1、Designation: E426 12Standard Practice forElectromagnetic (Eddy-Current) Examination of Seamlessand Welded Tubular Products, Titanium, Austenitic StainlessSteel and Similar Alloys1This standard is issued under the fixed designation E426; the number immediately following the designation indicates the
2、year 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 () indicates an editorial change since the last revision or reapproval.This specification has been approved for use by agencies of the
3、Department of Defense.1. Scope*1.1 This practice2covers procedures for eddy-current ex-amination of seamless and welded tubular products made ofrelatively low conductivity materials such as titanium, stainlesssteel, and similar alloys, such as nickel alloys. Austeniticchromium-nickel stainless steel
4、s, which are generally consid-ered to be nonmagnetic, are specifically covered as distin-guished from the martensitic and ferritic straight chromiumstainless steels which are magnetic.1.2 This practice is intended as a guide for eddy-currentexamination of both seamless and welded tubular productsusi
5、ng either an encircling coil or a probe-coil technique. Coilsand probes are available that can be used inside the tubularproduct; however, their use is not specifically covered in thisdocument. This type of examination is usually employed onlyto examine tubing which has been installed such as in a h
6、eatexchanger.1.3 This practice covers the examination of tubular productsranging in diameter from 0.125 to 5 in. (3.2 to 127.0 mm) andwall thicknesses from 0.005 to 0.250 in. (0.127 to 6.4 mm).1.4 For examination of aluminum alloy tubular products,see standard Practice E215.1.5 UnitsThe values state
7、d in inch-pound units are to beregarded as standard. The values given in parentheses aremathematical conversions to SI units that are provided forinformation only and are not considered standard.1.6 This standard does not purport to address all of thesafety problems, if any, associated with its use.
8、 It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3E215 Practice for Standardizing Equipment for Electromag-netic Testing of Sea
9、mless Aluminum-Alloy TubeE543 Specification for Agencies Performing Nondestruc-tive TestingE1316 Terminology 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 Q
10、ualification andCertification of Nondestructive Testing Personnel4NAS-410 NAS Certification and Qualification of Nonde-structive Personnel (Quality Assurance Committee)53. Terminology3.1 Standard terminology relating to electromagnetic testingmay be found in Terminology E1316, Section C, Electromag-
11、netic Testing.4. Summary of Practice4.1 The examination is conducted using one of two generaltechniques shown in Fig. 1. One of these techniques employsone or more exciter and sensor coils which encircle the pipe ortube and through which the tubular product to be examined ispassed. Some circuit conf
12、igurations employ separate exciterand sensor coils; whereas other configurations employ one ormore coils that concurrently function as both exciters andsensors. Alternating current passes through the exciting coilwhich by reason of its proximity induces current in the tubularproduct. The sensor coil
13、 detects the resultant electromagnetic1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-structive Testing and is the direct responsibility of Subcommittee E07.07 onElectromagnetic Method.Current edition approved Aug. 1, 2012. Published September 2012. Originallyapproved in 1971
14、. Last previous edition approved in 2007 as E426 - 98(2007). DOI:10.1520/E0426-12.2For ASME Boiler and Pressure Vessel Code applications see related PracticeSE-426 in Section II of that Code.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serv
15、iceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4Available fromAmerican Society for Nondestructive Testing (ASNT), P.O. Box28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http:/www.asnt.org.5Available from Aerospac
16、e Industries Association of America, Inc. (AIA), 1000Wilson Blvd., Suite 1700,Arlington, VA22209-3928, http:/www.aia-aerospace.org.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, Un
17、ited States.flux related to these currents. The presence of discontinuities inthe tubular product will affect the normal flow of currents andthis change is detected by the sensor. The encircling coiltechnique is capable of examining the entire 360-deg expanseof the tubular product.4.2 Another techni
18、que employs a probe coil with one ormore exciters and sensors which is brought in close proximityof the surface of the tubular product to be examined. Since theprobe is generally small and does not encircle the article beingexamined, it examines only a limited area in the vicinity of theprobe. If it
