It is tempting for certain members of the public and shipping industry to presume the latest incidents of bunker fuel contamination at Singapore port are similar to the ones earlier experienced at Houston during 2018.
Both events have been labelled under the category of ‘bunker contamination’ and multiple issues relating to fuel pumps and engines have been identically reported; inherently resulting in some to assume either are the same thing.
However, experts at chemical engineering and bunker fuel testing laboratories know the fundamental elements of both scenarios are completely different; producing, this time, a more adverse and – often irreversible negative effect – on vessel engines.
Houston bunker fuel contamination – a clean-up to fix
To share, Eurofins have found 4–Cumyl–Phenol, carboxylic acids (fatty acids), benzoic acid, cyclohexane, diol isomers and dehydroabietic acid and other oxygenated compounds, amongst others, in bunker fuel samples from Gas Chromatography-Mass Spectrometry (GC-MS) tests at Houston in 2018.
The chemicals have produced various chocking and sludging issues within the engine system (i.e. engine pistons, etc) of affected vessels at the U.S. Gulf Coast.
These incidents are caused by polymeric compounds (which are not a hydrocarbon) being left unburnt after the fuel combustion process. Instead, the compounds simply accumulate within the combustion chamber after ignition – resulting in the engine becoming choked over time.
To solve this and related issues, shipowners and operators typically employ manual labour and solvent solutions to unclog pipes and clean affected components.
The majority of vessels affected by contaminated bunker fuel from Houston have since returned to operate in the market.
Singapore bunker fuel contamination – irreversible damage
This round, a different type of contaminant, namely chlorinated organic compounds (COCs) (1,2-Dichloroethane, Tetrachloroethylene), has been found in an affected High Sulphur Fuel Oil (HSFO) cargo which was followingly supplied to ships as bunkers at Singapore port.
COCs are common in the petrochemical industry. Some are chemicals inherently found even in crude oil and others, especially light COCs, may be introduced as a result of additives, cleaning solutions or chemicals used for oil recovery, etc.
Light COCs mainly consist of chlorine compounds such as chloroform, carbon tetrachloride, chloroethylene, dichloroethane, trichloroethylene, etc.
Refineries have traditionally been able to accept COCs within the crude oil feedstock as long as the content is within the strict tolerance of 3-5 parts per million (ppm) due to their potential acidic nature.
To clarify, COCs do not change in chemical structure when kept under atmospheric conditions (i.e. bunker fuel tank). As such, the Total Acid Number parameter of ISO 8217 will be unable to determine the presence of COCs as laboratory tests are generally conducted under atmospheric conditions.
However, the application of high heat and pressure (i.e. engine environment) converts COCs into hydrochloric acid – a chemical known to be highly corrosive to metallic components.
For example, tetrachloride and dichloroethane as shown with equations (1) and (2) tend to convert into hydrogen chloride (HCl) during the crude oil refining process at ≥160°C.
Hydrolysis reaction equations of tetrachloride and dichloroethane during oil refining:
(1) CCl4(g) + 2H2O = CO2(g) + 4HCl(g)
(2) CHCl2CH3(g) + H2O = CH3CHO(g) + 2HCl(g)
Following, HCl will dissolve a tiny amount of water from the atmosphere and process to form a dilute hydrochloric acid solution which, in turn, results in serious corrosion to metallic components.
The concentration of hydrochloric acid is co-related to the level of COCs present in contaminated bunker fuel. Most metals suffer corrosion from HCl at all concentrations and temperatures.
To date, Eurofins’ Singapore laboratory has detected between 3,000 to 5,000 ppm of COCs within affected HSFO bunker stems.
This level of exposure to COCs, when converted into hydrochloric acid, causes irreversible damage to the structural integrity of the vessel engine and related components due to thinning of metallic material.
This development is something which shipowners and operators will not be able to solve with a clean-up and debunkering process (as compared to the earlier bunker fuel contamination cases at Houston).
Though the current bunker fuel quality standard of ISO 8217: 2017 does not specify the requirement/tolerance of COCs, it will be prudent for the shipping sector to follow similar tolerance levels set by the refining sector.
Our recommendation to shipowners and the bunkering sector is for players to accept COCs of between 5 to 10 ppm when found in marine fuel; while anything beyond 10 ppm and above should be avoided.
Related: Bunker contamination: The importance of timely GC-MS results
Published: 20 April, 2022