Offshore Container Seminar

DNV 2.7-1 – Design

Houston, October 10, 2011

Slide 2

Definition of Offshore Container:

A portable unit with a maximum gross mass not exceeding 25 000 kg, for repeated use in the transport of goods or equipment, handled in open seas, to, from or between fixed and/or floating installations and ships.

What is an offshore container?

Slide 3

In addition to the definition are the following limitations to the design:

� An offshore container is to have outer framework with Padeyes at or near the top. (waste skips may be constructed from flat steel plates forming the load bearing sections of the container) Sec.1.4.1.

� Protruding parts on the outside of the container frame that may catch or damage other containers or structures shall be avoided. (Padeyes and stacking guides may protrude above the top.) Sec. 4.1.3

� Is to consist of a primary structure frame and (optionally) secondary structures (walls, roof, etc.)

What is an offshore container?

Slide 4

Operational limitations for offshore containers:

� containers may be handled in maximum 6m significant wave height

� Design temperature -20°C (or colder)

� An offshore container shall be designed to withstand 30°tilting in any direction without overturning.

� Payload is not to protrude above or beyond the container perimeter

� Lifting set is to be permanently attached to the container

What is an offshore container?

Slide 5

Strength

Strength is calculated for:

� Lifting by lifting set

� Lifting by fork lift truck

� Local impact loads on the frame in sides and bottom

� Special calculations for pad eyes

� Load on walls and floor

Strength calculations are verified by prototype testing

Slide 6

Strength

Design approval:

� Strength is calculated:- Frame analyzes or simple manual calculations- Local strength, for instance padeyes, shear area in bottom fra,e

or lifting sets

� Review of the design- Materials- Minimum thickness- Welds, details and special requirements

� Drawings are stamped and returned, with or without comments

Slide 7

Frame analyzis is typically done for:

� long containers

� heavy containers

� open baskets

� containers with complex frames

May not be necessary for

� Smaller frames, for instance bottle racks

� Light containers

� Medium sized containers with strong frame

� Variants of well known designs

Strength

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Calculations and modelling

Primary Structure

� The Primary structure is identified from drawings

What is the primary structure?

• Load carrying and supporting frames and load carrying panels.

• Only the primary structure shall be considered in the design calculations.

Version Slide 910 October 2011

Add beam properties

Modelling of primary structure

Mirror about XZ-planMirror about YZ-plan

If the structure is symmetrical, it is only necessary to model ¼

Modelling/ calculations

Version Slide 1010 October 2011

Add lifting set

Use beam elements that do not transfer bending moments

Some programs may have special elements that only take tension loads

Modelling/ calculations

Version Slide 1110 October 2011

Add boundary conditions

To achieve a valid solution, the model must be restricted from movement in horizontal direction.

Top node is fixed

Modelling/ calculations

Version Slide 1210 October 2011

Modelling/ calculations

Lifting testAdd suitable loads

Payload and tare are to be distributed as realistic as possible

Evenly distributed in a general cargo container or node loads if there are fixed load points.

Load factor is 2.5 when using 4-point lifting and 1.5 using 2-point lifting.

Tare mass

Payload

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Analyse

1. Check the stresses. Note that allowable yield stress is:4-point lifting: 0.85 x R e (for steel)

Calculations and modelling

y

2. Check the deflection. Must not be greater than 1/300 of the span of the member.

Pz = 2.5 x R x g

3. Forces in the top node against the total design load.Must be equal to 2.5 x R x g

Slide 14

Design

Detail requirements

� Pad eyes

� Minimum material thickness

� Fork lift pockets

� Protrusions

� Top protection

� Doors and door locks are to be secured for unwanted opening

� Is the container to be weather tight?

� Painting and corrosion protection

Welding of padeyes

4.3.1: ” Main welds between the padeyes and the primary structure shall always be full penetration welds.”

Not Acceptable

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.

