1、Designation: E 690 98 (Reapproved 2004)e1Standard Practice forIn Situ Electromagnetic (Eddy-Current) Examination ofNonmagnetic Heat Exchanger Tubes1This standard is issued under the fixed designation E 690; the number immediately following the designation indicates the year oforiginal adoption or, i
2、n 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 made throughout in January 2004.1. Scope1.1 This practice describes p
3、rocedures to be followed duringeddy-current examination (using an internal, probe-type, coilassembly) of nonmagnetic tubing that has been installed in aheat exchanger. The procedure recognizes both the uniqueproblems of implementing an eddy-current examination ofinstalled tubing, and the indigenous
4、forms of tube-wall dete-rioration which may occur during this type of service. Thedocument primarily addresses scheduled maintenance inspec-tion of heat exchangers, but can also be used by manufacturersof heat exchangers, either to examine the condition of the tubesafter installation, or to establis
5、h baseline data for evaluatingsubsequent performance of the product after exposure tovarious environmental conditions. The ultimate purpose is thedetection and evaluation of particular types of tube integritydegradation which could result in in-service tube failures.1.2 This practice does not establ
6、ish acceptance criteria; theymust be specified by the using parties.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 determine the a
7、pplica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 543 Practice for Evaluating Agencies that Perform Non-destructive TestingE 1316 Terminology for Nondestructive Examinations2.2 Other Documents:SNT-TC-1A Recommended Practice for Personnel Qualifi-cation
8、 and Certification in Nondestructive Testing3ANSI/ASNT-CP-189 ASNT Standard for Qualification andCertification of Nondestructive Testing Personnel3NAS-410 NAS Certification and Qualification of Nonde-structive Personnel (Quality Assurance Committee)43. Terminology3.1 Standard terminology relating to
9、 electromagnetic ex-amination may be found in Terminology E 1316, Section C,Electromagnetic Testing.4. Summary of Practice4.1 The examination is performed by passing an eddy-current probe through each tube. These probes are energizedwith alternating currents at one or more frequencies. Theelectrical
10、 impedance of the probe is modified by the proximityof the tube, the tube dimensions, electrical conductivity,magnetic permeability, and metallurgical or mechanical dis-continuities in the tube. During passage through the tube,changes in electromagnetic response caused by these variablesin the tube
11、produce electrical signals which are processed so asto produce an appropriate combination of visual displays,alarms, or temporary or permanent records, or combinationthereof, for subsequent analysis.NOTE 1The agency performing the testing or examination shall meetthe requirements of Practice E 543.5
12、. Significance and Use5.1 Eddy-current examination is a nondestructive method oflocating discontinuities in tubing made of materials thatconduct electricity. Signals can be produced by discontinuitieslocated either on the inner or outer surfaces of the tube, or bydiscontinuities totally contained wi
13、thin the tube wall. Whenusing an internal probe, the density of eddy currents in the tube1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-structive Testing and is the direct responsibility of Subcommittee E07.07 onElectromagnetic Methods.Current edition approved January 1, 200
14、4. Published February 2004. Originallyapproved in 1979. Last previous edition approved in 1998 as E 690 98.2For 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 stand
15、ards Document Summary page onthe ASTM website.3Available from The American Society for Nondestructive Testing (ASNT), P.O.Box 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518.4Available from Aerospace Industries Association of America, Inc., 1250 EyeStreet, N.W., Washington, DC 20005.1Copyright AS
16、TM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.wall decreases very rapidly as the distance from the internalsurface increases; thus the amplitude of the response to outersurface discontinuities decreases correspondingly.5.2 Some indications obta
17、ined by this method may not berelevant to product quality. For example, an irrelevant signalmay be caused by metallurgical or mechanical variations thatare generated during manufacture but that are not detrimentalto the end use of the product. Irrelevant indications can maskunacceptable discontinuit
18、ies occurring in the same area. Rel-evant indications are those that result from nonacceptablediscontinuities. Any indication above the reject level, which isbelieved to be irrelevant, shall be regarded as unacceptableuntil it is proven to be irrelevant. For tubing installed in heatexchangers, predi
