INTERNATIONAL
STANDARD
ISO
17781
First edition
2017-07
Petroleum, petrochemical and
natural gas industries — Test
methods for quality control of
microstructure of ferritic/austenitic
(duplex) stainless steels
Industries du pétrole, de la pétrochimie et du gaz naturel — Méthodes
d’essai de contrôle de la qualité de la microstructure des aciers
inoxydables (duplex) austénitiques/ferritiques
Reference number
ISO 17781:2017(E)
© ISO 2017
ISO 17781:2017(E)
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Fax +41 22 749 09 47
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ii
© ISO 2017 – All rights reserved
ISO 17781:2017(E)
Contents
Page
Foreword .................................................. ................................................... ................................................... ................................................... ............................. iv
Introduction .................................................. ................................................... ................................................... ................................................... ....................... v
1
Scope .................................................. ................................................... ................................................... ................................................... ...................... 1
2
Normative references .................................................. ................................................... ................................................... .............................. 1
3
Terms, definitions and abbreviated terms .................................................. ................................................... ........................... 2
3 .1
4
5
.................................................. ................................................... ................................................... ............... 2
Abbreviated terms .................................................. ................................................... ................................................... ....................... 3
3.2
Terms and definitions
4.1
4.2
4.3
General .................................................. ................................................... ................................................... ................................................... 4
Casting test blocks ................................................... ................................................... ................................................... ....................... 6
Welds in the as welded condition .................................................. ................................................... ...................................... 6
Sampling of test specimens .................................................. ................................................... ................................................... ............... 4
Test methods ................................................... ................................................... ................................................... ................................................... . 7
General .................................................. ................................................... ................................................... ................................................... 7
Microstructural examination .................................................. ................................................... ................................................. 7
5.2.1 General ................................................... ................................................... ................................................... ............................. 7
5.2.2 Preparation of specimen .................................................. ................................................... ...................................... 7
5.2.3 Etching of specimens .................................................. ................................................... ............................................... 7
5.2.4 Microstructural evaluation of test specimens .................................................. ...................................... 8
5.3 Ferrite content measurement .................................................. ................................................... ............................................ 10
5.3.1 Test standard and conditions .................................................. ................................................... ........................ 10
5.3.2 Acceptance criteria .................................................. ................................................... ................................................ 11
5.3.3 Reporting .................................................. ................................................... ................................................... ..................... 11
5.4
Charpy V-notch impact toughness test .................................................. ................................................... ....................... 11
5.4.1 Test standard and conditions .................................................. ................................................... ........................ 11
5.4.2 Acceptance criteria .................................................. ................................................... ................................................ 11
5.4.3 Reporting .................................................. ................................................... ................................................... ..................... 12
5.5 Corrosion test.................................................. ................................................... ................................................... ................................ 12
5.5.1 Test standard and conditions .................................................. ................................................... ........................ 12
5.5.2 Preparation of test specimens .................................................. ................................................... ...................... 13
5.5.3 Acceptance criteria .................................................. ................................................... ................................................ 13
5.5.4 Reporting .................................................. ................................................... ................................................... ..................... 13
Annex A (informative) Chemical compositions of duplex stainless steels .................................................. ............... 14
Annex B (informative) Preparation and etching for microstructural examination ......................................... 16
5.1
5.2
Bibliography .................................................. ................................................... ................................................... ................................................... .................. 18
© ISO 2017 – All rights reserved
iii
ISO 17781:2017(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work o f preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters o f
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
di fferent types o f ISO documents should be noted. This document was dra fted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso .org/directives).
Attention is drawn to the possibility that some o f the elements o f this document may be the subject o f
patent rights. ISO shall not be held responsible for identi fying any or all such patent rights. Details o f
any patent rights identified during the development o f the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso .org/patents).
Any trade name used in this document is in formation given for the convenience o f users and does not
constitute an endorsement.
For an explanation on the voluntary nature o f standards, the meaning o f ISO specific terms and
expressions related to con formity assessment, as well as in formation about ISO’s adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www.iso .org/iso/foreword .html .
This document was
by Technical
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67, Materials,
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iv
.
offshore
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ISO 17781:2 017(E)
Introduction
T he a i m o f th i s do c u ment i s to e s tabl i s h com mon te s t me tho d s
ferritic/au s tenitic
(dup lex) s tai n le s s s te el s
app ly the s ame te s t pro ce du re s
for
for
for
qua l ity control o f m icro s truc tu re o f
the oi l a nd ga s i ndu s tr y, enabl i ng the manu fac tu rers to
thei r cl ients .
D uple x s ta i n le s s s te el s have a dua l pha s e m ic ro s truc tu re
con s i s ti ng o f
ferrite
and au s ten ite . I de a l ly,
the s e pha s e s a re pre s ent i n e qua l prop or tion s; a lthough i n a l loys wh ich a re com merci a l ly avai lable, the
ferrite
pha s e volu me
frac tion
c a n var y b e twe en 3 5 % and 6 5 %
for
pro duc ts i n the s olution a n ne a le d
cond ition . T hey are ch arac teri z e d b y h igh- ch rom iu m (19 % to 3 3 %) a nd low-nickel contents comp are d
with austenitic stainless steels.
Duplex stainless steels are prone to precipitation of intermetallic phases, carbides and/or nitrides
p o s s ibly
c au s i ng
embrittlement
a nd
re duce d
corro s ion
re s i s tance .
T he
formation
o f i nterme ta l l ic
pha s e s s uch a s Sigma, σ, and C h i , χ , o cc u rs dep end i ng on e xp o s ure ti me i n the approxi mate temp eratu re
range 590 °C to 1 000 °C (1 094 °F to 1 832 °F) and decomposition of ferrite to Alpha Prime occurs in the
range 300 °C to 540 °C (572 °F to 1 004 °F).
T he m ic ro s truc tu re
me chan ic a l
h i s tor y
o f comp onents
a s s o c iate d
and weld i ng. T he de s truc tive
with
or
fabric ation
ho t worki ng ,
weld s i s a ffe c te d by amongs t o thers
s olution
a n ne a l i ng
te s t me tho d s with accep ta nce
and
with
the therma l-
s ub s e quent
form i ng
c riteria s p e ci fie d herei n are con s idere d
relevant to veri fy that e xp o s u re ti me at ab ove s tate d temp eratu re ra nge s have b e en with i n accep table
l i m its and to en s u re that de s i re d corro s ion re s i s ta nce and me ch an ic a l prop er tie s are ob tai ne d i n fi na l
products.
