Preventive Maintenance

preventive-maintenance

Christer Idhammar, IDCON INC

Preventing and inspecting is considered preventive maintenance, while planning, scheduling and execution is corrective maintenance. Together they form a complete view of how we succeed in maintenance management.

Preventive maintenance and work management processes can be viewed as a chain that must not be broken. Prevention includes everything you do to prevent a problem such as lubrication, operating practices, and precision alignment of components, balancing components and more.

Inspections do not prevent anything unless the problems discovered are corrected before breakdowns occur. The very basic maintenance management link must not be broken: Early Discovery of a Problem - Prioritize urgency - Plan Corrective action - Schedule Corrective Action - Execute Corrective action is a vital foundation for any maintenance organization. It is often referred to as Condition Based Maintenance. (CBM). It has been proven in many organizations that if these four essential core processes are executed better and safety is improved, then reliability, and lower costs will be the guaranteed results.

 

Maintenance Prevention

With maintenance prevention we include everything done to prevent problems from occurring. Components of Maintenance Prevention (MP) include: cleaning, lubrication and contamination control, precision alignment, balancing, proper operations practices, and Fixed Time Maintenance (FTM). MP is important everywhere, but crucial on a ship because you only have so much to work with, a small storeroom and no possibility to order and receive anything on short notice. Instead we had to take great care of what we had on hand.

Cleaning is essential. I’m not talking general housekeeping here, but thorough and regular cleaning of all equipment and components. When the detailing is done and you inspect your work, well, then you are doing a visual inspection. And naturally, when equipment is clean it is easier to discover see abnormalities like loose fasteners and leaks. Another benefit is that it yields in longer life of equipment and components. Take an electric motor, for example. It does not take much contamination for it to increase temperature in windings and rotor by 18 F. It may seem small, but such a temperature increase will shorten an electric motor’s life by 50%. (You should be careful not to paint motors with too many layers of paint, for this very reason.) And most of us know that an electric motor will drain less energy the cleaner and cooler it is.

Lubrication and contamination control.Precision lubrication, which includes the right clean lubricant in the right volume at the right time, is absolutely key in achieving better reliability and lower costs. Lubrication needs to be a well-documented process that describes lubricant, volume and frequency in an optimally laid out route and in work orders for shut down oil changes and where lubrication that cannot be done safely when equipment is operating. Filtration of lubricants also has to be done to adequate standards, down to four microns for many oils and central lubrication systems. As a comparison, a human hair is about 70 micron thick. Modern tools should be used to measure that the right volume is reaching the lubricated object. To control contamination it is vital that lubricants are stored in a professional way. Due to lack of proper training, it’s common for lubricators to over-grease components. Too much grease will blow out seals and increase temperatures in bearings. And as if that wasn’t bad enough, when someone notices a hot bearing, it is not uncommon that more grease will be added, making the bearing even hotter. Electric motors are especially sensitive to this as the windings in the motor fill up with grease because the excess has nowhere else to go.

 

Alignment is another essential element that prevents problems. Alignment with precision not only prevents problems but also extends the life of sprockets, chains, sheaves, belts, and couplings. Precision alignments also prolong life and prevent problems in bearings and mechanical seals. Another benefit is reduced energy consumption for electric motor and other drives. A misaligned coupling increases temperature in both coupling and bearings significantly, while a temperature increase in couplings, V-belts, and chains also indicate misalignment.

 

Alignment should be done when equipment is in operating temperature or with compensation for thermal growth. Jacking bolts should be installed to make precision alignment possible. Today most plants use laser tools making it easier to align and to keep track of previously-done alignments.

 

Precision balancing of rotating equipment—an impeller for a pump or an assembly for a shaft—prolongs component life, prevents problems and reduces energy consumption. Imbalance can be caused by many mechanical factors such as using too long or too short key ways after a rebuild, material build up on fans and uneven loss of material. Vibration measurement should be part of quality control for any rebuild of these components.

Operating practices are often a forgotten part of maintenance prevention. Poor operating practices commonly cause more than 50% of equipment failures and breakdowns. This is because operators are seldom trained in the function of the equipment they operate and what impact wrong startups can have on equipment Unfortunately, operators are just as rarely trained in how to inspect components.

It is crucial that craftspeople and operators are trained not only in "How" but also in the "Why." We call the training we do in equipment-care "Know Why Training."

Just like my aha-moment with knocking bolts, an operator needs to know why a steam system must start up slowly—we want to avoid water hammer and the consequences from overly rapid thermal expansion. When the steam pipe system is cold you have to open steam valves slowly because the steam will otherwise condensate too much. If too much condensation is built up in the system it can fill up a pipe to form a "water plug," traveling through the system at 85 - 90 miles per hour or 135 - 150 kilometer per hour. When this "plug of condensate" hits a pipe elbow, what we call a water hammer, it can damage the pipe. If the system provides rotating dryer cans with steam for heating, the steam inlet is through a bearing journal shaft. If the system is heated too fast, this journal heats up and expands faster than inner race of the bearing and this can cause the inner ring of a bearing to crack.

When an electric motor is frequently started the consequence is that windings might burn. This is because when starting up an electric motor, the amperage (A) spikes by the square.

Many plants have redundant equipment for critical steps in production. For example, duplicate lubrication pumps for central lubrication. It is necessary to operate these pumps an equal amount of time. Mark equipment as A and B equipment and then make sure operators shift to run only A equipment and then only B equipment. This will prevent moisture build-up in electric motors and bearings to be destroyed from brinelling caused by vibrations when rolling elements of bearing are in same position for a long time. Packing material in glands will dry up and leak when pump is started after being idle for long time.

 

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Christer Idhammar is the founder of IDCON, Inc., a management consulting firm (idcon.com).  This article was excerpted from a recent book authored by Mr. Idhammar entitled Knocking Bolts.  More information can be found on this book at https://www.idcon.com/reliability-and-maintenance-books/

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