Schiffstechnik | Ship Schiffstechnik | Ship Technology DNV GL revises shaft alignment rules After a joint development project (JDP) with marine insurers, classification society DNV GL has updated its shaft alignment rules to differentiate between Environmentally Acceptable Lubricants (EAL) and mineral oils in stern tubes The regulatory update is based on the first phase of the JDP, which was done in cooperation with The Swedish Club, Norwegian Hull Club, Gard and Skuld. The intention was to test the potential influence of EALs on failures in stern tube bearings. The JDP already entered the next stage, where oil film forming capabilities, mixed/boundary lubrication behaviour and lubricant degradation will be further scrutinized, the norwegian-german society announced during Nor-Shipping in Oslo. For now, the updated rules applying to newbuildings are effective since 1 July. Upsurge in bearing failurew On reason to initiate the project was an upsurge in stern tube bearing failures that coincided with the increased uptake of EALs after the introduction of regulations requiring their use in commercial vessels trading in U.S. waters in late 2013. Wiping was the dominant failure mode. Failures typically occurred during sea trials, mooring trials and at partly submerged propeller operation. In phase 1 the partners focused on mapping out differences in the load carrying capacity between the several times more expensive EALs and mineral oils. DNV GL has overseen detailed laboratory testing by Leonardo Testing Services Ltd. at the University of Sheffield, UK, and by INSAVALOR at INSA Lyon, France. »Phase 1 has looked into how pressure, temperature and shear rate influence the viscosity of the lubricants, thereby affecting the oil film thickness and the load-carrying capacity,« says Øystein Åsheim Alnes, principal engineer at DNV GL. He adds, the test results have proven that, in particular, the pressureand temperature viscosity properties of EALs are different to those of an equal grade mineral oil. »The findings show that while EALs provide safety margins that are equal to mineral oils in most operating modes, there are transient conditions where the EALs can have a reduced load carrying capacity,« Alnes emphasizes. In light of the results from the JDP, the classification society has added a viscosity influence parameter to the existing lubrication rule criteria for the aft most propeller shaft bearings. The own lubrication criteria do now provide yards and designers with a »strong tool« for optimizing stern tube bearing design, including both the lubricant viscosity and now the lubricant type. The way ahead For vessels in operation DNV GL recommends to switch to the next higher viscosity grade if converting from mineral oil to EAL. When more research data becomes available, a search for improved ways to handle the differential between mineral oil and EAL is planned. The study is still ongoing. While phase 1 and phase 2 are focusing on design issues (non-degraded lubricants), there are several operational challenges to EALs in stern tubes that the classification is also working on. These are amongst others accelerated wear rates of seals and bearings, hydrolysis, oxidation stability, change-over procedures and quickly rising metal content in oil samples.ED © DNV GL 56 HANSA International Maritime Journal 08 | 2019
Schiffstechnik | Ship Technology »We have done everything we need to do« The upcoming emission regulation not least indirectly affects lubrication. Global supplier Chevron feels prepared well with new products of the Taro Ultra range and optimised supply chains. However, for the future, there is a lot of »we don’t know what we don’t know« Energy group Chevron has asked its customers about their strategies for the upcoming »Sulphur Cap« of IMO. According to this survey, 80% of the customer’s vessels will be changing to 0.5 type fuel rather than opting for scrubbers or LNG. That brings a change from the predominantly used 70 and 100 BN down to a 40 BN product. However, the group will remain active in the markets of LNG or high sulphur fuels. In addition, methanol powered ships are being supplied. »We don’t believe there will be a ›one size fits all‹ for lubrication. The 40 BN will the main product for 0.5 fuel but it will also cover dual fuels. We have a 25 BN, which is dedicated for very low sulphur distillates and LNG. The 40 BN will be able to be used for 0.5 for normal steaming, but it can be used in the ECA regions as well. Our 100 and 140 BN products will be for high sulphur burning with emission control equipment,« Brand Manager Ian Thurloway tells HANSA . Looking at concepts including socalled »multi-fuels«, he again points at »the one size fits all« which does not exist: »It depends on what those multi fuels are. We work very close with the OEMs and we will do that when there is anything new coming up.« There have already been 65,000 hours of testing across 21 different applications, from LNG to distillates up to high sulphur fuels. A couple of weeks ago, Chevron has published a white paper for coping with the »IMO 2020 Sulphur Cap«. It explores the impact of ships burning fuels with differing sulphur contents to heavy sulphur fuel oil cylinder oil use. The paper also offers advice from lubrication experts on how to manage the transition between cylinder oils pre-and post-2020. »With our new structure, we strengthened our agility within the supply chain to change the coverage very quickly« Ian Thurloway Brand Manager – Chevron Apart from the work on the product side, Chevron, supplying over 700 ports around the world, has strengthened its supply chain. While Thurloway does not want to go too much into detail, he explains: »Some of the smaller ports may not have the flexibility to store all potential fuel products. With our new structure, we strengthened our agility within the supply chain to change the coverage very quickly.« It is about a system change and more integration of digital measures. Not on the horizon – at least not for the moment – is a partnering with start-ups, that aim to enhance business effectiveness, like the German player Closelink tries to do with a web-based platform for trade and procurement of lubricants. In order to make purchasing easier, Chevron recently launched an own system. The management of Chevron certainly expects more emission regulation in general, although the current shift is seen as a very big change. All in all, the group feels to have done everything it needs to do. The Brand Manager sums up: »For everybody there is a lot of ›we don’t know what we don’t know‹ at the moment. We are ready for 2020. What is going to happen with new hybrid fuels in 2021, 2022 and beyond, nobody knows, but we have the capabilities to test with these fuels, too.«MM © Chevron HANSA International Maritime Journal 08 | 2019 57
