development of corrosion-resistant steels and their ... 4.3 - (only ppt)development...development of...

P 1 © 2013 NIPPON STEEL & SUMITOMO METAL CORPORATION All Rights Reserved.

Development of Corrosion-resistant Steels

and their Application to Crude Oil Tankers

Taizo Yoshida NYK Line Jun Kato NYK Line Minoru Ito Nippon Steel & Sumitomo Metal Corporation Seiji Nishimura Nippon Steel & Sumitomo Metal Corporation Kazuyuki Kashima Nippon Steel & Sumitomo Metal Corporation


Outline 1. Introduction ・IMO requirements for corrosion protection of COT ・Benefits of Corrosion-resistant Steel (CRS) ・Environment and corrosion in COT 2. NSGPTM-1 for bottom plates ・Mechanical properties & IMO test method results ・Onboard Investigation results 3. NSGPTM-2 for upper deck ・Mechanical properties & IMO test method results ・Onboard Investigation results 4. CRS for ballast tank ・Background ・Onboard Investigation results


Corrosion protection measures by coating or use of corrosion resistant steel are to be adopted in the cargo oil tanks of crude oil tankers ◇Ship Type ： Crude Oil Tanker ≧ 5,000 dwt. ◇ Effectuation ： On or after 1 January 2013. ◇ Protection ： Bulkheads ～10% of the tanks height or 3m at center line. Bottom and entire structure to height of 0.3 m from the bottom.

Refer to “Guidelines on Corrosion Resistant Steel for COT”, Class NK

Fig. Area of application when uppermost means of access has not been provided

Fig. Area of application corrosion resistant steel

IMO requirements on corrosion protection of COT

NSGPTM-1 has already been certified by Class NK as corrosion-resistant steel.


4

Benefit of using CRS

1. Minimized repair work due to corrosion Easy to maintain quality No paint curing time required No deterioration by welding 2. No need for a protective coating and its repair


Environment and Corrosion in the Cargo Oil Tank (COT)

SR-242 Result

Flaky corrosion products Max. corrosion rate > 0.1 mm/year

Pitting corrosion occurs Max. corrosion rate 3～4 mm/year

SR-242 Result Bottom plate

Upper Deck

SR-242 Result

Environment : Not only crude oil, but also sludge, drain water (brain), and severe gases. Corrosion : There are 2 types.1) pitting corrosion (bottom), 2) general corrosion (upper deck)


NSGPTM-1 for Bottom Plates

(1) Typical composition and mechanical properties

(2) IMO test method results (3) Onboard Investigation results


7

Typical Composition of NSGPTM-1

(mass %)

A very small quantity of alloying elements is added to improve corrosion resistance. The composition of the developed steel fully satisfies IACS standards.

C Si Mn P S Ceq.

NSGPTM-1 (AH32) 0.12 0.26 0.96 0.014 0.007 0.331

Conventional steel (AH32) 0.14 0.20 1.09 0.018 0.006 0.322

IACS Standard (AH32) ≦0.18 ≦0.5 0.9～1.6 ≦0.035 ≦0.035 ≦0.36


8 Mechanical Properties of NSGPTM-1

Welding Condition Welding Method Shape of Groove Welding Material Heat Input

FAB V Wire (US-36 6.4mmφ)

Flux (PFI-52E) 125 kJ/cm

Backing Metal (FAB-1)

Good mechanical properties

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 50 100

Crac

k Rat

io %

Pre-heat Temperature ℃

SurfaceCross sectionRoot

No Crack

0

50

100

150

200

250

300

WeldMetal

FusionLine

HAZ1 mm

HAZ3 mm

HAZ5 mm

Abso

rbed

Ene

rgy

at 20

℃ｖE

20J

Notch Position

34 Spec. of AH32

FAB, L-direction 1 mm below the surface

Y-groove weld cracking test results Charpy impact tests results of welded joints

YP (N/mm2)

TS (N/mm2)

EL (%)

E-20 (J)

NSGPTM-1 (t=25mm) 462 554 22 273

KD36 Spec. ≧355 490-620 ≧18 ≧31


IMO Corrosion Test Results of NSGPTM-1

0

1

2

3

4

5

Conventional steel NSGPTM-1

Cor

rosio

n ra

te, m

m/y

IMO's criterion for corrosion-resistant steel

NSGPTM-1

10%NaCl solution (pH0.85, 30℃)

NSGPTM-1 has obtained type approval for CRS from Class NK.

