TT Talk - Too much concentration may be an emerging risk!
- Date: 15/10/2013
- Source: TT Talk 180
Concerns over the availability of good quality boards for container flooring are rising. As a result there is increasing need for rigorous compliance with test procedures. There has been much international focus on the accuracy of gross mass of cargo, as well as correct weight distribution in the draft CTU Packing Code. The capability of container floors is a necessary part of the equation.
Safety in the supply chain has been making headway recently. The International Maritime Organization (IMO) is moving towards tightening its regulations regarding the accurate declaration to the gross mass of containers. It has also passed comments on the draft CTU Packing Code to the UN Group of Experts. Both these developments will be sent for ratification at next year’s Maritime Safety Committee.
Unfortunately it is premature to forget about weight and weight distribution, but the threat comes from a different source. The International Institute of Container Lessors (IICL) and the Container Owners Association (COA) have been working together on container flooring issues, which include alternatives to the traditional hardwood ply boards and the, importantly, quality of the flooring material.
New container production so far in 2013 evidences a worrying trend: two of the three regularly used alternative materials have not been used, leaving only bamboo and bamboo hybrid boards providing a more environmental solution. Why are alternative flooring materials significant? The raw material for the boards traditionally used in container flooring is slow growing hardwood trees. Stocks and availability of harvestable and sustainable lumber is falling and log diameter is reducing making it harder to produce quality veneers for the plies (layers) used to build up the boards. Consequently there are fears that the quality of the boards provided for both new build and replacement is deteriorating.
A reduction in quality can be often equated to the strength of the flooring material and thus the link to mass and concentrated loads. Container operators are reporting increasing damages to the floors especially near the doors where fork trucks ‘land’ from loading ramps. The wheels of fork trucks constitute concentrated loads in this instance and repeated movements into and out of the container constantly stress the plies of the flooring material. Over its lifetime, a 40ft container regularly used for pallets or cargoes packed and unpacked by fork truck can experience nearly 5,500 loaded movements across the threshold.
The International standard ISO 1496 Series 1 freight containers – Specification and testing attempts to ensure that containers can withstand this by subjecting container to a floor test (generally test number 8). Many container owners use the test set out in Part 1 of the standard (General cargo containers for general purposes) as one of their regular production tests to ensure continuity of quality. However, it is necessary to look closely at the requirements of the test procedure. The original Part 1 test standard required that the test vehicle had an axle load of 5,460 kg, but this was changed to reflect the industry standard requirement for additional strength, known as ‘ISO and a third’. Accommodating this, manufacturers would have a test vehicle with a load of 5,460 kg and, when required, add supplementary test mass of 1,800 kg to bring the axle load up to the industry standard value – 7,260kg. However, this change was only made in Part 1 of the standard and Parts 2, 4 and 5 still only require the lesser axle load, as do many CEN standards for swap body floors.
As a result, test facilities at container manufacturers may retain the ability to alter the test load on their vehicle. It is, therefore, important that owners and surveyors check that the test vehicle is fitted with the appropriate test load and, if uncertain, request that the test load is weighed before each test is carried out.
Reading the test procedure also reveals two other important requirements. Firstly, that the test vehicle shall be manoeuvred over the entire floor area of the container. Secondly, the test should carried out with the container resting on four level supports under its four bottom corner fittings, with its base structure free to deflect.
Covering the entire floor is often difficult to define. Many test facilities will pass the test vehicle up the centre and then manoeuvre it up one side and then the other. This is not really sufficient and two additional passes (in and out) should be made at about a third width on each side. Additionally, to simulate the fork truck more accurately, the test vehicle should cross the threshold at the beginning and end of every pass.
Standing the container on supports is also not that simple, since the ISO test requires that records are made of any plastic or permanent deflection. Since the test criteria (ISO Technical Report (TR) 15070 Series 1 freight containers — Rationale for structural test criteria) requires measurement of residual deformation production tests need to be on a pad that facilitates access to the underside out of the unit. However, the values in these criteria only confirm the ability of the under structure to support a fork truck; they do not confirm that the flooring material is suitable. For this to be verified the floor panels need to be removed after testing to check for signs of cracking or internal delamination especially near the middle of the plies.
So, to protect your floor, make sure that you are happy with the material being used when they are first built and check:
· the test vehicle has the correct test load;
· that the plies are not delaminated after testing; and
· that at least five full passes are made by the test vehicle
Thereafter, the container can expect another 5,495 loaded movements in its life. Further information can be found in IICL Technical Bulletin 001 and Technical Bulletin 006.
We gratefully acknowledge the assistance in the preparation of this article of Bill Brassington of ETS Consulting, who is a member of the ISO Technical Committee 104 on Containers.
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Risk Management Director, TT Club