1. TSCF 2016 Shipbuilders Meeting
Corrosion-resistant Steels, NSGPTM-1, -2 for Crude Oil Tankers and their Performance
Hidehiko Sato NYK Line
Shunsuke Ogisu NYK Line
Hiroyuki Fujioka NYK Line
Minoru Ito Nippon Steel & Sumitomo Metal Corporation
Naoki Oda Nippon Steel & Sumitomo Metal Corporation,
Kazuyuki Kashima Nippon Steel & Sumitomo Metal Corporation
Thank you Chairperson. And good morning ladies and gentlemen.
I’m very glad to have this opportunity to present corrosion resistant steels here.
My name is Shunsuke Ogisu, from NYK LINE.
Today We would like to update these steels and their performance to apply crude oil tankers.

2. Outline Introduction 2. NSGPTM-1 for bottom plates
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
Onboard Investigation results
3.　NSGPTM-2 for upper deck
4. Conclusions
This is an outline of this presentation.
Firstly, We’d like to show the IMO requirement for corrosion protection of COT. I think this point are already known by all attendees, so just briefly ..　
and, benefit of using corrosion resistant steel, CRS, the Environment and corrosion in COT.
Secondly, We are going to show mechanical properties and onboard investigation results for VLCC’s applied NSGP-1 for bottom plates.
And next, let we show you mechanical properties and onboard investigation results for an aframax tanker applied NSGP-1 for upper deck.
And the conclusion , I am going to summarize the presentation.
Let me start from the IMO requirement for corrosion protection of cargo oil tank.

3. IMO requirements on corrosion protection of COT
◇Ship Type ：　Crude Oil Tanker ≧ 5,000 dwt. ◇ Effectuation ：　On or after 1 January ◇ Protection ：　coating or corrosion resistant steel
NSGPTM-1 and 2 have already been certified by several ship’s classes as corrosion resistant steel.
The overview of the IMO requirements on corrosion protection of COT is as shown here.
The NSGP-1 and 2 has already been certified by several ship’s classes as corrosion-resistant steel.
So, under this situation, What is the benefit apply it for tankers.
Fig. Area of application when uppermost means of access has not been provided
Fig. Area of application corrosion resistant steel
Refer to “Guidelines on Corrosion Resistant Steel for COT”, Class NK

4. Benefit of using CRS
No need for a protective coating, that is a benefit for the global environment by not using volatile organic compounds.
There is no concern about dispersion of coating quality before completion of ship building.
There is no concern about damage for protective coating during sludge removal work, that leads to minimize repair work and maintenance cost which are heavy in periodical dock inspection/expense items for ordinary VLCCs.
We are facing three benefit for using this
First, CRS do not need protective coating, so it is contributing the global environment by not using volatile organic compounds.
Secondly, There is no concern about dispersion of coating quality before completion of ship building
And third, .there is no concern about damage for protective coating during sludge removal work, that leads to minimize repair work and maintenance cost which are heavy in periodical dock inspection/expense items for ordinary VLCC’s.
From here, I would like to take over to Mr. Kaneko, he is the researcher and developer of these CRSs in Nippon Steen Sumitomo Metal Corporation,
And introduce detail of CRSs and their performance to apply crude oil tankers.
👇NSSMC 金子様ご担当
Firstly, let me show the environment and corrosion in cargo oil tank, before talking our corrosion resistant steels.

5. Environment and Corrosion in the COT
Upper Deck
SR-242 Result
Flaky corrosion products
Max. corrosion rate > 0.1 mm/year
Bottom plate
SR-242 Result
SR-242 Result
This is an overview of environment in cargo oil tanks in the VLCC.
This was revealed in the joint research project conducted by the SR242 committee.
It was established by the Shipbuilding Association of Japan from 1999 to 2001.
Inside crude oil tank, there is not only crude oil but also sludge and drain water on the inner bottom plate and several gases in the vapor space .
And there is two types of corrosion.
One is pitting corrosion on bottom plate. Its maximum corrosion rate is about 3 to 4 mm/year.
The other is flaky corrosion occurring on head structure. Its maximum corrosion rate is more than 0.1mm/year.
Then I’d like to talk about our corrosion resistant steels against these corrosion.
NSGP-1 for bottom plates and NSGP-2 for upper deck.
Pitting corrosion occurs
Max. corrosion rate 3～4 mm/year
Environment : Not only crude oil, but also sludge, drain water (brine), and severe gases.
Corrosion : There are 2 types.1) pitting corrosion (bottom), 2) general corrosion (upper deck)

6. NSGPTM-1 for Bottom Plates
Typical composition and mechanical properties
Onboard Investigation results
First I’d like to talk about the NSGP-1 for bottom plates.
Here, I’ll show you good mechanical properties excellent results of onboard investigations.

