Print this pageIdentifying Risk Factors In Machinery
Malcolm
J. Werner, P.E.
Course Outline
This two hour online course provides an overview of the basic knowledge required to identify the potential risk factors associated with machinery. The attendee will understand the information required to determine risk. Assessment of risk including survey techniques and risk mitigation are covered in a follow on course. The course reviews the importance of reliability, design, production, life cycle, environmental, and safety factors as they pertain to risk.
This course includes a multiple choice quiz at the end.
Learning Objective
At the conclusion
of this course, the student will:
Intended Audience
This course is intended for mechanical engineers working as plant or maintenance engineers or associated with the insurance industry or regulatory agencies.
Benefits for Attendees
This course will enable attendees to logically determine the information required to assess the risk associated with machinery.
Course Content
INTRODUCTION
Power plants, oil refineries, factories, and other manufacturing and industrial facilities utilize a variety of machines. It is important to identify high risk machines so those risks can be mitigated.Those risks can be to personnel, to the environment, or to the successful operation of the business.
Assessing risk is an important part of a plant engineer or maintenance engineer's responsibilities. Higher risk assets demand more rigorous attention to operations and maintenance.
Risks can be safety risks to plant personnel and neighboring communities, risk of damaging the environment, risk of failure to perform to the level required to meet business demands, and the risks of excessive costs to operate and maintain the asset.
If risks are not identified and assessed properly the resulting costs can be excessive.
If risk is underestimated, a failed machine can cause loss of life, release of toxins to the environment, or a loss of production that could mean financial ruin.
If the risk is overestimated, unneeded spare machines may be purchased, maintenance costs may be excessive due to unnecessary monitoring, repair or preventive maintenance, or perhaps the project will not even be started due to the anticipated liabilities and the cost of insurance.
The risk of each machine in a machine train (system) is assessed separately but the overall risk of the system is the risk of the highest risk machine in the train. For example, a train might consist of a motor, gearbox, and compressor. If any of these machines in the train fails the entire train is considered failed. If the risk of the motor and compressor is low but the risk of the gearbox is high, the entire train risk is high. The mitigation strategies for each machine in a train may be different.
Overall risk evaluation includes not only the risk associated with what may happen but also the likelihood of that event happening. The likelihood or frequency of failure is best based on operating history in the application.
Risk assessment can be applied to plants in design, plants prior to start up, and plants that are operational. Plants in operation that have documented machine histories can provide accurate information on the frequency of failure. Where history is not documented or in the case of new plants, frequency of failure must be based on manufacturer's and industry experience for similar machines in similar applications.
If the machines are already in operation, and are identified as high risk, it is imperative that the current condition of the machine be assessed. This assessment could include external inspection, internal inspection, thermal scanning, lubrication sampling, ultrasonic thickness measurement, vibration analysis, and other non destructive testing.
The risks associated with machinery can be grouped into the following categories:
General Reliability
Factors - Minor Problems, Cycling, Service Difficulty, Remote Location,
Life Risk Evaluation, Maintainability, Major Failures
Machine Design Factors - Power Factor, Energy Factor, Design Experience
Factor, Machine Motion, Machine Speed, Acceleration, Pressure, Lubrication,
Resonances.
Plant Production - Sensitivity Factors - Spared Machines, Throughput Affected, Loss of Production, Affect on Product Quality, Start Up Affects, Machine Output Capability
Life Cycle Costs - Purchase or Replacement Cost, O&M Costs, Energy Costs
Environmental Impact - Releases, Spills, Radiation, Thermal, Noise, Smells, Appearance, Long Term
Safety Hazards
- On-Site, Off-Site
GENERAL RELIABILITY
General reliability refers to the reliability of the specific machine. Does it require a lot of maintenance downtime? Is it available when it is needed? This is where the frequency of failure is addressed.
Minor Problems - The frequency of minor problems. Higher frequency means higher risk. Minor problems are defined as minor parts breakage or wear, the need for adjustment that can be easily rectified by operators, the need for maintenance that can be accomplished without special tools or spare parts, generally with simple tools and parts on hand. Minor problems are often poorly documented and costs unknown. An attempt should be made to quantify the number, type, frequency, and cost of maintenance.
Cycling - Machines that are frequently cycled are more likely to have problems than those that operate at a single operating point. Cycling is defined as changes in machine load, speed, or process. Identify the type of cycling if possible including the range of cycling. A good example would be a gas turbine driving an electric generator. If the machine is in base load service running continuously it is less likely to have problems than the same machine in peak load service that may be started and stopped several times a day.
