1、Designation: E 426 98 (Reapproved 2007)Standard Practice forElectromagnetic (Eddy-Current) Examination of Seamlessand Welded Tubular Products, Austenitic Stainless Steeland Similar Alloys1This standard is issued under the fixed designation E 426; the number immediately following the designation indi
2、cates the 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 (e) indicates an editorial change since the last revision or reapproval.This specification has been approved for use by agenc
3、ies of the Department of Defense.1. Scope1.1 This practice2covers procedures that may be followedfor eddy-current examination of seamless and welded tubularproducts made of stainless steel and similar alloys such asnickel alloys. Austenitic chromium-nickel stainless steels,which are generally consid
4、ered to be nonmagnetic, are specifi-cally covered as distinguished from the martensitic and ferriticstraight chromium stainless steels which are magnetic.1.2 This practice is intended as a guide for eddy-currentexamination of both seamless and welded tubular productsusing either an encircling coil o
5、r 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 heatexchanger.1.3 This practice
6、 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 The values stated in inch-pound units are to be regardedas the standard.1.5 This standard does not purport to address all of thesafet
7、y problems, if any, associated with its use. 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:3E 543 Specification for Agencies
8、Performing Nondestruc-tive TestingE 1316 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 Qualification andCertification of Nondestructive Testing
9、Personnel4NAS-410 NAS Certification and Qualification of Nonde-structive Personnel (Quality Assurance Committee)53. Terminology3.1 Standard terminology relating to electromagnetic ex-amination may be found in Terminology E 1316, Section C,Electromagnetic Testing.4. Summary of Practice4.1 The examina
10、tion 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 configurations employ separate exciterand sensor coils;
11、 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 detects the resultant electromagneticflux related
12、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 technique employs a probe coil
13、with one ormore exciters and sensors which is brought in close proximityof the surface of the tubular product to be examined. Since the1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-structive Testing and is the direct responsibility of Subcommittee E07.07 onElectromagnetic M
14、ethod.Current edition approved Dec. 1, 2007. Published January 2008. Originallyapproved in 1971. Last previous edition approved in 2003 as E 426 - 98(2003)e1.2For ASME Boiler and Pressure Vessel Code applications see related PracticeSE-426 in Section II of that Code.3For referenced ASTM standards, v
15、isit 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 Testing (ASNT), P.O. Box28518, 1711 Arlinga
16、te Ln., Columbus, OH 43228-0518, http:/www.asnt.org.5Available from Aerospace Industries Association of America, Inc. (AIA), 1000Wilson Blvd., Suite 1700,Arlington, VA22209-3928, http:/www.aia-aerospace.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 1942
17、8-2959, United States.Copyright by ASTM Intl (all rights reserved); Tue Jul 15 20:29:00 EDT 2008Downloaded/printed byGuo Dehua (CNIS) pursuant to License Agreement. No further reproductions authorized.probe is generally small and does not encircle the article beingexamined, it examines only a limite
18、d area in the vicinity of theprobe. If it 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.5. Significance a
19、nd Use5.1 Eddy-current examination 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 indicating devices, or both, or a
20、mechanical 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, and geometry) as well as otherf
21、actors 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 with a nationally recognized NDT
22、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 contractual agreement between the using
23、parties.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 PracticeE 543. The applicable edition of Practic
24、e E 543 shall bespecified 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 the changes in the electromagnetic respons
25、e 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 be capableof inducing current in the tube
26、 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 tube and sensing changes in the electricalc
27、haracteristics 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 proportional to magnetic-flux density. However,
28、 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 MechanismA mechanical device capable ofpassing th
29、e 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 inproper register or concentricity with the probe or examinationcoil. Where required, the mechanism shall be capable ofunifo
30、rmly rotating the tube or probe.7.5 Reference StandardThe standard used to adjust thesensitivity setting of the apparatus shall be sound 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 p
31、ermit the required spacing of theartificial discontinuities (at least 4 ft, and preferably longer).Artificial discontinuities made in the 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:FIG.
