Cleaning of Tanks and Cairbags

Erik Jeroen Eenkhoorn
Hengelo (O), The Netherlands


The transportation of bulk liquids has increased vastly over the past decennia. So has the diversity in modes of transportation, the tailoring of volumes to custom demands, the intensity and frequency of number of transports, the mandatory requirements, etc. etc. Conversely technology improvements have been non-spectacular and the application of innovations, if there were any, hardly noticeable. So, what are the new challenges? “Sloshing” and “Cleaning” in relation to bulk liquid transportation is the focus of an analyses on sustainability of the current situation and on improvements thereto. The initiative hereto being provided by recent research on “liquid slosh mitigation and products thereto”, refer [2].


Tank cleaning; mobile tank; Cairbag; inflatable component, liquid load securing.


Liquid transportation stakeholders and society in general are rapidly becoming aware of the advantages of applying (bulk) liquid load securing. Such (bulk) liquid securing can be ensured by using for example an inflatable component or a “Cairbag” inside the mobile tank. Especially the safety improvements resulting from a better stability, when sloshing of liquids during transportation is eliminated, are becoming obvious. Additionally, a Cairbag can make the transportation tank emission free. The variable volume type of Cairbag contains all air which otherwise would be free inside the tank. The liquid can hence not evaporate during any stage during (off-)loading, storage and transportation of the mobile tank. No evaporation consequently results in no vapours being available for emission.

In view of the (many) advantages of (bulk) liquid securing, and in view of the disadvantages of using baffle plates, Cairbag products are anticipated to be applied for the transportation of non-ADR products commencing soonest. Such use for ADR liquids is subject to authorization, ultimately by the UN(ECE) and may therefore commence somewhat later. The use of a Cairbag for transportation of an ADR bulk liquid in a mobile tank is expected (by author) to become initially allowed, i.e. not to become mandatory immediately. The complexity of relevant issues may become clearer for example by this paper which addresses only the cleaning interface related topics of applying a Cairbag. This complexity and its consequences on legislation aspects is currently subject to official UNECE (Tank Work Group and working party 15) assessment, refer [3].

In view of the vast number of combinations of type of mobile tank, type of liquid, type of Cairbag and of materials possible for the fabrication of a Cairbag, it seems appropriate to identify a structural approach for determining the cleaning possibilities which are to result in at least the mobile tank and a Cairbag to meet the cleanliness requirements for the next bulk liquid shipment.

The use of a Cairbag to secure a bulk liquid cargo may or will have an impact on the cleaning of the mobile tank. This paper addresses firstly the alternative cleaning operational possibilities of tanks and Cairbags:

  1. No cleaning of tank and Cairbag
  2. Cleaning of tank and Cairbag simultaneously (Cairbag remains inside tank)
  3. Cleaning of tank and Cairbag separately (Cairbag is removed from tank and cleaned individually outside tank)
  4. Avoiding cleaning

The structure of this paper progresses than to increase the complexity by addressing the various logistic possibilities resulting from whether a prior used Cairbag is suitable and required for and remain or be repositioned again in the mobile tank for its next planned shipment of cargo.

Ultimately, this paper aims at concluding the cleaning related consequences of improving the safety of bulk liquid transportation by securing such liquid load using a Cairbag.

The ruling perception of the transportation industry is that “Cleaning” is as undesirable as “Sloshing”, both result in adverse consequences. Cleaning obviously increases costs, takes time and adds to planning uncertainties. Cleaning quality uncertainties are often the blamed cause of liquid quality changes during transportation. Sloshing, far less obviously, results in instability of the means of transportation and thereby for an increased risk in accidents. It also results in an increase of fuel consumption by the means of transportation. Means meant to mitigate sloshing effects, like baffle plates, make the means of transportation more expensive and reduce the pay-load.

This paper identified the challenge to explore opportunities to eliminate, mitigate both above mentioned “evils” with solutions attractive for the conservative transportation industry. This paper therefore aims at identifying “easy”, but quality and economics improving solutions within the complexity of the cleaning topic. Such solutions are to match trends in the development of, especially sustainability, values in current societies to become viable. And do so.

This paper concludes with recommendations for engineering and design details to be further researched and implemented to enhance the changes of success of setting new HSEQ standards in bulk liquid transportation. Note: H; health (hygienic), S; safety (slosh elimination), E; environmental (sustainability improvements), Q; quality (of both liquid and transportation).


Bulk liquid load securing can be done in several ways. This paper is based on the new liquid load securing product named the “Cairbag”, which always comprises an inflatable component positioned inside the mobile tank. There are two fundamentally and principally different varieties of a Cairbag; the fixed and the variable volume Cairbag. The fixed version is used to reduce the pay-volume of the tank such that a 100% payload fill does not cause the truck to be overloaded. The variable volume version fixates the liquid and avoids sloshing at any fill rate between 0-100% and allows for multiple (off-) loading addresses.