19、 is desired to examine the entire volume of thetubular product, it is common practice to either rotate thetubular product or the probe. In the case of welded tubularproducts frequently only the weld is examined by scanningalong the weld zone. In the case where the tubular products arejoined by weldi
20、ng and the probe is rotated, the probe is orbitedabout the central axis of the tube such that a circumferentialexamination of the tube and/or weld may be made. The depthof penetration of the interrogating magnetic fields into thetubular product may be smaller for this type of probe coilcompared to t
21、he encircling coil.5. Significance and Use5.1 Eddy-current testing is a nondestructive method oflocating discontinuities in a product. Changes in electromag-netic response caused by the presence of discontinuities aredetected by the sensor, amplified and modified in order toactuate audio or visual i
22、ndicating devices, or both, or amechanical marker. Signals can be caused by outer surface,inner surface, or subsurface discontinuities. The eddy-currentexamination is sensitive to many factors that occur as a resultof processing (such as variations in conductivity, chemicalcomposition, permeability,
23、 and geometry) as well as otherfactors not related to the tubing. Thus, all received indicationsare not necessarily indicative of defective tubing.6. Basis of Application6.1 If specified in the contractual agreement, personnelperforming examinations to this practice shall be qualified inaccordance w
24、ith a nationally recognized NDT personnel quali-fication practice or standard such as ANSI/ASNT-CP-189,SNT-TC-1A, NAS-410, ASNT-ACCP, or a similar documentand certified by the certifying agency, as applicable. Thepractice or standard used and its applicable revision shall beidentified in the contrac
25、tual agreement between the usingparties.NOTE 1MIL-STD-410 is canceled and has been replaced with NAS-410, however, it may be used with agreement between contracting parties.6.2 If specified in the contractual agreement, NDT agenciesshall be qualified and evaluated in accordance with Specifica-tion E
26、543. The applicable edition of Specification E543 shallbe specified in the contractual agreement.7. Apparatus7.1 Electronic ApparatusThe electronic apparatus shallbe capable of energizing the examination coils or probes withalternating currents of suitable frequencies and shall be capableof sensing
27、the changes in the electromagnetic response of thesensors. Equipment may include a detector, phase discrimina-tor, filter circuits, modulation circuits, magnetic-saturationdevices, recorders, and signaling devices as required for theparticular application.7.2 Examination CoilsExamination coils shall
28、 be capableof inducing current in the tube and sensing changes in theelectrical characteristics of the tube.NOTE 2Fill factor effect is an important consideration since couplingvariations can affect the examination significantly.7.3 Probe CoilsProbe coils shall be capable of inducingcurrent in the t
29、ube and sensing changes in the electricalcharacteristics of the tube (Note 3). Probes generally consist ofan exciting coil and sensing coil or Hall element mounted in acommon holder. A Hall element is a semiconductor that byreason of the Hall effect is capable of responding in a mannerdirectly propo
30、rtional to magnetic-flux density. However, whenused with an exciting coil, it should be remembered thateddy-current flow is influenced by the excitation frequency.NOTE 3Lift-off effect is an important consideration since couplingvariations can affect the examination significantly.7.4 Driving Mechani
31、smA mechanical device capable ofpassing the tube through the examination coil or past the probe.It shall operate at a uniform speed with minimum vibration ofcoil, probe, or tube and maintain the article being examined inFIG. 1 Sketch Showing Encircling-Coil and Probe-CoilTechniques for Electromagnet
32、ic Examination of Tubular ProductsE426 122proper register or concentricity with the probe or examinationcoil. Where required, the mechanism shall be capable ofuniformly rotating the tube or probe.7.5 Reference StandardThe standard used to adjust thesensitivity setting of the apparatus shall be sound
33、 and of thesame nominal alloy, temper, and nominal dimensions as the lotof tubes or pipes to be examined on a production basis. It shallbe of sufficient length to permit the required spacing of theartificial discontinuities (at least 4 ft, and preferably longer).Artificial discontinuities made in th
34、e tube or pipe shall becentered as nearly as possible on one inside or outside diametersurface of the tube and shall preferably be of one of thefollowing types:7.5.1 HolesHoles that are usually drilled completelythrough the wall may be used. Care should be taken duringdrilling to avoid distortion of
