Flexitanks Catch a Rising Tide


Back in 1991, when Ronald Stevens was starting in the flexitank industry, perhaps 12,000 of these industrial shipping containers were moved around worldwide. Today its probably more than 700,000 moves a year, he estimates, and many of the trips involve base oils, synthetics base stocks and finished lubricants.
Now president of Braid Logistics North America in Houston, Stevens said, Ive seen it evolve globally, and lubricants have become an important part of this business. While food and wine are also big users, speaking just for us, industrial fluids are about 55 to 60 percent of the total moves. Especially here in Houston, about 50 percent of our moves involve base oils and lubricants. We are shipping for major oil companies, like Shell, ExxonMobil and Calumet.
If youve ever bought bag-in-box wine, flexitanks are simple to picture; just think bigger. Lots bigger. A thick polyethylene bag, with capacity to hold more than 6,000 gallons of product, is fitted into a standard, 20-foot ISO shipping container. The bag is filled, the intermodal container is sealed, and all goes by truck and/or ship to its destination. Upon receipt, the contents are pumped out or discharged by gravity. The ISO container heads back for another trip, while the empty bag is disposed.
The key technology – the bag – has changed greatly over the years, Stevens recalled. Originally, the material used was rubber; bags were returnable and they cost $3,500 each. But you also had to pay to get them cleaned, pressure-tested and returned undamaged, so the cost was closer to $4,200. It was a nightmare.
Users now have a choice of single-layer bags, or multilayer bags, usually made of high density polyethylene and intended for one-trip use, he added. The multilayer bags can be more difficult to fully discharge, while the thick, single-wall bag may be less flexible – its apt to get folds and knuckling. Thats why Braid has two polyethylene engineers on staff. We extrude our own film, using a proprietary polyethylene formulation, and its rated to a 700 percent elongation property. The outside layer is woven polypropylene. We make the bags in China, in Thailand, and in England. The plant in China is our most modern – its like a clean room – and theyre testing the welds, the film, the valves, everything, every day.
Nikhil Agarwal, global head of base oils and lubricants at Sunrise Petroleum in Sharjah, U.A.E., says the bag-in-container option is especially good for smaller blenders in developing markets, who may not have the capital to afford or infrastructure to handle ISO tanks or bulk parcels. The up-front costs are more manageable, since customers have less cash tied up in inventory, Agarwal said., and we can reach smaller customers than we could otherwise.
Currently, his company ships 20 to 30 loads of base oil a month in flexies, sometimes with as high as 50 flexitanks per order. Most are going to buyers in Africa, India and the Middle East, and also to further points in Asia.
To keep costs even lower, Sunrise Petroleum manages the shipping arrangements itself, rather than handing that task off to a specialty freight forwarder. Dunnage costs are also lower with flexitanks than with an ISO tank, and the buyers get more actual product in each 20-foot container than they would with drums, Agarwal said.
Base oil trader Ray Masson, of Puma Crown in the United Kingdom, highlighted a major advantage: You can offload from a container ship, and take the container by truck inland to the blending plant. Were seeing a lot of Mexico-bound shipments going this way, or going down by truck from Brownsville, Texas, rather than by bulk parcel ships landing in Veracruz. Its a good option for those who do not have shore storage or warehouse space, he added.
One TEU shipping container holds about 15 to 18 tons, and cost of the bag alone can be around $600, said Masson. Youll also need the bulkhead to hold it in place, plus padding – usually corrugated paperboard – to protect it from contact against the containers bottom and sides. The protective rear bulkhead may be one solid piece, or individual slats or bars, and the interior of the containers must be inspected for any protruding nails or sharp metal prongs, before the bag is fitted in place.
As for the bags, the materials have to meet an ISO standard, and are made of an inert plastic, Masson said. They have to protect the base oil or lubricant from color changes or from oxidation. Some bags are better, some cost more.
Flexitanks also offer a creative storage solution, Samer Akram, director of operations at Unichem Services (Pty) Ltd. suggested last year at the ICIS African Base Oils & Lubricants Conference. First, he urged that flexitanks be used to bypass overcrowded tanker ports such as Durban, South Africa. Unlike shipments arriving via parcel tanker, he enthused, the shipping containers can be transferred directly to trucks for delivery, so flexitanks can serve as a cost effective and door-to-door package for – or from – deep inland and difficult-to-reach destinations.
Once at their destination, the flexies can be pressed into service as in-house storage tanks. This idea requires far less capital and time than building fixed storage tanks, Akram said. Oil removal requires a special pump costing about $1,000, but thats a one-time purchase.
