4、il.NOTE 1For convenience, the term tube or tubular product willhereafter be used to refer to both pipe and tubing.1.2 The procedure is specifically applicable to eddy-currentexamination methods using an encircling-coil assembly. How-ever, eddy-current techniques that employ either fixed orrotating p
5、robe-coil assemblies may be used to either enhancediscontinuity sensitivity on the large diameter tubular productsor to maximize the response received from a particular type ofdiscontinuity.1.3 This practice is intended for use on tubular productshaving outside diameters from approximately14 to 10 i
6、n. (6.35to 254.0 mm). These techniques have been used for smaller andlarger sizes however, and may be specified upon contractualagreement between the purchaser and the supplier.2. Referenced Documents2.1 ASTM Standards:3E 543 Specification for Agencies Performing Nondestruc-tive TestingE 1316 Termin
7、ology for Nondestructive Examinations2.2 Other Documents:SNT-TC-1A Recommended Practice for Personnel Qualifi-cation and Certification in Nondestructive Testing4ANSI/ASNT CP-189 ASNT Standard for Qualification andCertification of Nondestructive Testing Personnel42.3 Military Standard:MIL-STD-410E No
8、ndestructive Testing Personnel Qualifi-cation and Certification53. Terminology3.1 GeneralStandard terminology relating to electromag-netic examination may be found in Terminology E 1316,Section C, “Electromagnetic Testing.”4. Summary of Practice4.1 The examination is conducted using one of two gener
9、altechniques shown in Fig. 1.4.1.1 One technique employs one or more exciter and sensorcoils that encircle the tube and through which the tubularproduct to be examined is passed. Some circuit configurationsemploy one or more coils that concurrently function as bothexciters and sensors. Alternating c
10、urrent passes through theexciting coil which, by reason of its proximity, inducescorresponding currents (eddy currents) to flow in the tubularproduct. The sensor coil detects the resultant electromagneticflux related to these currents. The presence of discontinuities inthe tubular product will alter
11、 the normal flow of currents andthis change is detected by the sensor. The encircling-coiltechnique is capable of examining the entire circumference ofa tubular product.4.1.2 Another technique employs a probe coil with one ormore sensors that are in close proximity to the surface of thetubular produ
12、ct to be examined. Since the probe is generallysmall and does not encircle the article being examined, itexamines only a limited area in the vicinity of the probe. This1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-structive Testing and is the direct responsibility of Subcom
13、mittee E07.07 onElectromagnetic Method.Current edition approved July 1, 2006. Published July 2006. Originally approvedin 1966. Last previous edition approved in 2001 as E 309 - 95(2001).2For ASME Boiler and Pressure Vessel Code applications see related Recom-mended Practice SE 309 in Section V of th
14、at Code.3For 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.4Available fromAmerican Society for Nondestructive Te
15、sting (ASNT), P.O. Box28518, 1711 Arlingate Ln., Columbus, OH 43228-0518.5Available from Standardization Documents Order Desk, Bldg. 4 Section D, 700Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2
16、959, United States.technique is frequently used for examination of welded tubularproducts in which only the weld is examined by scanning alongthe weld zone.4.1.3 The magnetic permeability of ferromagnetic materialsseverely limits the depth of penetration of induced eddycurrents. Furthermore, the per
17、meability variations inherent inferromagnetic tubular products often cause anomalous testresults. A useful solution to this problem involves the applica-tion of a strong external magnetic field in the region of theexamining coil or probe. This technique, known as magneticsaturation, is applied to a
18、magnetic material, such as a steeltube, to suppress the magnetic characteristics of permeability,hysteresis, etc., so that the material under examination iseffectively rendered nonmagnetic. When achieved, this condi-tion allows an eddy-current system to measure and detectelectrical resistivity and g
19、eometrical variations (including de-fects) independent of concurrent variations in magnetic prop-erties.4.1.4 Changes in electromagnetic response caused by thepresence of discontinuities are detected by the sensor, ampli-fied, and modified in order to actuate audio or visual indicatingdevices, or bo
20、th, a mechanical marker, or a signal-recordingdevice, or a combination of these. Signals can be caused byouter surface, inner surface, or subsurface discontinuities if theeddy-current frequency provides sufficient depth of penetration(see 11.1). The eddy-current method is sensitive to metallur-gical
21、 variations that occur as a result of processing, thus allreceived indications are not necessarily indicative of defectivetubing.5. Significance and Use5.1 The purpose of this practice is to outline a procedure forthe detection and location of discontinuities such as pits, voids,inclusions, cracks,