© ISO 2017 – All rights reserved
v
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INTERNATIONAL STANDARD
ISO 17781:2017(E)
Petroleum, petrochemical and natural gas industries —
Test methods for quality control of microstructure of
ferritic/austenitic (duplex) stainless steels
1 Scope
T h i s do c ument s p e ci fie s qua l ity control te s ti ng me tho d s a nd te s t cond ition s
for
the ch arac teri z ation
of microstructure in relation to relevant properties in ferritic/austenitic (duplex) stainless steel
components supplied in the solution annealed condition and fabrication welds in the as welded
condition.
This document supplements the relevant product and fabrication standards with respect to destructive
testing methods including sampling of test specimens, test conditions and test acceptance criteria to
show freedom from deleterious intermetallic phases and precipitates in duplex stainless steels. In
add ition, th i s do c u ment s p e c i fie s the do c u mentation o f te s ti ng a nd te s t re s u lts b y the te s ti ng lab orator y.
NO TE 1
T h i s do c u ment i s b a s e d up on e xp er ience with dup le x s ta i n le s s s te el s i n o ffs hore o i l a nd ga s i ndu s tr y
ap p l ic ation s i nclud i ng to p s ide a nd s ub s e a hyd ro c a rb on s er vice , s e a water s er vice , a s wel l a s s tr uc tu ra l u s e .
NO TE 2
T he au s ten i te s p ac i n g i s rele va nt to the s u s cep tib i l i ty o f dup le x s ta i n le s s s te el s to hyd ro gen-i nduce d
stress cracking (HISC) in subsea applications where cathodic protection is applied. This falls outside the scope of
this document. Reference is made to DNV/GL RP-F112 [4] .
2 Normative references
T he
fol lowi ng
con s titute s
do c u ments
re qu i rements
are re ferre d to i n the tex t i n s uch a way th at s ome or a l l o f thei r content
o f th i s do c u ment.
For date d re ference s ,
on ly the e d ition cite d appl ie s .
For
u ndate d re ference s , the late s t e d ition o f the re ference d do c ument (i nclud i ng a ny amend ments) appl ie s .
ISO 148-1, Metallic materials — Charpy pendulum impact test — Part 1: Test method
ISO 15614-1 1) , Specification and qualification of welding procedures for metallic materials — Welding
procedure test — Part 1: Arc and gas welding o f steels and arc welding o f nickel and nickel alloys)
ASTM A 370, Standard test methods and definitions for mechanical testing of steel products
ASTM A 1058, Standard test methods and definitions for mechanical testing of steel products — Metric
ASTM A 1084, Standard test method for detecting detrimental phases in lean duplex austenitic/ferritic
stainless steels
ASTM E 3, Standard practice for preparation of metallographic specimens
ASTM E 562, Standard test method for determining volume fraction by systematic manual point count
ASTM E 1245, Standard practice for determining the inclusion or second-phase constituent content of
metals by automatic image analysis
ASTM G 48, Standard test methods for pitting
related alloys by use of ferric chloride solution
1)
and crevice corrosion resistance of stainless steels and
For the purpose of this document, the following documents are considered equivalent: ASME Boiler and
[2] .
p res s ure ves s el co de, s ectio n I X Welding and b razing qualificatio ns
© ISO 2017 – All rights reserved
1
ISO 17781:2017(E)
3
Terms, definitions and abbreviated terms
For the pu rp o s e s o f th i s do c ument, the
fol lowi ng
term s and defi nition s apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http://www.electropedia .org/
— ISO Online browsing platform: available at http://www.iso .org/obp
NO TE
For l i m itation s
in
chem ic a l
co mp o s itio n
o f e ach
s p e c i fic
m ateri a l
grade
o f dup le x
s ta i n le s s
s te el ,
reference is made to the appropriate product standards or UNS number. For nominal chemical composition of
f ff
f
Annex A.
dup le x s ta i n le s s s te el s a nd gro up i ng o
3.1
di
erent typ e s , u s e d with i n th i s do c u ment, re erence i s m ade to
Terms and definitions
3.1.1
centreline intermetallic stringer
group of intermetallic phases (3.1.4
) a l igne d with i n the m id-th ickne s s are a due to a l loy s e gregation
N o te 1 to entr y: T he y c a n b e o b s er ve d a s b o th co nti nuou s a nd d i s conti nuou s p re c ip itate s .
3.1.2
fabrication
bu i ld i ng o f s tr uc tu re s or e quipment b y c utti ng , b end i ng , a nd a s s embl i ng pro ce s s e s s uch a s weld i ng ,
rive ti ng , th re ade d
fa s teners
or o ther j oi n i ng me tho d s
3.1.3
ferritic/austenitic (duplex) steel
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f
f f
stainless steels
stainless steel
add itio n s
up
) w i th a h i gh- ch ro m iu m m a s s
to
5
%,
a nd
a
n icke l
mass
rac tio n (19 % to 3 3 %) w i th o r wi tho ut mo l yb denu m
rac tio n
i nter me d i ate
to
tho s e
o
er r i tic
a nd
au s ten i tic
3.1.4
intermetallic phase
solid-state compounds, containing two or more metallic elements, whose ordered structure differs
from that of its constituents
N o te 1 to entr y: I n dup le x s ta i n le s s s te el , the mo s t releva nt p h a s e s a re identi fie d a s σ- p h a s e , χ- p h a s e a nd R- p h a s e .
3.1.5
lot
fi n ite qua ntity o f pro duc ts
heat treatment load
N o te
1
to
entr y:
For
from
co nti nuo u s
applicable product standards.
the s a me he at (or melt) , s a me manu fac tu ri ng pro ce s s s tep s and s ame
a nd
s em i- conti nuou s
fu r n ace s ,
the
lo t
de fi n itio n
s hou ld
co mp l y
wi th
the
3.1.6
non-metallic precipitate
solid-state compounds, containing two or more elements, whose ordered structure differs from that of
its constituents
N o te 1
to entr y:
nitrides.
