Handle With Care: the difference between damage and fragility in shipping containers

Containers are, on the whole, rather good at protecting their cargo. Indeed, their protective qualities are largely why they were invented in the first place, as “traditional” break-bulk shipping saw cargo frequently getting dropped, slammed, crushed and soaked whilst in transit. The improvements in physical safety afforded to cargo are partly why the humble intermodal container has become a cornerstone of our modern, globalized economy.

However, containers have not always been a ubiquitous feature of shipping — as anyone who’s been in the industry long enough could tell you. Simple as it may seem to us today, the idea of loading goods into a sturdy steel box optimized for transportation only started gaining traction mid-way through the previous century. 

Of course, this “fool-proof” concept only works if the box is indeed sturdy enough to withstand the tribulations its contents must face as they journey across the globe. It’s easy to dismiss any concerns over container durability by pointing to their material construction: steel is strong, so it can surely handle whatever the world throws at it (figuratively or literally). Similarly, the Titanic was positively unsinkable due to its materials and design, and we all know how that turned out. A shipping container will spend more time at sea than the Titanic ever did, so it’s therefore worthwhile asking: how tough is it?

Breaking the Box

Let’s begin with a formal definition of a container’s physical resistance. One of the ISO standards concerning intermodal containers specifies that a container should be able to support a total of 192,000 kg of mass (under 1.8 g of acceleration) through its corner posts [3]. The container’s floor is supported by steel cross-beams, which (depending on the specific model) can carry loads of up to 28,200 kg [4].

From the above, it would seem that containers are quite strong after all, and there is nothing to worry about. However, the continuous physical stresses a container endures throughout its 12-year operational lifespan take their toll on these structures, gradually weakening them (as we’ll soon discuss in more detail). Moreover, strong corner posts will not protect the container’s walls and roof from physical impacts. The corrugated steel sheets used to make these are just 2 mm thick [5], and do not have any additional reinforcement to cope with the stresses and impacts containers endure on a regular basis.

If anything: just imagining that containers are not only exposed to salt water and waves, but are also part of our road traffic, one might now expect containers to suffer physical damage on a regular basis. Available data indicates that this is indeed the case, with estimates for the proportion of containers which are damaged at any given moment ranging from 7-9% [6] [7] up to 20% [8] [9]. The shipping industry is acutely aware of the prevalence of damage within its container fleet, and regularly submits units through dedicated inspection, maintenance and repair facilities [9]. Although the process isn’t perfect, container damage is a supply-chain problem that, to some extent, is being addressed and mitigated.

Factory Settings?

If container damage can be repaired — and generally is repaired (sooner or later), that may seem to be the end of the story. On paper, if a box is found to be damaged, there are only two outcomes: repair the damage and return the unit into circulation, or scrap and replace it. Therefore, it would follow that all containers must either be physically damaged or structurally sound and available for use.

There are multiple issues with this simplification, the most immediate being the fact that repair work does not necessarily bring a container back into perfect shape. Filler/caulking materials such as silicone and chloroprene [5] may not be as durable as the original steel they replace; the steel itself will be weakened by any welding work that’s needed to make repairs [10]. Overall, the patchwork of repairs a container accumulates over its life simply won’t hold up as well as a “fresh” box with untampered steel will. Given the unrelenting stresses both boxes will be going through on a regular basis, these patchwork containers are likely going to find themselves needing an ever-increasing amount of repair.

It doesn’t stop there. Steel, like all materials, is not immune to the ordinary wear-and-tear that come with repeated strain and it will gradually become weaker with use: the technical term for this is material fatigue [11]. The prominent, recurring physical stresses containers endure make them prime candidates for material fatigue, which will thus be making increasingly larger contributions to the frequency and severity of specific damages as the container ages. However: unlike these localized, incidental damages, the container’s material fatigue cannot be repaired and will only worsen over time.

Fragile, Not Futile

Both the material fatigue and the patchwork of repairs conspire to make an older container weaker and more susceptible to damage, when compared to a new, “healthy” container under the same conditions. There is no universal term for containers in this deteriorated state: here at ConexBird we prefer to use “fragile”. Just as a delicate, fragile egg may not do well after being hit by a large wooden mallet, a “fragile” container may not do well after being hit by the rough-and-tumble of the high seas.

There is no clear-cut point in a container’s life at which it switches from being “healthy” to being fragile and a liability to the supply chain. Rather, its deterioration is a gradual process which tends to accelerate as the container ages, with the unit’s commercial “usefulness” declining in tandem. Eventually, the value-adding revenue obtained from the container will become outweighed by the increasing downtime, repair costs and corollary issues its fragile nature entails.

Nomenclature or not: container owners have, in fact, recognized the issue of fragility within their container fleets and do take steps to mitigate its impact. Naturally, existing damage inspection procedures are a good place to start, as they will be happening anyway and should be able to determine whether a container remains seaworthy, before or after any repair work is performed. In theory, container inspections will be able to identify those units which would remain unsound even after extensive (and uneconomical) repair, and which should be removed from circulation to be sold for scrap.

Unfortunately, the container inspection process is imperfect and fallible in real life, which is why shipping lines also take other measures to reduce the prevalence of fragility within the container fleets they operate. These solutions range from keeping all containers in circulation below a certain age, to removing entire production batches of containers from circulation based on the eminent fragility of some individual units [12].

‍Sink or Swim

As they stand, each of the above solutions to the “fragility problem” will help remove some fragile containers from circulation, but not all of them. In addition, each method carries its own set of costs and inefficiencies which reduce the net benefit of its application. A more fundamental issue underlying all fragility-management techniques is the lack of awareness of the core problem itself. Some within the industry refuse to acknowledge that fragile containers even exist, despite the evidence pointing to its inevitable emergence within a productive container fleet. Others may conflate the fundamental characteristic of fragility with the immediate, superficial damage it manifests itself through. 

Whatever the reasons for these misunderstandings may be, they ultimately fail to recognize the pressing, very real concerns of container fleet management. Container owners/operators spend over $110 billion every year managing their container assets [13]: any steps that can be taken to reduce this titanic sum would be welcomed by shipping lines whose margins grow ever slimmer, and who are finding it ever harder to stay afloat in these turbulent times.

The sinking of the Titanic in 1912 reminded the world that what you don’t know can hurt you. Fragility, like sea ice, is a product of natural forces which will always remain a problem and which must not be wilfully ignored. We should therefore seek not to eliminate these issues entirely (a futile task) but to anticipate and circumvent them. Icebergs still pose a threat to ships in the North Atlantic [14], but improved protocols and advances in technology allow seafarers to cross the ocean safely without the constant threat of an unexpected collision. Similarly, the shipping industry has made some headway towards recognizing and addressing the fragility inherent to its container fleet. Nonetheless, there is still much more which could be done to stop container fragility affecting our vital supply chains, and which eventually will be done as we harness our knowledge and wisdom to continue building a stronger, smarter, safer world.