Appendix V3.08

U-864 SUPPLEMENTARY REPORT

Material Testing of Steel Plate from Side of Keel Box on U-864 DNV GL AS

APPENDIX v3.08 Environmental measures for the wreck of U-864 Material Testing of Pressure Hull Specimen Project name: Environmental measures for the wreck of U-864 DNV GL AS

Project Management & Technical Services Program P.O.Box 300 1322 Høvik Norway Tel: +47 67 57 99 00

Report title: Material Testing of Pressure Hull Specimen Customer: DNV GL AS, Contact person: Date of issue: 2014-02-20 Project No.: PP079848 Organisation unit: Project Management & Technical Services

Program Report No.: , Rev. Document No.:

Prepared by: Verified by: Arild Oscar Tjærnes(DNV GL AS) Torstein Alexander Pettersen (DNV GL AS) Dato: 12.5.2014

Mario Søfferud (DNV GL AS)

Reference to part of this report which may lead to misinterpretation is not permissible

APPENDIX v3.08 Environmental measures for the wreck of U-864 Material Testing of Pressure Hull Specimen

Table of contents

1 EXECUTIVE SUMMARY ..................................................................................................... 1

2 INTRODUCTION .............................................................................................................. 2

3 TESTING ........................................................................................................................ 3 3.1 Visual Examination 3 3.2 Chemical Composition Analysis 5 3.3 Metallographic Examination 6 3.4 Thickness Measurements 8 3.5 Hardness Measurements 8 3.6 Mechanical testing 9

4 CONCLUSIONS ............................................................................................................. 10

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1 EXECUTIVE SUMMARY The German submarine U-864 was torpedoed by the British submarine Venturer 9th of February 1945, approximately 2 nautical miles west of the Island Fedje in Hordaland. The submarine was loaded with war material, and according to historical documents approximately 67 ton of floating metallic mercury in steel canisters stored in the keel.

In 2013 DNV-GL was assigned by the Norwegian Coastal Administration to carry out a pre-project that will assess the possibility of recovering the mercury canisters from the wreck parts before capping the wreck parts and the polluted seabed-area.

As part of this task, a steel sample from the keel side plate of U-864 has been taken, in order to determine the material properties.

The steel sample taken has been tested in the DNV laboratories at Høvik, Norway. To assess the properties of the material, the following tests have been performed:

• Visual inspection • Chemical composition analysis • Metallographic examination • Thickness measurement • Hardness measurement • Mechanical testing

The main conclusions are:

• The chemical composition is as expected for low-carbon steel plate. The sulphur level is somewhat high, which is shown in the microstructure as a relatively high amount of MnS inclusions. The microstructure is otherwise normal for hot rolled plate.

• The impact testing gave an average of 38.5 J at 0 °C, which is above what is considered brittle.

• The tensile strength is also as expected for this type of material, with a relatively low tensile strength of 440 MPa and good ductility. This strength level/hardness corresponds to a S235 (EN10025) type of steel, or grade NV B.

• Due to little corrosion in the plate, the reduction in plate thickness is minimal. • When cutting this steel plate, no special considerations should be necessary.

Equipment for cutting soft carbon steel should suffice.

2 INTRODUCTION The German submarine U-864 was torpedoed by the British submarine Venturer 9th of February 1945, approximately 2 nautical miles west of the Island Fedje in Hordaland. U-864 was on its way from Germany via Norway to Japan. The submarine was loaded with war material, and according to historical documents approximately 67 ton of floating metallic mercury in steel canisters stored in the keel. The torpedo split the submarine into two parts. The wreck parts were discovered by the Royal Norwegian Navy at a depth of approximately 150-175 m. Several studies have revealed feasible measures for pollution abatement. The risks related to these measures have been assessed and indicate the following:

• High mercury concentrations in the soil, especially around the wreck parts. • The bow section is inclining and has a high risk of sliding downhill. (Geotechnical

unstable) • Torpedoes and ammunition in general. • Oil in the wreck. • The condition of the two wreck parts. • The condition of the mercury canisters.

In 2013 DNV-GL was assigned by the Norwegian Coastal Administration to carry out a pre-project that will assess the possibility of recovering the mercury canisters from the wreck parts before capping the wreck parts and the polluted seabed-area. As part of the assignment, competent subsea companies have been invited to discuss feasible solutions and cost pertaining to the proposed solutions.

