The real price of cargo tank cleaning

Everywhere one looks today, there are clear indications of growing awareness for optimisation, sustainability and safety in the chemical tanker market. *

allast water management, exhaust gas emissions control, routine orders for ‘economical’ steaming, super smooth hull paints etc, etc, are all designed to lessen the impact of transporting chemicals from manufacturing sites to receiving facilities.

One process, the pre-loading inspection, that actually defines whether a vessel is ready and able to transport these products, is apparently immune to similar scrutiny, because the consequences of off-specification cargo are seemingly insurmountable. This provides commercial interests carte blanche to force vessels to clean further and further in the name of ‘product quality’.

But what is off-specification cargo? Herein lies the biggest challenge, because the term ‘off-specification’ is not black or white, it is a very nice shade of grey which provides the perfect landscape for commercial subterfuge.

All cargoes are shipped to some kind of quality specification, which should provide sufficient security or insurance to protect the interests of the vessel nominated to carry the cargo. But the key word here is SHOULD because as noted, quality is not black or white, and just because a product meets the agreed quality specification, does not necessarily mean it meets every requirement of every cargo receiver. So technically, a received cargo could meet the quality requirements as specified in the charter party, but still be off-specification.

Most commonly, this refers to traces of the ‘first’ previous cargo in the received cargo, although there are a growing number of cases where the second, third (and even eighth) last cargo have been detected at levels that are seemingly unacceptable for the cargo buyer. But just like the term ‘off-specification’, which is negotiable and therefore impossible to exactly quantify, the term ‘unacceptable’ is equally unquantifiable; the question being, how much previous cargo in the received cargo is required to render the received cargo as useless or ‘not fit for purpose’.

This is not really a cargo quality issue any more, it is more a case of analytical ability.

The fact that cargo receivers have access to laboratories that can routinely analyse products for contaminants at concentrations as low as parts per billion, essentially means any detectable level of contamination in the received cargo, will theoretically put it off-specification, regardless of published and/or agreed upon, cargo quality specifications.

It needs to be recognised that if the received cargo does contain ‘something’ that it did not contain prior to loading onto the vessel, then of course technically that cargo is contaminated. But the point here is this, if 10 parts per billion of the third last cargo is really sufficient to render the received cargo as unusable, then in the future, commercial interests will really have no other choice than to use either dedicated tonnage or stainless steel for transporting more and more chemical cargoes, which comes at a price, that at the moment they seem unwilling to accept.

Consider also the disproportionation between analytical technology and the pre-loading inspection. As rapidly as analytical capabilities are advancing, the pre-loading inspection of vessels steadfastly remains the same as it was 50 years ago as two choices:

  1. Visual inspection?
  2. Wall wash inspection?

The wall wash inspection is of course the stricter of the two techniques, but honestly, how can randomly splashing methanol or acetone over less than 0.5% of the internal surface area of the cargo tank be accepted, as providing any guarantee that the received cargo will not contain 10 parts per billion of the third last cargo?

Moreover, there are more and more wall wash inspections now, with stricter and stricter specifications. But simply having an apparent need and the ability to test the wall wash samples to lower levels of contamination will never make the wall wash inspection any more worthwhile, because at the end of the day, the sample is still based on ‘randomly splashing methanol or acetone over less than 0.5% of the internal surface area of the cargo tank’. This sample could be tested for the presence of any contaminant at any concentration, but fundamentally, it does not represent 99.5% of the cargo tank (or any of the cargo lines). So what is the point?
This may sound like a stupid question,but it is crucial to understand, because it is creating a tidal wave within the industry that is pushing vessels to a breaking point.

Every time a receiver’ rejects’ a cargo, there is a domino effect starting with commercial interests making pre-loading inspection specifications stricter, (because what else can they do?) and eventually stopping back at the vessel.


The primary consequence of this effect is quite simply that vessels are being forced to clean further and further prior to loading whatever the next cargo might be, which clearly involves cleaning for longer periods of time, generally at elevated temperatures, thus consuming more and more fuel and liberating more and more SOx, NOx and COx into the atmosphere.

At the same time, far higher volumes of cleaning chemicals are being consumed, all of which are ultimately discharged into the sea. This is perfectly legal and within the constraints of MARPOL, but morally it cuts to the quick, because it needs to be recognised that in the vast majority of cases, after the first round of chemical washing, there is very often little or no benefit repeating a process that has already been completed. To para-phrase Einstein, repeating a process time and time again, expecting the result to change is the first sign of insanity ..

So what is the answer? In a perfect world the answer is greater transparency, recognising the fact that having the ability to test for lower and lower levels of contamination in any received cargo, does not always mean that the received cargo is off-specification or unfit for purpose.

As long as the received cargo meets pre-agreed quality specifications, then this particular obligation of the shipowner is satisfied. If the cargo receiver has a genuine concern about a previous cargo or a specific cargo group, this has to be documented and quantified in the recap, before any contracts are agreed. Hiding actual cargo quality concerns behind a wall wash inspection should not be a defence for off specification cargo for commercial interests, because the wall wash inspection is worthless, providing no reassurances and absolutely no guarantee that the shipped cargo will be on specification or not.

Real example -
A vessel recently carried a cargo of vinyl acetate monomer (VAM) from the Far East to Europe.

All nominated cargo tanks were wall washed with methanol and VAM prior to loading, tested for colour, hydrocarbons, inorganic chlorides, distillation properties and water, all of which were found to be acceptable.

