GB/T 40393-2021 PDF English
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Corrosion of metals and alloys -- Accelerated corrosion test for intergranular corrosion susceptibility of austenitic stainless steels
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GB/T 40393-2021: PDF in English (GBT 40393-2021) GB/T 40393-2021
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 77.060
CCS H 25
Corrosion of metals and alloys -- Accelerated corrosion test
for intergranular corrosion susceptibility of austenitic
stainless steels
(ISO 21610:2009, MOD)
ISSUED ON: AUGUST 20, 2021
IMPLEMENTED ON: MARCH 1, 2022
Issued by: State Administration for Market Regulation;
Standardization Administration of PRC.
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Normative references ... 5
3 Terms and definitions ... 6
4 Specimens ... 6
5 Test methods ... 11
6 Evaluation of intergranular corrosion ... 13
7 Test report ... 17
Appendix A (Informative) The technical differences between this document and ISO
21610:2009 (including their reasons) ... 18
Appendix B (Informative) Recommended sizes of standard specimens and the chemical
and electrolytic cleaning steps to remove corrosion products ... 20
References ... 23
Corrosion of metals and alloys -- Accelerated corrosion test
for intergranular corrosion susceptibility of austenitic
stainless steels
Warning -- Some of the reagents used in this test method are corrosive and shall
be handled with care. If the skin is splashed by it, rinse immediately with water;
severe cases shall be treated immediately.
1 Scope
This document specifies an accelerated test method for determining the susceptibility
to intergranular corrosion of austenitic stainless steel.
This document applies to the testing of a variety of metal products, including double
rolled metal, welded joints, deposited metal, and weld metal.
Note 1: The results obtained by this method are the same as those obtained by the methods in the ISO
3651-1 and ISO 3651-2 standards, but the accelerated corrosion test cycle is shorter.
Note 2: This document specifies two test methods:
--- Method A: Corrosion test in copper sulfate and concentrated sulfuric acid solutions in the presence
of metallic copper;
--- Method B: Corrosion test in copper sulfate, sulfuric acid, and copper fluoride solutions in the
presence of metallic copper.
2 Normative references
The following documents are essential to the application of this document. For the dated
documents, only the versions with the dates indicated are applicable to this document;
for the undated documents, only the latest version (including all the amendments) is
applicable to this standard.
GB/T 10123 Corrosion of metals and alloys -- Basic terms and definitions (GB/T
10123-2001, ISO 8044:1999, IDT)
ISO 3651(all parts) Determination of resistance to intergranular corrosion of
stainless steels
a) For plate specimens, segmental specimens, cylindrical specimens with a diameter
not exceeding 5 mm, and tubular specimens with a diameter not exceeding 5 mm,
angle bending should be (90±3)°;
b) Annular and tubular specimens with a diameter exceeding 5 mm should be
flattened and formed into cones;
c) Examine the curved surfaces in cross-sectional regions with sufficient thickness
to identify intergranular cracks.
4.4 Machining the blank to prepare the specimen of the required thickness:
a) The metal plate should be sampled from one side only; if one of the sides is treated,
then take samples from the treated side;
b) The rolled metal (rolled sections and profiles), forgings, castings, and tubular
samples should be sampled from a suitable surface;
c) The hot-deformed or cold-deformed pipe should be sampled from the outside;
d) The hot-rolled pipe should be sampled from the inner or outer surface;
e) The pipe that has been exposed to the service environment should be sampled
from the side that is in contact with the service environment.
4.5 The following kinds and types of specimens should be prepared from welded joints
(see Table 2):
--- Prepare Type I or Type II plate specimens from welded joints of plate metal, rolled
sections, castings or forgings;
--- Prepare Type II annular, tubular, or segmental specimens from electric welded
pipes;
--- Prepare Type I segmental, annular, or tubular specimens from girth welded joints
of pipe sections;
--- Prepare Type I or II plate specimens, or Type I segmental, annular, or tubular
specimens from welded joints of double-wall tubes.
4.6 For welded specimens (Table 2, Type I and Type II), the weld reinforcement should
be removed with a depth not exceeding 1 mm.
