1、Designation: E690 15Standard Practice forIn Situ Electromagnetic (Eddy Current) Examination ofNonmagnetic Heat Exchanger Tubes1This standard is issued under the fixed designation E690; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision
2、, 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.1. Scope*1.1 This practice describes procedures to be followed duringeddy current examination (using an internal, pr
3、obe-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 forms of tube-wall dete-rioration which may occur during this type of service.
4、 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 establish baseline data for evaluatingsubsequent performance of the product after expo
5、sure 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 establish acceptance criteria; theymust be specified by the using parties.1.3 This s
6、tandard 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 applica-bility of regulatory limitations prior to use.2. Referenced Documents2.
7、1 ASTM Standards:2E543 Specification for Agencies Performing NondestructiveTestingE1316 Terminology for Nondestructive Examinations2.2 Other Documents:SNT-TC-1A Recommended Practice for Personnel Qualifi-cation and Certification in Nondestructive Testing3ANSI/ASNT-CP-189 ASNT Standard for Qualificat
8、ion andCertification of Nondestructive Testing Personnel3NAS-410 NAS Certification and Qualification of Nonde-structive Personnel (Quality Assurance Committee)4ISO 9712 Non-destructive TestingQualification and Cer-tification of NDT Personnel53. Terminology3.1 Standard terminology relating to electro
9、magnetic ex-amination may be found in Terminology E1316, Section C,Electromagnetic Testing.4. Summary of Practice4.1 The examination is performed by passing an eddycurrent probe through each tube. These probes are energizedwith alternating currents at one or more frequencies. Theelectrical impedance
10、 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 produce el
11、ectrical signals which are processed so asto produce an appropriate combination of visual displays,alarms, or temporary or permanent records, or combinationthereof, for subsequent analysis.5. Significance and Use5.1 Eddy current testing is a nondestructive method that canbe used to locate discontinu
12、ities in tubing made of materials1This 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 June 1, 2015. Published June 2015. Originallyapproved in 1979. Last pre
13、vious edition approved in 2010 as E690 10. DOI:10.1520/E0690-15.2For 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 websi
14、te.3Available fromAmerican Society for Nondestructive Testing (ASNT), P.O. Box28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http:/www.asnt.org.4Available from Aerospace Industries Association of America, Inc. (AIA), 1000Wilson Blvd., Suite 1700,Arlington, VA22209-3928, http:/www.aia-aerospace.
15、org.5Available from International Organization for Standardization (ISO), 1, ch. dela Voie-Creuse, CP 56, CH-1211 Geneva 20, Switzerland, http:/www.iso.org.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshoho
16、cken, PA 19428-2959. United States1that conduct electricity. Signals can be produced by disconti-nuities located either on the inner or outer surfaces of the tube,or by discontinuities totally contained within the tube wall.When using an internal probe, the density of eddy currents inthe tube wall d
17、ecreases very rapidly as the distance from theinternal surface increases; thus the amplitude of the response toouter surface discontinuities decreases correspondingly.5.2 Some indications obtained by this method may not berelevant to product quality. For example, an irrelevant signalmay be caused by
18、 metallurgical or mechanical variations thatare generated during manufacture but that are not detrimentalto the end use of the product. Irrelevant indications can maskunacceptable discontinuities occurring in the same area. Rel-evant indications are those that result from nonacceptablediscontinuitie
19、s. 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, predictable sources of irrelevant indications arelands (short unfinned sections in finned tubing), dents,scratche
20、s, 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 generally not able to separate theindication generated by the end of the tube from indications ofdiscontinu
21、ities 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 specified in the purchasespecification, contractual agreement, or elsewhere, and mayrequire agreement between
22、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 configuration of tubes to beexamined,6.1.4 Extent of examination, that is, length, tube sheet areas,straight length onl
23、y, 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 material to be used forfabricating the reference standard,6.1.7 The type(s), method of manufacture, location,di
24、mensions, and number of artificial discontinuities to beplaced on the reference standard,6.1.8 Allowable tolerances for artificial discontinuities, andmethods for verifying compliance,6.1.9 Methods for determining the extent of end effect,6.1.10 Maximum time interval between equipment refer-ence che
25、cks,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, and6.1.14 If specified in the contractual agreement, personnelperforming examinations to this practice shall be qu
26、alified inaccordance with a nationally recognized NDT personnel quali-fication practice or standard such as ANSI/ASNT-CP-189,SNT-TC-1A, NAS-410, ISO 9712 or a similar document andcertified by the certifying agency, as applicable. The practice orstandard used and its applicable revision shall be iden
27、tified inthe contractual agreement between the using parties.6.1.15 If specified in the contractual agreement, NDT agen-cies shall be qualified and evaluated in accordance withSpecification E543. The applicable edition of SpecificationE543 shall be specified in the contractual agreement.7. Apparatus
28、7.1 Electronic Apparatus:7.1.1 The electronic 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
29、 tends to maximize theresponse from abrupt changes 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 sm
30、all, short defects.Electrical signals produced 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 informat
31、ion basedupon the amplitude or phase of the electrical 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
32、oscilloscope or impedance plane presentation, maybe used when necessary to augment the alarm circuits. Thismay be necessary, for example, to find small holes, indicationsof which tend to be nearly in phase with the response fromlands in skip-fin tubing. Since the lands cause very largesignals to occ
33、ur, phase discrimination may not prevent irrel-evant alarms from tube support, if the alarm is set to reject thehole. By observing an oscilloscope or oscillograph, however,the ability to detect this type of defect may be improved,especially in areas between the tube supports.7.3 Examination CoilsExa
34、mination coils shall be capableof inducing current 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, localiz
35、ed conditions, which change rapidlyalong the tube length, 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 requir
36、ements judged to be necessary for theparticular examination situation.E690 1527.4 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 wit
37、hin itsinfluence is often balanced against 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
38、 SystemsIn a differential-coilprobe system, 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 th
39、e instrument responds only tounbalance voltages (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 i
40、n the tube wall as compared to the original 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 sign
41、al at frequencies below or above, or both, 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. W
42、hether theprobe is traversed through the 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-
43、in circuitry to indicate phase differences 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,contam
44、inants in or about the tube such as sludge, 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 provideinfor
45、mation to aid in evaluating the condition 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 typean
46、d dimensions), environmental factors, type 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 bemonit
47、ored over subsequent shutdowns, or be corrected, 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, a
48、nd anyknowledge of the type of defects, that 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
49、 diameter ring of amaterial similar to the 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 es