2
I n dup le x s ta i n le s s
s te el ,
the rele va nt no n- me ta l l ic
p re c ip itate s
a re ch ro m iu m
c a rb ide s
a nd
© ISO 2017 – All rights reserved
ISO 17781:2017(E)
3.1.7
pitting resistance equivalent number
PREN
number indicating the resistance of stainless
steel
(3.1.8) to pitting corrosion related to chemical
composition and derived from one o f the equations PREN = % Cr + 3,3 % Mo + 16 % N or PREN = % Cr +
3,3 × % (Mo + 0,5W) + 16 × % N (mass fraction)
Note 1 to entry: All PREN limits are absolute limits based upon the heat analysis. The calculated value is not to be
rounded.
3.1.8
stainless steel
steel with at least 10,5 % mass fraction or more chromium, possibly with other elements added to
secure special properties
3.1.9
type 20Cr duplex Group A
ferritic/austenitic stainless steel (3.1.8 ) alloys with 24,0 ≤ PREN < 28,0
3.1.10
type 20Cr duplex Group B
ferritic/austenitic stainless steel (3.1.8 ) alloys with 28,0 ≤ PREN < 30,0
3.1.11
type 22Cr duplex
ferritic/austenitic stainless steel (3.1.8 ) alloys with 30,0 ≤ PREN < 40,0 and Cr ≥ 19 % (mass fraction)
3.1.12
type 25Cr duplex
ferritic/austenitic stainless steel (3.1.8 ) alloys with 40,0 ≤ PREN < 48,0
3.1.13
type 27Cr duplex
ferritic/austenitic stainless steel (3.1.8 ) alloys with 48,0 ≤ PREN ≤ 55,0 and Cr ≤ 33,0 % (mass fraction)
3.2
Abbreviated terms
For the purposes of this document, the following abbreviated terms are used.
ASTM American society for testing and materials
CVN Charpy V-notch
HIP hot isostatically-pressed
NA
not applicable
OD
outside diameter
PREN pitting resistance equivalent number
QL
quality level
T
ruling section thickness
UNS unified numbering system
© ISO 2017 – All rights reserved
3
ISO 17781:2017(E)
4 Sampling of test specimens
4.1
General
The test samples shall be made from a sacrificial product or from a prolongation/extension o f a
product in the final solution annealed condition with location o f test specimens as defined in Table 1
representing the thickest product within the lot. Alternatively, a representative test block may be used
when agreed with the purchaser.
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ISO 17781:2017(E)
T
Product
a
b
l
e
1
—
S
Test sample
Plates, and
Prolongation of
seamless tubes, the product
pipes and fittings
Welded pipes Prolongation or
and fittings
welded extension piece
Bars and long Prolongation
solid forgings
without weld
end
a
m
p
l
i
n
g
o
f
t
e
s
Product
dimension
All
All
OD or section
thickness
<50 mm (2 in)
OD or section
thickness
≥50 mm (2 in)
Sacrificial prod - All d
Flanges and
other hollow uct or prolongacontour shaped tion at weld end
forgings with
weld end including tees
HIP products Sacrificial prod with weld end uct or prolongation at weld end
with greatest
wall thickness
HIP products Sacrificial prod without weld uct or prolonend b
gation at cross
section with
greatest wall
thickness
Castings
All
Section thickness <50 mm
(2 in)
Section thickness ≥50 mm
(2 in)
Sacrificial
Test block
product or test thickness
block (see 4.2) <50 mm (2 in)
Test block
thickness
≥50 mm (2 in)
t
s
p
e
c
i
m
e
n
s
d
e
p
e
n
d
e
n
t
o
f
p
r
o
d
u
c
t
Test method
Test direction a
Thickness location
CVN
Corrosion,
Microstructure
CVN
Corrosion c ,
Microstructure
CVN
Corrosion,
Microstructure
CVN
Corrosion,
Microstructure
CVN
Transverse
Transverse
Mid-thickness
Full thickness b
Transverse
Transverse
Mid-thickness
Full thickness b
Longitudinal
Transverse
Mid-thickness
Surface to centre b
Longitudinal
Transverse
1/4 thickness
Surface to centre b
Both longitudinal
and tangential to
centre bore
Corrosion,
Longitudinal or
Microstructure tangential
CVN
Any direction
Corrosion,
Microstructure
CVN
Corrosion,
Microstructure
CVN
Corrosion,
Microstructure
CVN
Corrosion,
Microstructure
CVN
Corrosion,
Microstructure
Mid-thickness
weld end
Any direction
Any direction
Full thickness b
weld end
Mid-thickness
weld end
Full thickness b
weld end
Mid-thickness
Surface to centre b
Any direction
Any direction
1/4 thickness
Surface to centre b
Any direction
Mid-thickness
Any direction
Within hatched
area (see Figure 1)
Any direction
a For definition o f test directions, re ference is made to ASTM A 370/ASTM A 1058.
b For products with large sections, the corrosion test specimen shall be taken transverse to the longitudinal axis with
dimensions o f approximately 6 mm × 25 mm (1⁄4 in × 1 in) by thickness. For very large sections, the thickness dimension o f
the specimen can be cut so that one-half to two-thirds of the product thickness is tested.
For welded products, the test specimens for corrosion testing and microstructure examination shall include weld
metal and the heat affected zone of parent metal. For products with wall thickness exceeding 25 mm, more than one (1)
c
specimen can be taken to cover full thickness. In such a case, all specimens shall fulfil the specified criteria.
d When flange body thickness <50 mm (2 in) or weld end OD ≤100 mm (4 in), test specimens may be taken from the
flange body mid-thickness in tangential direction.
For all products, the mid-length o f the test specimens shall be located one T or minimum 50 mm to any
second sur face provided this is feasible within the size o f the test sample/sacrificial product.
CVN testing is required when the wall thickness is ≥6 mm, wherever geometry permits.
For all products, the notch axis of CVN test specimens shall be positioned perpendicular to the closest
outer surface.
© ISO 2017 – All rights reserved
5
ISO 17781:2017(E)
For welded products, two (2) sets of three (3) CVN impact toughness test specimens shall be taken from
mid-thickness of the component, one (1) with notch located in base material and the other notched in
the weld metal.