35、 the tube (or pipe) and hole.7.5.2 NotchesNotches may be produced by electric dis-charge machining (EDM), milling, or other means. Longitudi-nal or transverse notches or both may be used (Note 4).Orientation, dimensions (width, length, and depth), and con-figuration of the notches affect the respons
36、e of the eddy-currentsystem. Notch depth is usually specified as a percentage ofnominal wall thickness of the tubular product being examined.Notches may be placed on the outer, inner, or both surfaces ofthe reference (calibration) standard. Outer surface notchesprovide an indication of system respon
37、se to discontinuitiesoriginating on the outer tube surface, whereas inner surfacenotches provide an indication of system response to disconti-nuities originating on the inner tube surface (Note 5).NOTE 4Longitudinal notch standards are normally used when exam-ining with rotating probe systems.NOTE 5
38、The density of eddy currents decreases nearly exponentiallywith increasing distance from the surface nearest the coil, and thesensitivity to subsurface discontinuities decreases with the change in depthallowing the use of phase analysis techniques.7.5.3 The configuration, orientation, and dimensions
39、 (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 agreement between supplier andpurchaser.8. Adjustment and Standardization of ApparatusSensitivity8.1 Select the apparatus, examination
40、frequency, coil orprobe, or both, design, phase discrimination, and other circuitryas well as speed of examining which shall demonstrate thesystem capability for detecting the discontinuities of interest.8.2 Fabricate the applicable reference standard in accor-dance with the agreement between the pu
41、rchaser and tubingsupplier.8.3 Adjust the apparatus to obtain an optimum signal-to-noise ratio with the minimum sensitivity required to detect theartificial discontinuities in the reference standard. Do thisunder conditions (such as examining speed) identical to thoseto be used in production examina
42、tion of the tubular products.8.4 Determine the end effect by using a special referencetube or pipe containing a series of notches or holes near one orboth of the ends and passing this reference standard through thesystem at production examination speeds. If notches or holesare placed near only one o
43、f the ends, pass the tube through thesystem backwards and forwards.9. Procedure9.1 Standardize the apparatus at the start of the examinationrun using the reference standard. The recommended maximuminterval between re-standardization is four hours althoughmore or less frequent re-standardization may
44、be done byagreement between using parties, or whenever improper func-tioning of the equipment is suspected. If improper functioningis found, re-standardize the apparatus and re-examine all tubesor pipes examined during the period since the last successfulstandardization.9.2 Pass the lot of tubes or
45、pipes to be examined through theexamination coil or past the probe coil of the apparatusadjusted to the sensitivity as described in Section 8. Set asidetubes or pipes with discontinuities indicated by the apparatus.It is recommended that tubes with discontinuity indications bere-examined in accordan
46、ce with the purchase specification.9.3 Tubes or pipes may be examined in the final drawn,annealed, heat treated, as-welded, or other step in processing.The point in processing at which examination is made shouldbe agreed upon by the supplier and the purchaser. The tubesshould be free of any substanc
47、e that may interfere with theexamination.10. Supplemental Information Regarding Eddy-CurrentExamination of High Alloy Steels and Similar Alloys10.1 In the eddy-current examination of austeniticchromium-nickel stainless steels it has been found that exami-nation frequencies ranging from less than 1 k
48、Hz to more than1 MHz can be used. The more commonly used operatingfrequencies are in the range, 1 kHz to 125 kHz. The exactfrequency used will depend on the application.ExampleIf thin-walled tubular products are to be exam-ined or surface rather than subsurface discontinuities are to bedetected, hig
49、her frequencies are used. For heavy-walled tubes,subsurface discontinuities well below the surface require theuse of a lower frequency. Choice of examination frequencywill determine the size of discontinuity that can be detected.10.2 As in any eddy-current examination, the depth andorientation of the discontinuity below the entry surface willaffect the magnitude of signal received from it. Sensitivityvaries significantly with distance from the examination coils.10.3 Under certain conditions austenitic stainless steels canbe magnetic. For example, delta ferrite may be p
