Your Reliability Engineering Professional Development Site
This Plant Maintenance articles series relates to doing maintenance and care on operating plant and equipment. It includes coverage of maintenance engineering issues, and topics on the maintenance of process plant operating assets and industrial equipment.
The Plant Maintenance series of articles are provided with the permission of Feed Forward Publications and Lifetime Reliability Solutions.
NOTE: The series does not include coverage of related commercial or vendor software or database management applications.
The very best asset managers have maintenance under control.
Their entire organization’s systems and methods are tuned to preventing unplanned stoppages. They only do that which has first been thought through and prepared for.
But most importantly they understand the key factor to excellent asset care and work toward it continuously and energetically.
Keywords: preventative maintenance, reliability-centered maintenance, RCM, total productive maintenance, TPM. [Read more…]
Weld preheating is the purposeful application of heat to warm metal to a desired temperature prior to welding.
Preheating slows down the cooling rate of the weld and gives the metal more time to form a good microstructure, release internal stresses and dissipate hydrogen from the weld.
Keywords: thickness, weld puddle, cooling rate, temperature. [Read more…]
When a bolt and nut is tightened to draw the bolt head and nut together it stretches the shank, deforms the threads and loads the object trapped between the bolt head and nut.
The bolt shank acts like a spring being pulled apart and it tries to return to its unloaded condition.
The amount of tension developed in the shank is dependent on the number of turns of the nut.
The size of the torque required to turn the nut has little to do with the tension applied to the bolt shank.
Rather the amount of torque needed to turn the nut reflects the slipperiness of the threads.
Keywords: bolt tension, yield stress, the coefficient of friction.
This article covers some of the problems that can occur with bucket elevators and provides possible remedies.
Bucket elevators lift bulk materials from one level to another.
They are used on powders, granules, grain, chip shaped products and lumpy materials.
They function well when designed properly for the duty, and used as designed. [Read more…]
Many equipment breakdowns and stoppages occur because of improper clearance between holes and shafts.
The shaft is too tight in the hole; the center of the hole is not at the center of the shaft making it off-center; one part is loose on another and slips out of place or does not seal as it should. [Read more…]
A gearbox is used to control the operating speed of industrial equipment.
It converts a high input speed to a lower output speed and so permits one driver element, such as an electric motor, to do numerous duties.
Failure of the gearbox causes the equipment and associated plant to stop.
Proper selection, care, and maintenance of gearboxes is critical to your company’s continued profitability. [Read more…]
Chemical corrosion occurs at increased rates in agitated conditions.
Typical iso-corrosion curves for alloy metals no longer apply. These curves only show corrosion rates at various chemical concentrations and temperatures in stagnant conditions.
A typical curve is shown below. The curves are available from alloy metal suppliers on request.
When metals are selected for agitated corrosive conditions the curves can only be used in a relative sense.
They help grade the metal selection but they cannot provide absolute corrosion rates. [Read more…]
A benchmark is the end distance point from the start.
In the world of maintenance, it is the name for the targets that an organization sets for itself in an improvement program.
Benchmarking is often against world-best practice and it is used to provide direction and focus in an organization’s efforts to improve.
When RAV is chosen as the benchmark it means that the annual cost of maintaining the plant will be measured against the value of the plant.
RAV is a percentage of the cost to replace the plant. The lower the RAV the more effective the maintenance effort. [Read more…]
Vibration in equipment is the result of unbalanced forces.
Out-of-balance is corrected by adding or removing material so that when the equipment is operating the unbalance is controlled to an acceptable level.
Keywords: spring stiffness, damping, center of rotation, center of mass, natural frequency, isolation mount, counterbalance, out-of-phase. [Read more…]
Coatings provide industry with low-cost solutions to difficult chemical corrosion problems.
This article covers the use of rubber, fiberglass, and epoxy linings.
Keywords: rubber lining, resin, composite glass fibers, overlap joints, adhesive, primer, corrosion barrier, repair. [Read more…]
Bridging is the name given to the self- created arch that develops just above the outlet of a bulk material silo or hopper as it empties.
A bridge forms when wall friction holds up the ends of the arch.
To overcome bridging the wall friction must be reduced or prevented from occurring. [Read more…]
Control valves regulate the flow of a liquid or gas by opening or closing internal passages.
They form part of a control loop used to control a process. The control valves respond to instructions from the controller and adjust the internal openings accordingly.
Keywords: sensor, setpoint, trim, actuator, sealing class, tuning, proportional, integral, derivative. [Read more…]
Net positive suction head losses (or why you can suck through a straw).
Pumps cavitate and run dry when the pressure leading into them falls below the vapor pressure of what they are pumping. At vapor pressure, the liquid boils into a vapor and fills the pipe.
In order to know that the pressure to a pump is always above the vapor pressure, it is necessary to calculate that the pressure losses from pipe friction and suction lift will not cause the pressure to drop under the vapor pressure.
The presence of dissolved gas in the liquid complicates the problem. [Read more…]
Pressure vessels must be regularly inspected and be maintained in a safe operating condition.
New Australian laws stipulate that all pressure vessels must have a Hazard Level rating (‘A’ highest to ‘E’ lowest) which reflects the vessel’s safety risk (see AS3920.1).
The higher the risk the more stringent the requirements for operating and inspecting the vessel.
Keywords: receiver, non-destructive testing, internal inspection. [Read more…]
Get mechanical seals working properly.
Mechanical seals are used to keep the bulk contents of rotating equipment such as pumps and compressors from escaping. They do this by sealing the shaft that protrudes from the casing.
They require quality installation and operating conditions for a long life. [Read more…]