atw 2018-02

inforum

atw Vol. 63 (2018) | Issue 2 ı February

DECOMMISSIONING AND WASTE MANAGEMENT 106

Material

Material

description

A comprehensive description of the

sample shape and treatment has been

published [19]. Further experiments

included contact samples where

different steels were screwed together

in close contact and corrosion tests

under γ irradiation. The whole suite of

steels under investigations ale listed in

Table 1.

Two different sample types were

produced to test the materials for

mass loss, pitting corrosion, crack

corrosion and stress corrosion

Material

number

Density

g/cm 3

Ni based alloys Hastelloy C4 Ni Mo 16 Cr 16 Ti 2.4610 8.669

Ti alloys Titan – Palladium Ti 99.7 – Pd

Ti 99.7 - Pd EG

Fe based alloys Fine-grained steel FStE 255

TStE 460

15 Mn Ni 6.3

DC 01 / St 12

ST 37-2

Cr-Ni steel

Cu alloys

Nodular cast steel

Ni-Resist D2

Ni-Resist D4

Nirosta

GGG 40.3

GGG-Ni Cr 20.2

GGG-Ni Si Cr 30.55

X2CrNi19-11

Cu.99

Cu-Ni 70/30

Cu-Ni 90/10

Ni alloys Nickel 99.9

Ni/Cu 70/30

| | Tab. 1.

Metal alloys for construction of waste canisters under investigation at KIT-INE.

3.7025

3.7035

1.0566

1.8915

1.6210

1.0330

1.0038

0.7043

0.7660

0.7680

1.4833

1.4306

4.0000

4.7000

4.9000

2.4068

2.4360

4.593

4.593

7.814

7.671

7.512

7.85

7.856

6.955

7.36

7.596

8.022

7.956

9.198

8.866

8.998

8.48

8.51

cracking (SCC). For the determination

of the mass loss, sheet metal specimens

with the dimensions 40 mm ×

20 mm were cut in the respectively

available sheet thicknesses. The mass

loss was determined only in the case

of samples in the delivery condition.

The susceptibility to pitting corrosion

as well as the susceptibility to crack

corrosion could be assessed also.

The Ni-Resist steels have been

included in the investigation program

because these steels are specified for

handling salt solutions such as sea

water. Lower uniform corrosion rates

were expected as in the case of fine

grained steel. After the exposure time,

the samples were recovered from the

corrosion medium and the specimens

were cleaned from the adhering salts

and corrosion products by pickling in

suitable solutions according to ASTM

guidelines [20]. Then the specimens

were cleaned in alcohol and examined

for general and local corrosions as

well as for stress corrosion cracking.

The general corrosion (integral corrosion

rate) was calculated from the

integral weight losses determined by

gravimetry and from the respective

material densities. The specimens

were examined for local corrosion and

stress corrosion cracking by microscopic

evaluation and with the help of

metallographic cross-sections, measurements

of pit depths and surface

profiles.

Results and discussion

General corrosion

Due to the fact that localized corrosion

processes are observed in the

experiments, the mass loss rate is used

for comparisons. The general corrosion

rate relies on uniform corrosion

of the surfaces and is not considered

reasonably for alloyed steel. Figure 1

and Figure 2 show the mass loss and

the corresponding mass loss rates for

a) mass loss

b) mass loss rate

| | Fig. 1.

Measured mass loss and mass loss rates of Hastelloy in MgCl 2 -rich (red) and NaCl solution (blue) as function of time at various temperatures.

a) mass loss

b) mass loss rate

| | Fig. 2.

Measured mass loss and mass loss rates of Cr-Ni steels (1.4306 and 1.4388) in MgCl 2 -rich (red) and NaCl solution (blue) as function of time at 150 °C.

Decommissioning and Waste Management

Corrosion Processes of Alloyed Steels in Salt Solutions ı Bernhard Kienzler

More magazines by this user