22、or abrupt dimensional variations in ferro-magnetic tubing using the electromagnetic (eddy-current)method. Furthermore, the relative severity of a discontinuitymay be indicated, and a rejection level may be set with respectto the magnitude of the indication.5.2 The response from natural discontinuiti
23、es can be signifi-cantly different than that from artificial discontinuities such asdrilled holes or notches. For this reason, sufficient work should(a) Encircling Coil.(b) Probe Coillongitudinal scanning of weld seam only.(c) Probe Coilscanning along a spiral path.FIG. 1 Encircling-Coil and Probe-C
24、oil Techniques for Electromagnetic Testing of Tubular ProductsE 309 95 (2006)2be done to establish the sensitivity level and set-up required todetect natural discontinuities of consequence to the end use ofthe product.5.3 Eddy-current examination systems are generally notsensitive to discontinuities
25、 adjacent to the ends of the tube. Theextent of the end effect region can be determined in accordancewith 8.6.6. Basis of Application6.1 The following acceptance criteria may be specified inthe purchase specification, contractual agreement, or else-where, and may require agreement between the purcha
26、ser andthe supplier:6.1.1 Time of examination or point(s) in the manufacturingprocess at which the material will be examined,6.1.2 Maximum time interval between equipment calibra-tion checks,6.1.3 Methods for determining the extent of end effect,6.1.4 Size and type of product,6.1.5 Type, method of m
27、anufacture, dimensions, location,and number of artificial discontinuities to be placed on thereference standard,6.1.6 Methods of verifying dimensions and allowable toler-ances of artificial discontinuities,6.1.7 Extent of examination, and6.1.8 Disposition of material with indications.6.1.9 Operator
28、Qualification and CertificationIf required,NDT personnel shall be qualified in accordance with a nation-ally recognized NDT personnel qualification practice or stan-dard such as ANSI/ASNT-CP-189, SNT-TC-1A, MIL-STD-410, or a similar document. The practice or standard used andits applicable revision
29、shall be documented in the contractualagreement between the using parties.6.1.10 Qualification of Nondestructive AgenciesIf speci-fied in the contractual agreement, NDT agencies shall bequalified and evaluated in accordance with Practice E 543. Theapplicable edition of Practice E 543 shall be specif
30、ied in thecontractual agreement.7. Apparatus7.1 Electronic ApparatusThe electronic apparatus shallbe capable of energizing the coils or probes with alternatingcurrents of a selected frequency and shall be capable of sensingthe changes in the electromagnetic response of the sensors.Equipment may incl
31、ude appropriate signal processing circuitssuch as a phase discriminator, filter circuits, etc., as requiredfor the particular application.7.2 Encircling-Coil AssemblyThe encircling-coil assem-bly shall consist of one or more electrical coils that encircle thearticle being examined.7.3 Probe-Coil Ass
32、emblyThe probe-coil assembly nor-mally contains an exciting coil and a sensor, although in somecases the exciter and sensor are one and the same.7.4 Magnetic Saturation SystemThe magnetic saturationsystem shall consist of a suitable method of applying a strongmagnetic field to the region of the tube
33、 adjacent to the coil orprobe-coil assembly so as to render that region of the tubeeffectively nonmagnetic. Typical systems employ either per-manent magnets or electromagnets.7.5 Driving MechanismThe movement of the tubethrough the coil or past the probe shall be performed at uniformspeed and with m
34、inimum vibration of the tube, coil, and probe.7.6 Reference StandardThe standard used to adjust thesensitivity of the apparatus shall be free of interfering discon-tinuities and shall be of the same nominal alloy, temper, anddimensions as the tubes to be examined on a production basis.It shall be of
35、 sufficient length to permit the spacing of artificialdiscontinuities to provide good signal resolution and be me-chanically stable while in the examining position in theapparatus. Artificial discontinuities placed in the tube shall beone or more of the following types. (See Fig. 2.)7.6.1 NotchesNot
36、ches may be produced by Electric Dis-charge Machining (EDM), milling, or other means. Longitudi-nal, transverse, or both may be used (Note 2). Orientation,dimensions (width, length, and depth), and configuration of thenotches affect the response of the eddy-current system. Notchdepth is usually spec
37、ified as a percentage of nominal wallthickness of the tubular product being examined. Notches maybe placed on the outer, inner, or both surfaces of the referencestandard. Outer surface notches provide an indication ofsystem response to discontinuities originating on the outer tubesurface; whereas in
38、ner surface notches provide an indication ofsystem response to discontinuities originating on the inner tubesurface.NOTE 2Longitudinal notch standards are normally used when testingwith a rotating-probe system.7.6.2 HolesDrilled holes may be used. They are usuallydrilled completely through the wall.
