沥青集装箱软包装 · Bitumen Flexitank and Bag-in-Container into China

柔性罐（flexitank）是一次性聚乙烯内袋，设计对象是常温、非危险液体。沥青常温下是固体，必须热装热卸，而柔性罐没有加热盘管，也没有保温层，到港后袋内是一整块冷却的沥青，泵不出来。聚乙烯熔点低于沥青泵送温度，热装本身就有破袋风险。集装箱内可行的是集装箱沥青罐、加热罐式集装箱、可熔袋和全新钢桶。

A flexitank (柔性罐) is a single-use polyethylene bladder fitted inside an ordinary dry container, and it was designed for non-hazardous liquids that are liquid at ambient temperature. Bitumen is a solid at ambient, has to be loaded hot and has to be discharged hot, and a flexitank has no heating coil, no jacket, no insulation and no connection for an external heat source. Whatever temperature the cargo goes in at, what arrives is a cooled block that cannot be pumped out. The material limit compounds the problem rather than softening it: polyethylene melts below the temperature at which bitumen is pumped, so filling a bladder with hot binder puts the containment film at or beyond its own melting range while it is being asked to restrain twenty tonnes of dense liquid. The formats that actually carry bitumen inside a 20-foot container are the bitutainer (集装箱沥青罐) or a heated tank container, meltable and jumbo bags carrying solid binder, and new steel drums. This page explains each one, and says plainly what to ask when an offer quotes bitumen in flexitanks at a rate that looks too good.

A flexitank — also sold as a flexibag — turns an ordinary 20-foot dry container into a single-voyage bulk liquid tank. The bladder is a multi-layer polyethylene inner with a woven polypropylene outer sleeve, laid on a protective liner across the container floor and restrained at the door end by a steel bulkhead. Filling and discharge run through a valve, either at the bulkhead or on the top face of the bladder. Working capacities in commercial use run from roughly 16,000 to 24,000 litres. After one voyage the bladder is cut out and disposed of; nothing is cleaned, returned or repositioned.

The commercial appeal is easy to see and it is real. There is no tank container to lease, no empty equipment to reposition after discharge, no drums to buy at origin or dispose of at destination, and the box itself is an ordinary dry container that any liner can supply and any terminal in the world can handle. For a shipper moving base oil, lubricants, non-hazardous chemicals, latex or food-grade liquids in parcels of twenty-odd tonnes, that combination is hard to beat. Flexitank operations are covered by the Container Owners Association Code of Practice for Flexitanks, and shipping lines normally approve both the flexitank supplier and the specific nominated cargo before a booking is accepted.

设计前提 · What the design quietly assumes about the cargo

Every one of those advantages rests on four assumptions, and they are worth writing out because bitumen fails all four rather than one:

• The cargo is liquid at ambient temperature, so no heat has to be added at either end of the voyage.
• The cargo stays liquid unattended through a winter transit, a terminal dwell and an inland leg, with no thermal management of any kind.
• The cargo is non-hazardous, so the box moves as ordinary dry cargo on an ordinary booking.
• The cargo is light enough that volume rather than weight is the binding constraint — which is where the entire cost argument comes from.

三个不同的东西 · Flexitank, bag-in-container and meltable bag are not synonyms

A large part of the confusion in this corner of the market is vocabulary rather than engineering. Bag-in-container (集装箱软包装) describes a shape, not a technology, and it covers two products that behave in opposite ways. A flexitank is a bag holding a liquid under its own hydrostatic head, restrained by a bulkhead and discharged through a valve. A meltable bag or jumbo bag is a bag holding a solid block of bitumen that was filled hot at the point of production and allowed to cool into shape long before it ever saw a container. The first is a tank; the second is a mould. Treating the two as one category is exactly what allows an enquiry about bitumen in flexible packaging to be answered with a quotation for something that cannot physically work.

常温下是固体 · The cargo is a solid at the temperature the box lives at

Start with the property that is measured rather than argued about. Penetration is determined at 25 °C by allowing a 100 g needle to sink into a conditioned sample for five seconds, under JTG E20-2011 method T 0604. A 70# binder is accepted between 60 and 80 tenths of a millimetre — the hash number is a nominal penetration with a band either side of it, not the two ends of the band in the way an ASTM 60/70 designation is written. Either way, the test itself is the point, because that is the vocabulary of a solid. It asks how far a needle goes in, not how fast the material pours, because at 25 °C nothing pours. The ring and ball softening point for 70# class A is a minimum of 46 °C under T 0606, and softening point is not the same thing as pumpable — it marks where the binder stops carrying load, tens of degrees below the temperature at which it will move through a pump at a useful rate.