The required thickness of the specimen should be achieved by machining, and the metal
should be removed from the side that is not in contact with the corrosive medium. If it
is not sure which side is in contact with the corrosive medium, the machining should be
processed on the side where the weld metal is least heated during the welding process.
If it is necessary to reduce the wall thickness of the specimen, sampling should be
carried out in accordance with 4.4.
4.7 The inspection of electrodes, filler wires, and strips shall be carried out through the
fabricated surfacing or weld metal.
The surfacing metal shall be tested with plate specimens (see Table 2). The specimen
shall be cut from the multi-layer surfacing metal made of the inspected welding material
(the surfacing metal substrate is not used for specimen preparation, and can be prepared
from materials with similar chemical compositions). When the chemical composition
of the metal substrate is similar to that of the surfacing metal, the number of surfacing
metal substrates not used for specimen preparation can be reduced to 3 layers.
The weld metal is tested with plate specimens cut from the upper layer of the multi-
layer welded seam of the welded joint. The welded seam thickness of the cut specimen
area should not be less than 15 mm. The chemical composition of the plate used for the
welded joint should be similar to the chemical composition of the weld metal.
Welded backing plates can be used when using thin plates to obtain the welded seam of
desired thickness. The chemical composition of the steel for welded backing plate is
similar to the thin plate. When welding the edge of the thin plate specimen initially, the
entire surface of the welded backing plate should be similarly treated.
Weld metal testing should be carried out on plate welded specimens (see Types I and II
in Table 2) prepared from specially-made welded joints. The welded joints are made of
intergranular-corrosion-resistant steel and welding consumables to be evaluated.
4.8 The recommended size of the specimen is shown in Appendix B, and different
specimen sizes can also be used.
4.9 When testing plates, pipes, metal profiles, wires, and strips, at least two specimens
should be prepared for each group.
For all types of steels and alloys, at least 4 specimens (two of which are used for
comparison) should be prepared for each forging, casting, and weldment.
The control specimen should be bent 90°±3° and not be exposed to the boiling test
solution. If the specimen needs to be inspected from both sides, then the specimen
should be bent into a “Z” shape.
4.10 The sensitization treatment of unstabilized steel is as follows: on the premise of no
special requirements in the technical documents, if the unstabilized steel does not
contain titanium or niobium, the maximum carbon content is greater than 0.03% and it
is used under the delivery conditions, then the sensitization treatment test should be
carried out on the specimen of the delivery conditions.
(11±1)mL HNO3 (ρ20=1.35 g/mL);
(955±3)mL H2O;
Temperature: 40 °C~50 °C;
Current density 0.5×104 A • m-2~0.6×104 A • m-2.
The oxide coating on the specimen should be thoroughly removed, and the specimen
should be carefully rinsed with water after etching.
It can be removed by other etching solutions or methods that can ensure the complete
removal of the oxide coating. For intergranular corrosion-resistant steels, it is necessary
to prevent preferential erosion or pitting along the grain boundaries.
When there are any differences in the test results, only the above solutions should be
used for etching.
4.12 During the polishing or grinding process of the specimen, the surface should be
prevented from overheating, and the surface roughness of the processed specimen
should not exceed 0.8 µm.
Unless otherwise stated in the technical documents, specimens made of cold-deformed
and heat-deformed tube or cold-drawn metal products, or made of metal products with
special surface treatment, should not be polished or ground.
4.13 Mark the specimen before testing. At one or both ends of the specimen, the position
with a distance of 5 mm~10 mm from the edge shall be marked by means of steel
stamping or electrical discharge machining.
4.14 Degrease the specimen with a suitable organic solvent (reagent grade) before
testing. The degreasing step may be omitted if the specimen is placed directly in the test
vessel after the etching or rinsing step.
5 Test methods
5.1 Method A
5.1.1 Method principle
The steel specimen shall be placed together with the metallic copper in a solution made
up of H2SO4 and CuSO4 • 5H2O, and the concentration of which shall be higher than
the concentration of the solution extracted by the method specified in ISO 3651-2.
This method is an accelerated test method and can be used for the verification of steel
grading specified in ISO 3651-2.
