ISO 9350:2025

International
Standard
ISO 9350
First edition
Corrosion of metals and alloys —
2025-08
Testing method of corrosion
resistance for hafnium at high
temperature and pressure
Corrosion des métaux et alliages — Méthode d'essai de la
résistance à la corrosion du hafnium à haute température et
pression
Reference number
© ISO 2025
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Significance . 2
6 Reagents and materials . 2
7 Apparatus . 2
8 Hazards . 3
9 Sampling, test specimens and test units . 3
10 Preparation of apparatus . 3
11 Calibration and standardization . 3
11.1 Coupon preparation .3
11.2 Autoclaves .4
11.3 Use of control coupons.4
11.4 Calibration .5
12 Conditioning . 5
12.1 Test water quality .5
12.2 Autoclave load restrictions .5
12.3 Test conditions .5
12.3.1 Temperature .5
12.3.2 Pressure .5
12.3.3 Time .5
12.3.4 Tests .5
12.4 Specimen preparation .6
12.4.1 Etched specimens .6
12.4.2 As-manufacturer specimens .6
13 Procedure . 6
13.1 Inspection of specimens . .6
13.2 Dimensions, weight and inspection .6
13.3 Autoclaving .6
13.3.1 Placing of test specimens .6
13.3.2 Venting method A .6
13.3.3 Refreshed autoclaving, method B .7
13.4 Post-test measurements and inspection .7
14 Calculation or interpretation of results . 7
14.1 Calculation of mass gain .7
14.2 Visual interpretation of surface appearance .8
14.3 Invalid tests .8
15 Test report . 8
Annex A (informative) Guide to specimen preparation . 9
Bibliography .11

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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This document was prepared by Technical Committee ISO/TC 156, Corrosion of metals and alloys.
Any feedback or questions on this document are directed to the user’s national standards body. A complete
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iv
Introduction
Hafnium has a high-capture cross section for thermal energy. It is used in nuclear reactors. Hafnium is
typically manufactured into rods, plates, sheets and strips. It is used as a neutron absorption material.
This document establishes a test method for the corrosion of hafnium. The water corrosion test is a useful
way to evaluate the properties of hafnium. The corrosion test can determine the performance of hafnium
products in reactors. The parameters of the corrosion test are different to the parameters of tests for other
materials. This is why a test method for the corrosion of hafnium is necessary.
This document establishes a corrosion test and requirements for hafnium material and provides a basis for
consistency across different laboratories. This document also gives the performance prediction of hafnium
products in service.
v
International Standard ISO 9350:2025(en)
Corrosion of metals and alloys — Testing method of corrosion
resistance for hafnium at high temperature and pressure
WARNING — The use of this document can involve hazardous materials, operations and equipment
(see Clause 8). It is the responsibility of the user of this document to consult and establish appropriate
safety and health practices and determine the applicability of regulatory limitations prior to use.
1 Scope
This document specifies:
a) the determination of mass gain;
b) the surface inspection of products of hafnium when corrosion tested in water at 360 °C.
This document is applicable to hot-work or cold-work hafnium rods, wires, plates, sheets and strips.
This method has been widely used in the development of hafnium products. It is applicable for use in its
entirety to the extent specified for a product acceptance test, rather than merely a means of assessing
performance in service of pressurized water reactor.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
etching
process to remove surface metal by action of acids in water
3.2
control coupon
hafnium specimen of known performance used to monitor the validity of the test
4 Principle
Specimens of hafnium are exposed to high-pressure water at 360 °C for 672 h. The corrosion is normally
measured by the gain in mass of the specimens and inspected by the appearance of an oxide film on the
specimen surfaces. The test pressure in water is 18,7 MPa. The pressure is also determined by the contractor
requirements.
5 Significance
Specimens are normally tested after careful etching and rinsing. Specimens with as-manufactured surfaces
may also be tested without further surface removal.
6 Reagents and materials
During the test, unless otherwise stated, only reagents of recognized analytical grade and only water as
described in 6.1 or 6.2 are used.
6.1 Grade A water, purified water having an electrical resistivity of not less than 1 MΩ·cm at 25 °C as
measured before the start of the test.
6.2 Grade B water, deionized or demineralized water having an electrical resistivity of not less than
0,5 MΩ·cm at 25 °C. Grade A water can be used instead of grade B water.
6.3 Detergents and solvents for specimen cleaning including ethanol and acetone.
6.4 Concentrated hydrofluoric acid (HF).
6.5 Concentrated nitric acid (HNO ).
6.6 Control coupon.
6.7 Argon gas, of purity 999,9 ml/l or higher.
7 Apparatus
The apparatus consists of equipment for:
a) etching the specimen when required;
b) measuring the specimens’ surface area and mass, the water resistivity and pH, the test temperature and
pressure, the etch and rinse temperature;
c) performing the water corrosion tests at elevated temperatures and pressures.
7.1 Etching equipment, comprising an acid bath, a running water rinse and a deionized water rinse for
proper metal removal and stain-free rinsing. Polyethylene or polypropylene tanks are commonly used with
a bottom feed for running water rinses. Polytetrafluoroethylene (PTFE) tank can also be used for running
water rinses. Specimen hangers are generally made of type 300 series stainless steel. When many specimens
are processed, a mechanical dipper for the etching process is useful.
7.2 Autoclaves, constructed of type 300 series stainless steel or nickel base alloys such as W. Nr.2.4816 or
W.Nr.2.4642. The autoclave is fitted with devices for measurement and control of pressure and temperature,
safety devices and venting valves. Control systems for pressure and temperature are adequate to meet the
requirements of this document. Sample holders and other internal accessories are also constructed of type
300 or type 400 series stainless steel, or nickel-base alloys such as W. Nr.2.4816 or W.Nr.2.4642.
7.3 Specimen size measuring equipment, accurate to 20 μm.
7.4 Analytical balance, accurate to 0,1 mg.

8 Hazards
The chemicals used in preparing specimens for this test are hazardous. Detailed information on the safe
handling of organic compounds, acids and products of hafnium are obtained from the commercial market.
High-temperature, high-pressure autoclave operation is in accordance with the manufacturer's instructions.
Cold water is not added directly to the autoclave vessel in order to accelerate cooling upon the completion of
testing.
9 Sampling, test specimens and test units
The size and the quantity of the test specimens, the method of selection, surface preparation and test
acceptance criteria are specified in the product specification or by agreement between the purchaser and
the seller as stated in the purchase contract.
Each specimen and control coupon is individually identified.
10 Preparation of apparatus
10.1 General requirements for new or reworked autoclaves (7.2) and parts of autoclaves previously used
for testing materials other than in accordance with this document are as follows:
a) Before specimens are tested in a new or reworked autoclave, or in one having new valves, tubing,
gaskets, etc. which are in contact with the test specimen, clean the apparatus thoroughly, wipe with
ethanol or acetone (6.3) and rinse twice with grade B water (6.2).
b) Dry the autoclave or auxiliary equipment by vacuum cleaning, or drain and wipe with a clean, lint-free
cloth. Inspect carefully to ensure freedom from contamination. Visible contamination includes lubricant,
residues, dust or dirt, loose oxides or rust, or an oil or grease film on the water surface, internal surface,
gasket or
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