hull struct

7/31/2019 Hull Struct.

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- Symposium 1N M R I

Tanker Structureand

Hull Failure Strength

Hajime Kawano and Masaru Hirakata,

National Maritime Research Institute, Japan.


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Contents;

Introduction

. Large-scale oil spill accident by t ankers

. I MO rule movement on tanker st ructure

Aging effect of ship hull

. Typical st rengt h degradation by aging

. Hull plate corrosion data propert ies

. Degrading of longitudinal bending st rength

Failure st rength of aging t anker hull

. Basic mechanism of large- scale hull failu re

. Case study Conclusion


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1-1 Large-scale oil spill accident by tankers


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1-2. IMO rule movement on tanker structureHistory in VLCC structural changes (1)


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1-2. IMO rule movement on tanker structureHistory in VLCC structural changes (2)


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1-2. IMO rule movement on tanker structureEnhanced Survey Program on tanker structure


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1-2. IMO rule movement on tanker structurePhase out of single hull tankers


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2.Aging effect on ship hull2-1. Typical strength degradation by aging

(1) Corrosion a. Corrosion in frame member

b. Corrosion in platingc. Local corrosion

(2) Fatigue crack

(3) Degradation of paint coating


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2-1. Typical strength degradation by aging(2)

(1) Corrosion a. Frame corrosion b. Plat ing corrosion c. Local corrosion(2) Fat igue crack(3) Coating degradation

Corrosion in bot t om plat ing ;

1) horizontal/ vert ical plat ing2) splashed zone or not3) effect of fluid velocit y4) effect of high t emperature, etc


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(1) Corrosion a. Fram e corrosion b. Plat ing corrosion c. Local corrosion(2) Fat igue crack(3) Coating degradation

pitting corrosion

raised by high stresses grooving corrosion , etc.

Typical local corrosion on str inger : below

grooving corrosion alongfill et w eld of deck longl.


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(1) Corrosion

a. Fram e corrosion b. Plat ing corrosion c. Local corrosion(2) Fat igue crack(3) Coating degradation

Fat igue crack at side longit udinal,

in 2nd generation VLCC damages.

Fatigue crack grow that f il let w elded corner.


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2-1. Typical strength degradation by agingDegradation tendency with increase of ship age

(a) Trend in degradation mode (b) Trend in number of failures


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2.Aging effect of ship hull2-2. Hull plate corrosion data properties

Corrosion rate analysis by using class NK database


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2-2. Hull plate corrosion data propertiesexample for deck structure


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Allow able dim inut ion Level by Class Society spec.


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2-2. Hull plate corrosion data propertiesSchematic diagram on aging ship strength


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2.Aging effect of ship hull2-3. Reduction in mid-ship section modulus

Estimated results on average tendency ofthe VLCC mid-ship section modulus;

(1) IMO requirement :

within 10% loss of Z

(2)Average corrosiondamage is withinIMO requirement.

Note:

analyzed---- imaginary scatter

Z at Deck( Cumulative Prob. : 50%)

0.9

0.92

0.94

0.96

0.98

1

1.02

0 5 10 15 20 25

Service Year

Z_a

ct./

Z_b

uilt

Double Hull Tanker

Single Hull Tanker


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3. Failure strength of aging tanker hull3- 1. Basic mechanism of large- scale hull failure


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3-1. Basic mechanism of large-scale hull failureAs to hull break-up mode

Trigger element for tanker hull break-up

(1) Buckling/collapse at Deck structure in Sagging

(2) Crack propagation at Bottom structure in Sagging

(3) Crack propagation at Deck structure in Hogging

(4) Buckling/collapse at Bottom structure in Hogging

i) break-up occurs in high wave Sagging M.> Hogging M. ii) deck back surface is the most severe corrosive space

in hull circumstances, and so forth.

(m ult i- site damage)


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3-2. Case studyOutline of the Nakhodka casualty

Date: 1977.1.02, 02:40amLocation: Okino-shima NNE 106kmwave condition: H1/38m, Tave9 sec

Fr.153Fr.137

Failed and broke in t w o


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3-2. Case studyLoading pattern at the Nakhodka casualty

Loading patt ern at t he casualty ; excess t o a standard loading pat tern

values : Load (i n kl) at t he casualt y indicates a standard condit ion.


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3-2. Case studyCorrosion wastage at the Nakhodka casualty

Measurement result ; 20-35% of plate thickness reduced due to corrosion


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3-2. Case studyApplied force at the Nakhodka casualty

VBM and VSF w ere obtained by using non-linear ship mot ionand response simu lation softw are.


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3-2. Case studySimulation cal. on ultimate collapse of Nakhodka

Simulat ion result show ed ;the break-up started at the deck structure on about Fr.153.


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3-2. Case studyEstimated results on load and strength

Causes of t he Nakhodka casualty;(1) Excessive corrosionmade t he Nakhodkas vert ical bending

st rength about one half to that of as built .

(2) So, the most severe w ave loadin a year at Japan sea, lether broke up.

(3) I n addition to t he above, the non-standard loading patt ernat t he accident had enlarged the wave load.


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4. Conclusions(1) Large-scale oil spill from tankers w ere not yet ext erminated.

And one crit ical factor must be hull excessive corrosion t hat

might be overlooked, so that it should be st rongly requiredst rict implementat ion of t he ESP and excluding sub-standardtankers.

(2) From the analysis of corrosion measurement data at t heclassNK inspect ions, not only average w astage rate but alsoincrease of standard deviat ion of the rate are key factors to

understand the ship ageing and the influence.

(3) As to hull breaking up, it seems that excessive corrosion andsevere w ave condit ion are tw o main players and a possiblet rigger failure migh t be a buckling/ collapse of deck st ructureat t he t ime of high w ave of sagging.

I n anyw ay more act ions are necessit ated, not only t o preventcasualt ies but also to m it igate the oil out flow and the damageof t he ocean, to keep our global environment clean.

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