Manifold, pump-stack, first-foot and final-loaded samples were taken and tested for appearance, colour, water content, distillation properties, acidity and inhibitor content and were all found to be acceptable.

The vessel arrived in Europe and the cargo was tested for the presence of aromatics, maximum 0.1 ppm (100 parts per billion) because this was the cargo receiver’s requirement and the cargo was rejected for the presence of 120 ppb aromatics.

Last cargo on the vessel? Mixed xylenes .. a pure aromatic cargo. The vessel’s owner had no idea of this specification, but worse, nobody thought to test any of the load port samples for the presence of aromatics. And let’s be realistic here, 120 ppb is the same as 120 seconds in a period of 31.7 years - not a lot of aromatics.

The unanswerable question of course is this; could the vessel have cleaned any further? Unexpectedly, my opinion is NO because how is it possible for a vessel to measure or determine that such trace amounts of aromatics have been completely removed from all part of the cargo system? But I also did some digging and found that according to the World Health Organisation (WHO), the maximum limit of xylenes in drinking water is 0.5 parts per million

Not only is the purity of VAM seemingly higher than the quality of drinking water, but more seriously any vessel cleaning with freshwater potentially runs the risk of contaminating subsequent cargoes with aromatics, just by using ‘pure’ water.

If this trend continues, the alternative is going to be extremely expensive in the long term, because vessels will be forced to only carry the same cargoes or cargo groups, which massively reduces flexibility and increases freight rates.

Let us end with an outrageous example of pre-loading inspections gone mad, with a sting in the tail. The subject vessel was stainless steel and presented with a last cargo of methanol in all cargo tanks. After the carriage of methanol, it has to be accepted that the vessel’s cargo tanks and lines will generally be extremely clean after minimum, or no cleaning, (just ventilation) and suitable for virtually any next cargo; particularly in stainless steel cargo tanks.

The next nominated cargo in this case was benzene and for some reason the charterers decided that a wall wash inspection was required prior to loading:
Inorganic Chloride 1 ppm maximum
Colour APHA     5 maximum
(ASTM D1209)
Hydrocarbons    Pass
(ASTM D1722)
Permanganate time 60 minutes minimum (ASTM D1363)

These specifications are particularly interesting (and ridiculous) when one considers that under ASTM D2359 and D4734, which list the industry recognised export specifications for benzene, there is no requirement for inorganic chloride, or permanganate time. Furthermore, the maximum colour of the loaded benzene cargo is 20 APHA and the only potential source of contaminants that might be identifiable in the ASTM D1722 hydrocarbon test are ‘non-aromatic hydrocarbons’ with a maximum specification of 0.1% or 1,000 ppm.

Perhaps the only significant potential contamination of the benzene cargo after methanol would be for the presence of oxygenates, but there is no such requirement in the ASTM specifications, presumably because benzene is a finished product and will not be undergoing further chemical processing.

Can there be any justification for such a wall wash specification? Apart from, there is no justification, and sadly no control and nothing stopping cargo interests from demanding whatever they want for a pre-loading inspection, ‘in the name of product quality’.

As it turned out, the vessel washed the cargo tanks with freshwater, ventilated until all traces of the methanol were removed, before rinsing with de-ionised water to remove any last traces of inorganic chloride, only for two tanks to be rejected (apparently) for the presence of inorganic chlorides.

The vessel argued that the cargo tanks were clean and eventually a second inspection was carried out, without any additional tank cleaning undertaken. Sanity prevailed, the two cargo tanks were indeed found to be load ready and the vessel was accepted for loading, but only after a delay of 16 hours which was completely unnecessary and effected both the owner and the charterer.

Without making the point that two wall wash inspections taken from the same cargo tank will, in the vast majority of cases, produce different results, (which one is correct?), surely common sense should have taken over here and the vessel should have been accepted for loading without a need for any wall wash inspection? But ok, loading commenced, and a manifold sample taken at the start of loading, confirmed that the product was seemingly acceptable (visibly) at the point of delivery:

At this point the cargo valve on board the vessel was opened in order to introduce the benzene into the nominated cargo tanks in readiness for first foot sampling and analysis.

Fortunately, this vessel was familiar with the L&I Maritime approach to cargo operations and accordingly, the duty officer was prepared to take regular manifold samples throughout the first foot loading operation. The reason for saying that this was ‘fortunate’ is self-explanatory after seeing the sample drawn 5 minutes after the cargo valve was opened.

No words are needed to describe this scenario, but sadly such incidents are not unusual and the worst of it is that the vessel is very often blamed for this kind of contamination because seemingly the cargo shipper can never make a mistake. Had the vessel not taken extra manifold samples they would undoubtedly have been dragged into the argument of trying to prove that the contamination did not come from the vessel’s cargo lines, (even though the last cargo was methanol and there was washing water analysis to prove the cleanliness of the cargo lines).

Needless to say, the shippers could not really dispute the contamination was derived from the loading terminal, but of course the vessel had the responsibility of cleaning up the cargo tanks again, even though they had already jumped through ridiculous hoops, achieving a wall wash standard that had absolutely no bearing on the ability of the vessel to load.

Interestingly, there was no wall wash inspection when the cargo tanks were re-presented. Was this some kind of backhand apology?? But surely, any concerns that the charterers had switching from methanol to benzene would pale into insignificance compared to switching from ‘brown sludge’ to benzene? And what would have happened if the receivers of the benzene cargo had found traces of the same brown sludge in the cargo??
What is really going on here??

* This article was written by Guy Johnson, Director , L&I Maritime (UK) Ltd.








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