19、ctable sources of irrelevant indications arelands (short unfinned sections in finned tubing), dents,scratches, tool chatter marks, or variations in cold work.Rolling tubes into the supports may also cause irrelevantindications, as may the tube supports themselves. Eddy-currentexamination systems are
20、 generally not able to separate theindication generated by the end of the tube from indications ofdiscontinuities adjacent to the ends of the tube (end effect).Therefore, this examination may not be valid at the boundariesof the tube sheets.6. Basis of Application6.1 The following criteria may be sp
21、ecified in the purchasespecification, contractual agreement, or elsewhere, and mayrequire agreement between the purchaser and the supplier.6.1.1 Type of eddy-current system, and probe (coil assem-bly) configuration,6.1.2 Location of heat exchanger, if applicable,6.1.3 Size, material, and configurati
22、on of tubes to be exam-ined,6.1.4 Extent of examination, that is, length, tube sheet areas,straight length only, minimum radius of bends, etc.,6.1.5 Time of examination, that is, the date and location ofthe intended examination, and the expected environmentalconditions,6.1.6 The source and type of m
23、aterial to be used forfabricating the reference standard,6.1.7 The type(s), method of manufacture, location, dimen-sions, and number of artificial discontinuities to be placed onthe reference standard,6.1.8 Allowable tolerances for artificial discontinuities, andmethods for verifying compliance,6.1.
24、9 Methods for determining the extent of end effect,6.1.10 Maximum time interval between equipment refer-ence checks,6.1.11 Criteria to be used in interpreting and classifyingobserved indications,6.1.12 Disposition of examination records and referencestandard,6.1.13 Contents of examination report, an
25、d6.1.14 If specified in the contractual agreement, personnelperforming examinations to this practice shall be qualified inaccordance with a nationally recognized NDT personnel quali-fication practice or standard such as ANSI/ASNT-CP-189,SNT-TC-1A, MIL-STD-410E, NAS-410, ASNT-ACCP, or asimilar docume
26、nt and certified by the certifying agency, asapplicable. The practice or standard used and its applicablerevision shall be identified in the contractual agreement be-tween the using parties.NOTE 2MIL-STD-410 is canceled and has been replaced with NAS-410, however, it may be used with agreement betwe
27、en contracting parties.6.1.15 If specified in the contractual agreement, NDT agen-cies shall be qualified and evaluated in accordance withPractice E 543. The applicable edition of Practice E 543 shallbe specified in the contractual agreement.7. Apparatus7.1 Electronic Apparatus:7.1.1 The electronic
28、apparatus shall be capable of energiz-ing the probe coils with alternating currents of suitablefrequencies, and shall be capable of sensing changes in theelectromagnetic response of the probes. It is important to notethat a differential coil probe system tends to maximize theresponse from abrupt cha
29、nges along the tube length, while asingle coil probe system usually responds to all changes.7.1.2 Since many gradual changes are irrelevant, a differen-tial coil system may permit higher gain than an absolute coilsystem, which enhances the response to small, short defects.Electrical signals produced
30、 in this manner may be processed soas to actuate an audio or visual readout, or both. Whennecessary, these signals may also be further processed toproduce a permanent record. The apparatus should have somemeans of providing relative quantitative information basedupon the amplitude or phase of the el
31、ectrical signal, or both.This may take many forms, including calibrated sensitivity orattenuation controls, multiple alarm thresholds, or analog ordigital readouts, or combination thereof.7.2 Readout Devices, which require operator monitoring,such as an oscilloscope or oscillograph presentation, may
32、 beused when necessary to augment the alarm circuits. This maybe necessary, for example, to find small holes, indications ofwhich tend to be nearly in phase with the response from landsin skip-fin tubing. Since the lands cause very large signals tooccur, phase discrimination may not prevent irreleva
33、nt alarmsfrom tube support, if the alarm is set to reject the hole. Byobserving an oscilloscope or oscillograph, however, the abilityto detect this type of defect may be improved, especially inareas between the tube supports.7.3 Examination CoilsExamination coils shall be capableof inducing current
34、in the tube and sensing changes in theelectrical characteristics of the tube. The examination coildiameter shall be selected to yield the largest practical fill-factor. The configuration of the examination coils may permitsensing both small, localized conditions, which change rapidlyalong the tube l
