the korea shipbuilders’ association shipbuilders’ experience & feedback on iacs c ommon s...

The Korea Shipbuilders’ AssociationThe Korea Shipbuilders’ Association

Shipbuilders’ Experience & Feedback on IACS Common Structural Rules

1.1. IntroductionIntroduction

2.2. Technical Issues for Oil TankersTechnical Issues for Oil Tankers

3.3. Technical Issues for Bulk CarriersTechnical Issues for Bulk Carriers

4.4. Performance of IACS FeedbackPerformance of IACS Feedback

5.5. SoftwareSoftware

6.6. Concluding RemarkConcluding Remark

ContentsContents

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1. Introduction1. Introduction

Common Structural Rules (CSR)Common Structural Rules (CSR)

- Adopted at the End of 2005

- Effective since April 1, 2006

- Oil Tankers, Length ≥150m

Bulk Carriers, Length ≥ 90m

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Design Experience (Oil Tankers)

MR Aframax 1 Aframax 2 Suezmax VLCC

LBP 173.9 234 239 264 324

B 32.2 42 44 50 60

D 19.1 21.2 21 23.2 29.6

Ts 13.15 15 14.9 17.15 22

DWT 50 K 105 K 115 K 165 K 317 K

Classification LR KR/ABS DNV/ABS DNV KR/ABS

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Design Experience (Bulk Carriers)

Supramax Capesize

LBP 183.3 283

B 32.26 45

D 18.5 24.7

Ts 13 18.2

DWT 58 K 180 K

Classification KR/LR LR/BV

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2. Technical Issues for Oil Tankers2. Technical Issues for Oil Tankers

2.1 Weight Increase / Corrosion Addition

2.2 Minimum / Maximum Draughts of Abreast Full / Empty Conditions

2.3 D/B Floor Thickness Requirement (Bottom Slamming)

2.4 Shear Force Correction in way of Bulkhead Stringers

2.5 Prescriptive Requirement for Primary Support Member (PSM)

2.6 Effect of Toe Grinding on Fatigue Strength

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2.1 Weight Increase / Corrosion Addition [Unit : ton]

MR Aframax 1 Aframax 2 Suezmax VLCC

Weight

Increase

+415

(7.5%)

+1,000

(9.4%)

+940

(8.4%)

+1,200

(7.4%)

+2,000

(6.0%)

Note : Cargo Block Only

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Note: Design Corrosion Addition

of CSR <Pre-CSR(ABS)>

Received a letter from an Received a letter from an engineering company ;engineering company ;

“… preparing a bid for an FPSO to be converted from a 1996 DH VLCC … In our search for candidate tankers we looked closely at your hull (1997)your hull (1997) and found it in excellent condition. Ballast tank coatings, cargo tank under deck coatings, and tank bottom coatings are still in excellent excellent conditioncondition so there is virtually no corrosionvirtually no corrosion. We looked at another shipyard’sanother shipyard’s tanker tanker (1996)(1996) which was built with no coating under deck in the cargo tanks, and found general wastage around 2mm2mm on the deck on the deck plateplate; there was little or no wastagelittle or no wastage on uncoated structure (longs, transverse webs) lower in the cargo tanks.”

3mm<1mm>

3mm<2mm>

3.5mm<1.5mm>

4mm<1mm>

4mm<1.5mm>

3mm<2mm>

4.5mm<1.5mm>

3.5mm<1.5mm>

3.5mm<1.5mm>

2.5mm<1mm>

2.5mm<1mm>

2.5mm<1mm>

3mm<1mm>

7/31


2.2 Minimum / Maximum Draughts of Abreast Full / Empty Conditions

L. BHD Type Center L.BHDCenter L.BHD Two(2) L.BHDTwo(2) L.BHD

Rule reference

ConditionAbreast

Full Abreast Empty

Abreast Full

Abreast Empty

Prescriptive 0.6 Tsc 0.9 Tsc 0.6 Tsc 0.9 Tsc Table 8.1.6

FEA

Sea 0.6 Tsc 0.9 Tsc 0.8 Tsc 0.55 Tsc Table B.2.3/

B.2.4Harbor 1/3 Tsc Tsc 0.7 Tsc 0.65 Tsc

Note : Tsc = Scantling Draught

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Condition Draught

Abreast

Full Condition

Tmin ( l( lhh / L ) / L ) x Tsc

But not lesser than heavy ballast arrival condition

Abreast Empty Condition

Tmax ( L / l( L / lhh ) ) x Tsc

But not greater than Tsc

Min./Max. Draught Requirements (Proposed by KOSHIPA)

