The international standard ISO 8217 ‘Petroleum products -- Fuels (class F) -- Specifications of marine fuels’ has long been relied upon by shipowners and charterers alike as the go-to reference when ordering a vessel’s bunkers or specifying fuel requirements in charterparties. In 2024, the seventh edition was published.
The previous edition of ISO 8217 was released in 2017, and since then the marine bunker landscape has changed quite considerably. The introduction of the IMO global sulphur cap in 2020 saw the development and widespread take-up of VLSFO (very-low sulphur fuel oil) products, and the more recent drive to decarbonise the shipping industry has led to increased interest in biofuels.
As such, the 2024 edition addresses both VLSFOs and their diverse characteristics, and biofuels and their blends.
Those familiar with previous editions of ISO 8217 will be used to the two-table format, providing quality specifications for distillate fuels (DM grades) and residual fuels (RM grades). The 2024 edition separates the fuel types further and now has four tables:
Table 1: Distillate and bio-distillate marine fuels
Table 2: Residual marine fuel with a sulphur content below or at 0.50% by mass (for VLSFO and ULSFO (ultra-low sulphur) products)
Table 3: Bio residual marine fuels
Table 4: Residual marine fuel with a sulphur content above 0.50% by mass (‘High sulphur’ products, typically used in vessels with an exhaust gas cleaning system (‘scrubber’))
The scope and the general requirements in Clause 5 have been amended.
There are numerous other changes to the 2024 edition when compared with previous ones, but here we will consider the more prominent revisions and additions.
We’ve now had over four years of experience with using VLSFOs since it became what is probably the most popular fuel option for owners and operators following the introduction of the IMO global 0.50% sulphur cap for marine fuels.
The transition to VLSFOs has largely been managed well, with shipboard engineers adapting to the new challenges, as they always do. There have, however, been pain points experienced that have been shared by the wider industry.
The first challenge has been the uncertainty in fuel characteristics from stem to stem. Like Forrest Gump’s proverbial box of chocolates, the vessel is unsure on what they’re going to get until the bunkers have been delivered. Before 2020, when an order for bunkers was made, the buyer usually specified IFO 180/380 and the crew would be pretty confident in knowing what they would get and how to handle it.
But VLSFOs are varied, with viscosities (its resistance to flow or how “runny” it is) ranging widely. Some are of a paraffinic nature (waxy) which are very different to those products that more resemble a traditional residual ‘heavy’ fuel oil.
Tables 2 and 3 of the 2024 edition look to address this variability. One of the ways is to introduce minimum viscosity levels for all VLSFO (and ULSFO) residual and bio-residual grades of fuels.
At the lighter end, RMA 20 and RF 20 have been set a minimum viscosity of 2 mm²/s (or centistokes (cSt)) which is the typical limit imposed by engine manufacturers for fuel injection. Grades RME 180, RF 80 and RMG 180 have been set at 20 mm²/s, which has been determined to be the limit for handling and use. The minimum viscosity for grades with maximum viscosity of 380 mm²/s (including those in ‘high sulphur’ Table 4) has been set at 120 mm²/s.
This results in no overlaps in viscosity between the grades that existed before. Now, if specifying the 2024 edition in bunker purchases or charterparty warranties, if a 380 grade is requested, then there should be confidence that the vessel will not be supplied with a fuel of viscosity below 120 mm²/s. This means the shipboard engineers will have a better idea of what they are going to get and how to manage that fuel on board.
Some VLSFO products, particular those of a more ‘waxy’ nature, can begin to solidify at relatively high temperatures, causing headaches for the shipboard engineers when it comes to storage and handling.
Some fuel testing laboratories introduced additional tests when carrying out post-bunker analysis for their shipowner clients, which supplemented the usual ISO 8217 suite of tests. A common addition was the ‘wax appearance test’ (WAT) and ‘wax disappearance test’ (WDT). In conjunction with the Pour Point test (which is an ISO 8217 parameter), the crew can make more informed decisions on heating requirements for storage and transfer.
It is understood that the WAT and WDT were considered for inclusion into ISO 8217:2024, but it was decided that although these provide potentially useful operational information on the use of a product, there are limitations, with CIMAC noting that “the test provides a temperature when waxes appear and disappear, but has no indication on the amount of wax, nor the effect on the fuel”.
It has become apparent that some VLSFOs have suffered from stability issues. The stability of a fuel is defined as its ability to remain in a similar condition to that produced after the refining process, so it maintains its homogenous mixture during normal storage conditions. If a fuel becomes unstable, sludge can form, blocking filters, pipes and tanks, as well as contributing to poor combustion conditions and potentially cause damage to engine components.
