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ABS-LED RESEARCH IDENTIFIES KEY EAL EVALUATION REQUIREMENTS
ABS, in partnership with Vickers Oil and Imperial College
London, has completed a joint study on the use of
environmentally acceptable lubricants (EALs) on stern
tube bearings. The study evaluated EAL properties
relative to mineral oil-based lubricants and concluded oil
viscosity is the primary property in selecting an EAL.
“Interest in EAL performance has grown following an
increase in the number of new build stern tube bearing
failures in 2014,” said Derek Novak, ABS Senior VP of
Global Engineering and Technology.
“Working closely with our project partners in an
extensive study of EAL properties, we found oil viscosity
is the main determinant in choosing the optimal EAL for
normally operating stern tube bearing installations.”
Primarily driven by US EPA requirements put in place
in 2013, EALs were intended to replace mineral oil
lubricants in marine vessels. During this joint project,
ABS and its partners identified, through
experimental research, key
characteristics of EALs compared to
mineral oil lubricants:
■ Viscosity of EALs is more stable than
that of mineral oils, with respect to
changes in temperature
■ EALs demonstrated relatively lower
pressure-viscosity coefficients than
mineral oils, indicating EALs may form
thinner oil films, potentially
insufficient to protect surfaces from
wear under edge loading conditions
■ Using EALs with higher pressureviscosity
coefficients, compared to
other EALs of the same viscosity, may
provide some safety margin in shaftalignment
sensitive installations
■ EALs may offer less margin in shaft
misalignment conditions, therefore
particular attention should be taken
for correct shaft alignment
■ Using EALs with higher viscosity,
compared to a mineral oil of lower
viscosity, may provide additional
tolerance for edge loading wear.
“The results of this study offer
important insights into both viscosity
selection and the more specialized area of
pressure-viscosity coefficient behaviour,
where no universally-adopted
measurement standard exists,” said
Vickers Oil Technical Director, Chris
Wholley.
“By tackling this issue together with
ABS and Imperial College London, we
were able to develop a deeper
understanding of lubricant behaviour in a
journal bearing, operating both normally
and under edge loading conditions, which
will help us to give the best advice to
owners and operators wishing to reduce the adverse
effects of shaft misalignment, and inform our product
development process.”
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