70 BN Cylinder Oil Old design engines versus Newest design engines Figure 1 | Iron content is determined as a measure of wear in a 70-BN MDCL while the feed rate is varied in old design engines and newest design engines. (Figure courtesy of Chevron Marine Lubricants.) COLD CORROSION Wolpert indicates that cold corrosion occurs as a consequence of slow steam-ing that reduces engine load leading to lower combustion chamber tempera-tures and lower cylinder liner temper-atures. He says, “Under these condi-tions, more sulfuric acid, a combustion product from the sulfur present in the fuel, condenses on the liner surface and causes corrosive wear that is often termed cold corrosion. MDCLs with 70 BN are not adequately formulated to neutralize the increased acid levels.” Wolpert believes that different lu-bricants and operating adjustments are needed to minimize cold corrosion. He says, “One solution has been to introduce lubricants with higher base levels (100 BN) and higher lubricant feed rates, sometimes above 1.2 grams per kilowatt-hour. These operating ad-justments have been approved by the engine manufacturers to prevent corro-sion. In addition, OEMs have begun to support the use of 140-BN lubricants as one means to provide adequate basic-ity for neutralization, yet reduce overall feed rates to reduce lubricant consump-tion and total operating costs.” While Soobramanien sees cold cor-rosion in some older vessels following slow steaming guidelines, the problem seems to be prevalent among newer en-gines in recently built ships. She says, “Newer engines are operating at higher pressures resulting in more of the sul-fur in the fuel being converted to sul-furic acid. Extreme corrosive wear can be observed in modern engines even under normal operation.” Huot agrees that cold corrosion is widely seen in marine diesel engines and indicates that a condition monitor-ing program is essential to make sure any operating issues can be promptly handled. She says, “Serious cold cor-rosion is found in at least one engine out of 10 since the appearance of new designs in 2010. Without monitoring, a ship operator cannot know what is oc-curring. Testing needs to be done each time that refueling takes place because signiﬁcant shifts in sulfur levels are possible that may impact engine opera-tion and the onset of cold corrosion.” As part of a condition monitoring program, Huot advises, “The lubricant supplier needs to assist the ship owner with ﬁnding the optimum lubricant feed rate, perform condition monitor-ing and reduce downtime costs.” Thurloway feels that specially for-mulated 140-BN MDCL can be designed to minimize cold corrosion in the most modern ultra long stroke slow speed engines using a high-sulfur-containing HFO. He adds, “Cold corrosion can be managed effectively using the correct base number lubricant in conjunction with MDCL oil monitoring to ensure that the correct feed rate is used.” Figure 1 shows how condition moni-toring is done to evaluate the iron con-tent, a measure of wear in the lubricant, 15 In the 13th Century, Italy’s Salvino D’Armate made the ﬁrst eyeglass, providing the wearer with an element of magniﬁcation to one eye.