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2.3 D/B Floor Thick. Requirement (Bottom Slamming)

42mm (HT32 )42mm (HT32 )By Prescriptive Req. 42mm(HT32)42mm(HT32)

ttmeanmean = = 65 65 MpaMpa<<164 164 MpaMpa(Criteria)(Criteria) 40%40% ONLYONLY

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- Coefficient ffdistdist must be

lesserlesser, since floor length is short.

- Effect on stiffness of stiffness of bottombottom longitudinalslongitudinals is necessary.

fdist

ffbtm-lgbtm-lg

Prescriptive Requirement

??

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2.4 Shear Force Correction i.w.o. Bulkhead Stringers

POSITIONMax.

StressStress Criteria

Deviation

Below No.1 STR.

160 Mpa 188 Mpa - 15 %- 15 %

Below No.2 STR.

161 Mpa 188 Mpa - 14 %- 14 %

Below No.3 STR.

220 Mpa 252 Mpa - 13 %- 13 %

26mm (HT32 )26mm (HT32 )By Prescriptive Req.

28mm (mold )28mm (mold )By Prescriptive Req.

28mm (mild )28mm (mild )By Prescriptive Req.

O.T

.BH

D

No.1STR.

No.2STR.

No.3STR.

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2. Technical Issues for Oil Tankers2. Technical Issues for Oil TankersPrescriptive Requirement FE Analysis

?? ??

??

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2.5 Prescriptive Requirement for Primary Support Member (PSM)

CSR specifies as follows;

“The section modulus and/or shear area of a primary support member and/or the cross sectional area of a primary support member and a cross tie may be reduced to 85% of the prescriptive requirementsprescriptive requirements provided that the reduced scantlings comply with the FE cargo tank structural analysisFE cargo tank structural analysis”

14/31


LOAD CASE 10 LOAD CASE 20

Subject requirement is based on simple formula with simple formula with unclear assumptionsunclear assumptions, which can be dealt with by FEA properly and transparently.


D = 0.2 D = 0.2 llbdg-dtbdg-dt D = 0.13D = 0.13 l lbdg-dtbdg-dt

Z =Z =1000 M1000 MC C σσyieldyield

LOAD CASE 30 LOAD CASE 40

LOAD CASE 50 LOAD CASE 60 LOAD CASE 70 LOAD CASE 80




FE Analysis15/31


LOAD CASE 10LOAD CASE 20

Subject requirement is based on simple formula with simple formula with unclear assumptionsunclear assumptions, which can be dealt with by FEA properly and transparently.


D = 0.2 D = 0.2 llbdg-dtbdg-dt D = 0.13D = 0.13 l lbdg-dtbdg-dt

Z =Z =1000 M1000 MC C σσyieldyield

LOAD CASE 30LOAD CASE 40LOAD CASE 50LOAD CASE 60LOAD CASE 70LOAD CASE 80LOAD CASE 90LOAD CASE 10LOAD CASE 11LOAD CASE 12LOAD CASE 13LOAD CASE 14LOAD CASE 15LOAD CASE 16LOAD CASE 17LOAD CASE 18LOAD CASE 19LOAD CASE 20

FE Analysis16/31



CSR specifies as follows;

“The benefits of weld toe grinding should not be taken should not be taken into consideration at the design stageinto consideration at the design stage. However, an exception may be made for the weld connection between the hopper plate and inner bottom if the required design fatigue life can not be satisfied by means of practical design options such as increasing local thickness, extending weld leg length and modifying local geometry. The calculated fatigue life is to be greater than 17 years excluding grinding is to be greater than 17 years excluding grinding effectseffects.”