NSGPTM-1 Large reduction

9

Condition

Solution

NaCl 10 mass%

pH 0.85 Adjusted by HCl solution

Amount 20 ml/cm2 or more Change Every 24 hr.

Gas Air open Temperature 30°C

Specimen Size 25×60×5 mm

Surface #600 emery paper Repeat N=5

Duration 72 hr. (base metal) 168hr. (weld joint)

Immersion Dipping specimen


Onboard Investigations of VLCCs Applying NSGPTM-1

(1)The first NSGPTM-1 applied VLCC at the 3rd inspection (7.5 years)

(2) NSGPTM-1 subsequently applied 8 VLCCs to all COTs and 4 of them were investigated at the 1st inspection (2.4-3.1 years)


Onboard Evaluation Results of VLCC using NSGPTM-1 at 7.5-years

1P

1C

1S

2P

2C

2S

3P

3C

3S

4P

4C

4S

5P

5C

5S

FWD

The CRS applied 6 tanks without protective coating: Inspection area


0

200

400

600

800

1000

1200

1400

VLCC-1(5 yrs)

VLCC (7.5 yrs)

Conventional steel NSGPTM-1

Pit c

ount

at o

ver 4

mm

in d

epth

in o

ne ta

nk

Max.

Ave.

NSGPTM-1

NSGPTM-1 Showed Good Pitting Corrosion Resistance Even After 7.5 Years Service

Large reduction

Fig. Observed pit count at over 4 mm in depth for conventional steel and NSGPTM-1

Conventional steel NSGPTM-1 7.5 years


Direct Evidence of Termination of Pit Growth

0

5

10

15

20

0 5 10 15 20Pit D

epth

at 3

rd D

ock

(7.5

yea

rs) ,

mm

Pit Depth at 2nd Dock (5 years) , mm

No.4 starboard tank

7.5-year inspection

5-year inspection

Pit growth stops after dock inspection, no longer deepened.

3.4 mm in depth

3.2 mm in depth


Termination of Pit Growth at Dock Inspection (SR242) Conventional Steel without Coating

★ : Pits over 4mm at 1st inspection (repaired) ■ : Pits less than 2mm at 1st inspection (NOT repaired)

● : Pits over 4mm at 2nd inspection (repaired)

Old pits(■) did not grow! New pits(●) appeared at different points.

82 83 84 85 86 87 88 89 90 91 92

PORT

STBDFWD


Termination of Pit Growth

K. Kato, et al., “Study on Localized Corrosion on Cargo Oil Tank Bottom Plate of Oil Tanker”, World Maritime Technology Conference, San Francisco, Oct. 2003.


Onboard Evaluation Results of 4 VLCCs using NSGPTM-1 for All COTs

1P

1C

1S

2P

2C

2S

3P

3C

3S

4P

4C

4S

5P

5C

5S

FWD

The CRS applied all tanks without protective coating: Inspection area

Ship Main route Service period

VLCC-A Middle East South America

East Asia North America 2.4 years

VLCC-B Middle East East Asia

Southeast Asia North America

3.1years

VLCC-C Middle East East Asia 2.8 years VLCC-D Middle East Southeast Asia 2.9 years


0

100

200

300

400

500

VLCC-2 VLCC-A VLCC-B VLCC-C VLCC-D

Conventional steel

NSGPTM-1

Pit c

ount

at o

ver 4

mm

in d

epth

in o

ne ta

nk

Max.

Ave.

First dock inspection results (after 2.4 to 3.1 years)

NSGPTM-1

NSGPTM-1 Showed Good Pitting Corrosion Resistance in all 4 VLCCs

Fig. Observed pit count at over 4 mm in depth for conventional steel and NSGPTM-1

Large reduction

Conventional steel

NSGPTM-1 4 VLCCs


Effect of Navigation Routes on Pit Number

NSGPTM-1 shows good corrosion resistance regardless of the navigation route.