For forgings, HIP products and fittings, dimensioned sketches shall be established showing type, size
and orientation o f test specimens to be taken from a prolongation o f product or a sacrificial product.
4
.
2
C
a
s
t
i
n
g
t
e
s
t
b
l
o
c
k
s
Test blocks shall be integral or gated with the casting(s) they represent and shall accompany the
castings through all heat treatment operations. During any heat treatment o f products, which the test
block represents, the test blocks shall be tack welded onto the casting and shall accompany the castings
through all heat treatment operations. Alternatively, a sacrificial product may be used as a test sample.
The thickness of the test block shall be equal to the thickest section of the casting(s) represented. For
flanged components, the largest flange thickness should be used as the ruling section.
Dimensions of test blocks and location of test specimens within the test blocks are shown in Figure 1 for
integral and gated test blocks, respectively. All test specimens shall be taken within the cross hatched
area. When the thickness T o f the test block is ≤50 mm, the longitudinal axis o f test specimens shall be
located in the centre of the test block.
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F
4.3
i
g
u
r
e
1
—
I
n
t
e
g
r
a
l
a
n
d
g
a
t
e
d
t
e
s
t
b
l
o
c
k
f
o
r
c
a
s
t
i
n
g
s
Welds in the as welded condition
Test specimens for weld procedure qualification shall be taken in accordance with the requirements o f
ISO 15614-1 or applicable design code.
The test specimens for microstructural examination shall comprise a cross section of the weld metal,
heat a ffected zones and base metal o f parts joined in full thickness.
The ferrite content shall be determined in the weld metal root and the last bead of the weld cap 2 mm
(0,08 in) below the surface. For welds with thickness less than 5 mm (0,2 in), the ferrite content shall be
determined through the full thickness.
In total, three sets of CVN test specimens shall be taken from the following positions from the weld
cap area:
— weld metal;
— fusion line;
6
© ISO 2017 – All rights reserved
ISO 17781:2017(E)
— fusion line +2 mm (0,08 in).
When the weld thickness exceeds 25 mm (1,0 in), two (2) additional sets of specimens shall be taken
from the weld root area 2 mm from the internal surface, one (1) from the weld metal and one (1) from
the fusion line +2 mm (0,08 in).
The corrosion test specimen shall include the external and internal surface and a cross sectional surface
including the weld zones in full wall thickness. The test specimens shall have a dimension of full wall
wall thickness, e.g. exceeding 25 mm (1,0 in), more than one (1) specimen can be taken to cover full
th ickne s s b y 2 5 m m (1 , 0 i n) a long the weld and 5 0 m m (2 , 0 i n) acro s s the weld . For pro duc ts with gre at
th ickne s s . I n s uch a c as e, a l l s p e ci men s s ha l l
fu l fi l
the s p e ci fie d c riteria .
5 Test methods
5.1 General
L ab orator y te s t me tho d s
for
eva luation o f the m icro s tr uc tu re o f duplex s tai n le s s s te el are a s
fol lows:
a) metallographic microstructural examination;
— check for presence of intermetallic phases and non-metallic precipitates;
— determine ferrite content;
b) CVN impact toughness testing;
c) ferric chloride corrosion test.
T here a re s evera l p a rame ters o f the materi a l m ic ro s truc tu re th at c an i n fluence the te s t re s u lts and the
u s e o f a l l th re e te s t me tho d s , as
far
as prac tic a l, i s ne ce s s ar y to demon s trate accep table qua l ity.
T h i s do c u ment s p e c i fie s how te s t re s u lts shou ld b e do c u mente d b y the te s t hou s e . M ateria l cer ti fic ation
reporting requirements are outside the scope of this document.
5.2 Microstructural examination
5.2.1
General
M icro s tr uc tu ra l exa m i nation s s ha l l b e c a rrie d out b y trai ne d and exp erience d te ch n ici an s .
5.2.2
Preparation of specimen
Metallographic preparation of duplex stainless steels shall be in accordance with ASTM E 3 and shall be
f
f
casting) after etching.
p ol i s he d to a me ta l lo graph ic fi n i sh s u itable
With
me chan ic a l
p ol i s h i ng ,
a 1
μm
or l ight op tic a l e xam i nation at m i ni mum 4 0 0 × (2 0 0 ×
d ia mond
fi na l
p ol i sh
or e qu iva lent
s ha l l
be
used
as
or
m i n i mu m .
P re ferab ly, a fi na l oxide p ol i sh (e . g. col loida l s i l ic a/a lum i na) s hou ld b e u s e d .
E le c tro p ol i sh i ng may b e u s e d a s an a lternative to me cha n ic a l p ol i s h i ng.
T he
use
o f conduc tive
mou nts
c an
a ffe c t the
s ub s e quent
mounted into a resin (thermo-setting or cold-setting).
5.2.3
S ample s
shou ld
con s e quently
be
Etching of specimens
T he b a s e c a s e e tch ant to de te c t i nterme ta l l ic ph as e s a nd the
b e p er forme d a fter fi na l p ol i sh i ng u s i ng the
—
e tch i ng.
fol lowi ng
ferrite
b a lance ele c trolytic e tch i ng shou ld
s olution:
2 0 % to 4 0 % NaOH or KOH s olution .
© ISO 2017 – All rights reserved
7
ISO 17781:2017(E)
In the case that it is of interest to detect nitrides/carbides, the following combination of two (2) solutions
in sequence with examination in between should be used (or using two test specimens):
1) 10 % oxalic acid solution or V2A etchant, followed by
2) 20 % to 40 % NaOH or KOH solution or, alternatively, see 5.3.
NOTE
For guidance on effect of different etching solutions, reference is made to Annex B. Exact etching
parameters (e.g. time, voltage, etc.) are typically established by trial and error, and can depend on factors such as
cathode material and area, specimen sur face area and alloying content.
5.2.4
5.2.4.1
Microstructural evaluation of test specimens
General
The microstructure shall be examined by optical microscopy at a magnification su fficient to observe
the presence o f any intermetallic phases and/or nitride/carbide precipitates. The entire metallographic
specimen shall be examined in the as-etched condition; starting at low magnification and followed by
progressively higher magnifications (screening).
