Castrol Marine challenges scavenge drain oil analysis methodology

Concerns over corrosive wear risk in cross-head engines led Castrol Marine to question the rigor of some widely used scavenge drain oil analysis (SDA) techniques.
Factors influencing scavenge drain oil characteristics include fuel sulfur level, cylinder oil BN level, system oil contamination and operating profile. Accuracy is critical in SDA interpretation, not least because it supports feed-rate assumptions that are critical to cylinder oil performance, Castrol said.
“It is not possible to analyze results accurately without comprehensive knowledge of the fuel oil, the new and used system oil, feed rates and operational data collected from the engine at the time of sampling,” said Paul Harrold, Castrol Marine technology manager. “Our view is that there are potential shortcomings in ship-based magnetic analyzer type SDA approaches because they cannot identify corrosive wear.” Cylinder wear could be assumed to be under control due to a low response on ferro-magnetic analyzers where, in fact, corrosion is taking place, Harrold said.
However, Castrol notes that mid-range cylinder oils were initially claimed as a complete solution for all conditions. “We make no apology for renewing counseling caution on SDA methodology as the full consequences of lubricant selection when slow steaming continue to emerge,” says Harrold.
“We have seen cases where magnetic iron levels appeared satisfactory, but our inductively coupled plasma (ICP) laboratory results showed an increased iron content. Corrosive wear in excess of acceptable limits was present and required a lubricant change as well as optimized feed rates…. We want our customers to take well-informed decisions based on the predominant operating conditions their ships face and the accurate technical picture, rather than adopting cylinder lubrication choices for reasons driven by the commercial position of the supplier,” said Harrold.
In 2011, the International Council on Combustion Engines (CIMAC) Working Group Marine Lubricants confirmed that laboratory-based tests provided the most reliable sources for SDA. It warned that tests using onboard equipment could not be considered exhaustive.
(April 10, 2013)