Designation: E570  

−  15

Standard Practice for

Flux Leakage Examination of Ferromagnetic Steel Tubular
Products 1
This standard is issued under the fixed designation E570; the number immediately following the designation indicates the year of 
original
original adoption or, in the case of revis
revision,
ion, the year of last revision.
revision. A number in paren
parenthese
thesess indicates the year of last reappr
reapproval.
oval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.

This standard has been approved for use by agencies of the U.S. Department of Defense.

1. Sco
Scope*
pe* E1316 Terminology
E1316  Terminology for Nondestructive Examinations
1.1 This practice covers
covers the applic
application
ation and standardization
standardization 2.2   Other Documents:
of equipment using the flux leakage test method for detection SNT-TC-1A Recommended
SNT-TC-1A  Recommended Practice for Personnel Qualifi-
of outer surface, inner surface, and subsurface discontinuities cation and Certification of Nondestructive Testing Person-
in ferro
ferromagnet
magnetic
ic steel tubul
tubular
ar prod
products
ucts (Note 1)
1) of uniform nel3
cross section such as seamless and welded tubing. ANSI/ASNT CP-189 ASNT
CP-189  ASNT Standard for Qualification and
Certification of Nondestructive Testing Personnel 3
NOTE  1—The term “tube” or “tubular product” will be used to refer to
both pipe and tubing. NAS-410 NAS CertCertifica
ificatio
tion
n and Qua
Qualific
lificatio
ation
n of Non
Nonde-
de-
4
structive
structive Perso
Personnel
nnel (Quali
(Quality
ty Assur
Assurance
ance Commit
Committee)
tee)
1.2 Thi
Thiss pra
practic
cticee is inte
intende
ndedd for use on tub
tubula
ularr pro
produc
ducts
ts
ISO 9712 Non-destructive Testing—Qualification and Cer-
having outside diameters from approximately  ⁄ 2  to 24 in. (12.7
 1
tification of NDT Personnel 5
to 610 mm) with wall thicknesses to 1 ⁄ 2  in. (12.7 mm). These
techniques have been used for other sizes, however, and may
3. Terminology
be so spspec
ecifi
ified
ed up
uponon co
cont
ntra
ract
ctua
uall ag
agre
reeme
ementnt be
betw
twee
een
n th
thee
purchaser and the supplier. 3.1 Definitions of terms relating to flux leakage examination
are provided in Terminology  E1316
 E1316..
1.3 This practice
practice does not establish acceptance
acceptance criteria;
criteria; they
must be specified by the using parties.
4. Summ
Summary
ary of Practice
Practice
1.4 The values stated in inch-poun
inch-pound d units are to be regar
regarded
ded
as the standard. The values given in parentheses are mathemati- 4.1 This method consists
consists of the following steps:
cal conversions to SI units that are provided for information 4.1.1 The tube wall is magnetized at the area under exami-
only and are not considered standard. nation to a proper level approaching magnetic saturation.

