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Accidents seem to happen at the mostinconvenient times, so it is important toknow who to turn to when they happen.When a 50,000-ton product tanker endedup with a hull breach while taking oncargo in a loading facility in Venezuela,the owner turned to Miami Diver LLC,a founding member of the Subsea Solu-tions Alliance, a global network of spe-cialized underwater ship repair contrac-tors that also includes Parker DivingService LLC and Trident BV.

The following is a chronological re-view of the events, from the accident,through damage review until the success-ful repair of the vessel.

The TankerThe vessel is a 50,000 MT ice-classed

product tanker (Fig. 1), built in 2009. The183-m-long double-hull ship is classed byDNV and RINA. In the area of the dam-age, the hull is constructed from 13.5-mm-thick higher tensile steel AH36.

The AccidentIn May 2012, the tanker was loading

jet fuel in a tanker port in Venezuela.During the loading operation at the ter-minal, the tanker sank deeper into thewater with every ton of cargo being

Repair of a Hull15 m below theWaterline

BY UWE ASCHEMEIER AND KEVIN PETERS

UWE W. ASCHEMEIER (uwe@miamidiver.com) is the sr.

welding engineer for the SubSea Solutions Alliance.

KEVIN S. PETERS (kevin@miamidiver.com) is the president of Miami Diver LLC, a

member of the SubSea Solutions Alliance.

Since circumstances prevented the vesselfrom entering dry dock, the repairs had to

be completed while it was afloat

Fig. 1 — This 189­m vesselrequired an underwaterrepair after it had its hullpierced sufficiently enoughto let seawater enter itswater ballast tank.

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pumped into the tanks. Nobody knewthat a submerged obstacle, most likely inthe form of a broken pile, was hiddenbelow the waterline, invisible to the offi-cers and crew of the vessel. While in-creasing her draft through the increasingweight of the cargo, the submerged pil-ing finally pierced its way through thehull of the vessel, allowing the ingress ofseawater into the portside water ballastwing tank.

Damage AssessmentDespite the damage, the tanker left

Venezuela and sailed to Aruba in theCaribbean Sea, where an initial evalua-tion of the damage was performed by alocal dive company. After the assess-ment, the owner of the tanker contactedthe Miami Diver office in Curaçao.

The damage proved to be severe (Fig.2), preventing the vessel from sailing toits destination. Class would only allowthe vessel to continue the journey if thehull breach was fixed permanently. Since

the vessel was fully loaded, dry-dockingwas out of the question. The repairsneeded to be performed with the vesselafloat. It was discussed with the ownerand class to sail to Curaçao and performthe repairs with the vessel at berth in theclear waters of the sheltered Caracas Bay.Miami Diver’s engineering departmentdeveloped a detailed repair procedurethat was submitted and agreed to by theowner and class, suggesting a no condi-tion once the repair was completed.

Attending the VesselWith the arrival of the vessel in Cu-

raçao, a team of divers, welders, and thewelding engineer were deployed fromMiami, Long Beach, and Curaçao to at-tend the vessel. The initial inspectiondive revealed an approximate 400- × 500-mm hole in the hull of the vessel and de-formed hull plating in the vicinity of thehull breach. In addition to the aforemen-tioned damages, the bilge keel andgrounding bar were also found to be dam-

aged — Fig. 3.The bilge keel and grounding bar had

to be trimmed back to allow for the in-stallation of the cofferdam and the insertplate. The trimmed bilge keel andgrounding bar were mechanically pro-filed to match the original form.

Templating, Engineering,and Building theCofferdam

To allow the repair work to be per-formed under dry conditions, a coffer-dam was engineered by Miami Diver.

To ensure that the cofferdam wouldbe large enough to enclose the area ofthe deformed hull, divers laid out thearea the cofferdam needed to cover andcommunicated the measurements to theengineering department.

Since the damage was in the turn ofthe bilge, the transition between the flatbottom and sidewall of the ship, diverstemplated the contour of the area to be

Fig. 2 — Damage to the hullviewed from the outside.

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enclosed by the cofferdam. The area cov-ered by the cofferdam needed to be largeenough to cover the deformation in thehull caused by the impact.

Based on information and sketchesprovided by the divers, the cofferdam wasmodeled to meet the required 4-timessafe working load at 14 m depth. Com-plete built drawings were produced to en-sure the cofferdam was built in accor-dance to the modeling profile.

The cofferdam was built from 8-mmASTM A36 steel in the facilities in Cu-raçao — Fig. 4.

Preparing the Insert PlateThe deformed and breached shell

plate section needed to be removed andreplaced with a rectangular insert plate,approximately 2185 × 1422 mm in size,with the corners prepared with class-required radii.

The insert plate, fabricated from 15-mm-thick EH36 class-approved steel wascut to size, prepared for welding with anapproximate 37.5-deg bevel and rolled to

match the curvature of the hull. Thepreparation of the insert plate was per-formed locally in Curaçao.

The track with customized ceramic

backing tiles develop by Miami Diver wasfitted around the peripheral edge of theinsert.

Lifting lugs were welded onto the rec-

Fig. 3 — Schematic of the vessel showing where the hull was pierced and bilge keel damage.

Fig. 4 — The cofferdam under construction.