The assessment o f the microstructure shall be made with a magnification o f minimum 400 × for all
product forms, except for castings where a 200 × magnification shall be used.
The presence and location of intermetallic phases and/or nitride/carbide precipitates shall be noted
and recorded with micrographs representative of the location(s) with the highest concentration of
intermetallic phases and the locations with the highest concentration of nitride/carbide precipitates. If
intermetallic phases and nitride/carbide precipitates are not detected, a representative micrograph at
or near mid-wall thickness shall be recorded. Micrographs shall be reported at the actual magnification
and shall include aGet
scalemore
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5.2.4.2
Acceptance criteria
The following acceptance criteria for intermetallic phases and precipitates shall apply.
a) intermetallic phases
The microstructure shall basically be free from intermetallic precipitates. However, discrete/stand-
alone intermetallic precipitates can be tolerated provided these are located in isolated areas and not
homogeneously distributed throughout the test specimen, and that the maximum dimension o f each
precipitate does not exceed 10 µm.
Micrographs included in Figure 2 are showing examples of microstructures representative of wrought
and cast products containing such isolated areas with intermetallic precipitates to a level that can be
considered borderline acceptable.
In case centreline intermetallic stringers are present, this shall be reported and acceptance of the
product shall be based upon CVN and corrosion test results.
For welds tested in the as welded condition, the microstructure shall be free from intermetallic phases.
Discrete/stand-alone intermetallic particles are acceptable given the maximum dimension of these is
≤10 µm, alternatively, the acceptance criteria o f ISO 15156-3 shall apply.
8
© ISO 2017 – All rights reserved
ISO 17781:2017(E)
a
)
W
r
b
)
F
i
g
u
r
e
2
o
C
—
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a
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d
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m
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l
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4
e
2
0
s
0
%
%
o
f
N
K
O
b
o
r
a
O
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d
e
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o
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h
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0
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×
b
l
×
m
e
m
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d
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t
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n
a
n
d
-
a
l
o
n
e
intermetallic particles for wrought products and castings
© ISO 2017 – All rights reserved
9
ISO 17781:2017(E)
b) non-metallic precipitates
I f carbide or nitride precipitates are observed, the findings shall be reported and documented, and the
acceptance shall be based upon the corrosion and CVN impact toughness test (see Table 2 and 5.5).
NOTE
Nitrides precipitate along grain boundaries and within the ferrite phase (see References [5], [6], [7]
and [8 ]). Such precipitation can decrease resistance to hydrogen embrittlement in components under cathodic
protection. Avoidance o f hydrogen embrittlement subsea is principally achieved by appropriate design to limit
service stresses/strains (see DNV/GL RP-F112 [4] ), but excessive nitride precipitation is to be avoided. While
determination of the nitride phase balance is impractical, the presence of nitrides in the ferrite phase reduces
the CVN impact toughness property, increases micro hardness in the ferrite phase and reduces the breakthrough
pitting corrosion potential (see Reference [7 ]). Quality control to avoid excessive nitrides is there fore best
achieved by meeting the impact and corrosion properties given in this specification and applying appropriate
design criteria where hydrogen embrittlement is a credible threat (see DNV/GL RP-F112 [4] ).
5.2.4.3
Reporting
The microstructural examination test report issued by the test laboratory shall, as a minimum, include
the following information:
— reference to examination procedure;
— identification o f the test specimens;
— location and orientation of extracted specimen(s);
— specimen size;
— etching method(s) used;
— magnification Get
usedmore
for examination;
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— relevant micrographs;
— statement o f findings/presence o f intermetallic phases and precipitates. I f intermetallic phases
or precipitates are identified, a micrograph with a scale bar from a view with the most densely
populated area shall be included together with a description of their distribution over the examined
specimen (s);
— statement whether the acceptance criteria are fulfilled;
— name/signature/identification o f technician.
5.3
5.3.1
Ferrite content measurement
Test standard and conditions
The ferrite content shall be determined by either point counting according to ASTM E 562 or by image
analysis according to ASTM E 1245.
The ferrite content measurement shall cover the section thickness as stated in Table 1 at views equally
spaced over the section thickness and the mean ferrite content value shall be reported.
The relative accuracy shall be 20 % maximum.
To expose the ferrite phase, the specimen shall be etched in 20 % to 40 % NaOH or KOH solution,
Beraha’s etchant (ASTM E 407, number 212 [3] ) or an alternative acceptable etchant as mentioned in
Annex B.
10
© ISO 2017 – All rights reserved
ISO 17781:2017(E)
5.3.2
Acceptance criteria
The ferrite content, in percentage by sur face/volume fraction, shall be as stated below for all duplex
grades:
— 35 % to 60 % in base material;
— 35 % to 65 % in solution heat treated weld metals;
— 30 % to 70 % for welds in the as welded condition.
5.3.3
Reporting
The ferrite content examination test report issued by the test laboratory shall, as a minimum, include
the following information:
— procedure reference and method of counting;
— location of extracted specimen;
— specimen size and etching agents used;
— magnification used during examination;
— digital micrographs with scale bar showing typical microstructure including their location;
— ferrite content; mean value of all examined views;
— the type and size o f grid used, i f applicable, number o f fields examined and relative accuracy;
— statement whether the acceptance criteria are fulfilled;
— name/signature/identification o f technician.
5.4
Charpy V-notch impact toughness test
5.4.1
Test standard and conditions
CVN impact toughness testing shall be carried out according to ISO 148-1 (KV8 ),
ASTM A 1058 at a temperature specified in Table 2 or lower.
NOTE
5.4.2
ASTM A 370 or
The use of a hammer with smaller notch radius is considered conservative and therefore acceptable.
Acceptance criteria
The minimum absorbed energy o f full size specimens is specified in Table 2 . Two quality levels are
defined. Selection o f the quality level shall be made by the end user or purchaser.
NOTE
Quality level II is in line with the acceptance level applied to the type 22/25 Cr duplex SS grades for
more than 20 years and is the recommended level for most oil and gas applications. Quality level I is intended
for special applications only. Selection o f Quality level I can limit the availability o f products with large cross
sections.
