Muhammad Usman, LR’s FOBAS product manager assesses the impact of quality variance of VLSFO on machinery equipment and offers some recommendations going forward.
IMO 2020, a global sulphur cap of 0.50% on marine fuels, has had a marked impact on stakeholders in maritime and beyond. Before this landmark regulation came into force on 1st January, concerns were raised by different industry stakeholders regarding availability, quality and pricing of compliant fuels as well as the consistent implementation of the regulation and how it would impact vessel operation. However, since the switchover the industry has shown its well-known resilience and generally concluded ‘so far so good’ without any major issues.
How has the regulation impacted operations?
As the majority of the world fleet was prepared for this change, the message from most ship operators is that the switchover has gone smoothly without any major issues. Nevertheless, huge variability in the quality of 0.50% fuel, has still caught a few by surprise. Excluding fuels which are considered unmanageable such as those that considerably exceed the ISO 8217 limit, ships have had to make adjustments to ensure smooth operations, whether that’s onboard fuel segregation, temperature management at various points of the fuel system, or combustion performance. Since the sulphur cap entered into force, Lloyd’s Register’s (LR) fuel oil bunker analysis and advisory service (FOBAS) has reported various issues including excessive sludge generation in purifiers, unstable combustion and loss of fuel pressure at engine inlet. In one case, fuel with a pour point of 27 oC solidified in an unheated tank loaded from Singapore, however when the ship sailed to a colder climate (<10 oC) it was unable to transfer fuel from storage to a settling tank. In cases where fuel solidifies, ships are advised to remove the fuel from the tank manually, which is often highly resource intensive and can cost ship operators time and money.
What has been the impact to the machinery equipment due to the quality variance of VLSFOs?
Some ships using VLSFO have reported problems to FOBAS at various points of its fuel machinery system, such as blocked fuel filters, sludging at separators, loss of pressure at pumps and excessive wear of engine cylinder components. In the past, approximately 5% of FOBAS investigations comprised of issues related to damaged and excessive wear of liner/piston. However, since the switchover, we have seen an increase to 40% of cases involving liner scuffing issues on two-stroke main engines with piston ring malfunction.
For example, one ship reported excessive wear and damage to the piston rings. The subsequent investigation found that the feed rate was too excessive for the operating condition, which is dependent on the fuel’s sulphur content, Base Number (BN) of the cylinder lube oil and the condition type of the engine, as well as incorrect material in the piston rings, with fuel quality being a possible contributory factor. The ship found the two-stroke piston rings of four units jammed/stuck in the ring grooves resulting in a blow-by, which continued to exacerbate the problem causing disruption to the lubricant film and increased the scavenge temperature. A probable reason for this was poor atomisation by the injectors, often due to incorrect viscosity and degraded injection performance of high-pressure pumps and injectors.
The ship was advised to take the following measures to improve the situation:
- Check / overhaul fuel injectors to ensure optimum performance
- Ensure fuel injection viscosity is maintained as per OEM guidelines
- The delta between the maximum pressure during combustion in a cylinder (Pmax) and maximum compression pressure (Pcomp) which is measured just before the fuel injection, is maintained as per OEM’s operations manual. High difference could indicate blow-by and lower than usual difference may indicate an issue with the injection timings.
- Draw regular scavenge drain oil samples to evaluate the levels of liner wear, ring groove wear, soot, and residual base number of cylinder oil.
- Regularly inspect the piston rings and liners through scavenge ports.
- Monitor operation of fuel purifiers to reduce the possibility of catfines and/or water going into the engine and causing excessive wear.
- The choice of appropriate base number cylinder lubricant with optimum feed rate and dispercancy characteristic based on VLSFO quality and operating conditions.
The ship implemented actions based on above guidance and no further problems have been reported. In most cases, vessel technical staff tend to be in the best position to evaluate and make judgements based on the suggested course of actions.
What does this mean for owners/crew?
For a ship’s crew and fuel buyers, there is a new norm in terms of how they order the fuel and how it is managed onboard. The era where the majority of fuels were 380 cSt and systems were set up for that fuel grade has now ended. LR’s FOBAS data indicates that around 52% of VLSFO are in the range of 80-180 cSt, whilst only 18% are above 180 cSt. This shows a massive shift with viscosity, widely spread between lower viscosity ranges. This is similar to the density of the fuels with larger variances observed. Therefore, a ship’s crew needs to be proactive; firstly, they need to have information about the quality of the fuel coming onboard, and then make fuel system adjustments to suit fuels characteristics for smooth operation.
Is there an increased risk of downtime?
Ships machinery equipment is quite resilient with redundancies built into the system. Though in extreme cases, ships may experience complete engine breakdown with loss of propulsion, a potentially hazardous outcome. Since 1 January, LR FOBAS has not reported or been informed of such an extreme case whereby a ship has experienced a complete engine breakdown though there have been a number of operational issues, some of which have been described in this article. So, it is imperative for a ship’s crew to be able to bring the system back from a degraded position to a running order. Some ships may have to spend more time on maintenance when in port which may impact the vessel schedule. However, this would depend on a number of factors, with most ships being able to complete certain maintenance tasks within scheduled time frame.