Weld Failures in Ships

7/29/2019 Weld Failures in Ships

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"She is cracking up Captain and there is not a

decent weld to see or "Weld failures in ships"By Dr Jasper Graham-Jones

Support from Dr Brian Mellor, Engineering Materials Consultancy Service,

Southampton University.

The opinions expressed are purely personal and do not represent any other person or organisation.

Dept of Mechanical and ManufacturingEngineering, University of Portsmouth

Anglesea Road, Portsmouth, PO1 3DJ

Tel: 023 92 842113

Fax :023 92 842351

email [email protected]


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Ship Failure & Loss of Life

x 1930s Welded ships, Manual Metal Arc

x Liberty Ship failures. WW2 +250 ships fractured or

cracked; 19 of these broke completely in two.

x Fracture Mechanics comes of age!

x Factors:- stress concentration, high tensile stress,

relatively low temperature, susceptible steel

Titanic (14 April 1912) Weak rivets andBrittle steel hull.


3/53

Esso

Manhattan

29 March

1943 at the

entrance to

New York

Harbour

John P. Gaines,

November 1943. Vessel

broke in two off Shumagin

Aleutians With the loss often lives


4/53

Schenectady,

A liberty Tanker,

16 January 1943,

split in two while

moored in calmwater.

Only 24 hrs old


5/53

Post-War Ship Failures

x Tyne Bridge, Kow loon Bridge, Longitudinal beam cut

and weld either side of the bulk head frame 65. Poor

welding design, laminar tearing, fractures, etc?

x

Derbyshire 9/10 Sept 1980, associated with poorstructural strength, and poor design of hatch covers.

(doubled skinned)

x Torrey Canyon, Ran aground (19th March 1967)

x Costly Billions: insurance and life expectancyx Many Lives, Environmental Damage: who is affected?


6/53

Welding Methods

x Manual Metal Arc (Most common in ship building)

x MIG (Easy to use, but not as portable)

x TIG (Mix of above, but harder)

x Submerged metal arc.x Gas welding

x Solid phase bonding (explosive welding, Friction Stir)

x

Electron beam & Laser Welding


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Welding Defects

x Solidification cracking

x Lack of fusion

x Lack of penetration

x Porosity (Hydrogen)x Distortion

x Fatigue, Corrosion, Embrittlement, etc.


8/53

Welded Joints & Defects

Butt Joint

Lap Joint

Tee, joint

Corner Joint

Edge weld

Fillet and

Full

Penetration


9/53

Ship Failure 2


10/53

Tanker 1 Failure

x Force 8 gale in the Indian Ocean, land 800 mile.

x Noise & vibration at the bow

x Witness:- Irish deckhand, Mast Lights

Bow disappears???What would YOU do next?

Sailed 1200 miles in reverse to destination in India.


11/53

No.1


12/53

No.2


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17/53

Photo 37, Side longitudinal 27 Cracked through(1) Fatigue crack at toe of Bracket

(2)Longitudinal detached (cracked or never connected?)

1

2


18/53

Photo 38 Bracket at side longitudinal 29, Note renewed bracket is smaller than

original. Remains of original bracket are visible


19/53

Not renewed and L26 fractured at weld


20/53

Highly corroded non-renewed longitudinal (see photo 46)


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What happen?

x Many experts sent to photograph and assess ship.

x Design change to a fuel efficient engine thus no bow

fuel tank installed.

x

Fuel tank considered as a stressed member.x Corrosion Fatigue, cracks originating from the welds on

one side. Rapid crack growth, considerable distortion,

and final fracture on far side.


22/53

Tanker Failure 2

x Background, Super tanker 250,000 Tonnes, 20,000 T

water ballast, Oil cargo just unloaded.

x Greek owners, Japanese built, USA standards, British

Insurer (Lloyds), repaired in Singapore.

x Failed in Amsterdam, Holland at Shell Oil terminal.

Loud bang and ship moved and strained on its ropes

from the quay side.

Shi F il


23/53

Ship Failures

30m

etreFracturein

25-3

0mmSteelplate


24/53

Failure

x Initial unexpected soft grounding

x Loud bang, and ship movement caused by 20kT of

water.

x

Dry dock: 30m (90ft) crack through 25-30 mm thicksteel plate.

x Many internal weld failures and buckled steel members.

x Repair cost 10 million, not including loss of trade


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What happened?

x 30m brittle fracture, then escaping ballast water causes

bent steel sections and failed welds.

x Material of poor quality. (low temperature brittleness,

sulfide inclusions)

x Weld failures, Examine Standards, for general ships.

Fillet or Fully Penetrating welds

Fracture in bottom plating


27/53

Fracture in bottom plating

of oil tanker

18 m fracture in 25 mm thick bottom plating.


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29/53

Inside theb ll


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centre ballasttank

Port transverse web frames.