The flexi-storage option is also being promoted by TransOcean Bulk Logistics. Its version, called the StoreBulk system, uses a standard 20-foot shipping container to hold product or raw materials on site. Once filled and stored in place, the contents are readily available for peak demand periods or backup supply in case of need.
Were seeing this used as a hurricane season storage option, observed Mark Reader, TransOceans business development manager in Houston. In those cases, the container box may be stored on the ground rather than on its wheeled chassis, which can reduce the demurrage. However, for static storage we dont recommend it for beyond 12 months.
Not everyone is comfortable shipping or storing in flexitanks. Some balk at the idea of losing 6,000 gallons of valuable product in one fell swoop, should a bag break. They also dont want the cleanup headaches it would entail.
Others say that theyd use flexies if they could go by rail, but worry the containers would be knocked about too much. Indeed, experience has taught Erica Kurth, operations manager at SIA Flexitanks in Houston, to be wary of rail transport. SIAs four-layer bags are made to its strict specifications by a partner in China. It also offers a seamless bag, which eliminated worry about burst seams.
The Association of American Railroads has procedures for certification testing, and suppliers are working to design rail-worthy flexibags, said Kurth. Yet, in my experience, its better to use railcars to move the product to a port, and unload there into flexitanks that are going on by truck or ship. With railroads theres a lot of switching and shunting, stopping and backing up, and jerking motion. That builds pressure inside the bag and the liquid sloshes around hard. The forces are so strong that you get bulging on a regular containers walls, which weakens them.
Ive worked with flexitanks for five years – and you need to be very, very cautious about rail, she added.
Others are hopeful that rail forces can be tamed by good engineering. Mark Reader of TransOcean says his companys flexitanks hold AAR approvals, and we have done thousands of these rail shipments without problem. It comes down to the container selection, the quality of the bag and the quality of the bulkhead. But you have to be sensible – railroads arent known for handling their rolling stock gently.
Another frequent question involves thick, sticky liquids; how do you get it all out of the bag? One shipper of polyisobutene told LubesnGreases it is too difficult and time-consuming to pump such viscous products from flexitanks.
It does require patience, counseled Puma Crowns Ray Masson. Highly viscous products can have heat applied. You may need to heat to 60 degrees C. to unload bright stock, so you start heating the day before, then discharge when its ready.
SIAs Kurth advises installing a heater pad under the bag before it is filled, and then warming the contents for a couple days before attempting to pump out. (Even so, the PIB shipper said he was more at ease applying heat to a steel ISO tank.)
Can one use a regular truck trailer instead of an ISO container? Not for this job, Braids Ronald Stevens replied. The sidewall strength of a regular trailer is not up to that of an ocean container. Some suppliers have tried to fit a longer, lower profile tank into a regular truck trailer, so as to not stress the box, but then youre not able to carry as much product. Normal dry-freight containers also are usually poor candidates for the flexitanks. The interiors take a lot of abuse, and you get screws protruding and sharp metal burrs that can damage the bag. The ISO container, and the right flexitank supplier, will avoid those hazards.
Too Big to Fail?
Maritime insurers keep a close eye on flexitanks. Theyre the ones on the hook financially if a flexitank leaks during a voyage, or worse, spills into nearby cargoes. In heavy seas, the sloshing liquid can distort the ISO containers so far out of shape they bulge and become unstable. Specifying a protected stowage position for the container aboard the vessel might help – but it also adds cost.
As flexitanks get bigger, so do the risks, says the Hamburg-based International Union of Maritime Insurance. In 2013 it strongly warned against letting the standard flexitank size rise to 24 tons. In fact, its loss prevention specialists argued that 15 tons is the maximum weight that is safe for ships traveling in difficult waters, and capacity everywhere else should be capped at 18 tons. IUMI cited a Germanischer Lloyd research report that container sidewalls can be irreparably weakened by the fluid pressure in flexitanks greater than 18 tons and suffer catastrophic collapse as a result.
If limited to 18 tons, the economics of using flexitanks to ship base oils and lubricants become weaker, but its still better than many other options, flexitank manufacturers said. We safely ship 24 metric tons on a regular basis, commented Mark Reader of TransOcean. But if shippers are concerned, they can take out an insurance option for a small premium.
We ship very few 24,000-liter bags anyways, and theyre mostly wine, said Ronald Stevens of Braid Logistics North America, and for lubricant shippers, it doesnt help the cost savings to limit the container size to 18,000 liters.
– Lisa Tocci

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Flexi Tanks    Packaging    Packaging Containers