Diving into the Cause of Liquid Cargo Damage and Off-spec Bunkers

31/01/2024

Read time: 8 minutes

Category: Blog

Author: Gregory Vervalle

The Role of the Marine Cargo Chemist in Marine Surveying Explained

Surveying damage to liquid cargoes often involves complex chemistry. This is why we recommend joint surveys of mariners or engineers and marine chemists. The marine chemists’ in-depth knowledge of tanker vessel operations and on-board fuel treatment, and their familiarity with risks associated with liquid cargo shipments are crucial to establishing causes of the most complex types of damage.

Added Value

We are often asked, “Why involve a marine chemist if we’re using an accredited laboratory?” There are, in fact, multiple ways in which the marine chemist adds value. A lab, e.g., has no background in shipboard investigations. Besides, accreditations only apply to standardised testing methods. Yet additional testing, such as forensic testing, is not standardised. In addition, the initial testing protocol may need to be changed as a result of preliminary analysis results or specific shipboard findings. All of which may well offer valuable clues.

To quote Arthur C. Clarke, “Don’t pretend we have all the answers. But the questions are certainly worth thinking about.” Indeed, where liquid cargo damage and bunker disputes are concerned, you can never ask enough questions, as I’ll demonstrate with two case studies.

The Discolouration of Heptanoic Acid That Vanished

The first case study concerns a shipment of synthetic heptanoic acid, shipped from Houston to Antwerp. Having arrived in the Port of Antwerp, a transshipment of this cargo from the seagoing vessel into a Captain’s tank barge was arranged. The inspector appointed by the carrier took samples both before and after transshipment. However, at the end terminal, no tank barge samples were taken by the inspector appointed on behalf of cargo interests.

After discharge into the receiving shore tank, the colour of the product was off-spec. The specs for colour allow a maximum of 15 on the Platinum-Cobalt (Pt/Co) scale. Yet the shore tank sample showed a value of 25 on the Pt/Co scale.

Let's summarise the facts:

All load port samples were within spec
The vessel’s cargo tank sample before transshipment was within spec
The samples from the tank barge’s cargo tanks taken immediately after transshipment were within spec
No samples were taken from the tank barge prior to discharge at the end terminal
The shore tank sample before discharge was within spec
The shore tank sample after discharge was off spec

These facts lead to a preliminary conclusion as to when discolouration occurred, i.e.

either on board the tank barge during its voyage
or at the end terminal, between the jetty and the receiving shore tank

Having narrowed down the ‘where’, we needed to look into the question ‘how’. Potential causes could have been:

remnants of previous cargoes in the tank barge
cross-contamination with other cargoes stowed on board the tank barge, including a possible crack between two cargo tanks
leakage of hydraulic oil from a cargo pump
the influence of temperature
exposure to air

We have assessed these possibilities by means of elimination, using realistic simulations to verify the effect of contamination by other cargoes, hydraulic oil and previous cargoes on colour. In addition, part of the samples were also incubated at various temperatures and purged with nitrogen. And we didn’t stop there. We also tested various metals, which may cause discolouration of acids. And conducted more forensic analyses, such as GC-MS (gas chromatography-mass spectrometry) and NMR (nuclear magnetic resonance spectroscopy). None of these tests and analyses led to a conclusive answer.

Loss Mitigation and Court Survey

Confronted with the discolouration, cargo interests had various options to mitigate the loss. However, as the cause of the discolouration was unknown, cargo interests refrained from three of these options, i.e. blending, filtration and salvage sale. Instead, they opted for the costly option of distillation at their plant in Germany.

As no causal link was found and given the extent of the damage, cargo interests decided to appoint a court surveyor. However, they did so months after they had reconditioned the cargo. And by then, for some reason, the discolouration of the ‘after discharge’ shore tank samples had virtually vanished.

This led to the question whether discolouration was inherent to the product. Diving into the production process of heptanoic acid, we found that there are two techniques:

chemical processing of castor oil, which is a vegetable oil
pure chemical synthesis from petroleum derivatives

In case of chemical processing with bio-derived material, the product contains proteins, which may turn yellow and then, under certain conditions, decolourise of its own accord. And indeed, the laboratories involved did find proteins. However, the cargo interests maintain that their product was synthesised, not based on castor oil.

The persistence of the marine chemist has resulted in finding the cause, i.e. the presence of proteins. However, the origin of this protein contamination remains a mystery.

Fuel-Related Engine Problems

The second case concerns very low sulfur fuel oil (VLSFO) stemmed in Rotterdam.

Prior to starting consumption of this fuel oil, a vessel’s manifold continuous drip sample was tested, as per the owners’ standard testing protocol, for the parameters specified in table 2 of the ISO 8217 standard. All the results thus obtained met the required specifications and the vessel consequently started to consume the disputed oil.

Three weeks after starting consumption, the RPM of the main engine started to drop. Inspection revealed excessive wear of the main engine’s fuel pumps and cylinder liners and abnormal deposits on the fuel valve nozzles. As no problems were experienced prior to the consumption of this particular bunker, it appears that the damage is linked to the quality of the bunker.

The investigation carried out by our technical fuel consultant showed no remarks on the main engine’s maintenance programme and the conventional on-board fuel treatment. Also, the vessel’s receiving bunker tanks had been empty prior to stemming.

The Investigation

As part of the investigation, the ship’s retained continuous drip sample and the BDN sample, which had been delivered on board the vessel by the bunker barge, were retested in accordance with ISO 8217 table 2 and were again found within spec.

In addition, various GC-MS tests were carried out to assess whether the fuel complies with Clause 5 of the ISO 8217 standard. Clause 5 states that the fuel shall be free from any material at a concentration that causes the fuel to be unacceptable for use (…).

This forensic testing showed excessive concentrations of certain polar compounds that did not originate from regular petroleum refining. In addition, these compounds had acidic properties and may have an abrasive effect or cause excessive wear on engine parts.

The polar compounds may point towards the cause of the damage. However, the legal impact remains to be seen. Was the supplier in breach with ISO 8217 Clause 5? Although the fuel oil may be off-spec after all, is there a direct link with the damage?

Regrettably, there is no industry-wide database from which to draw conclusions, as data is not shared by the relevant bodies. Yet, such a database could show the correlation between types of off-spec fuels and engine damage.

Conclusion

The marine chemist cannot resolve the legal complexities related to bunker disputes or liquid cargo damage. However, the chemist plays a crucial part in determining the compounds with which liquids have been contaminated and works closely with the mariner or engineer to determine the cause of such complicated cases. It’s the marine chemist’s tenacity to get to the bottom of things, that ultimately makes the difference.