3 TESTING 3.1 Visual Examination The sample sent for examination was rust coloured. Very little local corrosion on the surface of the sample could be observed. Images of the sample as received are shown in Figure 1 and Figure 2.

Figure 1: Overview picture of received sample.

Figure 2: Overview picture of received sample opposite side, ref. Figure 1.

3.2 Chemical Composition Analysis A spectrographic analysis was carried out for the plate. The chemical composition of the material in question is given in Table 1. Table 1: Spectrometric analysis of the plate Element % C 0.220

Si 0.014 Mn 0.467

P 0.022 S 0.032 Cr 0.049

Ni 0.056 Mo <0.0010 Al 0.0013

Cu 0.063 Co 0.015 Ti <0.001

Nb <0.001 V 0.001 B <0.0002

W 0.007 Pb <0.001 Sn 0.005

As 0.011 N 0.011 Fe 98.8

3.3 Metallographic Examination The samples were ground, polished and etched according to standard metallographic procedure. A metallographically prepared sample can be seen in Figure 3 and a close-up in Figure 4. The microstructure is consisting of ferrite and pearlite. The material is most likely in as-normalised condition. Non-metallic inclusions in the plate material were observed. Representative microstructure for the plate is shown in Figure 5. Figure 6 is showing a close-up.

Figure 3: Metallographically prepared sample in as polished condition shows non-metallic inclusion in the plate material. Magnification 100X.

Figure 4: Close-up of Figure 3. Magnification 500X.

Figure 5: Microstructure representing the plate material consisting of ferrite and pearlite in as normalized condition. Magnification 100X.

Figure 6: Close-up of Figure 5 Magnification 500X. 3.4 Thickness Measurements The plate thickness was measured with a calliper and the thinnest part on the plate had a thickness of 6.5 mm and the thickest part was measured to 7.5 mm. The measurements were carried out along the plate edge. 3.5 Hardness Measurements Hardness measurements were carried out in the plate by means of a stationary Vickers hardness test equipment and 10 kpf load [HV 10]. The results are given in Table 2. The values correspond well to the measured tensile strength. Table 2: Hardness measurements carried out in the plate material

Sample location Single measurements ]HV]

Average values [HV]

Rolling direction 121-122-120 121 Transverse to rolling

direction 136-136-136 136

3.6 Mechanical testing 3.6.1 Tensile Test The testing was performed in accordance with the test standard: ISO 6892. Due to the thickness of the plate, a flat specimen was prepared. The results are presented in Table 3. Table 3: Results from tensile tests

Specimen No.:

Dim. [mm]

Area [mm2]

Proof strength ReH /Rp0.2

Tensile strength Rm

Elong. L0=60 [%] [kN] [MPa] [kN] [MPa]

Base material

19.88 x5.69 113.12 30.9 273 50.24 440 35.1

Figure 7: Stress-strain curve for the plate.

02468

1012141618202224262830323436384042444648505254565860

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37

Load

[kN

]

Displacement [mm]

Tensile test of plate U-864

U-864 plate

Rp0.2 = 273 MPa

Rm = 440 MPa

3.6.2 Charpy V-Notch Impact Tests The testing was performed in accordance with the test standard: ISO 148. Dimension of test specimens: 5 x10 mm Sampling : Test specimens were sampled approx. 1 mm below surface, and with the notch perpendicular to the surface. The results are presented in Table 4. Note: due to non-standard size specimens, the average value is multiplied by 1.5 for the corresponding full size specimen average. Table 4: Results from Charpy V-notch impact test

Sample Test temp.

[°C]

Impact energy, KV 300, [J]

Single values

[J]

Average

[J]

Calculated for full size

[J]

Base material 0 24 26 27 26 38.5

4 CONCLUSIONS Based on the tests performed, the following is concluded:

• The chemical composition is as expected for low-carbon steel plate. The sulphur level is somewhat high, which is shown in the microstructure as a relatively high amount of MnS inclusions. The microstructure is otherwise normal for hot rolled plate.

• The impact testing gave an average of 38.5 J at 0 °C, which is above what is considered brittle.

• The tensile strength is also as expected for this type of material, with a relatively low tensile strength of 440 MPa and good ductility. This strength level/hardness corresponds to a S235 (EN10025) type of steel, or grade NV B.

• Due to little corrosion in the plate, the reduction in plate thickness is minimal. • When cutting this steel plate, no special considerations should be necessary.

Equipment for cutting soft carbon steel should suffice.

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