Offshore Containers

Part 6: Good and bad design

Designing of steel structures for offshore lifting

Bad design: padeyes

• Padeyes are to be on line diagonally

(Tolerance + 2.5 grades)

• Padeye are exposed for damages

• Hole greatly exceeds 6% of shackle pin diameter.

Shocking Bad design- Padeyes on ISO Freight Containers

Pad eye not acceptable & considered dangerous for the following reasons:

• Fillet welded.

• Hole greatly exceeds 6% of shackle pin diameter.

• Pad eye is not in line with pad-eye in diagonally opposite corner of container.

• Sticking outside boundary of Container.

• ISO-containers are not suited for use offshore.

Bad design: padeyes

• padeyes are welded with fillet welds on the ouside of the frame• Padeye plate is not in the correct angle• 2 shackles are joined together

Bad design: padeyes and ISO container

Padeye attached later on an ISO-container:

• padeye-construction gives lack in continuity between toprail and corner post

• ISO-containers are not suited for use offshore (for instance the top beam is only a thin L-beam

A poor attempt at converting an ISO container.

Good design: padeyes

Padeye (padeye) slotted through the corner post

• Gives good foundation for the padeye

• Gives full penetration welds without large welds

• Do not require any specific material quality

• Angel can be adjusted according to need

Good design: padeyes

Padeyes slotted through the corner post

Comment: Sharp edge on padeye to be grinded

Good design: padeyes

To obtain full penetration welding with this design the base plate is slotted into the top frame. Padeye is being prepared and welded with full penetration. Base plate are to have ”Z”-quality.

Recessed into the Top Rail.

Accepted design

Depends on how it is done:

padeye on container with ISO-corner:

•Vertical weld are to have full penetration welding

•weld to horizontal corner plate may be fillet welds

•Angle between padeye and ISO-corner makes it difficult to weld, requires proper weld preparation

Bad design: padeye

The padeye must be positioned such that there is sufficient space for the shackle and eye of the wire ropes

Bad design: Skid

Skid protrudes beyond container parameters.

Good and bad design: Doors

Door mountings are unprotected – Bad design

Good design

Bad design: Fork lift pockets

Old container: Cracks in bottom frame due to not sufficient shear area above fork lift pockets

Good design: Fork lift pockets

Reinforcement (increased shear area) above fork lift pockets.

Alternative reinforcements above fork lift pockets(wall plates are thin secondarystructure)

Bad design

• Door locking mechanism and hinges unprotected

• Other unacceptable protrusions

• Fork pockets have no shear area above

Bad design: Bolted connection

Top frame bolted: Oval bolt holes not acceptable

Good design

• Protruding parts on the outside of the container frame that may catch or damage other containers or structures.

• Deflector plates to prevent snagging shall be applied.

Strength and stiffness in baskets

Frame work construction in the sides gives good stiffness to long baskets.

Bad design

• Padeyes not in line with slings

• Holes for shackle bolt too big

• Are full penetration welding used?

• Cylinders protrudes above frame

• Snagging hazard for slings in cylinder

Strong container with some errors 1:

• Protection of top

• Slings may be caught• Chains may corrosion on tank (which is made from acid proof steel)

Strong container with some errors 2:

AND:Too small clearance between tank shell and frame

Bad Design-Tank support

Tank is supported on the fork pockets.

RESULT?

Bad Design-Tank support

It is cracking!

It corrodes!It will soon be falling apart!

Offshore container with folding crane on roof, protected by a rail (and by tarpaulin during transport)

Bad design

DNV required that the rails were removed at the corner.

Container for stacking

Such knobs for stacking often gives damages at bottom of containers that are put on top.

Good and Bad design: lifting set

Bad design-Long slings may cause problems

Good design-Top link at working height for deck operator (< 1.3 m above the ground)

Top protection of open top containers:

“The top of all open frame containers and of all open top containers with permanent internal fittings, machinery or other installations where crane hooks or forerunners may snag, shall be protected with grating or plates. This may be fixed, hinged or removable. Top protection shall be capable of being secured.”

Good design: Top protection

Good and Bad design: Force continuity

� Lack of force continuity in the primary structure

Knee bracket shall be used