Development of Corrosion Resistant Steel for Cargo Oil Tanks

Transcription

1 Development of Corrosion Resistant Steel for Cargo Oil Tanks 6 September 2007 Sumitomo Metal Industries, Ltd. < 1 >

2 1. Corrosion Problems of Cargo Oil Tank 2. Research Results by The Shipbuilding Research Association of Japan 3. Corrosion Mechanism, Simulated Test Method and Corrosion Resistance of Developed Steel Deck Plate Bottom Plate 4. Mechanical Properties of Developed Steel 5. Onboard Test Results of Developed Steel (Upper deck) 6. Summary Contents < 2 >

3 Corrosion Problems of Cargo Oil Tank general corrosion Deck plate maximum corrosion rate > 0.1mm/y cost of repair coating, recoating vapor space crude oil drain water cost of inspection and repair pits initiate at defects of paint film < 3 > Bottom plate pitting corrosion

4 1. Corrosion Problems of Cargo Oil Tank 2. Research Results by The Shipbuilding Research Association of Japan 3. Corrosion Mechanism, Simulated Test Method and Corrosion Resistance of Developed Steel Deck Plate Bottom Plate 4. Mechanical Properties of Developed Steel 5. Onboard Test Results of Developed Steel (Upper deck) 6. Summary Contents < 4 >

5 The Shipbuilding Research Association of Japan Panel #242 (SR242 committee) University & National Laboratory Ship Owner SR242 committee Class Steel Maker Shipyard Field examination of VLCCs were carried out research by SR242 < 5 >

6 Corrosion at Deck Plate corrosion rate corrosion environments corrosion products Deck Plate > 0.1mm/y (Maximum) inert gas (O 2, CO 2, SO 2 ) H 2 S (from crude oil) cyclic wet & dry condition rust (FeOOH), elemental S [ layered structure ] vapor space research by SR242 crude oil < 6 >

7 Examples of Analysis Results of Gas Composition in Vapor Space of Cargo Oil Tanks COT No. 3S 4C 4S 5C Crude Oil type A B C D Cargo loading ratio 93% 89% 92% 31% H 2 S [vol. ppm] Gas [vol.%] H 2 O [vol.%] O CO SO x [vol. ppm] N CxHy CO High concentration of H 2 S exists in vapor space research by SR242 < 7 >

8 Appearance of Upper Deck Plate flaky corrosion products research by SR242 < 8 >

9 Loss in Thickness of Upper Deck Plate with Age Average Loss (mm) Age at inspection (year) 0.1mm/y Maximum corrosion rate is over 0.1 mm/y research by SR242 < 9 >

10 Pitting Corrosion at Bottom Plate pitting rate corrosion environments corrosion products 4mm/y maximum inert gas (O 2, CO 2, SO 2 ) H 2 S (from crude oil) drain water (Cl - ) crude oil, elemental S rust, FeS, elemental S crude oil Bottom Plate research by SR242 drain water < 10 >

11 Examples of Chemical Analysis Results of Water Sampled from the Bottom of Cargo Oil Tanks [ ppm ] tank Na Cl SO 4 2- S 2 O 3 2- T-Fe ph A < B < C < Chloride is detected in high concentration research by SR242 < 11 >

12 Appearance of Specimen Exposed at the Bottom of Cargo Oil Tank pits 10mm exposed for 2.5 years research by SR242 < 12 >

13 1. Corrosion Problems of Cargo Oil Tank 2. Research Results by The Shipbuilding Research Association of Japan 3. Corrosion Mechanism, Simulated Test Method and Corrosion Resistance of Developed Steel Deck Plate Bottom Plate 4. Mechanical Properties of Developed Steel 5. Onboard Test Results of Developed Steel (Upper deck) 6. Summary Contents < 13 >

14 Corrosion Mechanism at Upper Deck Plate < dawn : 25 C (wet) > < daytime : 50 C (dry) > deck plate deck plate water inert gas H 2 S Wet & Dry cycle elemental S inert gas H 2 S rust Corrosion in low ph water ph = 2 4 O 2 H 2 O+SO 2 H 2 SO 3 H 2 SO 4 H 2 O+CO 2 H 2 CO 3 < 14 > elemental S 2H 2 S + O 2 2S + H 2 O FeOOH corrosion product contains a lot of elemental S (60% max.)

