SThe handling of hipboard fuel and the documentation of onboard handling procedures are of paramount importance in dealing with cargo hold issues and disputes. Skuld has found that bunker disputes can be very costly and time consuming for both the member and the club. The best way to avoid cargo hold issues and disputes is to properly handle onboard fuel and follow good documentation practices.
It may come as no surprise, but there has been a general increase in disputes over bunker quality in relation to VLSFOs following the 2020 sulfur cap. This is due to the characteristics of VLSFO fuel oils and to improper/mishandling of fuel on board. We are very grateful to Walter Dekkers, Bunker Consultant (technical) at Van Ameyde Marine, for sharing his experience and providing his loss prevention advice on this topic.
Seen from the angle of bunker disputes, it is essential that the owners, managers or operators concerned take the necessary measures to secure their legal situation. Ideally, if all precautions have been taken, subsequent damage and litigation can be avoided, or at least cannot be attributed to lack or mismanagement of onboard fuel handling.
Let’s consider actions that can prevent operational issues and time-consuming disputes related to on-board fuel handling.
There are different stages and types of fuel processing:
Cleaning (settling, purification and filtration)
Proper fuel storage arrangements on board the vessel can make all the difference. Even on-spec fuels can cause problems if fuel tanks and lines are not clean, fuels are not properly separated, and fuel temperatures are too high or too low.
In the event of a dispute, it is essential that the storage conditions can be proven; accurate documentation of all measures in place is essential.
Ships can carry different types of fuels: distillates only, or for example a combination of HSFO, VLSFO, ULSFO, diesel or gas oil. Each grade of fuel must be strictly separated by proper tank arrangements and piping.
But even different bunker deliveries of the same quality must be stored in separate tanks; especially today that VLSFO consists of different mixing components. The very different VLSFO properties, such as density and viscosity, and others, can lead to compatibility issues when these basic rules are not followed.
Another concern is the much shorter “shelf life” of VLSFOs during which the fuel remains homogeneous and stable, compared to traditional residual HFOs. This is not only due to the (complex) nature of the mixtures, but is also closely related to the storage temperature, which can cause heat stress.
Marine residual fuels must be heated to reduce viscosity. The necessary temperatures depend on the characteristics of the fuel, but also on its location in the ship’s fuel system. Recommended temperatures in the storage tank, settling or service tank, separator or at the engine all differ. In addition to training and knowledge, it is important that engineers, in order to know the characteristics of the fuel, have the analysis results readily available.
However, when using VLSFO, two other properties are also important: cold flow properties and stability. All of these properties can conflict:
Many VLSFOs have a relatively low viscosity and do not require much heating.
However, cold flow properties may require higher temperatures, which in turn may adversely affect the stability of VLSFOs when stored for a longer period.
There are a variety of tests related to cold flow properties, but only one is part of the ISO8217 standard: pour point. The pour point is the temperature at which the fuel no longer flows. To avoid this, heating is necessary, but prolonged storage at high temperature will destabilize the fuel, one of the consequences of which is the formation of sludge (= precipitation of asphaltenes).
To avoid heat stress, fuel in the storage tank should not be overheated: it should only be transferred to the settling tank. We are still on a learning curve when it comes to VLSFOs, but it seems that the “rule of thumb” of +10°C above pour point, typically used for residual HFOs, is no longer sufficient. in some cases. A waxy fuel is best stored at a temperature of +15°/+20°C above the pour point. Particular attention should be paid to double bottom storage tanks and low sea temperatures (in winter).
We have seen VLSFOs with a very high WAT – “wax appearance temperature” – the temperature at which wax crystals form. These fuels should preferably be avoided (we recommend a maximum of 50°C). Experience shows that the WAT can be significantly higher than the pour point, compared to what is usually observed with distillates (cloud point versus pour point).
The same goes for VLSFOs close to the Total Sediment Potential (TSP) limit on delivery, so between 0.07% m/m and 0.1% m/m in the event that the fuel also has a WAT raised. Unfortunately, the WAT test is not part of the ISO8217 standard; table 2 specifications.