7. Typical Composition of NSGPTM-1
(mass %) 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
≦0.36
・A very small quantity of alloying elements is added to improve corrosion resistance.
・The composition of the developed steel fully satisfies IACS standards.
This is the typical composition of NSGP-1.
A very small quantity of alloying elements is added to improve corrosion resistance.
And the composition of the NSGP-1 fully satisfies the IACS standards.
And NSGP-1 is TMCP steel.

8. Mechanical Properties of NSGPTM-1 Good mechanical properties8
Mechanical Properties of NSGPTM-1
Mechanical properties YP
(N/mm2) TS EL
(%)
E-20
(J)
NSGPTM-1 (t=25mm)
462
554 22
273
D36 Spec.
≧355
≧20
≧34
Impact test results of welded joint
Welding procedure : FAB
Notch position WM FL
HAZ
1mm
3mm
5mm
E0 (J)
117
103
193
208
Here is an example of results of tensile strength and Charpy impact test result of the NSGP-1.
These satisfy the standard requirements.
Here is the results of the Charpy impact tests of welded joint.
The absorption energy is enough to the standard requirements.
So the NSGP-1 has good mechanical properties.
Good mechanical properties

9. Onboard Evaluation Results for VLCCs Using NSGP-1 for COT Bottom Plates
Next, let me show you onboard evaluation results for 7 VLCC’s using NSGP-1 for COT bottom plates.

10. Onboard Investigations of VLCCs Applying NSGPTM-1
TSUGARU
TOKITSU MARU
TAKAMATSU MARU
TAKAOKA
The NSGP-1 subsequently applied 8 VLCCs to all COTs after the first NSGP-1 applied VLCC without paint coating partially.
Here are photographs of VLCC’s applied NSGP-1.
Then, let me describe a service period and main routs of the 7 VLCC’s.
(1)The first NSGPTM-1 applied NYK’s VLCC will be at the 5th inspection (Over 12 year Service Period)
(2)NSGPTM-1 subsequently applied NYK’s 8 VLCCs to all COTs and their service periods are ranged from 5 years to 8 years.

11. Table 1: List of VLCCs provided with NSGPTM-1
Service period
Main route
Application
of CRS
VLCC-A
12.2 years
Middle East / Japan
All COTs
bottom Plates,
6 COTs
unpainted
VLCC-B
8.0 years
Middle East / East Asia / South America / North America
bottom plates,
all COTs
VLCC-C
7.6 years
Middle East / East Asia / Southeast Asia / North America
VLCC-D
6.8 years
Middle East / East Asia
VLCC-E
6.9 years
Middle East / Southeast Asia
VLCC-F
5.3 years
Middle East / East Asia / Southeast Asia
VLCC-G
5.0 years
This table shows service periods, main route and application of NSGP-1 for 7 VLCC’s. The longest service period is 12.2 years. And main routes of the VLCC’s are shown here. VLCC-A is from middle East to Japan. For VLCC-B and C, main routes are from middle east to east Asia and from south America to north America. For VLCC-D, the main route is from middle east to east Asia. For VLCC-E, main route is from middle east to southeast Asia. And for VLCC F and G, main routes are from middle east to east Asia or southeast asia.

12. Onboard Evaluation Results of VLCC using NSGPTM-1 at 10years
The CRS applied 6 tanks without protective coating: Inspection area
This figure shows the portions applied to the NSGP-1 for VLCC-A.
The NSGP-1 was used for all the COT bottom plates, while in the No. 3 and 4 COTs, it was used without paint coating.
We inspected pit count over 4 mm in depth in this area.

