Container Handling

Freight units may be subjected to severe treatment during their lifetime, the main causes arise due to damage of units during handling. Integrity of containers is covered by mandatory strength tests in ISO 1496 Part 4 that apply specifically to strength of bottom corner fittings that must be satisfactorily complied with for them to be issued with a CSC Plate.

Mishandling is by far the most serious cause of accidents and it is incumbent on lifting operators to implement 'best practice' as laid down in the International Standard ISO 3874:1997(E), Series 1 freight containers- Handling and securing. The relevant part of this document, is Allowable Lifting Methods and covers all aspects of lifting freight units stating what is "Allowed" and what is "Not Allowed" for both loaded and unloaded units, The statutary limits concerning MGW and load distribution of containers are also covered in 4.2 Packing Loading and emptying in the same document. >

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Container Corner Fittings

The specification for corner fittings are given in ISO 1161/BS 3951 and Lloyds Register Guidance Note A. They are manufactured from both steel and aluminium and are secured within the container's main frame by side rails, end rails and corner pillars by welding. In the case of steel fittings these are made from Spheroidal Graphite Ductile Iron (SG Iron) . The exact composition is usually a manufacturers own impact resistant "Special Steel" to withstand shock loading when secured to rail wagons and shunted.
Before the mechanics of brittle fracture were fully undestood, corner fitting impact strength requirements omitted any reference to this failure mode and many corner castings on containers carried on rail cars, failed in colder climes. Nowadays corner castings for working at low temperature of -40°C are fitted as standard.

Corner fittings guidelines

Bottom Corner Fitting

Side and end apertures have the same profile.

Top Corner Fitting

Lugs used in the side aperture only, NEVER the end.

The top corner fittings are NOT THE SAME as those at the bottom. The bottom fittings have identical lifting apertures in the side and end faces and either can be used for lifting fully loaded containers. The top corner fittings are primarily used for lifting via the top face apertures, the end aperture is profiled to suit a hook and must only be used for lifting empty containers. The side aperture has the same profile as the bottom apertures and can be used for lifting empty units and, in exceptional circumstances, used for handling light process units.

Allowable Lifting Methods

A summary of specified lifting methods is given in ISO 3874, this replaces BS 3951:1989 previously used as the main reference when container handling. The current standard refers to the lifting of CTU's as being "Allowed" or "Not Allowed" methods of lifting and provides detailed charts for all specified lifting methods. The main methods of lifting freight units from their corner fittings are shown below.

Top Lift (6.2) Spreader

Four point vertical lift from bottom corners, side or end apertures.

Top Lift Sling (6.3)

For empty or lightly loaded Units. Never when laden.

Bottom Lift Sling (6.4)

Single Point Lift. Main method for lifting fully laden CTU's. See below.

End Lifting

Not a classified method in ISO 3874 but in widespread use for Side Loaders.

Top Lift Spreader (6.2)

These spreaders are normally used for rapid throughput of standard ISO containers at all modern ports and are substantial telescopic fully automatic devices lifting with ISO twistlocks via top corner box apertures. However, when handling Out of Gauge units, ancilliary gear is often used to couple the spreader to the OOG cargo unit for lifting from the bottom corner fittings with vertical slings. This ancilliary gear often takes the form of a simple basic "Dumb Bell" type adapter, shown here, made from two corner castings connected by tubular section. They can be quickly connected to the spreader twistlocks, the sling assemblies being connected to bottom lifting lugs.
OOG cargo should be uniformly distributed resulting with Central of Gravity hence the load is carried equally by all 4 vertical slings.

Top Lift Sling (6.3)

For lifting empty and very light Process Units. This method uses the TOP corner fitting's side apertures only, the top end aperture has a different profile to that of the side. The end aperture was designed to be used with a hook and only for lifting empty containers. Lifting lugs must NEVER be used in the END apertures of top corner fittings. Certain freight units, in particular Flat Racks, have their end apperture blanked off to prevent hooks from being used. The main problem with using the top corner fittings is the necessity to gain access at an elevation of at least 8ft. The example shown here is a lightly loaded process unit that could only be lowered from the top into position to avoid ground level obstructions. This is a prime example where the "Handling by unspecified lifting methods.(5.2)" clause cited below has been implemented.

Bottom Lift Sling (6.4)

This is the most common method for both Side and End lifting. The basic method uses a pair of two leg slings with lugs at one end and a hook at the other, this configuration is referred to as Single Point Lifting.
Depending on both the lifting height and weight of unit being lifted some intermediate gear may be required. The example here shows a container being lifted using slings with spreaders, these are usually steel tubes strong enough to react the axial compressive force induced by slings where attached to spreader. These prevent slings making contact with container's top side edge rail with the possibility of serious damage. When handling empty or light non ISO Standard process units, spreaders are often dispensed with to minimise lifting gear requirements. Other typical sling arrangements used are shown below for various height and weight limitations, Many types of lifting gear assemblies are available off the shelf or for hire.

When spreaders are used the sling force in the portion above the spreader is greater than that below, therefore, the sling angle in the plane of sling assembly at the spreader should be as great as possible to reduce the higher loading of sling portion between spreader and hook.

Typical Bottom Lift Sling arrangements

Two Leg Slings

For empty containers or light process units. Forces at contact points on top side rails.

Top Lifting Beam

For minimum head room and limited lifting height. Substantial heavy beam is required.

Truss & Single Spreader

Beam replaced by truss. Spreader under compression.

Two Spreaders

Most common type, spreader forces half those for single spreader

When Single Point Lifting with any of these arrangements the Centre of Gravity ALWAYS aligns itself with the top lifting point. For eccentrically loaded containers this could result with serious problems arising from the unpredictable motion of container during alignment.

Limiting Transportation Loads

Eight axle transporter.

Since most cargo platforms are transported by road, the factor that governs the MGW of any unit is the limiting Vehicle axle loading. This is in the form of a mandatory weight restriction that may vary from the country of origin and any other country through which the load may pass, there may even be weight restrictions on roads that need addressing.
In the UK and EU the axle loading results with a maximum Gross Trailer Weight (GTW) of 48 tonne and is normally shown on a plate or sticker fitted to the vehicle.
Since the minimum weight of transporting vehicle must be 3.5 tonne the maximum possible

MGW of payload

is 44.5 tonne. In reality the payload will be less since transport vehicle may be well above the minimum quoted here.

Handling by unspecified lifting methods. (5.2).

Over the years there have been many developments in container handling, in particular, the now ubiquitus Side Lifting Machines for which there is still no reference to this lifting mode in ISO 3874. Not all freight units, fitted with ISO corner fittings resemble ISO Containers and may not even carry a

CSC Plate

In addition, the method of handling them could fall outside the remitt of the "Allowable Lifting Methods" cited above but must still comply with International Standard Practices. Once again this falls upon the auspices of a "responsible person". Who else?

Now that BS 3591 is obsolete ( Withdrawn) there is greater flexibility to the interpretation of the current ISO Standard and clause 5.2 has been added to Section 6 of the current standard and applies to the lifting of both non standard freight units under exeptional operating situations.