Service Difficulty - A factor to adjust for harsh conditions. These conditions would include erosion, corrosion, dust, moisture, and environmental extremes. Document the types and ranges of these types of conditions if present. The same electric motor could be in service inside an environmentally controlled electronics manufacturing plant or outside exposed to dust and rain.
Remote Location - Remote machines are higher risk since it's more difficult to make decisions based on limited information. Here we must consider the availability of the right information and the distance from the operators to the machine. Concentrate on the path of communications required to make decisions. The more difficult the path to get information, the higher the risk factor.
Life Risk Evaluation - Brand new machines and older machines nearing the end of life are higher risk. Is it a machine that has been operated within limits over a moderate life or an older machine that has been run at maximum? Identify the history of the machine. If possible determine the number of these machines in service and the general experience in similar applications.
Maintainability - Is defined as the degree of difficulty required to maintain the machine based on experience. Higher cost is associated with machines that are more difficult to maintain. This information can be based on the experience of the local maintainers or on the need for special tools, the availability of spare parts, the relative time required for assembly and set up compared to actual repairs and other factors. Consider inspection intervals. Machines requiring downtime for mandated inspections such as gas turbines, require more maintenance.
Major Failures - Major failures are expensive both in terms of maintenance costs and lost production. We must determine the frequency of failure requiring significant down time or repair costs. It would be ideal to know the number of failures per year.
MACHINE DESIGN FACTORS
The way a machine is designed has an Affect on risk. The categories are based on general machine characteristics. In general machines that are larger, run faster, and change motion are higher risk.
Power Factor - Power is an indication of the size, complexity, and cost of a machine. All affect risk. What is the power output range of the machine? Is this considered high output for a machine of this size?
Energy Factor - How much energy is stored in the machine during operation? More energy means more risk. Identify the amount of stored energy in the machine. How much energy would be released if the machine failed catastrophically? Would this energy likely be contained?
Design Experience Factor - Newer designs or no experience means more risk. Is this machine an experiment or a highly proven design? Was this machine scaled up or down from a successful design? How much? Scaling a pump design 20% might be reasonable while 50% should probably be considered a new design.
Machine Motion - Multiple direction motion raises risk Reciprocating machines are generally more risky than rotary machines. Some machines may rotate, stop, then rotate in the opposite direction. Are these changes rapid or gradual?
Machine Speed - In general, higher speeds mean higher risks. What is the machine speed (revolutions per minute, linear feet per minute, etc.)? Is this a higher speed than other similar machines in the same service?
Acceleration - Higher rates of acceleration mean higher risk. What is the acceleration rate from stop to operating speed?
Pressure - Higher pressure means more stress and sealing problems. What is the operating pressure? What types of seals are being used?
Lubrication - Friction and its associated heat are enemies of machine life. Reliable lubrication reduces risk. Is there lubrication? Is the lubrication dry, grease, oil? Is the lubrication controlled? Is the lubricating medium cooled?
Resonances
- If known are a useful tool in assessing risk. Resonances are often incorrectly
called "critical speeds". Often published resonances are based on
rotor alone, only one machine in the train (system, i.e. motor/gearbox/pump)
rather than the entire train as a system, and on empty (no fluid or gas) response.
Obviously, machines that run near a resonance are more at risk than those that
operate far from resonant frequencies.
PLANT PRODUCTION - SENSITIVITY FACTORS
Machine problems that affect plant production are extremely costly. Simple machines that affect production can be riskier than larger machines that may cost more to maintain but have little or no Affects on production.
Spared Machines - Identify the availability of spare machines. Are there redundant machines available such that one or more machine failures will not affect production? Is there a program to rotate the use of spares?
Throughput Affected - The machine is higher risk if it can affect the plant production rate. While it might not cause a loss of production it could affect the plant's capability to produce surplus product.
Loss of Production - The machine's poor performance or minor faults may not affect production rate but a machine shutdown could cause loss of production. When the machine is shutdown for maintenance how much production is lost per hour? What's the market value of that product? For example, when the waste heat boiler in a copper smelter goes down, 100,000 pounds per hour of copper are lost. At the market price of $0.70 cents per pound each hour lost costs $ 70,000.
Effect on Product Quality - Product quality effects can be subtle since we don't often think of the quality of intermediate processes. An example could be an air compressor. Perhaps the pressure and moisture content of the output air affect quality downstream.