 Figure 1. Three dimensional schematic of a fixed volume Cairbag

Figure 1. Three-dimensional schematic of a fixed volume Cairbag positioned inside the tank of a tank truck.

Figure 2. Three dimensional schematic of a variable volume Cairbag  

Figure 2. Three-dimensional schematic of a variable volume Cairbag positioned inside the tank of a tank truck.


Cleaning operations alternative 1: There is “no cleaning” as there are “no cleaning” requirements.

The “no cleaning required” operations alternative is in many cases applicable, for example for tank trucks used for fuel distribution from refineries to fuel stations. The tank trucks are dedicated for the transportation of only fuel, often even for the same type of fuel. But even in case the tank or one compartment of such fuel tank truck would switch from being loaded with “diesel” to “gasoline or Euro 95” or vice versa, no harm is done by not cleaning the tank compartment prior to loading the differing product. Remains of the prior product in the tank, after completion of its off-loading, are so little that the next product being loaded is not affected in terms of quality nor will it become “off spec”.

A mobile tank not requiring cleaning on a regular intensive basis, does not automatically imply that a Cairbag placed inside such tank also does not have to be cleaned. The interactions between a liquid and the inner wall of a (steel or aluminum made) tank may differ from interactions between such liquid and any Cairbag material. Liquids, or components thereof, may adhere to the Cairbag outside, possibly even with an increasing layer thickness over time. The possible formation of such layer is likely to affect the performance and functionality of the Cairbag. The possibility of liquids solidifying on the Cairbag outer surface with layer forming, whereby such layers do not reduce or disappear during the off-loading of the liquid, are hence to be avoided.

When a Cairbag application is considered for a tank truck which does not require regular intensive cleaning, the choice of the material of which the Cairbag is manufactured is to include a “cleaning” criterium. In case there appears to be more than one type of material suitable for the intended Cairbag application, the “no cleaning required” feature of one or more of the optional materials, may be evaluated as preferable, thus resulting in the “no cleaning required” operations alternatives remaining applicable. It is envisaged that providing such information and ensuring the reliability of such information based for example on long term track records, will be the responsibility of the manufacturer and suppliers of envisaged Cairbag materials. The logic of this based on the quality assurance and guarantees on the material for the intended Cairbag application are provided by the material manufacturer and suppliers. It is envisaged that obtaining such information and ensuring the reliability of such information may be difficult or even be impossible. Dedicated testing may be an option for verification of claimed material behavior or may even be required in case none of the available material alternatives provides for adequate quality guarantees. Such tests are to focus on the behavior of sample materials during prolonged exposure to the specific liquids intended to be secured for their transportation by the Cairbags envisaged to be made of such materials. However, in a “worst case” there may not be any materials guaranteeing to result in a “no cleaning required” operations alternative when used as Cairbag material.
In which case the Cairbag is made of a material resulting in the Cairbag requiring to be cleaned (regularly, i.e. possibly after each cargo delivery). This results in “cleaning operations alternatives 2 or 3”, as detailed hereinafter, to become applicable.

The use of a Cairbag product to secure a liquid cargo, which does not require any cleaning of either the mobile tank or the Cairbag upon completing its transportation and prior to being loaded with a subsequent cargo is attractive for obvious reasons. However, the cleanliness quality assurance aspect requires a “once-off” engineering effort on the topic of Cairbag material selection for each type of liquid. Once the cleanliness quality assurance results are considered “proven”, the results are to remain available in a Cairbag Material database, for which the Cairbag manufacturer, supplier remains to be responsible. Proper cleanliness quality assurance will avoid the Cairbag application to result in an increase in cleaning related cost.

Conclusion on cleaning operations alternative 1:

Any type and seize of Cairbag may be used inside a mobile tank not requiring cleaning in between cargoes, provided the material used for such Cairbag also conforms to the cleanliness requirements without cleaning.

Prior to moving on to the subject of cleaning being required in current situations of tanks without Cairbag application, there may be cleaning mitigation opportunities. There may be situations in which a variable volume Cairbag is likely to reduce and possibly eliminate the need for cleaning, for following reasons:

  • The Cairbag avoids any free air to be present in the tank at any moment in the transportation of liquid process. There is thus no possibility for liquid remains to “dry-up” and thereby attach or fixate on to the inner tank wall.
  • Liquid cargo left clinging on the inner tank wall remain “moist” and thereby remain moving on a viscosity and, or a gravity basis.
  • The Cairbag inflates during the liquid discharge from the tank, the Cairbag thereby forces the (“moist”) liquid cargo remains down, squeezing it between its outer-wall and the inner tank wall.