A container standing on a quay is at ambient. A container on a chassis is at ambient. A flexitank has no mechanism of any kind for changing that, because it was never asked to have one. So the cargo has to be liquid going in, liquid coming out, and there is nothing in the system to bridge the two. For bitumen the gap between the temperature the cargo must be at and the temperature the container will be at is well over a hundred degrees, twice, at both ends of the voyage.

装货 · Loading: the film is colder than the cargo, and it gives way first

Take the loading step on its own terms. Penetration-grade bitumen is hot-loaded at typically 150 to 170 °C and handled through pumps in a window of roughly 130 to 160 °C. Now look at what is supposed to hold it. Low-density polyethylene melts at approximately 105 to 115 °C, high-density polyethylene at approximately 130 to 135 °C, and the woven polypropylene outer sleeve at approximately 160 to 170 °C — and the sleeve is a sleeve, not the containment layer.

Those two sets of numbers do not overlap with a margin; they overlap in the wrong direction. The temperature at which the cargo must be pumped sits at or above the melting range of the material that is meant to contain it. Nothing about the geometry helps: the bladder rests directly on the container floor with no bunding beneath it, the load is a free liquid mass with no baffles or compartments, and surge in transit is precisely what the bulkhead and the film are there to absorb. Absorbing surge is a mechanical duty, and a film that is at or near its melting range has no mechanical duty left to give.

卸货 · Discharge: the step with no answer

This is where the conversation ends, and it deserves the bluntest treatment because it is the part that offers tend to defer. Bitumen has to be discharged hot. To discharge it hot, heat has to be put back into a cargo that has been cooling steadily since the load port.

A flexitank has no heating coil, no steam jacket, no electrical element, no insulation and no connection point for an external thermal oil or steam supply. The container around it is a standard dry box, also uninsulated. Thermal mass in twenty tonnes of bitumen buys hours, and in a well-lagged system perhaps a day or two; it does not buy an ocean voyage, a terminal dwell and an inland leg. What reaches the receiving plant is a solid block of bitumen inside a polyethylene bag inside a steel box, and no procedure exists for getting it out.

The comparison with the formats that do work is the instructive part. A steel drum can go into a drum melter or a hot room and the binder is recovered. A meltable bag goes into a melting unit whole and the film enters the mix with the binder. A bitutainer carries its own burner, elements or coil and is heated in place before the bottom valve is opened. In every one of those cases there is a defined, equipment-backed way of adding heat at destination. A flexitank has none and cannot be given one, because the only way to bring a polyethylene bladder to bitumen pumping temperature is to destroy it. That is not a limitation that better operating procedure can work around.

破袋 · What a rupture actually means with this cargo

The consequence of failure is wildly out of proportion to the saving. A flexitank failure with a cold non-hazardous liquid is a bad day: cargo loss, a contaminated container, a cleaning bill, an insurance claim of predictable size. The same failure with bitumen at handling temperature is a release of twenty tonnes of dense liquid at well over 100 °C inside an unbunded steel box, usually at the moment the doors are opened, in a working container terminal.

Hot bitumen burns are the dominant handling injury in this trade and the standing first-aid guidance is specific: cool the affected area with clean cold running water for at least 20 minutes, never peel adhered bitumen from the skin, and never attempt to strip it with solvent, because the adhered layer is sterile and protective and removing it removes skin with it. Obtain medical attention for anything beyond minor contact. An offer that places that outcome one seam weld away from a routine terminal operation is not a cheaper way of doing the same job; it is a different job with a different risk register, and the risk sits with whoever opens the doors.

重量而不是容积 · Weight, not volume, is the binding constraint

There is also a quieter point that removes the economic case before the engineering case is even heard. A flexitank earns its keep on light cargoes, where a box fills volumetrically before it weighs out and the bladder captures the space that drums and their voids waste. Bitumen has a specific gravity of roughly 1.01 to 1.06 at 25 °C under ASTM D70, so a 20-foot container carrying it weighs out long before it fills.

That is exactly why the loading figures in the table below top out where they do, well short of the plate limit on the container door: every one of them is set by weight or by the stack, and none of them is set by the space a bladder would recover. The volumetric headroom a flexitank exists to capture is simply not present for this cargo. So when a flexitank is proposed for bitumen it is being proposed for its cost structure alone — and that cost structure is cheap precisely because it leaves out the tank, the insulation and the heating system, which are the three components that make bitumen discharge at the other end.

承运人接受与危险品状态 · Carrier acceptance and dangerous goods status

One further line worth checking rather than assuming. Flexitanks are handled commercially as a non-hazardous ambient liquid format, and lines normally approve both the flexitank supplier and the nominated cargo before accepting a booking. Bitumen carried at or above 100 °C is UN 3257, elevated temperature liquid, n.o.s., Class 9, which brings its own transport document, marking and terminal acceptance questions. A single booking cannot be both a non-hazardous ambient liquid and a Class 9 elevated temperature cargo.