1.5   This sta

standa
ndard
rd does not pur
purpor
portt to add
addre
ress
ss the saf
safety
ety NOTE  2—Tubes subjected to magnetic inspections can retain various
concerns, if any, associated with its use. It is the responsibility strengths and configuration of residual magnetic fields depending upon the
magnet
mag netiza
izatio
tion
n tec
techni
hnique
que.. If the res
residu
idual
al fiel
field
d res
result
ulting
ing fro
from
m a giv
given
en
of the user of this standard to establish appropriate safety and  technique can interfere with subsequent applications of the tube, then a
health practices and determine the applicability of regulatory supplemental demagnetization process may be required.
limitations prior to use.
4.1.2
4.1.2 A flu
fluxx se
sens
nsor
or co cont
ntain
ainining
g mag
magne netic
tic tr
tran
ansd
sduc
ucer
erss is
2. Referenc
Referenced
ed Documents
Documents plac
placed
ed on or ababov
ovee th
thee ou
outs
tsid
idee su
surf
rfac
acee of th
thee tu
tube
be in ththee
magnetized area.
2.1   ASTM Standards:2 4.1.
4.1.3
3 Ei
Eith
ther
er th
thee tu
tube
be or th thee flu
fluxx se
sens
nsor
or is mo
moveved
d at a
E543 Specification
E543  Specification for Agencies Performing Nondestructive constant speed in the direction of the magnetic field so that the
Testing sensor scans the entire surface of the tube.
4.1.4
4.1.4 Each magnetic
magnetic transduc
transducer er in the flux sensensor
sor is con
con--
1
This practice is under the jurisdiction of ASTM Committee E07  on Nonde- nected to an electronic console which amplifies, filters, and
structive Testing
structive Testing and is the direct responsibility
responsibility of Subc
Subcommitt
ommittee
ee   E07.07 on
Electromagnetic Method.
Current edition approved June 1, 2015. Published July 2015. Originally approved
3
in 1976. Last previous edition approved in 2009 as E570 - 09. DOI: 10.1520/E0570- Available from American Society for Nondestructive Testing (ASNT), P.O.
P.O. Box
15. 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http://www.asnt.org.
2 4
For referenced ASTM standards, visit the ASTM website, www.astm.org, or Availab
vailable
le from Aerospace
Aerospace Indust
Industries
ries Association
Association of Ameri
America,
ca, Inc., 1250 Eye
contact ASTM Customer Service at service@astm.org. For  Annual Book of ASTM  St., NW, Washington, DC 20005.
5
Standards volume information, refer to the standard’s Document Summary page on Available from International Organization for Standardization (ISO), 1, ch. de
the ASTM website. la Voie-Creuse, CP 56, CH-1211 Geneva 20, Switzerland, http://www.iso.org.

*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. United States

1
 E570 − 15

electronically processes the signals such that significant dis- 7. Interferences

continuities are indicated (visually, audibly), and marked with
7.1 There are some manufacturing processes that produce
paint, or automatically removed from the production line, or
tubing with surface conditions that could interfere with or
both.
obscure signals related to inner surface discontinuities. In the
4.1.5 A suitable means for assuring near magnetic saturation examination of heavy-walled tubing having these conditions,
of the product (subject to periodic check or calibration) must be the ability to examine reliably for inner surface discontinuities
provided as part of the examination to verify the capability of  may be affected.
detection of outside diameter and inside diameter discontinui-
ties. 7.2 When examining tubes with large rapid surface
variations, false signals may be caused by the sensors bouncing
5. Significance and Use along the surface of the tubes.