© ISO 2017 – All rights reserved
11
ISO 17781:2017(E)
T
a
b
l
e
2
—
M
i
n
i
m
u
m
a
b
s
o
r
b
e
d
e
n
e
r
g
y
r
e
q
u
i
r
e
m
e
n
t
s
f
o
r
C
h
a
r
p
y
V
-
n
o
t
c
h
i
m
p
a
c
Type of duplex Temperature a
Quality
level
Product
Plates, pipes c
20Cr Group A
a nd fi tti n gs
20Cr Group B/
22Cr/25Cr/27Cr
a
b
–46 °C/
–50 °F
Bars
Forgings,
castings and
HIP
Welds in as
welded
condition
s
o
r
b
(J) b
e
d
a
e
n
e
r
g
u
g
h
n
e
s
s
t
e
s
t
i
b
s
o
r
y
b
(J) b
e
d
e
n
e
r
g
Transverse
Longitudinal
Transverse
105
105
70
NA
80
80
55
NA
NA
QL I
QL II
QL I
QL II
QL I
QL II
QL I
QL II
85
65
85
65
70
55
45
35
60
45
50
35
n
g
y
Longitudinal
a nd fi tti n gs
Bars
Room
Forgings,
temperature, castings and
maximum of HIP products
28 °C/82 °F
Welds in as
welded
condition
Plates, pipes c
b
t
o
Minimum single
Minimum mean
a
t
60
45
NA
NA
65
50
65
50
45
35
40
27
45
35
NA
NA
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Te s ti n g at lo wer temp eratu re th a n s p e c i fie d s ho u ld b e co n s idere d accep tab le .
T he re duc tio n
fac to r s
o f energ y re qu i re ments
fo r
s ub - s i z e s p e c i me n s
s h a l l b e 5/6 a nd 2 /3
fo r
7, 5 a nd 5 m m wide
s p e c i men re s p e c ti ve l y.
c
This includes welded pipes and associated weld metal in the solution annealed condition.
5.4.3
Reporting
T he C VN te s t rep or t
from
the te s t l ab orator y sh a l l, a s a m i n i mu m, i nclude the
fol lowi ng
i n formation:
— standard of testing;
— test temperature;
— test location, direction and notch orientation of test specimen and specimen size;
—
ab s orb e d energ y va lue s;
—
s tatement whe ther the accep tance c riteri a are
fu l fi l le d .
5.5 Corrosion test
5.5.1
Test standard and conditions
A ferric chloride corrosion test in accordance with ASTM G 48, Method A shall be carried out for
3 + NaNO 3 test
solution in accordance with ASTM A 1084 shall be used. The test method and test temperature for the
different duplex grades base material and welds in the as welded condition shall be as stated in Table 3.
The test exposure time shall be 24 h for both tests methods.
Test temperature tolerance shall be ±1 °C (±1,5 °F).
typ e 2 2 C r duple x and h igher a l loye d grade s . For le aner duplex grade s , an i n h ibite d Fe C l
12
© ISO 2017 – All rights reserved
ISO 17781:2017(E)
Table 3 — Corrosion testing for di fferent grades o f duplex stainless steel
Material grade
Test standard
Minimum test
temperature base
material
Type 20Cr Group A
Type 20Cr Group B
Type 22Cr
Type 25Cr
Type 27Cr
5.5.2
ASTM A 1084
ASTM A 1084
ASTM G 48
ASTM G 48
ASTM G 48
(°C/°F)
18/64
30/86
25/77
50/122
60/140
Minimum test
temperature welds in
as weld condition
(°C/°F)
Not applicable
Not applicable
22/72
35/95
40/104
Preparation of test specimens
The whole specimen shall be pickled before being weighed and tested. Pickling shall be performed in
an acid solution following the guidance of ASTM A 380. An example for such a procedure is for 5 min at
60 °C in a solution o f 20 % HNO 3 + 5 % HF (volume fraction).
Where it is agreed to test non-pickled specimens, the test conditions are considered more aggressive
and the test should be accepted if passing the acceptance criteria.
5.5.3
Acceptance criteria
All surfaces of the test specimens shall be considered in the test.
The acceptance criteria shall be as follows.
— No pitting at 20 × magnification.
— The weight loss shall be less than 1,0 g/m 2 for products in the solution annealed condition.
— The weight loss shall be less than 4,0 g/m 2 for welds in the as welded condition.
Penetrant testing is recommended to judge i f pitting is present or not.
5.5.4
Reporting
The corrosion test report from the test laboratory shall, as a minimum, include the following
information:
— reference standard of testing;
— location of extracted specimen;
— specimen size and surface treatment/condition;
— test temperature and duration of test;
— magnification used during examination;
— weight of specimen before and after testing and weight loss in g/m 2 ;
— statement on presence of pitting;
— statement whether the acceptance criteria are fulfilled;
— name/signature/identification o f technician.
© ISO 2017 – All rights reserved
13
ISO 17781:2017(E)
Annex A
(informative)
Chemical compositions of duplex stainless steels
Table A.1
included in Table A.1
s hows the chem ic a l comp o s ition s
o f duple x s ta i n le s s s te el s . O n ly the a l loyi ng elements a re
. M a xi mu m level s o f i mpu rity elements are no t i nclude d, excep t
for
c arb on . T he
groupi ng o f a l loys i s b a s e d up on thei r nom i na l comp o s ition s and the group defi nition s i n th i s do c u ment.
T h i s me a n s that s ome a l loys may a l s o b elong to ano ther group dep endent o f the ac tua l a l loyi ng content.