So if an offer proposes bitumen in flexitanks, ask for the shipping line's written acceptance naming petroleum bitumen as the cargo, and ask the flexitank supplier for the same in writing. The request costs nothing, is entirely reasonable between commercial parties, and in practice it settles the question faster than any technical argument.

集装箱沥青罐 · The bitutainer, and how it differs

A bitutainer is an insulated, heated bitumen tank built into or onto a 20-foot ISO frame, so that it travels in a standard container slot on any ship, is lifted by ordinary cranes and reach stackers, and rides on an ordinary chassis. Indicative capacity is 20 to 25 MT. Heating is by a diesel-fired burner, by electric elements, or through a coil taking an external thermal oil or steam supply, depending on the build. Discharge is through a bottom valve, by gravity or through an on-board pump, once the unit has been brought back up to temperature at the receiving end.

Everything a flexitank lacks, a bitutainer has, and the difference is structural rather than a matter of degree. It is a rigid steel vessel rather than a disposable film. It is insulated, so it holds temperature rather than shedding it. It carries its own means of putting heat back into the cargo, so the discharge step exists as an engineered operation rather than a hope. And it is a durable asset rather than a consumable, which is why the commercial question attached to it is a question no flexitank ever raises.

That question is returnable or one-way, and a conventional heated ISO tank container adds a second one of the same kind, dedication — what the tank carried last and how it was cleaned. Both are commercial questions about an asset that has to go somewhere after discharge, and both are set out in full on the packaging page linked below rather than repeated here. The point that belongs on this page is why a flexitank raises neither. It raises neither because it is cut out and thrown away, and what is being thrown away with it is the tank, the insulation and the heating system. Those three items are the entire price difference, and they are also the entire discharge capability. A bitutainer is not a more expensive flexitank. It is the thing a flexitank leaves out.

可熔袋与吨袋 · The bag-in-container answer that does work

If the attraction of a flexitank was flexible packaging with no steel to dispose of, the meltable bag delivers that and is already an established format. A one-tonne meltable poly bag loads 20 bags and 20 MT per 20-foot FCL, the same as a jumbo bag, and the packaging enters the mix with the binder rather than becoming a disposal problem on a Chinese site.

The distinction from a flexitank is the entire point and it is worth restating in one line: a flexitank holds a liquid, a meltable bag holds a solid. The bag is filled hot at the point of production and the binder is allowed to cool into shape before it is ever loaded, so the bag functions as a mould rather than as a pressure vessel. Nothing is being restrained under hydrostatic head at 150 °C on a container floor, nothing has to be kept liquid across the voyage, and nothing has to be pumped out at the far end.

What it demands of a Chinese buyer is specific and should be confirmed before the order rather than after it. The receiving plant needs a melting unit that will take the whole bag, and lifting equipment to get a one-tonne unit off the container floor and into it. Beyond the equipment there is a specification question that belongs to the specifying engineer rather than the supplier: the bag film enters the mix, so confirm in writing that the project documents permit it, because acceptance under JTG F40-2004 is testing on the binder and the engineer is the person entitled to rule on what may be added to it. The behaviour of bags in a hot container on a southern routing is covered in full on the jumbo bag page linked below and is not repeated here.

全新钢桶 · Steel drums, and the loading arithmetic

Drums remain the format that asks least of the receiving end and travels furthest inland, and their relevance to this page is narrow but decisive: a drum answers the discharge question with a drum melter or a hot room, equipment that already exists at most sites that use binder at all. That is the test every format on this page has to pass, and it is the test a flexitank fails. The loading figures sit in the table below and are fixed by the container rather than by the destination. Specify new steel drums explicitly in the contract. Everything else about a drummed consignment into China — the inland weight ceiling, the tare and net-weight fields on the customs declaration, new against reconditioned as an acceptance term, and where the empty steel goes afterwards — is covered on the drummed bitumen page for China linked below.

什么时候不该用集装箱 · When the answer is not a container at all

One honest closing note on format selection. If the receiving end has dedicated heated tankage and continuous offtake, bulk beats every container format on cost per tonne and it is not close, because it removes the packaging and the melting step together. The container formats above exist for buyers who do not have that, or who are shipping to a project rather than to a terminal, or who need cargo that can be stored and positioned ahead of a northern season while construction is stopped. The question that decides the format is not which is cheapest per tonne in the abstract; it is what the receiving end can actually heat, lift and discharge. Bulk supply and the terminal question are covered on the pages linked below.