15 Simulated Corrosion Test (Upper Deck Plate) gas outlet specimens gas inlet NaCl solution < Test conditions > Temperature 50 C(20 h) 25 C (4h) [cyclic wet & dry condition] Gas * [A]13%CO 2-5%O %SO 2 -bal.n 2 (simulated inert gas) [B]simulated inert gas + 0.2%H 2 S * Gas A and B are blew alternately every 2 weeks < 15 >

16 Cross Sectional Analysis of Corrosion Product Formed on Steel after Simulated Corrosion Test 100μm layerd elemental S < 16 > Epoxy resin Corrosion product mixture of rust and elemental S rust (FeOOH) Fe O S Distribution of elements Steel Layered structure was reproduced in laboratory concentration high low

17 Corrosion Product after Simulated Test - Upper deck - α-feooh γ-feooh Fe3O4 Elemental S Others COT Simulated test [ mass % ] Corrosion product after simulated test was similar to cargo oil tank. Laboratory corrosion test simulates corrosion at upper deck of cargo oil tank. < 17 >

18 Corrosion Resistance - Deck Plate - Average corrosion loss (mm) Conventional Steel Test duration (days) < 18 > 1/2 Developed Steel Normalized corrosion rate conventional steel 84 days 1/2 developed steel

19 Mechanism for Improvement of Corrosion Resistance [upper deck] Dew water Steel + alloying elements Low ph (2~4) Rust Corrosion resistance in low ph water by alloying elements Ratio of corrosion rate Conventional steel H 2 SO 4 (ph=0.5), 24h Developed steel Corrosion resistance in low ph water < 19 >

20 1. Corrosion Problems of Cargo Oil Tank 2. Research Results by The Shipbuilding Research Association of Japan 3. Corrosion Mechanism, Simulated Test Method and Corrosion Resistance of Developed Steel Deck Plate Bottom Plate 4. Mechanical Properties of Developed Steel 5. Onboard Test Results of Developed Steel (Upper deck) 6. Summary Contents < 20 >

21 Pitting Corrosion Mechanism at Bottom Plate Drain water (Cl - ) (Neutral ph) Oil coating Inert gas Defect H 2 S Elemental S Bottom plate Pit (Anode) Cathode Anode : Fe Fe e Cathode : O 2 + 2H 2 O + 4e 4OH - S + 2H 2 O + 2e H 2 S + 2OH - (accelerate pitting corrosion rate) Pits initiate at the defects of oil coating film and grow rapidly by creating corrosion electric cell. < 21 >

22 gas outlet specimens simulated oil coating gas inlet synthetic sea water < Test conditions > Temperature 40 C Gas 13%CO 2-5%O %SO 2-0.2%H 2 S-bal.N 2 Appearance of specimen after corrosion test defect < 22 > Simulated Corrosion Test Bottom Platepit 10mm We reproduced pitting corrosion by laboratory test.

23 Corrosion Product after Simulated Test - Bottom - α-feooh β-feooh γ-feooh COT Simulated test [ mass % ] Fe 3 O 4 Elemental S Others 8 1 FeCO 3, FeS FeCO 3, FeS Corrosion product after simulated test was similar to cargo oil tank. Laboratory corrosion test simulates corrosion at bottom of cargo oil tank. < 23 >

24 Corrosion Resistance - Bottom Plate - Maximum pit depth (mm) Conventional Steel 1/2 Developed Steel Test duration (days) Normalized pitting rate conventional steel 56 days 1/3 developed steel < 24 >

25 Mechanism for Improvement of Corrosion Resistance [bottom] SE Cu S Fe O FeS Rust Drain Sulfide film Rust Steel H2S Sulfide film Steel + alloying elements Cross section high concentration Oil coating low Distribution of elements 200μm Sulfide film suppresses growth of pitting corrosion < 25 >

26 1. Corrosion Problems of Cargo Oil Tank 2. Research Results by The Shipbuilding Research Association of Japan 3. Corrosion Mechanism, Simulated Test Method and Corrosion Resistance of Developed Steel Deck Plate Bottom Plate 4. Mechanical Properties of Developed Steel 5. Onboard Test Results of Developed Steel (Upper deck) 6. Summary Contents < 26 >

27 Mechanical Properties of Developed Steel Plate thickness : 16.5 mm YP (N/mm 2 ) 432 Tensile Tests TS (N/mm 2 ) 504 EL (%) 24 Charpy Impact Test Test Temp. ( C) -20 Absorbed Energy ( J ) 258 <Spec.> Grade D / Mechanical properties satisfied the specification. < 27 >