Cleaning operations alternative 2: The mobile tank is cleaned with a Cairbag inside while tank and Cairbag are cleaned simultaneously.

The cleaning of a mobile tank and of a Cairbag remaining positioned inside such tank simultaneously, in case both require to be cleaned, is obviously preferable over cleaning the mobile tank and the Cairbag separately after removal of the Cairbag from the tank. It is easier and very probably cheaper to clean a mobile tank with a Cairbag inside simultaneously as it is less complex, less labor intensive and uses less cleaning detergents as compared to cleaning these separately. This cleaning operations alternative is especially attractive in cases of dedicated transport whereby the mobile tank transports identical liquid cargoes in each subsequent trip and whereby each trip requires cleaning and the use of an identical Cairbag each time.

Conversely the cleaning operations alternative of cleaning tank and Cairbag simultaneously is unlikely to be an option in case the mobile tank will be loaded with a liquid differing from the prior cargo, or when a next cargo would not require any or not the same Cairbag as the prior liquid cargo did. Also, in case of only the mobile tank or only the Cairbag requiring to be cleaned, it may be opportune to investigate the cleaning operational alternative of removing the Cairbag from the tank and subsequently clean either the tank or the Cairbag individually. See “cleaning operations alternative 3” hereinafter.

The cleaning of a mobile tank with a Cairbag inside simultaneously within one operation meets with a few concerns. These concerns include:

  • The cleanliness achievable versus the required cleanliness.
  • The possibility to use the same cleaning product(s) for both inner wall of the tank and the external wall of the Cairbag.
  • The cleaning method. Spray lance injection into the tank and using high pressure spray nozzles for the random spraying of (hot) water and detergents, chemicals, as is most commonly applied, may not be possible or may not be effective due to the presence of a Cairbag obstruction”.

The cleaning quality

“Cleaning Quality” is a “difficult” topic as there is no scientifically supported quantification of cleanliness. Such quantification is generally only available in medical applications. Here, the number of, say, bacteria per square centime are counted on a laboratory scale. This is however not done for the examination of cleanliness of mobile tanks. Generally, the cleanliness of a mobile tank during and upon termination of the cleaning is determined by visual inspection of the water, used for the cleaning, upon it exiting the mobile tank. In case the water exiting the mobile tank being cleaned, is considered “clean” enough for any “sufficiently long” period, as determined by individual judgement, the cleaning is considered to have been done successfully.

With the addition of a Cairbag inside a mobile tank, experiences during the research phase of the Cairbag products, revealed an increase in concerns on the cleanliness quality assurance of such Cairbag equipped tanks. Contamination, or deterioration of the quality of a liquid product being transported in a mobile tank is apparently often blamed to the lack of cleaning quality of a mobile tank after the prior shipment. The earlier mentioned lack of scientific standard adversely affects the gravity hereof.
The addition of a Cairbag in a tank increases the cleaning complexity and the management of the quality assurance thereof. Investigations during research so far did not result in documented or other scientific support for the afore statements. The afore is merely a conclusion of various discussions held with cleaning stations and liquid transportation companies. The topic of “cleaning quality” is envisaged to be updated in future versions of this paper, subject to mentioned supporting evidence becoming available.

The use of high-pressure spray nozzles.

Economics provide the common justification for applying high-pressure spray-nozzle based, (warm) water cleaning of mobile tanks. Spray nozzle cleaning requires an easy and complete surface access for water sprays, as is the case with the inner (steel, aluminum or other metal made) wall of mobile tanks. A Cairbag only provides for a similar easy and complete surface access when fully inflated. A Cairbag should therefore preferably be inflated with the entire surface of the inflated component tensioned to allow for spray nozzle cleaning. This condition avoids remains of transported liquids to remain accumulated (i.e. not being removed) in folds, creases, wrinkles and pleats of the material. Such remains would thereby be inaccessible for nozzle sprayed cleaning liquids.

There are however two main obstacles for spray nozzle cleaning of a tank and a Cairbag simultaneously. The spot pressure exercised by the cleaning liquid sprayed by the nozzles is limited by the “peeling-off” surface stress value of the material used for the Cairbag. This stress value reflects the “bonding” strength between the coating and the carrier of the material. This is a limiting factor which does not apply for the metal made mobile tanks but does apply for all thermoplastic and rubber made products including a Cairbag. Ensuring enough distance, and thereby a enough pressure drop in the cleaning liquid, between spray nozzle and the Cairbag material, to avoid a to high contact pressure at all times during the cleaning operations does not seem to be a realistic option.

Furthermore, high-pressure spray-nozzles cannot be used for the cleaning of tanks with an inflated (larger volume) Cairbag inside for the obvious reason of space interference between nozzle and Cairbag. A small fixed volume Cairbag may be an exception to this. As, however a small fixed volume Cairbag is easily removable from a tank, when deflated, and in view of the remaining “peeling-off” risk of the material, this possibility will not be pursued here. Tanks with an inflated larger fixed volume or an inflated variable volume Cairbag must be concluded not to be able to be nozzle cleaned simultaneously.