5.1 This practice outlines a procedure for examining ferro- 7.3 For active pole magnetizing systems, a small air gap
magnetic tubular products using the flux leakage method. If  between the magnetizing system and material under examina-
properly applied, this method is capable of detecting the tion could cause a heavy accumulation of scale buildup on the
presence and location of significant longitudinally or trans- pole pieces.
versely oriented discontinuities such as pits, scabs, slivers,
DETECTION OF LONGITUDINAL
gouges, roll-ins, laps, seams, cracks, holes, and improper welds
DISCONTINUITIES
in ferromagnetic tubes under inspection. In addition, the
severity of a discontinuity may be estimated and a rejection
8. Apparatus
level set with respect to the magnitude of the electromagnetic
indication produced by the discontinuity. 8.1   Rotary Mechanism— T he rotary mechanism shall be
capable of rotating a magnetizing system or flux leakage
5.2 The response from natural discontinuities can be signifi-
sensors, or both, in unison around tubing that is being
cantly different from the response for artificial discontinuities
translated axially through the mechanism, thereby producing a
such as drilled holes or notches of equivalent depth. For this
helical scan over the surface. Good examination practices
reason, sufficient work should be done to determine the
require that the pole pieces of the magnetizing system rotate
conditions necessary to detect and mark  natural  discontinuities
uniformly about the tube and that the flux sensor ride on the
whose characteristics will adversely affect the serviceability of 
tube or be spaced uniformly above the surface of the tube
the tube, in order to establish acceptance criteria between the
during rotation.
supplier and purchaser.
8.2   Spin Feed Mechanism— The spin feed mechanism shall
6. Basis of Application be capable of positioning a magnetizing system or flux leakage
sensors, or both, on or near the surface of a translating rotating
6.1 The following criteria may be specified in the purchase
tube such that there is a uniform spacing between the pole
specification, contractual agreement, or elsewhere, and may
pieces of the magnetizing system and the tube. The flux
require agreement between the purchaser and supplier:
leakage sensors shall ride on the surface of the tube or be held
6.1.1 Acceptance criteria.
uniformly from the surface of the tube during examination.
6.1.2 Type, dimensions, location, and number of artificial
discontinuities to be placed on the reference standard. 8.3   Magnetizing System:
6.1.3 Size and type of tubing to be examined. 8.3.1 An active field magnetizing system consists of a
6.1.4 Extent of examination (that is, full length, weld zone suitable means of applying a strong adjustable transverse
only if welded, etc.). magnetic field to the region of the tube under the flux sensors
6.1.5 Disposition of material with discontinuity indications. and shall be capable of bringing that region of the tube to near
6.1.6 Methods of verifying dimensions of artificial discon- saturation. Typical systems employ either permanent magnets
tinuities and allowable tolerances. or controllable electromagnets. If permanent magnets are used,
6.1.7 Time of inspection, that is, the point(s) in the manu- a means shall be provided to adjust the spacing of the pole
facturing process at which the material will be inspected. pieces in order to reach the proper magnetization level. Refer
to Section 13 for application of longitudinal magnetic fields.
6.1.8 Nondestructive testing (NDT) personnel shall be
qualified in accordance with a nationally recognized NDT 8.3.2 A residual field magnetizing system consists of a
personnel qualification practice or standard such as ANSI/  means of applying a circular residual magnetic field to an entire
ASNT CP-189, SNT-TC-1A, NAS-410, ISO 9712 or a similar tube before the tube is inspected. Typical systems employ a
document. The practice or standard used and its applicable centrally positioned conducting rod through which a high
revision shall be specified in the purchase specification or direct current is passed; alternatively, the current may be
contractual agreement between the using parties. conducted through the tube itself. The current produces a
circular active magnetic field which is concentric with the
6.1.9 If specified in the purchase specification or contractual
current distribution. When the current ceases, there remains a
agreement, NDT agencies shall be evaluated and qualified as
residual magnetic field which is circular, concentric with the
described in Practice E543. The applicable edition of Practice
tube, and wholly contained within the tube wall.
E543   shall be identified in the purchase specification or
contractual agreement between the using parties. 8.4  Flux Leakage Sensors:

2
 E570 − 15

8.4.1 The flux sensor shall consist of magnetic field trans- of the tube wall that is periodically perpendicular to all radii of 
ducers that respond to variations in magnetic flux density. the tube (Fig. 2(a)). Rotation of the tube with the magnetizing
These sensors generally consist of one of the following types: poles held stationary will also produce the same effect (Fig.
electromagnetic coils, Hall probes, magneto diodes, 2(b)).
magnistors, or magnetoresistors. These sensors are normally 9.1.5 Relative motion between the flux sensor and the flux
used to detect the flux leakage directly from the discontinuity leakage field caused by the discontinuity is generally utilized to
in the tube; however, they may also be used to detect flux generate a voltage in the flux sensor. The amplitude of the
leakage patterns that have been transferred from the tube to a voltage generated by the sensor is generally indicative of the
strip of magnetic tape. The flux sensors should be of sufficient severity of the discontinuity when all other factors are constant.
number and length so as to provide 100 % coverage while The flux leakage field measured at the outside surface of the
scanning the tube surface to be examined at the desired tube resulting from an inside surface discontinuity is much
examination speed. Their location (with respect to the mag- broader than the leakage field from a discontinuity of equal
netic pole pieces and the tubular product) should result in severity located on the outer surface of the tube, resulting in a
maximum response to the leakage field caused by a disconti- lower signal frequency for the inner surface discontinuity  (Fig.
nuity in the tubular product. 3(a) and 3(b)). Several types of equipment utilize this infor-
8.4.2 The depth and orientation of a discontinuity below the mation to determine whether the discontinuity is located on the
outside surface will affect the magnitude of the signal received inner or outer surface of the tube.
from it. Sensitivity decreases significantly as the distance 9.1.6 Near saturation is required to provide repeatable and
between the flux leakage sensor and the tube under examina- reliable indications for the presence of outer surface, inner
tion is increased. Therefore, the sensors should remain clean surface, or subsurface discontinuities. A suitable measuring
and have uniform contact with the tube surface, or if air riding means or reference samples or both are required to properly
the sensors should be held at a uniform distance above the adjust the equipment for operation at the required sensitivity
surface of the tube. and magnetization level.
8.5   Electronic Instrumentation— The electronic apparatus 9.2 The examination of tubular products for transverse
shall be capable of amplifying signals from the flux sensors and discontinuities utilizing a longitudinal magnetic field is dis-
processing them for the operation of alarms. Multiple probes cussed in Section 14.
may be used to increase the speed of examination. The signals
may be processed in two separate channels to result in a 10. Reference Standard
differentiation between inner and outer surface discontinuities.
10.1 The tubes selected for reference standards should be
Each of the two sets of electronic channels should contain its
first examined to ascertain that they are free of interfering
own sensitivity and threshold triggering controls for indepen-
natural discontinuities prior to the introduction of artificial
dent setting of percentage of wall rejection levels.
defects. The standard tube shall have similar electromagnetic
8.6   Driving Mechanism— A mechanical drive mechanism properties but the same nominal dimensions as the tubes to be
shall be used which is capable of rigidly holding and passing examined on a production basis. The standard shall be of 
the tube through the inspection apparatus at constant speed and sufficient length to permit the required spacing of artificial
concentric with the inspection apparatus. As required, the discontinuities and to be mechanically stable while in the
driving mechanism shall be capable of rotating and advancing, examining position in the apparatus. Artificial discontinuities
or just advancing the tube with a constant speed. placed in the tube shall be of the following types:
10.1.1   Notches— Longitudinal outside surface or inside sur-
9. Principles of Examination face notches may be produced either by air abrasive, milling, or
9.1 Conduct the examination of tubular products for longi- EDM (Electric Discharge Machining). Notch depth is usually
tudinal discontinuities employing a transverse magnetic field specified as a percent of nominal wall thickness with typical
and flux leakage detectors using one or more of the following values being 5, 10, 12 1 ⁄ 2, or 20 %. Notch width shall be the
techniques: minimum practical but shall not exceed 0.40 in. (1 mm). Notch
9.1.1 Obtain a transverse magnetic field by either (1) width and geometry are relevant variables that can affect signal
positioning north and south poles of a magnet on opposite sides response and should be taken into consideration in applying
of a tube on a diameter or chord as shown in Fig. 1(a) and 1(b); this method. Maximum notch length shall be specified. Lengths
or (2) passing a high direct current through a conducting rod of  1 ⁄ 4, 1 ⁄ 2, and 1 in. (6.3, 12.7, and 25.4 mm) are typical. Notch
centrally positioned in the tube under examination. orientation may be longitudinal or at an angle that is typical of 
9.1.2 Position a flux sensor (or sensors) containing magnetic the discontinuities produced by the particular manufacturing
field transducers on or near the tube surface and move at a process. Refer to Section 15 for transverse notches.
uniform speed over the area being magnetized. 10.1.2   Holes— When holes are used for calibration, they
9.1.3 At a discontinuity in the tube wall, the flux lines are should be made through the tube wall without causing perma-
distorted, producing a leakage field. The maximum flux leak- nent distortion of the tube. The diameter of these holes may be
age for a discontinuity normally occurs when magnetization is specified based on factors involving intended service or other
perpendicular to the discontinuity. appropriate criteria. Typical hole diameters range from 1 ⁄ 32
9.1.4 For active pole magnetization, rotation of the magne- through 1 ⁄ 8   in. (0.79 through 3.2 mm), although a 1 ⁄ 16-in.
tizing system about the tube results in transverse magnetization (1.6-mm) diameter hole is specified for use with all sizes of 

3
 E570 − 15

(a )

(b )

FIG. 1 Transverse Magnetization

tube and tubing in one widely used industrial standard. It is inspecting only the weld area, the discontinuities need be
considered good practice to include holes with diameters placed only in the weld area of the reference standard.
greater and smaller than the reference size used to set the
rejection level, since these provide a useful means of verifying 11. Adjustment and Standardization of Apparatus
adequate dynamic response of the equipment. Sensitivity
10.1.3  Hole and Notch Combination— Hole size and notch
configuration (type, orientation, and dimension, etc.) influence 11.1 The procedure for setting up and checking the sensi-
the levels of flux leakage signal response. Correlation between tivity of the apparatus is as follows:
these signals plus the method and tolerances used in their 11.1.1 Fabricate the reference standard as specified in the
measurement, shall be as specified in the agreement between agreement between purchaser and supplier.
the supplier and the purchaser. 11.1.2 Adjust the magnetizing system for the size material
10.2 In preparing a reference standard for welded tubes, to be inspected.
artificial discontinuities should be placed in both the weld 11.1.3 Center the sensing apparatus to properly receive the
metal and the parent metal, if both are to be examined. When material to be examined.