Table A.1 — Chemical compositions o f duplex stainless steels
Composition range given in mass percent
UNS
No. a
EN No. a
Cb
Cr b
Ni b
Mo b
Nb
Mn b
Cu b
Type 20Cr Group A duplex, 24,0 ≤ PREN < 28,0
S32001 1.4482 0,03 19,5 to 21,5
S32101 1.4162 d 0,04 21,0 to 22,0
S32202 1.4062 d 0,03 21,5 to 24,0
S82011 — 0,03 20,5 to 23,5
1.4655 0,03 22,0 to 24,0
1,0 to 3,0
0,6
1,35 to 1,7 0,1 to 0,8
1,0 to 2,8
0,45
1,0 to 2,0 0,1 to 1,0
3,5 to 5,5 0,1 to 0,6
0,05 to 0,17 4,0 to 6,0
1,0
0,20 to 0,25 4,0 to 6,0 0,1 to 0,8
c
0,18 to 0,26 2,00
0,15 to 0,27 2,0 to 3,0
0,5
0,05 to 0,20 2,00
1,0 to 3,0
Type 20Cr Group B duplex, 28,0 ≤ PREN < 30,0
S32003 — 0,03 19,5 to 22,5
S32304 1.4362 0,03 21,5 to 24,5
S31500 1.4424 0,03 18,0 to 19,0
S81921
0,03 19,0 to 22,0
3,0 to 4,0
3,0 to 5,5
4,25 to 5,25
2,0 to 4,0
1,5 to 2,0
0,05 to 0,6
2,5 to 3,0
1,0 to 2,0
0,14 to 0,20 2,00
0,05 to 0,20 2,5 0,05 to 0,60
c
c
0,05 to 0,1
c
0,14 to 0,20 2,0 to 4,0
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Wb
c
c
c
c
c
c
c
c
Type 22Cr duplex, 30,0 ≤ PREN < 40,0 and Cr ≥ 19,5 %
J92205
0,03 21,0 to 23,5 4,5 to 6,5
S31803 1.4462 0,03 21,0 to 23,0 4,5 to 6,5
S32205 1.4462 0,03 22,0 to 23,0 4,5 to 6,5
S31200 — 0,03 24,0 to 26,0 5,5 to 6,5
S32404 — 0,04 20,5 to 22,5 5,5 to 8,5
S32506 — 0,03 24,0 to 26,0 5,5 to 7,2
S32808 — 0,03 27,0 to 27,9 7,0 to 8,2
S32900 1.4460 0,08 23,0 to 28,0 2,5 to 5,0
S82011
0,03 20,5 to 23,5 1,0 to 2,0
S82122
0,03 20,5 to 21,5 1,5 to 2,5
S82551
0,03 24,5 to 26,5 4,5 to 6,5
a
b
c
d
14
2,5 to 3,5
2,5 to 3,5
3,0 to 3,5
1,2 to 2,0
2,0 to 3,0
3,0 to 3,5
0,8 to 1,2
1,0 to 2,0
0,10 to 1,0
0,60
0,75 to
2,00
0,10 to 0,30
0,08 to 0,20
0,14 to 0,20
0,14 to 0,20
0,20 to 0,30
0,08 to 0,20
0,30 to 0,40
c
1,50
1,0
c
c
2,00
c
c
2,00
c
c
2,00
2,00
1,0 to 2,0
1,00
0,05 to 3,0
c
1,10
2,1 to 2,5
c
c
1,0
c
0,15 to 0,27 2,0 to 3,0
0,5
c
0,15 to 0,20 2,0 to 4,0 0,5 to 1,5
c
0-10 to 0,35 1,5
2,0 to 3,0
T he chem ic a l co mp o s i tio n g i ve n b y the U N S N o s . a nd E N s te e l N o s . a re s i m i l a r, b ut no t e qu i va le nt.
Single values denote a maximum allowable.
C he m ic a l e leme nt no t vo lu nta r i l y adde d a nd wi th co m mo n l y o b ta i ne d re s idu a l le ve l .
These grades are patented.
© ISO 2017 – All rights reserved
ISO 17781:2017(E)
Table A.1 (continued)
UNS
No. a
J93404
J93380
S31260
S32520
S32505
S32550
S32750
S32760
S32906
S32950
S39274
S39277
S33207d
S32707d
a
b
c
d
EN No. a
—
1.4507
1.4507
1.4410
1.4501
1.4477
—
Cb
0,03
0,03
0,03
0,03
0,03
0,04
0,03
0,03
0,03
0,03
0,03
0,025
Cr b
Ni b
Mo b
Nb
Mn b
Type 25Cr duplex, 40,0 ≤ PREN < 48,0
24,0 to 26,0
24,0 to 26,0
24,0 to 26,0
24,0 to 26,0
24,0 to 27,0
24,0 to 27,0
24,0 to 26,0
24,0 to 26,0
28,0 to 30,0
26,0 to 29,0
24,0 to 26,0
24,0 to 26,0
6,0 to 8,0
6,5 to 8,5
5,5 to 7,5
5,5 to 8,0
4,5 to 7,0
4,5 to 6,5
6,0 to 8,0
6,0 to 8,0
5,8 to 7,5
3,5 to 5,2
6,0 to 8,0
6,5 to 8,0
4,0 to 5,0
3,0 to 4,0
2,5 to 3,5
3,0 to 4,0
2,9 to 3,9
2,9 to 3,9
3,0 to 5,0
3,0 to 4,0
1,5 to 2,6
1,0 to 2,5
2,5 to 3,5
3,0 to 4,0
0,10 to 0,30 1,50
0,20 to 0,30 1,0
0,10 to 0,30 1,00
0,20 to 0,35 1,50
0,25 to 0,30 1,50
0,10 to 0,25 1,50
0,24 to 0,32 1,20
0,20 to 0,30 1,00
0,30 to 0,40 0,80 to 1,5
0,15 to 0,35 2,00
0,24 to 0,32 1,0
c
0,23 to 0,33
Wb
c
c
c
c
c
c
1,0
1,0
c
c
0,5 to 1,0 0,5 to 1,0
0,2 to 0,8 0,1 to 0,5
c
0,5 to 2,0
c
1,50 to 2,50
c
1,5 to 2,5
0,5 to 1,0 0,5 to 1,0
c
0,8
0,2 to 0,8 1,5 to 2,5
1,2 to 2,0 0,8 to 1,2
Type 27Cr duplex, 48,0 ≤ PREN ≤ 55,0 and Cr ≤ 33,0 %
1.4485 0,03 29,0 to 33,0 6,0 to 9,0 3,0 to 5,0 0,40 to 0,60
1.4658 0,03 26,0 to 29,0 5,5 to 9,5 4,0 to 5,0 0,30 to 0,50
Cu b
1,5
1,50
T he chem ic a l c o mp o s i tio n g i ven b y the U N S N o s . a nd E N s te e l N o s . a re s i m i l a r, b ut no t e qu i va le nt.