Start Up Effects - If it takes a long time for a machine or process to stabilize after start up, trips and unscheduled shutdowns make for more risk. For example, while a draft fan repair could cause a boiler shutdown for only a couple of hours, it might take as much as twelve hours to return the boiler to full output. In this case a two hour repair would cost fourteen hours of production below maximum.
Machine Output Capability - This rates the machines capability as a single unit to meet the rate desired. For example, if 20,000 gallons per hour is required to meet production demands during peak periods and the pump is only capable of 15,000 gallons per hour as originally designed, the pump is a risk when trying to meet peak demands.
Any machine that can cause plant shutdown should be considered a high risk critical machine even though all other factors are low risk.
LIFE CYCLE COSTS
Purchase or Replacement of the Machine - Obviously more costly machines represent a higher risk. Also consider lead time. A machine could be relatively inexpensive but difficult to obtain. A low cost high risk machine that requires a long lead time for manufacture may represent more risk than a more expensive machine that can be purchased "off the shelf".
O & M Cost - Operations and maintenance costs can be three or more times higher than the purchase price over the life of the machine. Maintenance costs include labor, spare parts, modifications/upgrades, transportation, consultants, subcontractors, documentation, training, and tools. Operations costs include labor, supplies, facility costs, training, tools, and documentation.
Energy Costs (Thermal Performance/Efficiency) - Energy costs can be important factor and efficiency may require measurement. If energy costs are significant and there is no means to measure efficiency on a regular basis, there is risk that energy costs will be excessive.
Other Costs - Disposal costs, write-offs, and insurance costs. If a certain machine processes hazardous materials, disposal costs could be substantial. Insurance companies offer lower premiums to companies that can demonstrate that they have evaluated risks and mitigated them within reason.
ENVIRONMENTAL IMPACT
Higher potential damage to the environment rapidly escalates risk, potential fines, and punitive damages. Environmental damage can be immediate or occur over a long period time. Common hazards include leaks, spills, gas releases, thermal pollution, airborne particulate, and radiation. Facilities located near residential areas may impact the community through non-hazardous but offensive smells, noise, and even an unattractive appearance.
Here you should consult local laws as well as national regulations and good practices.
Changes in laws and standards mean that risks must be re-evaluated.
In general, any machine that has the potential to affect the environment outside of the plant boundaries should be considered a high risk critical machine even though all other factors are low risk.
Environmental risks must be mitigated.
SAFETY
If the machine is unavailable can safety be in jeopardy? If the machine fails can it cause injury or death to people inside or outside the plant? Is working in close proximity of the machine dangerous?
Any machine that can readily cause serious injuries should be considered a high risk critical machine even though all other factors are low risk.
Safety risks must be mitigated.
OTHER USEFUL INFORMATION
When you are documenting risk factors, it is an ideal time to gather other information that may be useful.
This information is generally required for best maintenance practices as part of the "master equipment list" that serves as a base for maintenance history and the database that is part of a computerized maintenance management system (CMMS).
This information generally includes:
Plant Tag Number - The unique identifying number associated with the machine in this specific application.
Machine Designation - A name that describes both the machine and its application such as "Sludge Pump" or "Nitrogen Compressor Motor".
Manufacturer - The name of the original machine manufacturer. Also note the current name of the manufacturing company if it has changed.
Model - The specific model number designation given to the machine by the manufacturer such as "5002".
Machine Type - The general type of machine such as "screw compressor".
Rated Output - This is the maximum output that can be sustained as rated by the manufacturer such as "500 HP maximum continuous".
Normal Output - This is the output expected by the user and can exceed the manufacturer's rating.
Rated Speed - This is the maximum speed for continuous operation. This is normally given in revolutions per minute for rotating machines but could be in linear speed for other machines.
Bearing Type - This is the types of bearings used in the machine. There may be amore than one type. Some examples would be "fluid film sleeve" , "rolling element", "tilt pad", etc.
Seal Type - This is the type of seals used in the machine and may include multiple types such as "packing", "mechanical", "labyrinth", "dry gas", etc.
Coupling Type - This is the type of coupling used to link the machine to other machines in the same machine train (system) such as "diaphragm" , "gear", "flange", etc.
Foundation Type - This the type of foundation used to support the machine and could be "reinforced concrete", "skid mounted", etc.
Course Summary
Assessing risk begins with gathering information. This course presented a basis for identifying information important to risk evaluation.
Engineers are encouraged to use their skills and knowledge to add to this basic list and to customize it for their specific application.
Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.
DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDHonline.com or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered professional engineer. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.