The alternative to clean a tank and a deflated Cairbag simultaneously is considered not to be realistic either, for the same reasons as mentioned above. The peeling-off risk of the material remains, while the deflated Cairbag will space-wise still interfere with the spray-cleaning nozzles. The material of a deflated Cairbag will without doubt be multiple-folded and thus to a large extend be less, not accessible for sprays in a spray-nozzle cleaning process.

The use of soaking possibly with cleaning detergents

As nozzles cannot be used and in case applying (warm or hot) water on a “no pressure” basis does not arrive at the required cleanliness, cleaning additives or detergents may be the solution. Reference is made to [1], Kruize H.J. (2018), for details on the state-of-the-art of tank cleaning with detergents. Cleaning additives are generally added to water, to an optimum, most effective, concentration and applied in a “soaking” condition at a preferred optimum, commonly above ambient, temperature. Soaking requires the cleaning liquid (water and detergent) to remain for some (by detergent manufacturer specified) time in between the inner wall of the mobile tank and the outside of the Cairbag. Upon completion of the soaking, the water, detergent and dissolved transported product remains, are drained from the tank. This is commonly followed-up by some flushing with clean (warm) water. This flushing continuing until the water exiting the tank is considered to be “sufficiently clean”.

“Soaking with detergent” cleaning requires usually a large volume (i.e. the total tank volume) of water and detergent to soak effectively. Meeting minimum concentration requirements of cleaning detergents or other cleaning products (solvents, etc.) causes the quantities of such to be used for cleaning to be linearly related to the soak-cleaned liquid volume. The quantities of (warm) water and cleaning detergents required for soak cleaning are therefore generally higher than for spray nozzle cleaning. This evidently results in soak cleaning generally being more expensive than spray nozzle cleaning. Furthermore, high-pressure spray nozzle cleaning generally can be done quicker and is therefore generally preferred as it is economically more attractive than “soaking with detergent” cleaning.

However, “Soaking with detergent” cleaning may be the only realizable alternative as nozzle spray cleaning of a tank and a Cairbag simultaneously is not possible. The analyses of this alternative way of simultaneous cleaning of a tank and a Cairbag results on logical principles in soak-cleaning of a tank and an inflated Cairbag inside also not to be possible. An inflated Cairbag cannot be submerged completely, i.e. with water, cleaning liquid, surrounding the full circumference of the Cairbag. The Cairbag will float and be forced against the highest part of the inner wall surface of the tank (identically to its liquid load securing functionality). The surfaces of the Cairbag and the inner tank wall, which are in contact, will not be cleaned as there is no access for the soak-cleaning liquid to these surfaces. This is regarded as a major justification for deciding this cleaning operation alternative having to be considered as “no-go”.

One consideration to the contrary may be the argument of reducing the size of the Cairbag inner tank wall contact surface during soak-cleaning as compared to the size during the liquid transportation. The operative argument here being that the liquid which was transported also could not have contaminated the contact surfaces and therefore do not requiring cleaning. Only dedicated testing can confirm the correctness and thereby the possible acceptability of such argument. To be noted is however, the Cairbag having to reduce its level of inflation to result in the reduction of contact surface. The cleaning quality thereby depends on the level of deflation, the minimum realizable inflation may be best.

Therefore, this may leave the option to soak-clean a tank and a virtually completely deflated Cairbag inside simultaneously. How would this work? A completely deflated Cairbag, if physically possible, would reduce to only its material volume. Realistically there will always be some remaining air volume, which is subject to the vacuum pressure applied. This air volume and pressure are to ensure all Cairbag material to remain “bend” and not to become “folded”, which is likely mandatory in view of the commonly specified long life-time requirements of the Cairbag. Considering the specific gravity of the materials commonly envisaged to be used for a Cairbag and the remaining air volume, a deflated Cairbag will remain (partially) floating. Partial submersion of a deflated Cairbag results in only the submerged part being cleaned in a soaking process. The non-submerged part will not be (soak-)cleaned. The tank therefore will have to be completely filled with soak-cleaning liquid. This is furthermore required to ensure the cleaning of the (variable volume) Cairbag right to the top of the tank at the point where the air and pressure measuring transfer connection is to the tank external Cairbag components. In view of the multiple bends in the material and the remaining minimal upward forces on the Cairbag, the contact surfaces between the Cairbag and the inner tank wall will be minimal and probably non-permanent and varying during a “somewhat turbulent” soak cleaning operations process. Once again, only dedicated testing can confirm the correctness and thereby the possible acceptability of this.