32、 1 Sketch Showing Encircling-Coil and Probe-CoilTechniques for Electromagnetic Examination of Tubular ProductsE 426 98 (2007)2Copyright by ASTM Intl (all rights reserved); Tue Jul 15 20:29:00 EDT 2008Downloaded/printed byGuo Dehua (CNIS) pursuant to License Agreement. No further reproductions author
33、ized.7.5.1 HolesHoles that are usually drilled completelythrough the wall may be used. Care should be taken duringdrilling to avoid distortion of 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 transve
34、rse notches or both may be used (Note 4).Orientation, dimensions (width, length, and depth), and con-figuration of the notches affect the response of the eddy-currentsystem. Notch depth is usually specified as a percentage ofnominal wall thickness of the tubular product being examined.Notches may be
35、 placed on the outer, inner, or both surfaces ofthe reference (calibration) standard. Outer surface notchesprovide an indication of system response to discontinuitiesoriginating on the outer tube surface, whereas inner surfacenotches provide an indication of system response to disconti-nuities origi
36、nating on the inner tube surface (Note 5).NOTE 4Longitudinal notch standards are normally used when exam-ining with rotating probe systems.NOTE 5The density of eddy currents decreases nearly exponentiallywith increasing distance from the surface nearest the coil, and thesensitivity to subsurface dis
37、continuities decreases with the change in depthallowing the use of phase analysis techniques.7.5.3 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 s
38、ubject to agreement between supplier andpurchaser.8. Adjustment and Standardization of ApparatusSensitivity8.1 Select the apparatus, examination frequency, coil orprobe, or both, design, phase discrimination, and other circuitryas well as speed of examining which shall demonstrate thesystem capabili
39、ty for detecting the discontinuities of interest.8.2 Fabricate the applicable reference standard in accor-dance with the agreement between the purchaser and tubingsupplier.8.3 Adjust the apparatus to obtain an optimum signal-to-noise ratio with the minimum sensitivity required to detect theartificia
40、l discontinuities in the reference standard. Do thisunder conditions (such as examining speed) identical to thoseto be used in production examination 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
41、of the ends and passing this reference standard through thesystem at production examination speeds. If notches or holesare placed near only one of the ends, pass the tube through thesystem backwards and forwards.9. Procedure9.1 Standardize the apparatus at the start of the examinationrun using the r
42、eference standard. The recommended maximuminterval between restandardization is 4 h although more or lessfrequent restandardization may be done by agreement betweenusing parties, or whenever improper functioning of the equip-ment is suspected. If improper functioning is found, restan-dardize the app
43、aratus and reexamine all tubes or pipes exam-ined during the period since the last successful standardization.9.2 Pass the lot of tubes or 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
44、pipes with discontinuities indicated by the apparatus.It is recommended that tubes with discontinuity indications bereexamined in accordance 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
45、in processing at which examination is made shouldbe agreed upon by the supplier and the purchaser. The tubesshould be free of any substance that may interfere with theexamination.10. Supplemental Information Regarding Eddy-CurrentExamination of High Alloy Steels and Similar Alloys10.1 In the eddy-cu
46、rrent examination of austeniticchromium-nickel stainless steels it has been found that exami-nation frequencies ranging from less than 1 kHz 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 appli
47、cation.ExampleIf thin-walled tubular products are to be exam-ined or surface rather than subsurface discontinuities are to bedetected, higher frequencies are used. For heavy-walled tubes,subsurface discontinuities well below the surface require theuse of a lower frequency. Choice of examination freq
48、uencywill 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 co
49、ils.10.3 Under certain conditions austenitic stainless steels canbe magnetic. For example, delta ferrite may be present in awelded product. Permeability may vary as a function of coldwork. Some nickel alloys, such as Monel Alloy (nickel-copperalloy), are magnetic in nature and others exhibit magnetism ifthere are slight residual stresses in the material.10.4 Welded stainless steel products can present a specialproblem in eddy-current examination. The weld area canusually be distinguished from the parent metal if the tubing hasreceived little or no working after welding