13. NSGPTM-1 Showed Good Pitting Corrosion Resistance Even After 10 Years Service
Conventional steel
Without paint
NSGPTM-1
Without paint
10 years
This figure shows the results in comparison with the conventional steel without painting of other VLCC at 5years.
And this figure shows, in case of conventional steel applied VLCC, the average number reached two hundreds, and the maximum number is over 1,000.
But in case of the NSGP-1 applied VLCC, even the maximum number is less then 100.
That is, the NSGP-1 showed good pitting corrosion resistance even after 10 years service.
Fig. Observed pit count at over 4 mm in depth
for conventional steel and NSGPTM-1

14. NSGPTM-1 Showed Good Pitting Corrosion Resistance in all 6 VLCCs
Conventional steel
Without paint
NSGPTM-1
Without paint
6 VLCCs
Large reduction
This figure shows the results in comparison with the conventional steel without painting of other VLCC at 2.5 years.
And this figure shows, in conventional steel applied VLCC, the average number reached one hundred, the maximum number is about 400.
In the NSGP-1 applied VLCCs, on VLCC-B to G the pit counts are much lower than conventional steels without painting.
Even VLCC-C, the worst VLCC, the average is only tens.
That is, the NSGP-1 showed good pitting corrosion resistance in all 6 VLCCs
Fig. Observed pit count at over 4 mm in depth
for conventional steel and NSGPTM-1

15. Termination of Pit Growth
at an Inspection Dock
Next, let me talk about termination of pit growth at an inspection dock.

16. Old pits(■) did not grow! New pits(●) appeared at different points.
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.
The termination of pit growth is firstly found by investigations of SR242.
Here is the onboard investigation fact described in SR242.
This figure shows the pit locations of certain tank, called pit map.
In this figure, pit in these green area was less than 2mm in depth at the 1st inspection.
And these red solid circles are new pits over 4mm in depth at the 2nd inspection.
That is, new pit over 4 mm in depth appeared at the different positions of the pits less than 2 mm in depth at previous inspection.
And it means the old pits did not grow.

17. Schematic Diagram for Termination of Pit Growth at an Inspection Dock
Here shows the mechanism of termination of pit growth considered.
Under servicing condition, there are sludge and corrosion products inside of the pits.
And during inspection these sludge and corrosion products are cleaned and dried for inspection.
And re-start of service the cleaned and dried pits are re-coated by new crude oil.
And nuclear of new pit tend to occur at the defect of thinner oil coat.
So pit growth stopped after docking.
But in the SR242, there is not any direct observation.
K. Kato, et al., “Study on Localized Corrosion on Cargo Oil Tank Bottom Plate of Oil Tanker”,
World Maritime Technology Conference, San Francisco, Oct

18. Direct Evidence of Termination of Pit Growth for NSGPTM-1
Appearance of the pit “C”
5-year
inspection
7.5-year
inspection
10-year
inspection
3.4 mm
in depth
3.2 mm
in depth
3.2 mm
in depth
In VLCC-A, from 1st to 4th onboard investigation,
we confirmed termination of pit growth at a dock inspection.
Here are 5 examples of observed pits from A to e (on the bottom plate in No. 4 starboard COT). As shown from this figure, pit depth did not change by .service periods.
And these photographs show appearance of the pit “c”. These appearances seem same and the depth of these pits is within the measurement error.
2nd Dock
3rd Dock
4th Dock
Figure Pit depth at the first, the second, the third and fourth dockings and appearance of pit “c” observed at 2nd, 3rd and 4th Dock Inspections.
Pit growth stops after dock inspection, no longer deepened. 　

19. Prevention against Pits by combining structural Countermeasure19
Prevention against Pits by combining structural Countermeasure
Based on some dock inspection results, there was a one trend that
pits exists under drain hole of lowest horizontal girder / side longitudinal.
Based on some dock inspection results, there was a one trend that pits exists under drain hole of lowest horizontal girder / side longitudinal.
We estimated that dropped sludge form drain holes may give damage to tank top plate, and it lead to occur pitts.
Then, We combined two structural countermeasures to some VLCCs. 　
Dropped drain damaged to oil coating easily.
We combined two structural countermeasures to some VLCCs. 　

