May 18, 2020 [Argus Media] – The 0.5% sulphur fuel oil market is in steep contango, but storage of the grade beyond 2-3 months can make it unstable and useless, according to fuel testing firm Veritas Petroleum Services (VPS).
Determining how long marine fuels can be stored before it suffers quality issues will differ between grades such as 0.5% fuel oil, 3.5% fuel oil and marine distillates. It can also differ between different 0.5% fuel oil blends. But 0.5% fuel oils run into quality issues sooner than 3.5% fuel oil or 0.1% marine gasoil, VPS commercial and business development director Steve Bee said.
The fuel type and storage conditions will impact the storage time of marine fuels. Straight run marine distillates can be stored for about a year at 20°C, and for 6-12 months in temperatures above 30°C, while 3.5% fuel oil can be safely stored for about six months.
In most cases, 0.5% fuel oil only has a shelf life of 2-3 months, according to Bee. VPS has also witnessed 0.5% fuel oils that have become unstable in less than three months. Safe storage time depends on the asphaltenes and paraffinic content of 0.5% fuel oils and 3.5% fuel oils. It also depends on levels of moisture and contaminants in the fuel. Contaminants can react with fuel and cause oxidation.
A short shelf life can pose problems now that Covid-19 lockdowns cause bunker demand to slump and storage tanks to fill up. Fuel oil stocks rose by 18% in the Amsterdam-Rotterdam-Antwerp (ARA) hub last week to reach 1.6mnt t — the highest since June 2018. Gasoil stocks went up by 12% to a three-month high of 2.4mn t.
Quality issues vary between different fuel types, but there are some common threads. Both 3.5% fuel oils and 0.5% fuel oils are prone to instability, sludging and issues with catalytic fines. But the grades differ in that 3.5% fuel oils are more likely to suffer from stratification, while 0.5% fuel oils are more likely to suffer from waxing. Marine distillates are also prone to waxing, oxidation and bacterial growth.
When fuels become unstable they may be beyond the point of recovery. “If the issues are related to stability and the fuel has flocculated, it cannot normally be saved,” Bee said. But using additives early in the storage period can prevent instability in some cases. Fuels that suffer from waxing can sometimes be recovered.
To prevent the fuel from deteriorating, VPS recommends monitoring the fuel and frequent testing of temperature, moisture, contaminants, sediments, stability, wax, pour point, water and bacteria.
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