35、ength, such as pitting or stress corrosion cracks,and those which may change slowly along the tube length orfrom tube to tube, such as steam cutting, mechanical erosion,or metallurgical changes. The choice of coil diameter should bebased upon requirements judged to be necessary for theparticular exa
36、mination situation.7.4 Single-Coil or Differential-Coil Probe Systems:7.4.1 Single-Coil Probe SystemsIn a single-coil probesystem, the signal obtained from the interaction between theexamination coil, and the portion of the test specimen within itsE 690 98 (2004)e12influence is often balanced agains
37、t an off-line reference coil ina similar specimen, often with the aid of electrical compensa-tion. In some systems, electrical balancing of the examinationcoil is accomplished entirely by the use of an electrical balancereference.7.4.2 Differential-Coil Probe SystemsIn a differential-coilprobe syste
38、m, the reference coil is identical to (again, oftenwith the aid of electrical compensation), and on the samelongitudinal axis as the examination coil. In this type ofconfiguration, both coils function simultaneously as examina-tion and reference coils, and the instrument responds only tounbalance vo
39、ltages (that is, differential voltages) between thetwo coils.7.4.3 In either the single or differential coil system, someform of original balance is attained and it is the disruption ofthis balance which provides the response signals that indicatedeviations in the tube wall as compared to the origin
40、al sample.7.5 Speed-Sensitive EquipmentEddy-current equipmentthat produces a variation in discontinuity signal response withvariations in the examination-scan speed. This is characteristicof equipment that employs filter networks to attenuate thedetected signal at frequencies below or above, or both
41、, anadjustable or fixed frequency. Speed insensitive d-c coupledequipment provides a constant discontinuity signal responsewith changing examination speeds.7.6 Driving MechanismA means of mechanically travers-ing the probe coil through the tube may be used. Whether theprobe is traversed through the
42、tube manually or mechanically,care should be taken to maintain as uniform a probe speed aspossible to produce repeatable indications of discontinuitieswhen using speed sensitive equipment.7.7 Phase-Selective SystemAn instrumentation systemthat includes built-in circuitry to indicate phase difference
43、s inthe response signal relative to the excitation signal. This abilityaids in discriminating between abnormal conditions in the tubewall (cracks, pitting, wear from the tube supports) and normalchange (lands in skip-fin tubing, the tube support itself,contaminants in or about the tube such as sludg
44、e, etc.). Phasemay also provide information on defect position relative to thetube-wall surfaces, and this information may be used toestimate the relative severity of defects.8. Reference Standards8.1 The purpose of this type of examination is to provideinformation to aid in evaluating the condition
45、 of each heatexchanger tube, and in assessing the likelihood of failureduring service. It is not possible to specify an all-inclusivereject level standard that would acknowledge all of the possiblecombinations of heat exchanger design (including tubing typeand dimensions), environmental factors, typ
46、e and amount ofuse, and acceptable level of operational shutdowns. Thepurpose of the standards is to standardize the instrument to finda number of common tube-wall changes of varying severity.The tube-wall deviations in a particular heat exchanger can bemonitored over subsequent shutdowns, or be cor
47、rected, at thediscretion of the user or through administration of a codespecific to a class of users. Specific types and sizes of artificialdiscontinuities should be chosen to reflect both the purpose ofthe eddy-current examination in particular situations, and anyknowledge of the type of defects, t
48、hat can be expected to occur.A special consideration in this type of examination is the highprobability of certain types of defects occurring in the area ofthe tube supports. It is recommended that a way of simulatingthe tube support (such as a simple outside diameter ring of amaterial similar to th
49、e tube support) be supplied, so that theinfluence of the tube support on the discontinuity signal may beobserved.8.2 The tube used when adjusting the sensitivity and phasesettings of the apparatus shall be of the same material,dimensions, and configuration as the tubes installed in the heatexchanger.8.3 It is important to note that artificial discontinuities maynot be representative of natural discontinuities and may notprovide a direct relationship between instrument response anddiscontinuity severity. They are intended only for establishingan approximation of sensitivity l
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