However, there may be an advantage for the horizontal cylinder-shaped Cairbags as used in tank-trucks and tank containers. Once such tanks have discharged their liquid cargo and assuming the Cairbag is provided with an extension “bellow” between the top tank connection flange and the horizontal cylinder part of the inflatable component, the Cairbag rests on the lower half of the tank. When the Cairbag is further deflated, i.e. to some extent vacuum sucked, the top half of the Cairbag sort of collapses (slowly) into the lower half of the Cairbag (creating a sort of “bathtub” shape. This allows for soak-cleaning liquid to be flown (via an open manhole top entrance, into this kind of bathtub. The upward forces remain to be avoided to well after the soak-cleaning liquid has commenced to overflow the bathtub. The Cairbag, very likely and subject to dedicated further testing hereto, will have been completely submerged in the soak-cleaning liquid, thereby likely ensuring the adequate and acceptable cleaning of the entire Cairbag surface. At some point in the cleaning process, when the top has been sufficiently long submerged, the Cairbag is slowly and partially inflated (while soak-cleaning liquid is at a same volume flowrate discharged from the tank) to the point whereby the Cairbag starts to float to the higher part of the tank. This condition is to be maintained also for an experimentally to-be-determined duration ensuring a sufficiently long soak-cleaning period of the lower part of the Cairbag.

The use of both spray-nozzle and detergent soak cleaning.

Especially smaller fixed volume type of Cairbag may be deflated and by design (see hereinafter) allow for being positioned on the lowest part of the tank prior to cleaning commencing. Firstly, enough cleaning liquids are to be added to the tank, ensuring virtual full submersion of the deflated Cairbag. The deflated Cairbag and its submersed position inside the tank will then allow for spray nozzles to be used inside the tank for cleaning the non-submerged inner tank wall. The pressure of the spray nozzles used in the cleaning process may be reduced, optimized to minimize, eliminate the peeling-off risk of the Cairbag material.

The use of intermittent flush-soak cleaning.

A further alternative may be provided by applying intermittent cleaning liquid supply and discharge. In this process the elevation of the (partially deflated) Cairbag changes frequently during the (soak-) cleaning process ensuring adequate cleaning of the entire Cairbag surface.

Tests done so far on cleaning a tank and a Cairbag simultaneously

Various tests focusing on the (internal) cleaning of tank-containers, with a Cairbag provision internally, have been done by Accede with Interbulk
Assistance and tank-containers in the tank cleaning facilities of Sutton’s in Hull (England). All such tests included a fixed volume Cairbag sufficiently small to allow it to remain inflated and high-pressure spray nozzle cleaning with cold water. The Cairbag was made dirty by spraying lemonade, sugar and flour on the outside (prior to cleaning commencing). Results generally confirmed that not all applied “dirt” was removed from the Cairbag. No Cairbag failure happened in the cleaning test and no peeling-off damage was observed.

Conclusion on cleaning operations alternative “2”: The simultaneous cleaning of tank and Cairbag appears to be only possible and attractive in case a Cairbag of the “variable volume” type is applied. The simultaneous cleaning of both requires a “soaking, likely with detergent application”, type of cleaning operation. The variable volume Cairbag system requires to be provided with a “cleaning” option in the pneumatic controls. Simultaneous cleaning of a tank and a Cairbag using high pressure nozzle spraying should not be considered, such may only be possible and (marginally) attractive in very few cases.

Cleaning operations alternative 3: The mobile tank is cleaned without a Cairbag inside and the Cairbag, as used in the prior, latest shipment is possibly cleaned and if so, separately from the tank it has been inside.

This cleaning operations alternative matches many different operational situations:

  • Only the tank or the Cairbag requires to be cleaned, the other not. The Cairbag is deflated and removed from the tank. The tank or the Cairbag is subsequently properly cleaned individually. The Cairbag is inserted in the tank again upon the completion of the cleaning operation.
  • The Cairbag is removed from the tank and abandoned, recycled and replaced by a new Cairbag which is inserted inside the tank once this tank has been cleaned.
  • It is easier, cleaning quality-wise, and / or economically more attractive to remove the relatively small (light weight) fixed volume Cairbag and clean it separately from the tank, as compared to cleaning them simultaneously.
    The tank and Cairbag require different, non-compatible means, detergents for their individual effective cleaning.
  • One shipment of liquids partially filling a mobile tank has been completed and details of the next possible shipment are unknown or certain not to be identical nor to allow for identical combination of tank and Cairbag as prior shipment nor to require a Cairbag at all. The mobile tank must be cleaned and prepared to be available for any potential future application (with or without Cairbag of whichever type and seize). The used Cairbag may be abandoned, recycled, cleaned at any off-peak cleaning time or even be re-used uncleaned if such would be acceptable.
  • The tank (like in a tank container) and Cairbag both have been rented and require to be returned to their respective rental companies in an identical condition as these were upon receipt by the hiring parties. New, next hiring parties may differ from the prior renting parties.

