DEVELOPMENT OF CORROSION RESISTANT STEEL FOR BOTTOM PLATE OF COT Y. - - PowerPoint PPT Presentation

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DEVELOPMENT OF CORROSION RESISTANT STEEL FOR BOTTOM PLATE OF COT Y. - - PowerPoint PPT Presentation

Dec 03, 2022 380 likes •579 views

DEVELOPMENT OF CORROSION RESISTANT STEEL FOR BOTTOM PLATE OF COT Y. Inohara, JFE steel corporation, Japan T. Komori, JFE steel corporation, Japan K. Kyono, JFE steel corporation, Japan K. Ueda, JFE steel corporation, Japan S. Suzuki, JFE steel

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DEVELOPMENT OF CORROSION RESISTANT STEEL FOR BOTTOM PLATE OF COT

  • Y. Inohara, JFE steel corporation, Japan
  • T. Komori, JFE steel corporation, Japan
  • K. Kyono, JFE steel corporation, Japan
  • K. Ueda, JFE steel corporation, Japan
  • S. Suzuki, JFE steel corporation, Japan
  • H. Shiomi, JFE steel corporation, Japan
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Contents

  • 1. Simulation Test of Inner Bottom Environment
  • 2. Development of Anti-Corrosion Steel for COT

(1) Pitting Corrosion Resistance of Developed Steel (2) Corrosion Resistance in Acid Solution

  • f Developed Steel

(3) Mechanical Properties of Developed Steel

  • 3. Conclusions
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Contents

  • 1. Simulation Test of Inner Bottom Environment
  • 2. Development of Anti-Corrosion Steel for COT

(1) Pitting Corrosion Resistance of Developed Steel (2) Corrosion Resistance in Acid Solution

  • f Developed Steel

(3) Mechanical Properties of Developed Steel

  • 3. Conclusions
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Corrosion Problem in COT

・A form of corrosion on inner bottom : Pitting of bowl shape ・On every dry docking (every 2.5 years) ⇒ Pitting corrosion, 4 mm and more depth, are repaired. ⇒ Many pitting corrosion = Much repair cost occur!

  • Max. Pitting Rate：4mm/y (10mm/2.5y)

20mm 10cm

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SLIDE 5

5 Sludge, Salt water H2S H2S Inert Gas Crude Oil Oil coat

Oil-coat Salt-water about 8%NaCl, Salt-water Sludge Solids in Oil Drops from ceiling (Sulfur, Rust) Cause of Pitting Full Load Condition

Crude Oil Salt-water Oil-coat Steel Sludge, S

Environment on Inner Bottom of COT

Oil-coat High Humidity (Acid Dew) Inert-gas Condition ・SO2, O2 contain Residue of Salt-water Sludge ・Solid in Oil ・Sulfur, Rust Ballast Condition

Ineat-gas (SO2, O2 +H2S) Oil-coat Steel Sludge, S

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Pitting Growth

Oil-coat Steel Pitting (Anode) Sludge, Rust, S (Cathode) Defect of Oil-coat Salt-water

Mechanism of Pitting Corrosion

(1) Protective Coating ・Oil-coat (3) Starting Point of Pitting ・Defect of Oil-coat ・Uneven Distribution of Water Factors of Pitting Growth (Cathode, Oxidizer, etc.) ・Sludge ・Rust, and S ・Inert-gas (SO2, O2, etc.) ・H2S (2) Salt-water ・Chloride Ion

Macro-cell corrosion Initiation and growth of pitting corrosion

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Simulation Test Method on the Inner Bottom

  • Fig. Pitting Corrosion Test Method.

313K 10%NaCl Specimen (with ‘Oil-coat’) Gas (include H2S)

Factors of Pitting Corrosion (1) Protective Coating (Oil-coat) (2) Salt-water (Chloride Ion) (3) Starting Point of Pitting and Accelerator (Sludge, S) Simulation Test Condition of COT Environment ・Oil-coat (gathered from actual VLCC) applied ・Simulated Gas (include 5%O2, H2S, etc.) ・10%NaCl Solution ・No oil-coat section with Sulfur < Laboratory Test Method > (1) Shot-Blast Finish (2) Applying the Oil-coat (3) Making the Starting Point of Pitting Corrosion (4) Test (5) After 36 days, The maximum pitting corrosion depth is measured.

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5 10 15 20 25 30 35 40 1 2 3 4 5 6 7 8 Depth of Pits (mm) Diameter of Pits (mm) Actual Pits

  • Lab. Test

Comparison between Lab. Test with Actual Ship

  • Photo. Pits on the Inner Bottom.
  • Photo. Pits on the laboratory Test.

The pitting corrosion shape of the

  • lab. test is similar to actual pitting

corrosion shape.

  • Fig. The Shape of Pitting Corrosion.

20 mm 10 mm

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Contents

  • 1. Simulation Test of Inner Bottom Environment
  • 2. Development of Anti-Corrosion Steel for COT

(1) Pitting Corrosion Resistance of Developed Steel (2) Corrosion Resistance in Acid Solution

  • f Developed Steel

(3) Mechanical Properties of Developed Steel

  • 3. Conclusions
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Concept of Anti-Corrosion Steel

“Anti-Corrosion Steel” : Resistance to Pitting Corrosion and Acid “Anti-Corrosion Steel + Zinc-primer” : Resistance to Pitting for Long Time

Improvement of Resistance to Pitting and Acid

(1) Forming of the surface film with resistance to acid

Prolongation of Effect of Zinc-primer

(2) Forming of thick and protective rust layer (3) Forming of un-resolvable corrosion products

One of the Protection Methods of COT

<add some elements>

Target Point

Reduction of Life Cycle Cost of Tanker

(= Reduction of Maintenance Cost of Tanker)

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Resistance to Pitting Corrosion

  • Fig. Pitting Corrosion Test Method.