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Fig. 5 — Diver welder weldinga lifting lug to the hull.

tangular insert plate to allow for easierhandling. After preparation of the insertplate was completed, the plate was placedinto the cofferdam.

Installing the CofferdamThe cofferdam was fitted with a

closed-cell foam gasket material aroundthe outer perimeter. It was centered andinstalled over the breach and deforma-tion, overlapping the weld zone 500 mm, to shield the welding area and heat-affected zone.

Weld fixtures were wet welded to theship hull (Fig. 5) by diver welders to holdthe cofferdam in place.

After installation, the cofferdam wasdewatered and checked for leaks prior tocutting and welding work to be per-formed from the inside.

Removing the DamagedShell Plate Section fromthe Inside

The damaged section of the hull plat-ing was removed by oxyfuel cutting frominside the cofferdam. The edges of thecut area (future weld joint) were groundsmooth and beveled (Fig. 6) to approxi-mately 37.5 deg. The corners were pre-pared with a 100 mm (4 in.) radii.

Preparing the Weld Joint To allow unrestricted access for re-

moval of the damaged hull section andinstallation of the new insert plate,frames needed to be cropped and/or tem-porarily removed. The welds between theweb frames and hull were carefully re-moved by gouging the weld. In the area

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Fig. 6 — Grinding performed to prepare the joint for welding. Fig. 7 — Insert plate being installed.

Fig. 8 — Welding the rootfrom inside the cofferdam.

of the intersection between the web ofthe frame and weld joint of the insertplate, weld access holes were removedfrom the web member, sufficient in sizeto allow unrestricted access to the weldjoint to be welded and tested.

Installing the New ShellPlating

After preparation of the weld joint,the insert plate was pulled tight againstthe outside of the shell plating with a con-sistent root opening of about 10 mm. Theplate was secured in place with weld fix-tures — Fig. 7. Prior to welding the in-sert plate, the previously cropped and/orremoved frame members were rein-stalled and tack welded into place. Thepreheat temperature of 80°C was con-trolled through heat-indicating crayons.

Root Opening withCeramic BackingCeramic Inclusion

While welding the root, welders expe-rienced a “popping” of the ceramic back-ing resulting in undesirable rejectable in-clusions in the root of the weld. It ap-

peared that the ceramic was emerged inthe seawater for too long, picking upmoisture that could not be releasedthrough preheating.

It was discussed with the owner andsurveyors to cut a 510- × 660-mm man-hole into the center of the insert plate,backgouge the root pass from the insertplate to remove all inclusions, and reweldthe root from inside the cofferdam. Themanhole was welded on ceramic backing.Both classification societies DNV andRINA agreed to the proposal.

After completion of the weld betweenthe insert plate and hull, the manhole wascut in the center of the insert plate to gainaccess to the root side of the original joint.

The root pass was removed by carbonarc gouging, followed by cleaning thejoint by grinding and rewelding the rootwith the SMAW process (Fig. 8) in theoverhead position.

Welding the Root from Inside the Cofferdam

After welding was completed, visualand ultrasound inspection was per-formed on the weld between the insertplate and hull plating. The weld did notreveal rejectable indications.

Reinstalling the ManholeCut­Out

The weld joint of the insert plate forthe manhole was prepared and weldedon ceramic backing. It was subject to vi-sual and ultrasound inspection after com-pletion. The welds passed without re-jectable indications — Fig. 9.

All temporary removed frames werereinstalled with weld sizes matching theoriginal weld sizes.

Welding

Underwater Wet Welding

Underwater wet welding was only per-formed to attach installation aids for thecofferdam, which were removed aftercompletion of the work.

All underwater wet welding was basedon AWS D3.6:1998 Class A welding pro-cedure qualifications (WPQ), employingthe wet shielded metal arc weldingprocess with Hydroweld FS electrodes.All welds were executed as multilayer fil-let welds in T- and lap joints.

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Fig. 9 — Large and small inserts asthey appeared from the water side.

Top Side Welding

Top side welding was per-formed as a permanent repair inthe dry. Top side welding was per-formed in accordance with theclass-approved welding proce-dure specification (WPS), em-ploying the flux cored arc weld-ing process (FCAW) under ashielding gas consisting of 75%argon and 25% CO2 and shieldedmetal arc welding (SMAW)process with class-approvedE7018 low-hydrogen electrodes.

Complete joint penetrationwelds were either welded on non-consumable ceramic backing orbackgouging the root and reweld-ing the root side of the joint.

Removing the Cofferdam

After removal of the coffer-dam (Fig. 10), previously weldedinstallation aids were removedand any weld metal remaining onthe hull was ground flush.

Underwater magnetic particle(MT) testing was performed onthe ship hull where installationaids for the cofferdam were re-moved.

Corrosion ProtectionAfter welding was completed

and the welds passed nondestruc-tive examination, corrosion pro-tection in the form of Hycote 151,an underwater, two-component,polyamine-cured epoxy coating,was applied over the welds, areasadjacent to the welds, and areaswhere the corrosion protectionhad been removed or burned offduring welding. This assisted inthe protection and reduction ofmetal wastage in those areas dueto immersion in saltwater by providing a permanent anticorro-sive protection. Preparation of thecoating of the internal paint system was performed by the ves-sel’s crew.�

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Fig. 10 — Divers removing thecofferdam.