In terms of storage, good practices boil down to:
- up-to-date fuel management procedures
- tanks and systems dedicated by fuel quality
- no mixing of different bunker deliveries
- receive bunkers in empty tanks
- maintain a temperature at least 15°C/20°C above the pour point in case of “waxy fuel”
- avoid VLSFOs with high wax appearance temperatures (stay below 50°C)
- avoid VLSFOs near or on the TSP limit
- minimize the storage time of VLSFOs, given the shorter “shelf life”
- avoid heating the fuel more than necessary so as not to disturb the stability reserve (minimize thermal ageing)
- Cleaning fuel (settling, purification and filtering)
There is no way to avoid receiving dirty fuel. This is why fuel tanks should be opened, inspected and cleaned regularly to remove any sludge (including cat-fines).
Settling and service tanks should also be checked frequently for water, sediment and solids at the bottom drains, preferably every quarter. Experience shows that the ship’s engineers mainly focus on the decanter which, at the right temperature, is indeed a first step in removing water and unwanted solids, but the service tank should not be forgotten. In both tanks, the viscosity of the fuel must be low enough to facilitate the sedimentation of solids and water at the bottom of the tank, hence the importance of adequate heating.
The removal of water is of great importance to avoid microbiological infection causing sludge formation, but to date few VLSFOs have suffered from this despite the lower viscosity of VLSFOs consisting largely of distillates.
The separator is an essential element to ensure that the fuel pumped into the engines is clean. A separator acts like a centrifuge, removing sludge, such as water, asphaltenes, metals, tar, rust, sand, etc. A distinction is made between the conventional purifier and clarifier, and the more modern automatic separator.
The different settings are of utmost importance. The Purifier needs the correct Gravity Disc based on Density. The separator bowl is emptied at set intervals or automatically at regular intervals, removing water and solids (scrubber). The sludge outlet should be checked regularly and adjustments to the settings made if necessary.
Suffice to say that the separators must also be maintained and cleaned at the intervals defined in the manufacturer’s manual, or more often depending on the properties of the fuel. To verify the effectiveness of the separator cleaning, “before” and “after” samples can be taken for analysis.
Research has shown that good practice rules for separators are low viscosity fuel in the cleaning process – i.e. higher temperatures – in combination with low flow rates: the longer the fuel spends in the separator, the cleaner it will be.
In order to respect the fuel consumption of the engine, it is therefore recommended to operate two separators in parallel. In general, separation temperatures should be 60°C (20-40cSt), 70°C (40-50cSt), 80-85°C (50-80cSt) and 98°C (>80cSt). Yet, the correct temperature ultimately depends on the properties of the VLSFO, including WAT.
It will not be surprising that filters are also indispensable. Separators do the heavy lifting, but they can’t remove all unwanted particles: 80% cleaning efficiency is considered good. Filters also need to be cleaned and replaced due to normal wear and tear as well as cleaning activities and detergents. If in doubt, replace!
Most ships use self-cleaning filter systems. The automatic cleaning system is based on backwashing: the flow of fuel is reversed to remove contaminants from the surface of the filter. These systems are usually equipped with a counter to count the flushing cycles, and it is a good indicator to recognize “dirty” fuel. To keep large cat fines away from the engine, it is recommended to use a 10 micron filter just before the inlet of the fuel injection pumps. This is the last safety notch!
The main actions to be taken can be summarized as follows:
- thoroughly document fuel processing and storage management
- clean and maintain tanks, separators and filters at regular intervals
- watch out for potentially unstable VSLFOs with poor cold flow properties
- adjust temperatures to match fuel characteristics at different locations in the system
- operate separators in pairs; in series or in parallel depending on the case
Proper handling of fuel on board means avoiding damage and, in its wake, costly litigation. In addition, the documentation of fuel treatment on board guarantees the legal position in the event of a dispute. If in doubt, contact an independent bunker consultant or your P&I Club, Skuld.