Single values denote a maximum allowable.
C hem ic a l e le ment no t vo lu nta r i l y adde d a nd wi th co m mo n l y o b ta i ne d re s idu a l le vel .
These grades are patented.
© ISO 2017 – All rights reserved
15
ISO 17781:2017(E)
Annex B
(informative)
Preparation and etching for microstructural examination
Examples of suitable etching methods are given in Table B.1 . These methods are generally applicable for
all commercially available duplex stainless steel alloys. The specified etchants are based on the ability
to reveal phases o f interest, achieve contrast between constituents, consistency and ease o f use. Exact
parameters are typically best established by trial and error and may depend on factors such as cathode
material and area, geometry o f the electrochemical cell, and specimen sur face area and alloying content.
The electrolytic etching techniques described are per formed as direct current electrolysis with
the specimen as anode. Cathode material may be, for example, stainless steel or platinum. Electrical
connection to the sample sur face can be made, for example, by touching it with a platinum (or other
noble material) wire. Electrolytic etching generally provides more reproducible and consistent results
than chemical and colour etching alternatives. Uneven etching of the specimen surface is, however,
o ften encountered, generally with heavier etching near edges.
For further in formation o f specific etchants, re ference is made to ASTM E 407 [3] .
Identification and evaluation o f non-metallic inclusions, cracks, pores, etc. is best per formed in the aspolished condition. Metallographic specimens should consequently also be examined in the as-polished
condition prior to etching and after each step in etching.
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© ISO 2017 – All rights reserved
ISO 17781:2017(E)
T
Method
a
b
l
e
B
.
1
—
E
x
ASTM E 407
Etchant No.
a
m
p
l
e
s
o
f
s
u
i
t
a
Composition
b
l
e
e
t
c
h
i
n
g
m
e
t
h
o
d
s
f
o
r
d
u
p
l
e
x
s
t
a
i
n
l
e
s
s
s
t
e
e
l
s
Application of etching
Electrolytic etching. Typically at 5 V to 7 V for 5 s to 60 s.
Lower voltages at longer times may also be used. Excellent for
10 % oxalic
13
delineating microstructure.
10 g oxalic acid Recommended for detecting nitride precipitates. May over100 ml H 2 O
etch intermetallic precipitates and small segregations quite
rapidly. I f a two-step etching procedure is per formed, a repol ishing or another specimen is recommended.
Poor contrast between austenite and ferrite phases.
Electrolytic etching. Typically at 1,5 V to 3,0 V for 5 s to 10 s.
20 % NaOH
220
V2A etchant 104 mod
20 g NaOH
100 ml H 2 O
5 ml HNO 3
50 ml HCl
50 ml H 2 O
Colours ferrite and intermetallic phases.
Recommended for ferrite measurements and the detection of
intermetallic precipitates. Considered not applicable for detection of nitrides.
Other solutions containing varying content o f NaOH or KOH
may also be used with similar results. The conditions for
etching should be adjusted and qualified to veri fy acceptable
results.
To be used fresh and never be stored.
Etching performed at room temperature and up to 60 °C.
Recommended etchant for detecting intermetallic phases and
nitride precipitates.
Poor contrast between austenite and ferrite phases. Not
suitable.
Electrolytic etching. Typically at 1,0 V to 2,0 V for 10 s to 120 s
60 % HNO 3
219
60 ml HNO 3
40 ml H 2 O
(with stainless steel cathode).
Highly sensitive to voltage and cathode material.
Good for delineating microstructure. Reveals intermetallic
phases and nitride precipitates. Darkens ferrite slightly.
Colour etching. To be used fresh.
Murakami’s 98
Beraha’s
212
10 g K 3 Fe(CN) 6
10 g KOH
100 ml H 2 O
Various modifications o f etchant composition may be used.
At 20 °C: Reveals carbides a fter short times. May reveal intermetallic phases (vaguely) a fter approx. 3 min.
At 75 °C to 100 °C: May reveal intermetallic phases clearly.
Etches/colours ferrite. Considered not applicable for detection
of nitrides.
Colour etching. To be use fresh.
Immerse at room temperature until sample colouration is
0,5 g to 1 g K 2 SO 5 observed.
HCl content may be varied depending in corrosion resistance
20 ml HCl
o f alloy.
100 ml H 2 O
Good contrast between austenite and ferrite phases.
Not applicable for detection of intermetallic phases and
nitrides.
NOTE These recommendations only cover a limited selection o f etchants. Numerous other etching procedures suitable for
duplex stainless steels can be found in published literature or acquired from other sources.
© ISO 2017 – All rights reserved
17
ISO 17781:2 017(E)
Bibliography
[1]
ISO 15156-3,
Petroleum and natural gas industries — Materials for use in H2S-containing
environments in oil and gas production — Part 3: Cracking-resistant CRAs (corrosion-resistant
alloys) and other alloys
[2]
[3]
[4]
[5]
ASME Boiler and pressure vessel code, section VIII Pressure vessels
ASTM E 407, Standard practice for microetching metals and alloys
DNV/GL RP-F112, Design of duplex stainless steel subsea equipment exposed to cathodic protection
N
J.O., & C
G. The physical metallurgy of duplex stainless steel. Sandvik Materials
[6]
N
D
I
.
High-performance
stainless
steels .
http:// www .nickelinstitute .org/ en/ TechnicalLit erature/ Reference % 2 0 B o ok % 20
Series/11021 _HighPerformanceStainlessSteels .aspx
B
G. R. F
and G. W
. Variation in Mechanical Properties and Corrosion
Resistance o f Different Alloys within the Generic Designation UNS S32760. Presented at Duplex
[7]
i l s s on
h ai
Technology, R&D Centre, S-81181 Sweden
ic ke l
yrn e
e ve l opm e n t
r anc i s
ns t i t u t e
arb u rton
2000, Houston, TX, USA, February 2000
[8]
M
J.
Mannesmann Forschung GmbH
and
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entz
M. F rom m e rt , K. M ah jou b , J S i e km e ye r
J. Kon r ad Correlation of nitride
precipitates and mechanical properties in 25%Cr – SDSS super duplex stainless steel
. Salzgitter
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