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Initial examination of ship.

x Design specified fully penetration welds.

x Although corrosion within standard (25% thickness).

x Many welds pulled out, many crack originate from

welds.

x Fillet welds not as strong, but easier and quicker to do

compared to fully penetrating.

x Ship has fillet welds????


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Selection of samples for laboratory


34/53

p yexamination


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Setup Metallurgical Inspection

x

Visit site, cut out 3/4 Tonne of samples.x Take before and after photos, detail exact locations and

record on samples. Securely pack in box for shipping

x Set up lab, dry storage, logging samples, photographs,

agree samples with all parties.x Layout in lab and agree which smaller samples to cut

from the main samples. Concentrated on fracture path.

Agree cutting method as some methods can damage

samples. (Make sure samples are not cleaned)

Laboratory


37/53

Laboratory

investigation

Underside of face plate on

transverse web just above

diagonal stiffener.

Transverse section at S. 16 mm gap

between transverse web and face

plate has been filled with weldmetal.

Laboratory


38/53

y

investigation

continued

Transverse section through

diagonal stiffener and upper andlower sections of transverse web.


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Results

x

Lack of penetration and fusionx Mix of old and new repair welds

x Considerable weld build up to conceal poor fit up.

x Some cracked welds not repaired (old fatigue marks)

and painted over (paint deep inside cracks).

x Although outside profile good, large pores at weld

centre.


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Weld details

x Poor fit up cured by filling gap with weld metal.

x Misalignment of upper and lower sections of transverseweb.

x True weld leg lengths as small as 2 mm. Corrosionreduced effective weld throat size.


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Weld details continued

x Weld between upper and lower sections of transverseweb should be a butt weld not a fillet weld.

x This had no effect on the static strength of the joint but

the fatigue strength of a butt weld is 1.6 times that of awell prepared fillet weld.

Welded structures fracture

l ld FE d l


42/53

Welds and structural failurealong welds so FE models

must replicate this.


43/53

Use sub-models of weld details

Load elongation on 5 mm

element corresponding to fillet

weld leg length.

Input into main FE model.

Pull off failure of fillet welded bracket.


44/53

Local Materials Properties

Use an instrumented

microhardness technique with a

spherical indenter to derive the

stress-strain curve for localregions of a weld.

Modelling of complex failuresequences in welded structures

using FE is hampered by lack of

local material properties.


45/53

Conclusions continued

x

The failure mode is only part of the story.

x Need to answer question, What is special about thispart?.


46/53

Tanker 2 failure conclusions

x Poor build and repair, (likely known to owner??)x Uneven loading with full ballast tanks.

x Soft mud grounding. (Owners requested non-grounding

berth)

x Ship unable to support own weight and that of ballast.

x Longitudinal split allowing water to rush out

(10KT/min) causing further damage.

x Some damage possible from dry dock.


47/53

Inspection, What happened?

x One man (US) to inspect a 250,000 t Tanker, built inJapan. Language problem?

x Ship access, individual weld inspection problems? Poor

inspection in difficult conditions.

x Why cant ships be inspected like planes????

x MONEY (Cost to benefit)


48/53

Overview

x

Ship losses are primarily caused by a number of events,perhaps even minor when considered individually in

isolation, which conspire together in a sequence which

leads inevitably to the loss

x

Failures will occur, and are required to be managed(Failure Management)

x There will be the inevitable differences of opinion

depending upon particular points of view and interest.

x You have to strive throughout to treat all possiblescenarios equally in terms of effort, time and depth of

analysis.


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Areas of Future Research

x Structural DesignModelling & Analysis of loading

x Life Cycle Risk Management

Corrosion rates, time variable stresses

x Production Technology

Good fit-ups & Production design detail

x People Dynamics & concepts of risk assessment.

Groupthink & Risky shift phenomenon'


50/53

Seacat propeller failure.

x New in service, Vibration from propeller.x Dry dock, Half a blade missing (1 of 3).

x Initial inspection, fatigue and brittle overload failure.

x

Detailed inspection, small pore, and welding heataffected zones around fatigue initiation sites.


51/53

Cause of propeller failure

x Overlay welded to repair a casting problem.x Poor finishing and NDT (Dye penetrate).

x Small pore, stress concentration, leading to fatigue

initiation.

x Crack growth, followed by multiple fatigue initiation

sites and rapid crack growth around welds

x Possible damage or excessive wear to bearings.


52/53

Metallurgical testing methods

x Eye, magnifying glass, (cracks, distortion)x Stereo low powered microscope. Cut samples, polish

smooth (stain) and examine for heat affected zones.

x High power microscope, Electron beam microscope

(Fatigue striations, inclusions, etc).


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Local materials properties

Use an instrumented microhardness technique with aspherical indenter to derive the stress-strain curve for local

regions of a weld.

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Weld Failures in Ships

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