The cleaning methods and tools thereto

The cleaning operations may be quite likely be multi-phased

  1. The pre-cleaning of tank and Cairbag inside simultaneously to allow for the safe removal of the Cairbag from the tank,
  2. The (possible) cleaning of the tank after the Cairbag has been removed, separately from
  3. The (possible) cleaning of the Cairbag

As to 1. The pre-cleaning of a tank still holding a Cairbag to allow for the safe removal of the Cairbag must ensure neither the tank nor the Cairbag to be exposed to conditions not compatible with the tank and Cairbag materials. Limitations to the pre-cleaning possibilities, resulting from this requirement, may require additional or more serious safety precautions to be applied for the safe removal of the Cairbag from the tank upon its limit pre-cleaning completion. These safety aspects are to be addressed and taken care of in the engineering and design phase or in the operational preparation phase of the Cairbag application.

As to 2. The tank may be cleaned using the cleaning operations, programs, procedures, etc. as were historically well-established long before the introduction of the Cairbag. This typically allows the tank to be high pressure spray nozzle cleaned as is common for cleaning tanks of tank-trucks and tanks of tank containers.

As to 3. Cairbags may be cleaned in many ways, primarily depending on the Cairbag material manufacturer recommendations and limitations thereto.

  • A Cairbag is preferably to be cleaned in the inflated condition to avoid liquid remains to remain accumulated (i.e. not being removed) from folds, creases, wrinkles and pleats of the material. The inflated Cairbag is preferably positioned on, and supported by, two vertical rollers, allowing the Cairbag to rotate over its horizontal central axis. The rotation of the Cairbag can be affected by the spray lance also used to spray (warm) water and possibly a detergent on the outside of the Cairbag. The spray lance shall be kept at enough distance from the nearest Cairbag material to avoid high pressure damage.
  • Soaking a deflated Cairbag in a sort of bath tub, i.e. basin filled with (warm) water and detergents, which is circulated with removal (by filtration) of debris and other prior liquid cargo remains. This may also be applied for an inflated Cairbag provided it will be rotated as the submersion of the Cairbag in the water with detergent will only be partial.
  • The Cairbag may be abandoned (recycled) and replaced by a new one. This would typically apply for food and medical liquid transportation applications with high(-est) cleanliness and hygienic requirements. This “once-off” use furthermore matches the common once-off use of (plastic) packaging material as use for these food and medical products.

Conclusion on cleaning operations alternative “3”:

The separate and individual cleaning of tank and Cairbag appears to be only possible and attractive in case a Cairbag of the “fixed volume” type is applied. The safe removal of the Cairbag from the tank and handling requires the Cairbag to relatively small and light in weight, i.e. of the fixed volume type typically. Once the Cairbag is removed, the tank can be cleaned traditionally.

Conclusion on all three cleaning preparations alternatives:

These three cleaning operations alternatives are estimated to cover at least 80% of all practical tank and Cairbag cleaning operations.

Cleaning operations alternative 4: The mobile tank and the Cairbag cleaning requirement is eliminated by using an “In-liner”, possibly provided with Cairbag functionality.

This cleaning operations alternative explores the possibility to use the “In-liner” technology and products as already available in the market. In-liners are “bags” which are placed inside (mobile) tanks to contain the liquid under hygienic, medical acceptable cleanliness conditions. The In-liners are for once”-of-use” only and (supposed to be) recycled once used. They contain all liquid to be transported by the mobile tank in such a manner that there is a no point in time any contact anywhere between the liquid and the mobile tank. These In-liners are made sufficiently strong to withstand dynamic forces and pressures which may occur due to liquid dynamics during transportation. This generally makes the In-liners more expensive as compared to an inner wall lining of the tank, virtually serving as a coating of such inner wall, only.

This cleaning operations alternative (“4”) recognizes the possibility to use recently completed research and patented technology and slosh eliminating components resulting thereof, refer [2], to develop a second generation of In-liners. This new generation of In-liners will differ in two design features from the existing first generation of In-liners:

  • The base “bag” will be shaped and sized exactly to the shape and dimensions of the mobile tank. It will “virtually serve as earlier mentioned “coating” and only serve to avoid contact between the liquid and the tank. As the base bag part of the In-liner will transfer any pressure occurring in the liquid directly on the inner tank wall it is positioned against and in full contact with, this part will not be subjected to forces nor pressures of any kind. The base bag can therefore be made of a relatively small thickness and thus be cheap. The base bag part of the In-liner will fill 100% of the mobile tank volume in its transportation mode.
  • The base bag will be complemented with a slosh elimination component. This slosh mitigation components either creates a ‘bag-in-a bag” to arrive at the fixed-volume version of the Cairbag or an “inner-membrane” to create the variable volume type of Cairbag. For the (patented) slosh mitigation technology and for specification on the applied functionality in mentioned components refer [2].

