Safety Alerts 647

Experience transfer Safety Alerts Svein Flogeland Product Manager, Offshore Class DNV Technical seminar on Mobile Offshore Units Mumbai, February 15th 2008

Damages and incidents „

Damages like cracks and indentations as well as incidents with potential for serious injury or loss of life are reported to the central units supporting DNV’s classed MOUs in operation

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Damages are logged in a data base and used for improvement of Inservice Inspection programs on a continuous basis

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Incidents are analysed for root cause often in co-operation with Owners

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Experience which may serve to prevent simlar incidents in the future are communicated with Owners at our annual Rig Owners’ Committee meetings as well as with surveyors at the annual Rig Co-ordinators’ Colloquium

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Safety alerts may be issued directly to Owners and through IACS if a damage or incident is considered serious with likelihood of appearing also on other, similar units

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Some examples of incidents The following incidents have happened over the last year: „

Aker H3 Cracks

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Bolt Corrosion on Shuttle Valve on BOP

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Excessive friction in fairlead

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Insulation of Hot Surfaces

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Near Casualty during Tank Inspections

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Explosion in Ballast Tank

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Steam piping failure

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Recent Experience – One Arrangement

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Recent Experience – Another Arrangement

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Crack revealed after removal of bracket

Crack under fillet

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BOP Shuttle Valve Failure „

While testing the functions on a subsea BOP, North Sea 2005, a shear ram shuttle valve failed, reducing the BOP functionality considerably.

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On pulling the BOP, it was noted that bolts holding the shuttle valve body together had sheared off.

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Bolts were sent to the DNV Laboratory in Oslo for analysis.

Bolts sheared at points A & B

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BOP Shuttle Valve Failure Results from the laboratory analysis were: „

Fractured bolts were low-alloy steel (CrMo type) meeting the mechanical requirements for ISO 898-1, Class 12.9. A thin layer of baked epoxy for corrosion control was noted.

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Valve body and endplate found to be AISI 303. These steels notoriously susceptible to corrosion in marine environments. DNV advise against use of such grades in potentially corrosive environment, including fluids for hydraulic control systems that may become contaminated by seawater.

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The failure mechanism was found to be stress corrosion cracking (SCC). High strength steels with SMYS > 1,000 MPa are generally recognised as susceptible to SCC also in absence of stimulators for hydrogen absorption such as H2S.

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DNV recommend a maximum strength of bolts for subsea applications corresponding to Property Class 8/8 or 9/8 (i.e. UTS 800MPa and 900 MPa).

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DNV recommend bolting carefully looked at during subsea BOP overhauls.

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Loss of winching power due to friction „

Unit carried out renewal survey

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Operator demanded ‘acceptance test’ of winches

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Test showed that up to 50% pulling power was lost at lower fairlead

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Owners should look carefully at available ‘pulling power’ as a lot of safety cases assume unit can winch off location up wind in an emergency

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New Pinion

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Fairlead Pinion damage

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Fairlead Pinion Bearing Damage

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Insulation of hot surfaces „

Oil leakage hitting hot spots on engines is the most common cause of engine room fires

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More than 60% of all engine room fires have been initiated by a hot spot

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DNV and IACS requires all Surfaces above 220°C to be insulated to avoid ignition of flammable liquids

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SOLAS Ch II-2 Reg 15.2.10 implemented July 1998 introduced same rule

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Hot surfaces Common trouble areas are: „

-Indicator valves

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-Cut outs for pressure/temperature sensors

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-Cylinder covers

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-Exhaust pipe from each cylinder

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-Transition in to exhaust manifold

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-Exhaust manifold, in particular overlaps between steel sheets and laggings

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-Foundation and lifting lugs on exhaust ducts and manifolds

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-Turbochargers, in particular flanges to such

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-Boilers Version

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Recent Fire due to Missing Shielding „

Ignition area of the fire close to noninsulated area

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Ventilation helped spread the fuel onto the hot exposed surface of the turbocharger flange

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Missing shielding to protect air intake

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Fuel leaked from the gasket of the fuel filter

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Conclusion „

More emphasis will be taken on surveys of insulation of engines

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During renewal surveys if surveyor suspects problems, more thorough evaluation may be required. - Use of laserbased Infrared Heat Tracers - Infrared Thermoscanning Video Equipment

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Near casualty during Surveys „

Normal precautions had been carried out - Gas freed - Watch man posted

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Team prepared to enter tank

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As they adjusted eyes (tropical daylight to dark tank), they realised grating on platform was not in position.

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Picture of tank access

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Picture of Tank Access

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Recommendations „

New safe working procedures recommended, including reference in access checklists to check grating is in place.

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A warning signboard placed inside each hatch coaming WARNING! BEFORE ENTERING THE TANK, MAKE SURE THAT THE HINGED GRATING PLATFORM IS IN CLOSED POSITION.

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Explosion in Ballast Tank Course of Events „

Repair job in a pre load tank

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Workers using gas torch

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During a break, the gas torch valves were closed

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Workers return from break and tank explodes when torch is ignited

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2 workers seriously burned, one died in hospital

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Explosion in Ballast Tank Probable Cause ƒ

Most probable cause was ignition of gas coming from gas torch

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Investigation revealed valve on torch was not tight, gas had accumulated in the tank during the break as there was no proper ventilation

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Explosion in Ballast Tank Lessons Learned ƒ

The conditions for the issuance of a hot work permit can change quickly and need regular follow up

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Continuous ventilation should be a condition of the permit. This may have prevented or reduced the accumulation of gas

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Gas equipment should be well maintained

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Isolation of gas torch should include isolation of gas bottles

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Steam piping failure „

During a conversion of a Tanker to FPSO a 10” cross-over steam pipeline was installed between an existing boiler in the machinery space and a new process boiler on the process deck area

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Steam piping failure „

The cross-over line suffered from two instances of malfunction during service 1. A tee-piece cracked during commissioning. Pipe stress analysis showed that the tee-piece had been exposed for very high stresses (displacement stresses), which was due to limited flexibility in the piping system 2. An expansion joint (belly) was wrongly installed (tie-rods had not been released), in combination with the fact that no “line stop” or “anchor” support was installed to “direct” the thermal expansion in the axial direction towards the expansion joint. The result was that the expansion joint tie-rods were ripped off (as a combination of pressure thrust forces and thermal displacement forces). The line moved approx. 250mm off position until it stopped against a bulkhead.

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Steam piping failure

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Steam piping failure

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Steam piping failure „

The risk potential of this incident was very high. Four people were working in the machinery space, close to the expansion joint when this happen. Luckily the expansion joint (belly) did not rupture, if that had happen the four workers most likely had been killed.

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Lesson learned 1. When doing newbuilding- or ”As-carried out” survey of steam piping systems inspect closely expansion joints (belly type) in order to secure that the tierods is properly released. Remove insulation if necessary 2. Inspect that supports and anchors are installed according to approved drawings 3. Note that expansion loops are recommended in preference to expansion joints (belly type) 4. If any doubt of pipe line integrity, contact OUiO, Høvik

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Steam piping failure „

The steam pipe was repaired changing out the tee-piece and changing the expansion joint (belly type) with expansion loop. Additonal supports were installed.

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