20. Prevention against Pits by combining structural Countermeasure20
Prevention against Pits by combining structural Countermeasure
Example 1 :Closed drain hole on lowest horizontal girder
Patented
No drain hole
For example, closed drain hole on lowest horizontal girder

21. Prevention against Pits by combining structural Countermeasure21
Prevention against Pits by combining structural Countermeasure
Example 2 :Closed drain hole on lowest side longitudinal.
Patented
No drain hole
Second, Closed drain hole on lowest side longitudinal.
Based on the continued inspection result,
We confirmed that combining structural countermeasures have good effectiveness for prevention of pits occurrence.

22. (1) Mechanical properties (2) Onboard Investigation results
NSGPTM-2 for Upper Deck
(1) Mechanical properties
(2) Onboard Investigation results
Then, I’ll show you the mechanical properties and onboard investigation results of the NSGP-2.

23. Mechanical Properties of NSGPTM-2 Good mechanical properties23
Mechanical properties YP
(N/mm2) TS EL
(%)
E-20
(J)
NSGPTM-2 (t=16.5)
432
504 24
258
DH36 Spec.
≧355
≧20
≧34
Impact test results of welded joint
Welding procedure : SAW ( 3 – electrode FCB )
Notch position WM FL
HAZ
1mm
3mm
5mm
E0 (J)
174
132
172
224
250
Here is an example of results of tensile strength and Charpy impact test result of the NSGP-2.
These satisfy the standard requirements.
Here is the results of the Charpy impact tests of welded joint.
The absorption energy is enough to the standard requirements.
So the NSGP-2 has good mechanical properties.
Good mechanical properties

24. Onboard Investigation of Tanker Applying NSGPTM-2
Upper deck
No.2
No.3
NSGPTM-2 was applied to an Aframax tanker for COT upper deck plates.
Here is the Aframax tanker applying the NSGP-2.
The NSGP-2 was used in the blue area without paint coating.
We inspected the thickness loss of the NSGP-2 and conventional steel at 2.7 years, 5 years, 8.1 years and 10 years.
Onboard investigation at 2.7, 5.0, 8.1and10years

25. Onboard Evaluation Results of Conventional Steel and NSGPTM-2
Obtained results are here. This figure shows the results in comparison with the conventional steel.
Corrosion loss of the NSGP-2 is less than 0.7 mm/10year and 38% down to conventional steel.
And it is considered that the corrosion loss of the NSGP-2 will not exceed 2 mm after 25 years.
Therefore, the NSGP-2 is the good corrosion resistant for upper deck.
Next, let me summarize this presentation.
Fig. Results of the exposure test on the upper deck of an Aframax tanker
・Corrosion loss is less than 0.7 mm/10years.
・It is considered that the corrosion loss will not exceed 2 mm after 25 years.

26. Conclusions NSGPTM-1 for Bottom Plate NSGPTM-2 for Upper Deck26
NSGPTM-1 for Bottom Plate
・Pit count of VLCCs applying the NSGPTM-1 was much lower than that of VLCCs using conventional steel. And structural countermeasure was found to be effective against pits.
・Direct evidence for termination pit growth was observed.
　・Approved for CRS from Class NK and ABS.
NSGPTM-2 for Upper Deck
・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.
　　・Approved for CRS from LR, Class NK and ABS.
3. The application of such CRSs has been very effective in minimizing repair work and the risk of failure in structural integrity.
4．NYK decided to use CRS on our new tankers from and shares the continuous dock inspection result with NSSMC.
Here are conclusions,
First, on the NSGP-1,
・Pit count of VLCCs applying the NSGPTM-1 was much lower than that of VLCCs using conventional steel.
・Structural countermeasure was found to be effective against pits as like closed drain hole on lowest horizontal girder/side longitudinal.
・Direct evidence for termination pit growth was observed.
・It was approved for CRS from Class NK and ABS.
Second, on the NSGP-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.
・Approved for CRS from LR, Class NK and ABS.
Third, the application of such CRSs has been very effective in minimizing repair work and the risk of failure in structural integrity.
Finally, NYK decided to use CRS on our new tankers from 2004 and shares the continuous dock inspection result with NSSMC.

27. Thank you for your attention!27
Thank you for your attention!
Thank you very much for your attention.