Anticipated (by author) is that the use of these new generation of In-liners, especially when series produced, will be more cost effective hence be more economical than the traditional cleaning of mobile tanks using for example high-pressure spray-nozzles. Furthermore, it is anticipated that mandatory requirements for example related to slosh mitigation, liquid load securing, but also on hygienic and liquid quality assurances, contamination avoidance, etc. will become more stringent and tighter. In-liners may also be designed and use materials which provide for a better insulation, which may result in less energy consumption of a liquid during transportation (and storage) in a mobile tank. Together with the reduction in energy consumption by the liquid, resulting from slosh elimination during transportation, the environmental improvements may enhance the use of the new generation In-liners.

The cleaning methods and tools thereto

The cleaning method of the “In-liner” application does not require “cleaning” in the traditional meaning. Cleaning is more: “avoiding the need to clean by avoiding contact between a liquid and the inner wall of its holder and replacing the provision thereto, every time”.

The tools thereto are, like the (“no”) cleaning operation alternative (“1”):

  • The once-off engineering and design of mobile tanks suitable to be used with the new generation type of In-liners. One of the key features the engineering and design will have to focus on, will be the new requirement to allow air (or other inflation gas) to be provided to, or distracted from, the air or gas filled component of the In-liner and allow the pressure monitoring thereof.
  • The development of the new generation of In-liner with slosh eliminating provision.
  • Possible tools to assist and simplify the replacement of such In-liner.

Summary of cleaning operations alternatives



fixed volume

variable volume





tech. pos.


tech. pos.



"1" no cleaning






"2" simultaneous


- spray nozzle





- soak, detergent

- combined


? / X

? / X


"3" separated

? /₰

? / X



"4" In-liner

? /₰

? /₰

? /₰

? /₰






= yes, good





X = no, difficult.






Figure 3; Overview of technical possibilities and easiness of cleaning related operations as a function of the type of Cairbag and the cleaning operations alternative.


As became apparent from the above, there are several cleaning operations alternatives. The complexity of the choice between these alternatives is aggravated by the sometimes-unknown cleaning effectiveness and by the dependence on only suggested and still to be proven technical solutions. The complexity is however not limited to these factors. Dealing with cleanliness quality assurance also must take practical and commercial aspects in account.

Situation 1. Applicable for both tank trucks and tank containers, provided with any type of Cairbag, not requiring any cleaning (“1”). This situation is typically applicable for dedicated transportation of “clean” products, i.e. products which do not produce deposits (of heavier components) nor adhere, “stick” to the inner tank wall and Cairbag. Fuels are typical products thereto as these are virtually always transported by dedicated tank-trucks which are not being used for transporting any other liquid ever. This is compliant with the “ADR” article 7.5.8 refer [3]. Cleaning commonly is only required prior to a tank (and Cairbag) inspection which may happen once every 3 years. The Cairbag must be removed from the tank for inspection access and safety reasons. Cleaning operations alternative “3” applies in these cases whereby the pre-cleaning is done using one of the cleaning operations “2” alternatives.

Situation 2. Applicable especially for tank trucks and far less likely for tank containers, provided with a variable volume type of Cairbag, requiring, and allowing for simultaneous, cleaning (“2”). Variable volume Cairbags are more likely to be used on tank trucks than on tank containers in view of their external components which may require more space than can be made available inside the dimensions of a (20’) tank container and which are prone to damage which may occur during the tank container handling operations. Tank trucks generally do not have these restrictions. Tank containers are seldom used to distribute one cargo at multiple delivery addresses or to collect partial cargoes at more than one address in one shipment and are hence likely to be applied with a variable volume type of Cairbag. Situation 2 may apply for tank trucks with multiple (off-) loading addresses for compatible, but different products, variably being loaded per consignment, and for dedicated transportation of one type of liquid which creates deposits and, or clings on the inner tank wall and, or the Cairbag during it being positioned inside the tank. This again is compliant with the “ADR” article 7.5.8 refer [3] and may hence be applied to any liquid irrespective of its classification.

Situation 3. Applicable especially for tank containers but also for tank trucks, provided with a fixed volume type of Cairbag, requiring separate cleaning (“3”). Tank containers will most commonly be provided with a fixed volume Cairbag. This allows for the use of any, and maximization of the, volume of tank in a 20’ container. This may be commercially attractive while ensuring the safe transportation of a smaller volume of liquid. Such volume may even be less than 80% of the tank volume without the tank requiring baffle plates to be installed. Note: This is currently still subject to official UNECE (working party 15) endorsement.