39、 Care should be takenduring drilling to avoid distortion of the tube and hole.7.6.3 The configuration, orientation, and dimensions (diam-eter of holes and the width, length, and depth of notches) of theartificial discontinuities to be used for establishing acceptancelimits should be subject to agree
40、ment between the purchaserand the supplier.8. Adjustment and Standardization of Apparatus8.1 Select the apparatus, examining frequency, coil or probeconfiguration, magnetic saturation system, phase discrimina-tion, and other circuitry, as well as speed of examination.(a) Longitudinal Notch (Milled o
41、r EDM) ID, OD, or both.(b) Transverse Notch (Milled, Filed, or EDM) ID, OD, or both.(c) Drilled Hole (Radially Through One Wall).FIG. 2 Various Types of Artificial DiscontinuitiesE 309 95 (2006)38.2 Fabricate applicable reference standards in accordancewith the agreement between the purchaser and th
42、e tubingsupplier.8.3 Adjust the field strength of the magnetic saturationsystem to obtain an adequate level of magnetization in the tubein accordance with 8.3.1 and 8.3.2. This is the minimum degreeof magnetization required for the successful examination of thetype and size tube represented by the r
43、eference standard.8.3.1 Adjust the eddy-current system sensitivity such thatwithout the application of the external magnetization field theexamination of the reference standard results in excessive“noise.” This condition is characterized by repeated alarmsfrom the instrument over the entire length o
44、f the tube.8.3.2 On repeated examinations of the reference standard,increase the magnetizing current or the magnetic field to thepoint where no further reduction in the tube “noise” is obtainedfrom a further increase in magnetizing field strength.NOTE 3It should be pointed out that there is sometime
45、s a falseindication of saturation that can result in acceptance of a false saturationlevel (Fig. 3).8.4 Adjust the apparatus to obtain an optimum signal-to-noise ratio by adjusting for the minimum sensitivity required toreliably detect the artificial discontinuities in the referencestandard. This sh
46、all be performed under conditions (such astesting speed) identical to those to be used in the productionexamination of the tubular products if the system is influencedby these conditions.8.5 While performing 8.4, or as a separate operation, rotatethe reference standard in either 90 or 120 increments
47、 todetermine the location of the “electrical” center in the exam-ining coil. Mechanically adjust the position of the tube withinthe coil to obtain nearly equal responses from the artificialdiscontinuities regardless of their circumferential location.8.5.1 Determine the electrical center of a probe c
48、oil withrespect to the probe field-to-material normality and uniformcircumferential lift-off. Adjust the probe field-to-material nor-mality such that uniform signals are obtained from the stan-dardization notches or holes regardless of their position withinthe intended examination area under the pro
49、be. This adjust-ment is typically encountered when a probe is scanned along aline such as a weld zone.8.5.2 Establish electrical centering of a rotating probe byadjusting the apparatus to obtain uniform signals from thereference notches or holes when positioned at 0, 90, 180, and270. This adjustment is typically accomplished by ensuringuniform probe lift-off around the circumference of the tube.8.6 The extent of end effect (Note 4) is determined by usinga special reference tube containing a series of similar notchesor holes near one or both of the ends (Fig. 4). To