This can also result in some VLSFOs having a short storage life. So, the fuel may seem fine at time of bunkering, but issues occur in storage. Furthermore, the instability of some VLSFOs can be accelerated by heat, which typically needs to be applied to prevent solidification during storage or when processed through centrifugal separators (purifiers and clarifiers) during onboard treatment.
The laboratory test under previous ISO 8217 editions for measuring a residual fuel’s stability was the ‘Total Sediment, Aged’ or TSA test. The 2024 edition now requires suppliers to test VLSFOs and residual bio blends for ‘Total Sediment, Potential’ (TSP) and report TSA and TSE (Total Sediment, Existent) so stability issues can be better monitored going forward.
Note that there are no limits for TSA and TSE for VLSFOs and residual bio blends; a limiting figure only applies to the TSP test result.
Under the 2017 edition, the concentration of FAME (Fatty Acid Methyl Esters, which are the acids that create biodiesel) was capped at 7% for DF grades and allowed only a trace amount for all other grades.
In the 2024 edition, Table 1 (distillate and Bio-distillate marine fuels) and Table 3 (Bio residual marine fuels) now allows blends up to 100% FAME content for DF and RF grades.
B100 FAME (which is 100% FAME content) will be considered a bio-distillate and categorised under Table 1.
However, it is important to note that ISO 8217 is an indication of the characteristics of the delivered or blended product. It is not a verification of the quality or characteristics of the FAME component, which would fall under the standard EN 14214 “Fatty Acid Methyl Esters (FAME) for use in diesel engines and heating applications — Requirements and test methods” or ASTM D6751 “Standard Specification for Biodiesel Fuel Blend Stock (B100) for Middle Distillate Fuels”.
Also, ISO 8217 is not concerned with sustainability criteria. Certification of the feedstock and the source of FAME must be documented separately.
CIMAC advise that there are an increasing range of new potential off specification biofuels being offered to the marine bunker pool under the guise of a biofuel or bio-oil. Suppliers in these cases, should be transparent to the receiving ship as to the specific bio blend composition and feedstock source. Under these circumstances the ship’s classification society and OEMs should be approached and before accepting the product, should discuss their specific risk mitigation requirements for assessing the suitability of the fuel use prior to carrying out a sea trial.
When a fuel is tested at a laboratory, satisfactorily passing the ISO 8217 parameters stated for the appropriate grade within the tables does not always mean that the product is ‘on-spec’. The fuel must also meet the requirements found in Clause 5.
Clause 5 addresses the ‘general requirements’, and previous editions typically provide that the fuel must be homogenous, conform to the parameters in the relevant tables, and be free from any material at a concentration that could jeopardise the safety of the vessel, adversely affect the performance of machinery or pose a threat to personnel.
Clause 5 in ISO 8217:2024 has been revised to allow any fossil, synthetic or biofuel mentioned in the text of Clause to be used at 100% or in a blend. It also limits FAME content of grades designed to not contain FAME at approximately 0.5%
It also requires the fuel to be free of organic chlorides, which means the total organic halogen content as chlorine must not exceed 50 mg/kg.
Despite ISO 8217 being updated through the years, it is still common for bunker suppliers to offer terms referencing old editions, such as 1996, 2005 or 2010. Similarly, bunker clauses in time charterparties (where the time charterer is obliged to provide the vessel with suitable bunkers) still reference outdated editions.
This happens for a number of reasons, particularly in circumstances where suppliers cannot provide bunkers meeting the more stringent requirements. However, engine manufacturers recommend always using the latest version of ISO 8217.
Terminology has become increasingly important when reference bunker requirements, whether in purchase orders or charterparties. It is no longer adequate to specify vague generic terms such as “IFO 380” or “HFO”. Also, a VLSFO could be a RMA, RME, RMG or RMK grade as long as the sulphur content is at or below 0.50%. So, when ordering fuels, specify exactly the grade in accordance with the tables in ISO 8217.
ISO 8217 is concerned with petroleum-based hydrocarbon fuels but allowing for blends with biofuel content. It does not, however, cover ‘alternative’ fuels that are being earmarked for adoption to meet the shipping industry’s drive to decarbonise, such as methanol, ammonia and hydrogen.
These new fuels have very different properties and characteristics that require different test methods and are subject to different regulations.
Quality standards for the different alternative fuels remain a work in progress. However, CIMAC report that a standard for methanol as a marine fuel is under development by ISO and is expected to be published by late 2024 or early 2025.
Recommended reading: CIMAC_Guideline_ISO_8217_2024_FAQ_02-2024_final.pdf
If you would like to learn more or wish to discuss any of your marine engineering consultancy needs, contact Alvin via a.forster@solis-marine.com or call +44 (0) 7909 672532.