The navigation routes of the 4 VLCCs are different

Ship Steel Main route Service period

VLCC-A

NSGPTM-1

Middle East South America

East Asia North America 2.4 years

VLCC-B Middle East East Asia

Southeast Asia North America

3.1 years

VLCC-C Middle East East Asia 2.8 years

VLCC-D Middle East Southeast Asia 2.9 years

VLCC-2 Conventional ND ND 2.5 years


NSGPTM-2 for Upper Deck

(1) Mechanical properties (2) IMO test method results (3) Onboard Investigation results


20

Mechanical Properties of NSGPTM-2

Good mechanical properties

Impact test results of welded joint

Mechanical properties YP

(N/mm2) TS

(N/mm2) EL (%)

E-20 (J)

NSGPTM-2 (t=16.5) 432 504 24 258 DH36 Spec. ≧355 490-620 ≧20 ≧34

Welding procedure : SAW ( 3 – electrode FCB ) Notch

position WM FL HAZ 1mm

HAZ 3mm

HAZ 5mm

E0 (J) 174 132 172 224 250


IMO Corrosion Test for Upper Deck

Simulated COT gas：13%CO2-5%O2-0.01%SO2-0.05%H2S-bal.N2 Wet & dry cycle：25℃⇔50℃ Dew point:≦36℃

Outlines of qualification test for upper deck


IMO Corrosion Test Results of NSGPTM-2

0

0.02

0.04

0.06

0.08

0.1

0 20 40 60 80 100 120

Cor

rosi

on lo

ss, m

m

Test duration, days

0.01

0.1

1

10

1 10 100 1000 10000

Cor

rosi

on lo

ss, m

mTest duration, days

1.53

IMO's criterion for corrosion-resistant steel: ≦2.0 mm at 25years

The increments of the corrosion decrease over time, and the estimated corrosion loss (1.53mm) for 25 years is less than 2 mm, which is the criterion for CRS.

Criterion ≦2 mm at 25 years


Onboard Investigation of Tanker Applying NSGPTM-2

NSGPTM-2 was applied to an Aframax tanker for COT upper deck plates.

Onboard investigation: at 2.5 and 5.0 years

Upper deck

No.2 No.3


Onboard Evaluation Results of Conventional Steel and NSGPTM-2

00.10.20.30.40.50.60.70.8

0 1 2 3 4 5 6

Ave

rage

corr

osio

n los

s, m

m

Test duration, years

Upper deck

Conventional

Developed

steel38% down

NSGPTM-2

Corrosion loss is less than 0.4 mm/5year (38% down to conventional steel). It is considered that the corrosion loss will not exceed 2 mm after 25 years.

Target: 2 mm / 25 years


Developed CRS to Water Ballast Tank

The IMO adopted the Performance Standard for Protective Coating (PSPC) in 2008.

The target of PSPC is of 15-year durability, and the 25-

year durability equivalent to the life of the ship is becoming increasingly expected.

Therefore, CRS for water ballast tanks is under

development.


Corrosion in Water Ballast Tank Upper Deck : Severe

Immersion part : Not so severe

Severe corrosion occurs at head structures. ⇒ The developed CRS was applied to some deck longitudinal

Refer to “Illustrations of Hull Structures” by Dr. Hirohiko Emi


Initial Appearance of Deck Longitudinal Applying CRS and Conventional Steel with Primer


3 years 5.5 years

Conventional steel

Developing CRS

Onboard Evaluation Results of Conventional Steel and the Developed CRS

Conventional steel rusted in 3 years. The developed CRS has not rusted even after 5.5 years.


29 Conclusions 1. NSGPTM-1 - Pit count of VLCCs applying the NSGPTM-1 was much lower than that

of VLCCs using conventional steel. - Direct evidence for termination pit growth was observed. 2. NSGPTM-2 - Corrosion loss for deck plate was 38% down to conventional steel (less

than 2 mm / 25year) by onboard investigation. It is thought that the corrosion loss will not exceed 2 mm after 25 years. 3. NSGPTM-1 & NSGPTM-2 minimizes the repair work, and removes the

need for a protective coating of paint and its subsequent repair. 4. Developed CRS for water ballast tanks - It has not rusted even after 5.5 years; conventional steel rusted in 3

years.


30

Thank you for your attention!

development of corrosion-resistant steels and their ... 4.3 - (only ppt)development...development of...

Documents