A fixed volume Cairbag product generally comprises nothing more than an inflatable component with an air fill and discharge provision including a manually operated open / closed termination valve, positioned inside the tank on top of the Cairbag in the manhole provision. This type of Cairbag product has no parts requiring a wall through-let, all Cairbag material remains inside the tank. As the desired or mandatory volume reduction is often relatively small, the inflatable component also is small and of little weight hence removable (when deflated). The easy removability enables an “ad-hoc” use and thereby provides for maximum commercial flexibility.

Situation 4. Applicable for both tank trucks and tank containers, irrespective of the type of Cairbag, for which cleaning will not result in acceptable cleanliness (“4”). This situation applies typically for liquid food, medical type of products of high hygienic standards. (No) cleaning is not an option, the In-liner remaining the only acceptable solution.

Consequences for the cairbag supplier

  1. The compatibility of Cairbag material with cleanliness requirements and with cleaning chemicals as used for cleaning the tank requires to be assured in the engineering & design phase of the Cairbag and requires to be verified in the operational preparatory phase of each transportation. Establishing (all relevant) material specifications is however common practice in engineering, so this not new. Neither is the quality control prior to transportation of a cargo, new.
  2. Each Cairbag shall be provided with clear and complete identification of all relevant information in print on its outside. For example:
    “Cairbag of Fixed volume of 5 cubic meter, made of; Valmex 7606 anti-static Thermoplastic Urethane made by “Low & Bonar”. Only to be used with Acidic Hydrochloride of 0-20% concentration”. Each Cairbag shall furthermore have a unique “Cairbag” code with a traceable track record being available on a Cairbag owner managed data base.
  3. A Cairbag, which is to be cleaned outside the tank, shall have design features specifically aiming at its easy removal from (and re-instatement into) tanks. Besides cleaning related features integrated in the Cairbag design, it may also be opportune to design special tools to assist such removal of Cairbags from tanks. Such tools may aim at:

i. a speedy expulsion of all air from the Cairbag,
ii. torsion of the deflated Cairbag to cause the Cairbag material to form a “compact type of sausage of relatively small diameter”,
iii. straps to enable attachment of the Cairbag to a lifting hook,
iv. a “condom” device which is to be mounted on top of the (open) manhole such that a dirty or contaminated Cairbag can be pulled out of the tank spill-free.
v. Hoisting facilities.

4. A Cairbag allowing for a “soaking, likely with detergent application”, type of the simultaneous cleaning operation of both tank and Cairbag shall be engineered and designed with dedicated “cleaning” provisions. The pneumatic and electronics design and components shall thereto allow for the deflation of the main chamber and of the air channels resulting in the required vacuum pressure and volume to meet the floating conditions for soak cleaning. The design requires the pneumatic control system to allow for a “cleaning” selection mode of operation. The deflation may be cleaning liquid fill driven.

5. The cleanliness quality assurance shall be established in a documented form. It shall be clear and unambiguous about the benchmark between “clean and not clean”. Furthermore, it shall detail the cleaning method, cleaning liquid composition and detergents, etc. to be used thereto, quantities, durations, temperatures, etc.

6. Care is to be taken of the fact that all thermoplastic and rubber sheet materials will absorb liquids to some 1 to 3% of their own weight (volume). Once such absorption level is reached no further absorption will take place, the material has reached its maximum saturation level. The absorption is irreversible, the absorbed liquid will remain, chemically bonded, within the thermoplastic or rubber material. Prior to exposing a Cairbag to the liquid to be transport, it may be opportune to submerge the Cairbag in a liquid preferred to be absorbed to avoid cleaning problems of the Cairbag thereafter.

7. The inflatable component of a Cairbag shall be provided with a type of bellow extension between the connection at the top of the tank where the air transfer and air pressure signals pass through the tank wall and its horizontal cylinder-shaped part to allow a deflated Cairbag to position itself optimally as determined by the cleaning operational requirements.


Thanks to H.J. Kruize for initial research into this subject and for providing essential input for this paper.
Thanks to “Interbulk” (now: “Den Hartogh”) for their support and for allowing various cleaning test in some of their tank containers.


[1] Kruize H.J. (2018), “Possibilities to clean the inside of mobile tanks in which an inflatable component is positioned”, University of Twente, The Netherlands.
[2] Eenkhoorn, E.J. (2017). Products to mitigate liquid sloshing, University of Twente, Enschede, The Netherlands. ISBN 978-94-6233-808-1
[3] United Nations Economic Commission for Europe, European Agreement concerning the International Carriage of Dangerous Goods by Road (“ADR”), Geneva, 30 September 1957.
[4] Eenkhoorn, E.J. (2019). Interfaces between Tanks and Cairbags, Accede b.v. Hengelo (O), The Netherlands. Paper in preparation.

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