Reliable Plant July August 2008

ADVISOR
MACHINERY LUBRICATION
WHO SHOULD DECIDE THE RIGHT
FREQUENCY FOR PM TASKS?
Routine, time-based preventive
maintenance is a fact of life for
production-critical equipment. But,
who should decide how often these tasks are
performed? Should it be the maintenance
team (led by the maintenance manager) or
the production manager and the operations
group? While the question may seem odd
(maintenance people should decide when its
work gets done, right?), many plants allow
production to define maintenance scheduling
by default.
Let me explain. In many plants, production
occurs 24/7, 52 weeks a year, perhaps with
the exception of a one- or two-week maintenance
shutdown. Under these circumstances,
careful planning needs to occur so the
backlog of maintenance tasks that can’t be
done with machines running can be
completed in the allocated outage period.
But when it comes to lubrication, many tasks
simply can’t wait a year (or longer) between
intervals. Take, for example, regreasing bearings.
With the exception of small and/or
low-speed element bearings, logic dictates
that bearings be regreased more frequently –
in some cases, as often as once per shift. But
unless the bearing is accessible during normal
operation, as opposed to being hidden
MARK BARNES
Mark Barnes is vice president of Noria Reliability
Solutions. In this role, he and his team work on
numerous and varied projects in the areas of
plant audits and gap analysis, machinery lubrication
program design, oil analysis program
design, lube PM rationalization and redesign,
lubricant storage and handling, contamination
control system design, and lubrication and
mechanical failure investigations.
As a Noria consultant,
his client list includes
Cargill, Alcoa, International
Paper, TXU, Southern
Companies, Eaton, BC
Hydro and Southern Cal
Edison. Contact him at
mbarnes@noria.com or
604-736-6243.
behind guards or machine interlocks, the only
time the bearing will be greased is when
production makes the machine available to
maintenance. In this case, production schedules
drive maintenance decisions.
The same logic applies to oil changes.
Consider a small yet critical centrifugal
pump. Many pumps of this type contain just
a few gallons (or less) of oil. But, changing oil
can be a real problem if the pump can’t be
shut down without taking down production;
and while some may advocate doing an oil
change “on the fly”, it’s not recommended or
the preferred course of action. Of course with
circulating systems, larger oil volumes
coupled with the ability to “sweeten” the oil
through bleed and feed (draining a small
amount of oil from the reservoir and
replacing it with an equal volume of new oil)
makes this less of a problem.
What about filter changes? Most circulating
systems have inline filters on the supply
side and, in some cases, return line filters. But
unless these filters are arranged in a duplex
configuration with the ability to valve off one
of the filters with the machine running, filter
changes won’t be determined by oil analysis
or differential pressure as best practice
dictates, but instead by machine availability
as determined by production schedules.
So, how can we avoid these problems?
We’re not about to advocate modifying
production schedules except in the most
exceptional cases. Instead, we must modify
the way we maintain our machines.
The place to start is during the design and
installation phase. In past columns, I’ve
talked about “maintainability” – having
machines designed and installed in such a
way that tasks like regreasing bearings or
changing filters can be done without the
need for intrusive system access.
Maintainability needs to be built in from the
outset, during equipment design. While it’s
possible to modify in-service equipment to
allow better intrinsic maintainability, it often
takes significantly more time, effort and
money to do this after the fact than it does
from the start.
The second consideration is in the selection
of lubricants and accessories (filters,
breathers, etc.). If accessibility to a machine is
limited to a year (or longer), the plant should
consider using premium lubricants such as
synthetics that will generally last longer than
conventional mineral-based lubricants and
may indeed last a year or longer without the
need for an oil change. Where contamination
is the driving force for a shortened PM
interval, consider using better breathers,
mechanical seals or large filters with greater
dirt-holding capacity. Or, perhaps equipping
the machine with quick connects to allow a
portable filter cart to be used to decontaminate
the oil while the machine is running is all
that’s required.
The final consideration is in efficient planning
and scheduling. When outages and
production schedules dictate PM intervals,
resource requirements will fluctuate from
periods of low demand to “all hands on
deck” when the machine becomes available
for maintenance. But when maintainability is
used, coupled with the appropriate use of
premium products and accessories, the highs
and lows of maintenance resource scheduling
are less pronounced. Likewise, through the
use of appropriate software tools that
provide for options such as job kitting,
dynamic job planning and current machine
operating status, maintenance can take
advantage of “golden opportunities” – times
when the machine is unexpectedly down for
production.
A common complaint I hear from maintenance
people is: “Production won’t let us
have the machines in order to properly maintain
them.” While there’s a measure of truth
to this statement, there’s plenty we can do to
insure that the maintenance team fulfills its
mandate to deliver reliability and availability
to the operations team.
22 July - August 2008 www.reliableplant.com