10%NaCl Specimen (with ‘Oil-coat’) Gas (include H2S)

  • Photo. Pitting Corrosion by lab.-Test.

10mm <Simulation Test of Inner Bottom> 1) apply ‘Oil-coat’ 2) pitting starting point : center, 2 mm 3) 313K 4) Evaluation : Max. Pitting Depth

The max. pitting depth of the anti-corrosion steel

decreases to about 65%

compared with conventional steel.

  • Fig. Resistance to Pitting Corrosion.

0.0 0.5 1.0 1.5 conventional steel with zinc-primer anti-corrosion steel with zinc-primer

  • Max. Pitting Depth (mm)

Test period : 36 days decrease to about 65%

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Presumption of the Amount of Pitting Corrosion

Anti-Corrosion Steel + Zinc-primer (Estimation) Conventional Steel + Zinc-primer

42

VLCC G

31

Number of pits in need of repair (4 mm depth or more)

Suez/M F Tanker Table Test Calculation of the Number of Pits.

There is a possibility that the number of pits in need of repair becomes “0” by applying the anti-corrosion steel.

  • Fig. Decrease of the Number of Pits in Need
  • f Repair by Decrease of Pitting Depth.

When the anti-corrosion steel is adopted, “Pitting depth decreases to about 65%” compared with conventional steel.

10 20 30 40 50

  • 1.9

2.0- 2.4 2.5- 2.9 3.0- 3.4 3.5- 3.9 4.0- 4.4 4.5- 4.9 5.0- 5.4 5.5- Pitting Depth (mm) Frequency measured

pitting in need

  • f repair : 31

needless

Extremely decrease!

10 20 30 40 50

  • 1.9

2.0- 2.4 2.5- 2.9 3.0- 3.4 3.5- 3.9 4.0- 4.4 4.5- 4.9 5.0- 5.4 5.5- Pitting Depth (mm) Frequency measured calculated

pitting in need

  • f repair : 31

“Pitting depth decreases to about 65%”

needless

4mm

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Contents

  • 1. Simulation Test of Inner Bottom Environment
  • 2. Development of Anti-Corrosion Steel for COT

(1) Pitting Corrosion Resistance of Developed Steel (2) Corrosion Resistance in Acid Solution

  • f Developed Steel

(3) Mechanical Properties of Developed Steel

  • 3. Conclusions
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0.0 0.2 0.4 0.6 0.8 1.0 1.2 Conventional Steel Anti-Corrosion Steel Corrosion Rate Ratio (conventional Steel = 1.0) pH=0.9

Resistance to Hydrochloric Acid

<Corrosion Factor Test of Inner Bottom> 1) 10%NaCl, + HCl 2) pH=0.9 3) 313K 4) Evaluation : Corrosion Rate

The corrosion rate of the anti-corrosion steel in the hydrochloric acid

decreases to about 14% compared with conventional steel.

  • Fig. Resistance to Hydrochloric Acid.
  • Fig. Test Method.

10%NaCl (pH=0.9) Specimen decrease to about 14%

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Contents

  • 1. Simulation Test of Inner Bottom Environment
  • 2. Development of Anti-Corrosion Steel for COT

(1) Pitting Corrosion Resistance of Developed Steel (2) Corrosion Resistance in Acid Solution

  • f Developed Steel

(3) Mechanical Properties of Developed Steel

  • 3. Conclusions
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Mechanical Properties

Table 1 Characteristics of Base Metal.

Energy (J) ≧31 326 CVN at 253K YS (N/mm2) IACS, 32D ≧315 Anti-corrosion Steel Thickness : 20 (mm) 399 ≧18 31 EL (%) 440～590 485 TS (N/mm2) Grade CVN： Charpy V notch test

Table 2 Characteristics of Weld Joint.

Notch position 149 FL 247 HAZ 1 (mm) 273 HAZ 3 (mm) 317 HAZ 5 (mm) ≧440 515 TS (N/mm2) Energy (J) ≧34 106 Charpy V notch test at 273K IACS, 32D Anti-corrosion Steel Thickness : 20 (mm) Welding method : FCB Heat input : 108 (kJ/cm)

  • WM

Grade

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Contents

  • 1. Simulation Test of Inner Bottom Environment
  • 2. Development of Anti-Corrosion Steel for COT

(1) Pitting Corrosion Resistance of Developed Steel (2) Corrosion Resistance in Acid Solution

  • f Developed Steel

(3) Mechanical Properties of Developed Steel

  • 3. Conclusions
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Conclusions

· The pitting corrosion test method that was able to simulate the pitting corrosion that occurred on the inner bottom plate of COT was established. · The corrosion resistant steel that strengthened the effect of the zinc-primer on the decrease of pitting corrosion was developed. The maximum pitting corrosion depth has decreased to about 65% compared with conventional steel. · The developed steel has mechanical properties and construction performance equal with those of conventional steel as steel plate for shipbuilding.

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END