28 Toughness of Welded Joint Plate thickness : 16.5 mm Method 3 electrodes, FCB (Single side 1 pass) Heat input 108 kj/cm edge preparation 3 Toughness of welded joint is good. < 28 > Notched Position W.M. F.L. F.L. + 1mm F.L. + 3mm F.L. + 5mm Absorbed Energy at 0 0 (J)

29 Corrosion Resistance of Weld Metal Ratio of corrosion rate [initialized by rate of base metal] [ Deck ] [ Bottom ] Base metal Weld metal Ratio of pitting rate [initialized by rate of base metal] Base metal Weld metal Corrosion resistance of weld metal is equivalent to that of base metal. < 29 >

30 1. Corrosion Problems of Cargo Oil Tank 2. Research Results by The Shipbuilding Research Association of Japan 3. Corrosion Mechanism, Simulated Test Method and Corrosion Resistance of Developed Steel Deck Plate Bottom Plate 4. Mechanical Properties of Developed Steel 5. Onboard Test Results of Developed Steel (Upper deck) 6. Summary Contents < 30 >

31 Shipyard A A B C D Certification of Classification Type AFRA-MAX AFRA-MAX AFRA-MAX VLCC VLCC LR, NK, ABS, DNV Trial Applications to Cargo Oil Tanks plates test coupons test coupons test coupons test coupons test coupons < 31 > Deck Exposure test Bottom plates test coupons - test coupons plates plates Developed steel has been applied to cargo oil tanks for trial

32 Onboard Test Results of Developed Steel (Upper Deck Plate) Test coupons were exposed in vapor space of 3 tanks for 1 year 1 Ratio of corrosion rate of developed steel to conventional steel Upper deck tank A tank B tank C Developed steel has good corrosion resistant in actual environments at upper deck < 32 >

33 1. Corrosion Problems of Cargo Oil Tank 2. Research Results by The Shipbuilding Research Association of Japan 3. Corrosion Mechanism, Simulated Test Method and Corrosion Resistance of Developed Steel Deck Plate Bottom Plate 4. Mechanical Properties of Developed Steel 5. Onboard Test Results of Developed Steel (Upper deck) 6. Summary Contents < 33 >

34 Summary 1. We established simulated corrosion test method. 2. We developed corrosion resistant steel plate for cargo oil tank which can be used at both upper deck and bottom. 3. Performance of developed steel : corrosion rate < 1/2 [ at deck plate ] pitting rate < 1/3 [ at bottom plate ] 4. Mechanical properties of developed steel satisfy the specification. 5. Corrosion resistance of weld metal is good. 6. Developed steel has good corrosion resistance in upper deck of actual cargo oil tanks. < 34 >

35 END OF PRESENTATION THANK YOU FOR KIND ATTENTION September 2007 Sumitomo Metal Industries, Ltd. < 35 >

36 Structure of Corrosion Product on Pit elemental S FeOOH Steel Conventional steel FeS FeOOH Sulfide Steel Developed steel 2FeS + 3/2O 2 + H 2 O 2FeOOH + 2S Sulfide film that is hard to dissolve improves corrosion resistance

37 Corrosion resistance of welded joints Simulated corrosion test for bottom on FCB welded joints Ratio of pit depth [initialized by conventional steel] HAZ (developed) corrosion depth of developed steel weld metal HAZ (developed) Ratio of pit depth [initialized by conventional steel] HAZ weld metal (conventional) HAZ (developed) developed developed conventional developed Corrosion resistance of welded joints was good No galvanic corrosion on these welded joints

38 Corrosion resistance of developed steel in sea water Corrosion rate (mm/y) months 0 Conventional steel Developed steel Corrosion resistance of developed steel is equivalent to conventional steel in sea water.

39 Test coupons on deck and bottom Grinded( ) + Grinded( ) Epoxy painted Silicon coated Conventional steel Deck Corrosion resistant steel Weld bead Grinded ( ) + Epoxy painted + Silicon coated φ Bottom Grinded ( ) A A Weld bead A A 300

40 Effect of oil coating on corrosion at bottom (simulated test) Corrosion loss, pit depth (mm) with oil coating without oil coating Test duration (weeks) Corrosion of specimen with oil coating is accelerated Generation of corrosion electric cell in this environment

41 Effect of H 2 S on corrosion at bottom (simulated test) Corrosion loss, pit depth (mm) with oil coating without oil coating H 2 S concentration (%) H 2 S accelerate corrosion in this environment.