Slide 17

Pad eyes

Poor weld quality observed on several containers in a series

Slide 18

Pad eyes

One pad eye removed due to suspicion of unacceptable welding

Slide 19

Pad eyes

What we found

Continuity

Slide 20

Connection between top rail and end structure is compromised

Continuity

Knee bracket

Not acceptable

Acceptable

Good solution

Side walls are not included in primary structure

Slide 22

Fork lift pocket design

Corrosion inside

fork pockets:

� May fall out

� Weakens pockets

� Problems reduced if pockets have bottom openings

Fork lift pocket design

Fork lift pocket design

Old container, heavy corrosion, but no cracks

Fork pocket design

Old container: Cracks in bottom frame due to inufficient shear area above fork lift pockets

Fork pocket design

Reinforcement (increased shear area) above fork lift pockets.

Fork lift pocket design

Alternative reinforcements above fork lift pockets(wall plates are secondary structures and are not included in the shear area)

Slide 28

Fork lift pocket design

Paragraph 4.4.6 i DNV 2.7-1 states the following:

“Fork lift pockets shall be located such that the container is stable during handling with fork lift truck. Container length, height, width and rating shall be taken into account. Pockets shall be located as far apart as practical. Centre distance shall be at least 900 mm (where possible), but need not be more than 2050 mm.”

This is supplemented by a Guidance Note with recommended distance between fork pockets related to length of container for loaded or empty lifting conditions

Protrusions

Skid protrudes beyond container perimeter

NOT APPROVED!

Protrusions

Protruding edge on padeye grinded down

Side protrusions� Door locking mechanism

and hinges unprotected

� Other unacceptable protrusions

� Pork pockets have no shear area

Cargo protruding

� Cylinders protrudes above frame

� Snagging hazard for slings in cylinder

ALSO:

� Padeyes not in line with slings

� Holes for shackle bolt too big

� Are the pad eye welds full penetration ?

This “Container” is notapproved to DNV 2.7-1

Container for stacking

This stacking guide may snag e.g. on deck rail on supply vessel. Alternative designs should be considered.

Container for stacking

Stacking guides

Slide 36

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.”

2006 edition, Sec. 4 Design

Slide 37

Plate top protection

Slide 38

2006 edition, Sec. 4 Design (cont.)

Top protection of open frame container

Certified before protection requiremes introduced in 2006

Slide 39

Net on skips and baskets

Protective nets are often used on open units like baskets and skips.

Such nets are not required by DNV 2.7-1.

Hooks for such nets should be placed in protected locations, not stick outside. Holes to attach hooks.must not be drilled in closed profiles

Slide 40

2006 edition, Sec. 4 Design (cont.)

Top protection lids on cargo baskets (not mandatory)

Door locking bars are unprotected

Protection of locking devices

Door protection accepted

Protection of locking devices

Tank Containers

Tank Containers

Tank containers are defined in Ch. 6.7 of the IMDG Code

� The IMDG Code uses the term ”Portable Tank” - The term ”Tank container” is only used for those portable tanks

that comply with the definition of ”Container” in the CSC Convention and for offshore tank containers

� A special type is ”MEGC” – Multiple-Element Gas Containers

Tank Containers

The IMDG Code Ch. 6.7:

� Portable tanks for liquids, solids and gases

� Portable tanks are at least 450 litres

� The term portable tank includes a shell fitted with service equipment and structural equipment necessary for the transport of dangerous substances. The portable tank shall be capable of being filled and discharged without the removal of its structural equipment. It shall possess stabilizing members external to the shell, and shall be capable of being lifted when full.

� Portable tanks must be designed and fabricated according to a “Recognized Pressure Vessel Code”

Tank Containers

20’ ISO tank container – not suited for offshore use

Tank Containers

On offshore tank containers the tank is supported on 2 saddles and with a strong surrounding frame

Where are the various requirements?