5.1.2 Test solution
Use analytical reagents to prepare the test solution: add (50±0.1) g of CuSO4 • 5H2O to
(1000±3) mL of water, and then gradually add (250±3) mL of H2SO4 (ρ20=1.84 g/mL).
5.1.3 Test steps
5.1.3.1 The test shall be carried out in a glass flask with a condenser tube, or a container
made of corrosion-resistant stabilized chromium-nickel steel with a lid and a condenser
tube. Spread a layer of copper chips on the bottom of the reaction vessel, and then place
the specimen in.
The following operations can be performed:
a) Use a perforated copper plate with a sharp edge (bore diameter shall be 5 mm~7
mm) to replace the copper chips, so that the upper and lower sides of the specimen
can be fully contacted with the copper plate; it helps to ensure that the test solution
can fully rinse the sample and the corrosion products are well removed. If there
is a discrepancy in the assessment of metal quality, copper chips should be used
for the test.
b) When the two sides of the specimen are in full contact with the copper chips or
copper plate, a multi-layer of specimens can be placed. The test solution should
be at least 20 cm higher than the uppermost specimens, copper chips, or copper
plate.
After the solution is poured into the container, heat it to the boiling point and boil it, see
5.1.3.3 for details.
5.1.3.2 The heating of the condenser tube shall be avoided.
5.1.3.3 The boiling time shall be (8.00±0.25) h. In the case of forced interruption of the
test, the specimen should not be taken out of the test solution. The test time is the sum
of all boiling periods.
5.1.3.4 If there is a difference in the results of the interrupted test, it is advisable to use
a glass flask and continuously expose the specimen to the boiling solution to repeat the
test. At this time, the amount of solution calculated according to the surface area of the
specimen should not be less than 10 mL/cm2.
5.1.3.5 After the test is finished in the boiling solution, rinse the specimen with tap
water and blow-dry it. Use 20%~30% nitric acid solution to remove the copper attached
to the surface of the specimen that cannot be washed away with water.
5.1.3.6 The test solution without discoloration can be reused. The exception is when
there is a dispute between the parties involved over the experimental results.
6.8 Check the bent specimen with a magnifying glass of 8 times to 12 times.
6.9 If no cracks (except longitudinal cracks or edge cracks) are found in the bent
specimen after the test, the material can be considered to be resistant to intergranular
corrosion. If cracks are found, the test can be repeated according to ISO 3651-2.
6.10 After exposure to the test solution and during or after bending:
a) The control sample is broken;
b) Cracks are found on the bent specimen after the test (except for longitudinal cracks
or edge cracks);
c) The thickness of the specimen is less than 0.1 mm, and no intergranular corrosion
is found;
d) Due to the size, the specimen cannot be bent.
Intergranular corrosion susceptibility shall be assessed by metallographic methods.
6.11 Before performing the intergranular corrosion susceptibility evaluation on the
specimen after the corrosion test, the specimen for the metallographic examination
should be cut from the cutting plane that is perpendicular to the tested surface of the
corrosion specimen. For the metallographic specimen prepared from the welded
specimen, the cutting line should be perpendicular to the welding fusion line, and the
cutting section should include the weld metal and the heat-affected zone metal. The
recommended length of the metallographic specimen (calculated by the surface to be
measured) is 15 mm~20 mm. The cutting section should meet the surface requirements
of the metallographic specimen. Metallographic specimens should be prepared in a
manner that does not produce corner breakage or burrs.
6.12 In order to show intergranular corrosion and evaluate the depth of corrosion cracks,
the metallographic specimens are inspected under a magnification of 200 after etching.
Erosion should only slightly corrode the grain boundaries. See B.2 for recommended
etching solutions and procedures. The entire surface area of the metallographic
specimen to be tested shall be examined. The maximum depth of corrosion shall be
assessed from 6 different fields of view. These fields of view shall contain the location
of the maximum intergranular corrosion depth.
6.13 If the maximum corrosion depth obtained by metallographic evaluation does not
exceed 30 µm, the material is resistant to intergranular corrosion (unless otherwise
required by the metal product specification). For metal product specimens with a
thickness of less than 1.5 mm, the maximum depth of corrosion should not exceed 10
µm.
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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