17/31


KOSHIPA carried out fatigue experiment &

analysis with a lot of test specimens.

18/31

3. Technical Issues for Bulk carriers3. Technical Issues for Bulk carriers

3.1 Weight Increase / Corrosion Addition

3.2 Hot Spot Stress for Fatigue Strength Assessment


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3.1 Weight Increase / Corrosion Addition [Unit : ton]

Supramax Capesize

Weight

Increase+460(8.2%)

+2,200(12.6%)

Note : Cargo Block Only

20/31


Note : Design Corrosion Addition of CSR <Pre-CSR(ABS)>

5.5mm<2.0mm>

6.5mm<1.0mm>

6.5mm<1.0mm>

5.5mm<2.0mm>

4.0mm<1.0mm>

3.5mm<1.5mm>

4.5mm<3.5mm>

4.5mm<1.5mm>

5.0mm<1.5mm>

3.5mm<1.0mm>4.0mm<2.0mm>

3.5

mm

<1

.5m

m>

3.0mm<1.0mm>

3.0mm<1.5or2.0mm>

4.0mm<1.5mm>4.0mm<1.5mm>

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3.2 Hot Spot Stress for Fatigue Strength Assessment


Hotspot Stress = ll x Extrapolated Stress

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0.5t

1.5t

1.0

s

0.8

s

: ExtrapolatedStress

Hotspot Hotspot Stress ?Stress ?

t

Hotspot Hotspot Stress ?Stress ?

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NOT MentionedNOT Mentioned

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4. Performance of IACS feedback4. Performance of IACS feedback

IACS CSR Maintenance Structure

??

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4.1 Time Required for Reply by IACS Hull Panel

Subject Ship TypeIssued to

IACS

Received Reply by Shipyard

Duration

Effect of Toe Grinding on Fatigue Strength

Oil Tankers

07.5.14 Not YetNot Yet > 4 months> 4 months

Bottom Forward DraughtOil Tankers

06.12.24 07.1.23 4 weeks4 weeks

Usage Factor for CrosstieOil Tankers

06.12.1 (SAJ)

07.3. (KOSHIPA) Not YetNot Yet > 5 months> 5 months

T.B Spacing on Enlarged LongL.(PMA)

Oil Tankers

07.6.19 Not YetNot Yet > 3 months> 3 months

Stress Increase Factor for Longls i.w.o BHD. for Fatigue

Oil Tankers

07.7 Not YetNot Yet > 2 months> 2 months

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4.2 Interpretation from Each Classification

Classification Item

Ship Type A B C D

Is hull girder strength check necessary for flooding case for IACS UR S25 ?

Bulk Carriers YESYES ?? YESYES NONO

Is a certain portion of dynamic load necessary for non-floodable empty holds in port ?

Bulk Carriers NONO NONO YESYES NONO


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5. Software5. Software

- Computational Softwares are incompleteincomplete yet.

- There is inconsistencyinconsistency between results of respective Classification Societies so far.

The result of any other Class’ software

(IACS) must be accepted for drawing

approval in due timein due time.

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6. Concluding Remark6. Concluding Remark

CSR is welcomed in principlewelcomed in principle because ;

- It utilizes high technologyhigh technology such as computerized calculation, introduction of dynamic loading and ultimate strength.

- Shipbuilders need to concentrate only only one (1)one (1) set rule.

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However, However,

- CSR contains several technical subjects, which are NOTNOT transparent / rationaltransparent / rational.

Hence, those should be reinvestigated and corrected as necessary with urgencywith urgency.

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RobustnessRobustness means

not necessarilynot necessarily the “Fat Boy”.“Fat Boy”.

??31/31

Thank YouQ & AQ & A

the korea shipbuilders’ association shipbuilders’ experience & feedback on iacs c ommon s...

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