A vessel experienced excessive purifier sludging after bunkering a Very Low Sulfur Fuel Oil (VLSFO). Testing of the manifold sample recorded a density of 919.6 kg/m³, a viscosity of 33.7 cSt at 50°C, a Total Sediment Potential (TSP) of 0.07% m/m, and a pour point below 12°C. Although the fuel complied with the ISO 8217 sediment limit of 0.10% m/m at the time of bunkering, the TSP was considered borderline. Viswa therefore recommended an Aging Study to assess whether the fuel would remain stable during storage and onboard use.
Much like certain products have a limited shelf life, some marine fuels may initially meet specification but gradually lose stability over time. Viswa’s proprietary Aging Study subjects the fuel to controlled accelerated aging conditions to evaluate its tendency to form sediment during storage. In this case, the fuel failed the Aging Study, indicating a considerable risk of deterioration. Following this early indication, the fuel remained onboard while its condition continued to be monitored.
The fuel subsequently deteriorated as predicted. Within 20 days, the TSP increased to 0.11% m/m, exceeding the ISO 8217 limit. By 45 days, it had risen further to 0.20% m/m, confirming a progressive loss of stability and substantial sediment formation. The vessel’s experience of excessive purifier sludge was consistent with the deterioration of the fuel during storage and was likely associated with the precipitation of asphaltenic material. The fuel’s relatively low viscosity and density may also indicate the presence of lighter or more paraffinic blend components, which can reduce the fuel’s ability to keep asphaltenes in suspension.
When an Aging Study indicates that a fuel may not remain stable for an extended period, the vessel can take proactive steps to reduce operational risk. These may include consuming the fuel within a shorter timeframe, avoiding prolonged storage or mixing with other fuels, and considering the use of a suitable fuel stability additive. Viswa can also provide guidance specific to each case on fuel handling, treatment, purification, additive use, and consumption strategy to help minimize the risk of sludge formation, filter blockage, and operational disruption.
This case demonstrates that a fuel may comply with ISO 8217 at the time of bunkering yet still become unstable during storage. Routine TSP testing provides an important assessment of the fuel at a specific point in time, while the Aging Study offers additional insight into how the fuel may behave over the following weeks. Early identification of limited storage stability can allow the vessel to accelerate fuel consumption, consider the timely use of a suitable stability additive, and take other preventive measures before deterioration leads to purifier overloading, filter blockage, increased sludge generation, and operational disruption.