Reducing the Cost of Ballast Tank Corrosion through Innovative Ship Design - An Economic Modeling...

8/10/2019 Reducing the Cost of Ballast Tank Corrosion through Innovative Ship Design - An Economic Modeling Approach.pdf

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Antwerp Maritime Academy

Content of this presentation

How it all started?

Do ships rust?

Ballast tanks and corrosion rates

What about sacrificial anodes?

What about corrosion rates and steelqualities?

Economic model comparing differentapproaches

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The Antwerp Maritime Academy : Academicmaster degree in Nautical Sciences & STCW95Certificates of Competence

Bologna declaration 1999: Scientific researchcompulsory alsoat university colleges

Topic self-evident

Corrosion and ships are historical enemies

Post Exxon Valdez => double hull construction fortankers accentuating the corrosion challenge.

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How it all started?


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Objectives

1) Written confirmation of an

increased corrosion

problem2) Numerous lab studies

between 1 parameter and

the rate of corrosion

1) Improved corrosion rate

model based on reality

=> better maintenance

2) Achievable corrective

measuresBasis

Target

IN SITU

RESEARCH

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Methodology

Development of a survey protocoland sample data sheet

Spelunking in the ballast tanks ofships of > 150 ships

Statistical interpretation with a

multidisciplinary team

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Do ships rust?

Definitely they do!

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Why do ballast tanks rust?

oe of the hys

Alternating wet/dry situation

Complex structure

Increased surfaces (double hull)

Use of high tensile steel Thermos effect

Difficult and expensive maintenance

Inadequate surface preparation and

coating application at construction

26 April 2012/7



The corrosion index CI

Adaptations to IACS:

11 sub-divisions

CI as a figure from 0to 10 or a % surface

G/F/P Corrosionindex

Weightedcorrosionin %

Breakdownof coatingor arearusted(Local)

Breakdownof coatingor arearusted(Scattered)

Localbreakdownof coatingor rust onedges orweld lines

Areaofhardrustscale

Good 0 0% 0% 0% 0% 0%

Good 1 1.175% 0.5% 0.5% 5% 0%

Good 2 2.35% 1% 1% 10% 0%

Good 3 3.95% 2% 2% 15% 0%

Good 4 7.675% 3% 3% 20% 0%

Fair 5 10.5% 5% 5% 25% 1%

Fair 6 15,5% 10% 10% 30% 3%

Fair 7 25% 15% 15% 40% 5%

Poor 8 30% 20% 20% 45% 10%

Poor 9 34% 25% 25% 47.5% 12.5%

Poor 10 38% 30% 30% 50% 15%

=> 1 single figure

represents the

tank condition

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or

CI


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Corrosion index

FAIR

POOR

GOOD

Scatter diagram & linear regression

Coating intact about 4.5 years

Corrosion about 1.7% per year.

GOODcondition about 10.4 years

POORafter about 22.1 years



Correlation between CI and ship

specific parameters?

Disappointing

No statistical correlation could be established

between corrosion rate and: Coating type (EpoxyCoal Tar Epoxy)

Trading area (World Wide, North Atlantic, Europe, Middle and Far

East)

Type of vessel (Tankers, Containers, Dredgers, Bulk, Others)

Length of vessel (



Presence of anodes

The advantage of the presence

of anodes (in our databsae)

could not be established

NOVA

Source of Variation SS df MS F P-value F crit

Between Groups 589.5537 3 196.5179 0.914721 0.437165 2.705838

ithin Groups 19335.52 90 214.8392

otal 19925.08 93

AAAAAH!

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The full database was sub-divided in :

tanks always wet

tanks alternating wet/dry

tanks always dry (not shown, too

small, neglected)

Each significant group was againsplitted in function of the presence of

sacrificial anodes

Of each group the average corrosion

rate was calculated (bar graph) andcompared with the linear regression

line (red axis)



Why?

Immersion time (only 50% of the time)Positioning/distribution

Evolution in time (function of thedamaged area)

Absence of an obligation => absence of acontrol mechanism

Anodes should be installed and maintained

the correct way or should be left out

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Relation chemical and physical

characteristics of ship construction steel and

corrosion rate 30 samples of grade A steel were collected

Experimental Korean corrosion resistant steel for use in ballast

tanks Exposed respectively 6, 12 and 18 months to naturalseawater

Always submerged

Alternating wet dry

Atmospheric humidity.

