HIGH LEAD (Pb) LEVELS IN STERNTUBES

Posted & filed under News.

Peter VickersIn April 2017, Peter Vickers was invited to speak at the ‘European Marine Engineering Conference’ in Amsterdam and provide an update on the work which Vickers Oils have been undertaking into the phenomenon of increasing levels of lead (Pb) in the sterntubes of a small number of vessels.

The Conference, organised by Riviera Maritime Media, addressed the operational, technological and engineering challenges facing ship operators. Many ship owners, managers, designers, equipment manufacturers, suppliers and class societies attended the event.

Peter’s presentation entitled ‘HIGH LEAD (Pb) LEVELS IN STERNTUBES’ considered the possible sources of elevated lead levels. Increasing levels of lead have been found in sterntube oil analysis from some vessels in some fleets, from multiple EAL producers.  The phenomenon has been reported in vessels with lead-free bearings and there does not appear to be any relationship to the condition of EAL or obvious pattern or consistency, with differences even observed between sister vessels.

The presentation concluded that

  • Elevated lead levels are being seen in tin based, lead-free bearings as well as ones containing lead, therefore, the source of the lead is not the bearing.

  • Evidence now points to presence of lead based coatings and paints in the sterntube system.

The paper was very well received and provoked significant interest from the delegates.

Below is a summary of the work Vickers Oils have undertaken into the phenomenon of increasing levels of lead (Pb) in the sterntubes of a small number of vessels, if you would like any additional information or a copy of the full technical report please Contact Us and complete the request form.

In recent years, routine lubricant analysis has highlighted an increasing level of lead (Pb) in the sterntubes of a small number of vessels.  The level has been above the International Association of Classification Societies (IACS) guidelines for sterntubes which states that the level should be <10 mg/kg and therefore has raised questions about bearing condition.

The problem has occurred not only on some vessels filled with Vickers HYDROX BIO formula but also on some vessels filled with competing EALs, using unrelated formulas. It should also be noted that there are occasional reports of elevated Pb levels in sterntubes with conventional mineral oils.

Vickers Oils has investigated the problem in depth, in cooperation with several customers and a leading Classification Society.  From the work undertaken, our interpretation is that:

  • HYDROX BIO is not the source since it does not contain any Pb.

  • It is not wear since none of the incidences have ever shown an accompanying increase in other bearing metal elements such as Tin (Sn) or Antimony (Sb).

  • The bearing is not the source of Pb since this phenomenon has occurred on both vessels with Pb-based bearings and also on Tin (Sn) based bearings with near-zero Pb content.

Elevated Pb levels are not caused by a change in the lubricant condition since there is no correlation with Total Acid Number (TAN) or water content.  Used oil analysis from sterntubes rarely shows oxidation or hydrolysis of the lubricant and shows no correlation with rising Pb.

Vickers Oils requested Lloyd’s Register Marine Technical Investigation Department (TID) to undertake an investigation of the elevated Pb concentration in the sterntube lubricant of a vessel at DD.  The conclusion was that there was “no evidence of selective corrosion or leaching found on the lead based white metal lining of the sterntube AFT bearing.”

Paint/coatings used to protect the gravity or other tanks in the sterntube lubricant system were identified as a possible source of Pb.  Red-lead is an anti-corrosive paint used to prime bare metal during fabrication. Whilst the ship yard and customer typically agree a detailed paint specification for all components, the type of shop primer to be used does not appear to be specified.

As part of the investigation, samples of paint scrapings and information about the paint/coating were gathered for vessels exhibiting high levels of Pb.  Specialist analysis was undertaken which identified high levels of Pb in the paint samples. The potential exists for this to be transferred to the lubricant during service and then to be detected in used oil analysis.

It appears that whilst some paint suppliers may be moving towards, or have moved to, the elimination of Pb entirely, some have not.  For the foreseeable future, the world’s fleet will include vessels with Pb containing paints.      

In summary, our investigations indicate that there is sufficient evidence to conclude that the most likely source of Pb is from paints or other surface coatings used in the sterntube lubricant system, most commonly the gravity tank.