MCL Debate Flares with MAN Advisories


Engine manufacturer MAN Diesel & Turbo recently issued service letters advising ship owners that using a single universal lubricant to handle the range of sulfur content in their bunker fuels could corrode cylinder liner walls in its newest engine designs.

Based on current technology and technical and economic aspects, two-cylinder lube oils with a high and a low BN [base number], respectively, will be the optimal solution for operation in the fuel sulfur range of 0.1 to 3.5 (or 5) percent, the Copenhagen OEM said in one of two service letters. It recommended a BN70or higher cylinder lube oil for its latest generation super-long-stroke engines (the Mark 9 series and all G-type engines) when using fuels with a sulfur content above 1.5 to 2 percent.

The marine lubricants industry has divided into two competing visions since 2008 over what marine cylinder lubricants (MCL) should be used and when.

One side maintains that that the proper lubricant depends on sulfur content and operating conditions, such as whether a ship is in an Environmental Control Area (ECA), on the open sea or engaged in slow steaming. For conventional MCLs, a BN70 product is typically used with medium- to high-sulfur fuel (1.5 to 4.5 percent) in global operation beyond designated ECAs. A BN40 ‍lubricant is designed for low-sulfur fuel (less than 2 percent) and suited for ships operating long-term or permanently within ECAs.

The other side proclaims a new era of innovation in which chemistry and formulation enable a mid-range BN oil to work effectively under any operating condition and across the range of sulfur content seen in bunker fuel. Proponents of the universal concept say their product can be used with fuel sulfur ranging from 0.5 to 4.5 percent.

In its recommendation, MAN noted that it did not have any objections to using an SAE 40 viscosity grade MCL that had a No Objection Letter in its older two-stroke engines (Mark 8 and previous designs). Nor did it object to using a BN50-60 cylinder oil with a No Objection Letter in the older engines-provided that prevailing relevant guidelines are followed.

Ideally, MAN noted, having one type of cylinder oil that is suitable for all fuel-sulfur levels could facilitate operation in and out of SOx [sulfur oxides] ECAs. It noted, however, that most international ships operating in and out of SOx-ECAs today are in regulated waters for less than two weeks at a time operating on low-sulfur heavy fuel. For those ships, it will not be necessary to change to lower BN lube oil, MAN said.

It added that the design philosophy of two distinct lube oils is based on observations and tests that show over-lubrication leads to over-additivation with consequential risk of calcium deposit formation and total suppression of corrosion, decreasing the scuffing tolerance. Moreover, under-lubrication may lead to under-additivation, which will lead to corrosive wear in cylinder liners and piston rings, and poor deposit-control on piston toplands, in ring grooves and on ring lands.

Castrol Marine greeted the announcement as vindication of its support for the conventional approach, while Total Lubmarine, a mid-range BN advocate, criticized its rivals reaction as a biased interpretation of MANs recently issued customer letters.

We welcome these recommendations from MAN, said Paul Harrold, Castrol technology manager, marine and energy lubricants, in Pangbourne, U.K. They support the exhaustive bench tests and shipboard trials that led to our own recommendations on cylinder oil selection in the slow-steaming era. The recommendations we make to customers must always be based on sound science.

While some cylinder oil suppliers have suggested that a single mid-range BN oil is sufficient for use with all marine fuels, under all operating circumstances, Castrol believes customers faced with the prospect of only one grade of cylinder oil to cover all operating scenarios may be putting themselves at a disadvantage, especially if they regularly use fuel at the upper and lower ends of the permitted sulfur spectrum, Harrold said.

He added, Castrols technical arguments have been challenged by a series of competitor product launches of lubricants conceived before slow steaming was even adopted, says Harrold. This direct advice from MAN corroborates our own tests on the real issue.”

Jean-Philippe Roman, technical director for Total Lubemarine in Lyon, France, in a written statement to Lube Report, disagreed.

MANs detailed technical documents, he said, contain recommendations for both existing engines, which currently represent approximately 99 percent of the marketplace, as well as future designs. It clearly states that single-oil solutions are approved for all engines except for Mark 9 and G series, which cannot be recommended at present.

Roman continued, Total Lubmarine respects the views of those that subscribe to conventional thinking; that cylinder oil should have a BN that matches sulfur content. With several relatively unproven so-called single oil solution products recently launched to the marketplace, claiming to match the benchmark set by Total Lubmarine in 2008, we appreciate why this has caused some confusion. Five years of hard, corroborated evidence dictates that it is misleading to categorize lubricants simply according to their basicity-mid-range certainly does not automatically equate to universal or single oil solution.

Total remains wholly convinced that the new chemistry developed over five years ago for Talusia Universal underpins the next generation of products. As such, we will continue to work closely with both OEMs and customers to prove-as we have consistently to date-that the single oil solution of tomorrow represents the future of marine cylinder lubricants, Roman concluded.

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