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Research started

2010 at the AMA



Results after 6 month permanent

immersion Experimental color method is

still experimental LPR & Tafel very confusing

results, apparently not the

best of techniques for this

kind of research

Weight loss = for us the most

reliable method

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Corrosion rate

Chemical& physicalproperties



Ordinate = Mass loss in gr/m2/yearComp 1 = Mn, C & FeComp 2 = Comp 1 +Si, Ni & Cu

Correlation between corrosion rate

and chemical composition

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Robust principle

component analysis &

quantile regression

Average corrosion rate

(42 samples) 526

g/m2/year

Average corrosion rate

CRS (2 samples): 377g/m2/year

It seems that CRS

corrodes 28%less thanthe average ship

construction steel quality

3 distinctive clusters

1: Korean

experimental CRS

for use in ballasttanks

2: High Tensile Steel

3: Grade A steel

1

CRS

3

Grade A

2

HTS


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Economic approach

Case II: Increased scantlings => no more steel replacements Case III: Improved paint system TSCF25 (Tanker Structure Co-operative Forum)

Case IV: Use of corrosion resistant steel

Case V: Grade A + PSPC15 + lifetime lasting aluminum anodes

Case I: Grade A steel + IMO PSPC15 coating + Zn

anodes (to be replaced every 5 years)


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Economic approach

Reduction of the costs

Costs taken into account

New building prices

Repair and maintenance

Time in dry dock + loss of revenue

Reduction DWT due to increased scantlings (case II)

Scrapping value

NPV calculated with 2% inflation rate and 4% discount rate

Sources

Bahrain Dry Docks price list 2008

Updates provide by IHC (ship construction Netherlands)

Antwerp Ship Repair

Damen ship yards

ArcelorMittal

POSCO

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General inflation rate of 2%

Discount rate of 4%

Increase of the steel price with 6% pro anno

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+

-

TCO = Total Cost Of Ownership & DR = Discount Rate

Economic approach

(NPV)

(NPV)


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Economic approach

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Grade A + PSPC+ Al CRSTSCF25

Increased scantlingsGrade A + PSPC+ Zn


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Monte Carlo Simulation

In the economic model 3 types of parameters aredistinguished

Fixed parameters deteied y the seleted ships odelsuch as LOA, BOA, DWT, surface ballast tanks etc.

Dependent parameters which are function of otherparameters f.i. cost of the anodes is function of thematerial, weight, cost of zinc or aluminum and theinstallation cost

Uncertain parameters which are allowed to vary between2 limits according a distribution model and taking intoaout a ost likely alue.

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Uncertain parameters

Uncertain

parameter

Symbol Min. Most

plausible

value

Max. Model Unit

Initial cost

PSPC15coating

PSPC15 40 45 60 Triangular /m2

Grade A steel(basic price)

AS 900 1,000 1,500 Triangular /t

Ratio CRS

versus grade A

RACRS

1.2

1.3

1.5

Triangular

Drydock/day CDD 2597 2885 3174 Triangular /day

Time charter

equivalent

TC 13,963 15,514 17,065 Triangular /day

Price zinc PZ 4 5 6 Triangular /kg

Price Aluminum PA 8 10 12 Triangular /kg

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distribution model uncertain parameters

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Minimum

MostPlausibleValue

Maximum


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Monte Carlo: Outcome

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TCO Case V TCO Case I TCO Case III TCO Case II TCO Case IV

Datenreihen1 22.740.271 22.779.409 22.931.627 26.497.959 27.855.352

18.000.000

20.000.000

22.000.000

24.000.000

26.000.000

28.000.000

30.000.000

32.000.000

TCO, mean value after 5,000 trialsError bar =

Well Matched

Freight loss

Price CRS


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Sensitivity

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Only the steel price is decisive

In case of construction in CRSprice ratio between grade A and

CRS is of moderate importance


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Conclusions

ieased satligs ot adisale. Loss of ago ayigcapacity is overwhelming.

Cases V, I, and III are very well matched. The correct choice is

is function of:

Actual and future cost of steel and coating

Financial parameters such as inflation and discount rates

Geuie haateistis of the supe pait ad the oosio

resistant steel.

CRS => Promising alternative for the present method of

constructing ballast tanks if the cost of the CRS dropssignificantly till < 1.1 x Grade A steel .

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Genuine qualities of TSCF25and CRS

The use of Corrosion Resistant Steel can onlybe considered if it lives up to the promisedqualities.

Corrosion resistance seems to be OK (28% less)Weldability has been studied and is OK

Mechanical properties are under investigation

TSCF25

is new and only scarcely applied. TSCF25

is under fire and certainly not generallyaccepted.

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Contact

Easy uestios ill e aseed ight aayAoyig uestios take a little it oe

time

[email protected]@hzs.be

[email protected]

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Reducing the Cost of Ballast Tank Corrosion through Innovative Ship Design - An Economic Modeling...

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