THE IMDG CODE HAS REQUIREMENTS FOR:

� Design requirements for the tank

� The tank shell (minimum thickness)

� Valves and fittings

� The tank supports

THE PRESSURE VESSEL CODE HAS REQUIREMENTS FOR:

� Tank shell and other pressurized parts

� The tank saddles

DNV 2.7-1 HAS REQUIREMENTS FOR:

� The frame

� The lifting set

� Protection of the tank and fittings

� The tank supports

Tank Containers

Recognized pressure vessel codes:

� USA: ASME VIII

� EN: Various EN standards for pressure vessels

� UK: alternatively PD 5500

� Other standard may also be accepted by DNV after special consideration

Types of tank containers

IMDG Chapter 6.7 “PORTABLE TANKS”

� 6.7.2 – Tanks for liquids and solids

� 6.7.3 – Tanks for non-refrigerated liquefied gases

� 6.7.4 – Tank for refrigerated (“cryogenic”) gases

� 6.7.5 – Multiple Element Gas Containers, MEGC(for non-liquefied gases)

Selection of a tank container to carry a particluar dangerous cargo

� Is the cargo classified? UN number? Danger class?- Check the info. sheet for dangerous goods

� What requriments apply for the tank container?- Check entry for the UN number in part 3 of the IMDG

- Check Tank Instruction, Special Provisions, etc.

� Use the Tank Instruction number to find the particular requirements to the tank

- Part 4.2 of the IMDG

� Select a tank container which fullfills these requirements, or design a new tank according to Part 6.7 in the IMDG

� Remember that the tank container must be certified!

Marine transport of Dangerous Goods

What are the requirements to carry a special cargo in a tank container?

What are the requirements to carry a special cargo in a tank container?

Tank Instructions:

� From Tank Instructions in column 13 we find Tank Instruction T7 for Methanol

NOTE: In older IMDG codes the tank instruction for Methanol, given in column 12, was T4.Column 12 was deleted on January 1st 2010 and only column 13 can be used for all tanks, new and old

What are the requirements to carry a special cargo in a tank container?

What are the requirements to carry a special cargo in a tank container?

EXAMPLE: Transport of methanol (UN No. 1230):

Tank instruction: T7Test pressure:4 bars

Minimum thickness: 5 or 6 mm depending on tank diameter

Safety valve: Normal, i.e. bursting disc not required

Bottom closures: 3 closures in series:

- Internal valve- External valve- A bolted blank flange or screw cap

Marking:

Protection on tank containers

These valves need protection, e.g. by plate or beam (can be removable or hinged

(This tank container was NOT certified by DNV)

Tank support

Tank is supported on doubling plates on the fork pockets.

(Tank Container not approved by DNV)

The result?

Tank support

It is cracking!

It corrodes!It will soon be falling apart!

Offshore gas cylinder racks – Bundles

Bottle racks:

�A) with loose cylinders: the gas cylinders are certified at manufacturer, the container frame must be certified to DNV 2.7-1

�B) If the gas cylinders are fixed and interconnected through a manifold with valves, the unit is defined in Ch. 6.2 of the IMDG Code as a gas cylinder ”bundle”

Gas bottle racks

Bottle rack: frame with 16 gas bottles

(Not connected by manifold –therefore not a ”bundle”)

Gas Bottle racks

Bottle rack:frame for 6 loose gas bottles

BUNDLES need to have the following certification:

- The IMDG Code Ch. 6.2 Receptacles for gases

- The gas cylinders are certified to applicable standards at themanufacturer

- For IMDG approval: ISO 10961 Gas Cylinders – Cylinder bundles- (For ADR/RID approval: EN 13769 Transportable Gas Cylinders -

Cylinder Bundles)

- USA: 49 CFR requirements?

- DNV 2.7-1 Offshore containere

Slide 62

Gas bottle racks – bundles

This bottle rack is a ”BUNDLE” according to the IMDG Code

Offshore gas cylinder racks –Bundles vs. MEGCs

� IMDG/ADR/RID Ch 6.2: Gas cylinder Bundles:- Max volume 3000 litres- Offshore use not specifically mentioned in the code, but offshore

containers must comply with MSC/Circ. 860- DNV interpretation: Approval to Ch. 6.2 can be combined with DNV

2.7-1

� IMDG/ADR/RID Ch. 6.7.5: Multiple Element Gas Cylinder Tanks – MEGCs

- No lower volume limit- ISO 10961 or EN 13769 not applicable- Offshore container certification (i.e. DNV 2.7-1) also required by the

IMDG Code

Slide 65