4
 E570 − 15

FIG. 2 Rotational Transverse Magnetization

11.1.4 Scan the reference standard (containing reference apparatus. It is recommended that all such tubes be reexamined
notches or holes or both) and adjust magnetization power, flaw in accordance with the purchase specification to determine the
channel sensitivity, and filter network as applicable for optimal acceptability of the tube under the applicable specifications.
signal-to-noise ratio. The tube is normally not translated 11.1.6 Standardize the examination apparatus at the start
(advanced) during standardization but all other conditions are and end of each examination run using the reference standard.
identical to those used in production inspection of the tubular Restandardize at least every 4 h, or whenever improper
product. After standardization, pass the reference standard
functioning of the apparatus is suspected. Whenever improper
through the inspection assembly at operating speed to demon-
functioning is found, restandardize the apparatus and reexam-
strate adequate performance.
ine all tubes examined during the period since the last proper
11.1.5 Pass the tubes to be examined through the inspection
standardization took place.
apparatus with the sensitivity adjusted as described above. Set
aside tubes with discontinuity indications indicated by the

5
 E570 − 15

(a ) Outer Surface Defect

(b ) Inner Surface Defect

FIG. 3 External Flux Leakage for O.D. and I.D. Discontinuities

11.1.7 Select the examination speed so as to provide assur- 14. Principles of Examination
ance of detecting the minimum length discontinuity prescribed
14.1 Conduct the examination of tubular products for dis-
in the specification.
continuities employing a longitudinal magnetic field and flux
DETECTION OF TRANSVERSE DISCONTINUITIES leakage detectors using one or more of the following tech-
niques:
12. Summary 14.1.1 Obtain a longitudinal field as shown in Fig. 4(a) by
12.1 The following sections define and clarify portions of  either (1) positioning north and south poles of a magnet on a
Sections 8, 9, 10, and 11 in regard to the examination of tubular sector of a tube; or (2) passing a direct current through
products for transversely oriented discontinuities by employing encircling coils centrally positioned about the tube under
a longitudinal magnetic field. examination.
14.1.2 Position a flux sensor (or sensors) containing mag-
13. Apparatus netic field transducers on or near the tube surface which is
13.1 The magnetizing system shall consist of a suitable magnetized as the tube moves through the magnetizing system.
means of applying a strong adjustable longitudinal magnetic 14.1.3 Passing the tube under examination through the
field to the region of the tube under the flux sensors, and shall magnetizing system results in magnetization of the tube wall
be capable of bringing that region of the tube to near saturation. that is longitudinal to the axis of the tube under examination.

FIG. 4 Longitudinal Magnetization

6
 E570 − 15

15. Reference Standard 17. Keywords

15.1 Dimensions of notches and holes remain the same as 17.1 electromagnetic (eddy current) testing; ferromagnetic;
covered by Section 10; however, notches should be produced flux leakage; NDT; nondestructive testing; steel; tubular prod-
transverse to the axis of the tube. ucts
16. Adjustment and Standardization of Apparatus
Sensitivity
16.1 Select the proper coils, magnetizing yokes, or perma-
nent magnets where required and follow procedures in Section
11.

SUMMARY OF CHANGES

Committee E07 has identified the location of selected changes to this standard since the last issue (E570–09)
that may impact the use of this standard.

(1)  Editorial revisions were made throughout the document. (4)  In  10.1.1, the maximum notch width was modified.
(2)  In 2.2 and   6.1.8,  changes such the addition of ISO 9712
were made to be consistent with Policy P-10.
(3)  In   10.1,   the reference standard material description was
revised to specify that the reference standard has similar
electromagnetic properties to the tubing being examined.

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