Thermography Assists In Maintaining Equipment Reliability
The rapid growth of thermography during the past decade provided a valuable tool to industry to improve plant reliability. Technological advancements in condition-monitoring equipment and hardware and software have given rise to unprecedented levels of data recording. These data, when used correctly, can be of significant value for analysis to determine the condition of industrial and commercial equipment.
Thermography can be used as a complimentary condition-monitoring technique alongside more commonly used techniques like vibration monitoring, ultrasonics, acoustic emission and wear and oil analyses, as it adds a new dimension to any good reliability program.
Over the years, large organizations developed their own particular strategies to deal with reliability, which in practice, have had varying degrees of success. Today, large companies commonly participate in reliability improvement seminars and conferences to share their good practices and techniques for the general advancement of reliability within industry. This has led to programs that identify plant-performance monitoring methods.
One method to calculate the efficiency of a facility is to examine the overall equipment effectiveness (OEE), the three most important determining factors of which are:
- Plant availability
- Plant rate (the volume a plant can produce)
- Product quality
Ideally, all three parameters would be 100%, and plant production would be at a maximum. Realistically, the parameters often fall quite short of this point. Adding down time to the OEE equation further reduces the efficiency of the plant and increases costs. Downtime generally falls within one of two groups: planned time (scheduled plant shutdowns) and unplanned time, or breakdowns.
Unplanned breakdowns tend to be the main focus of reliability issues (Fig. 1). Based on industry investigations of equipment failures, 80% of reliability issues are caused by around 20% of the plant equipment. Identifying this equipment and examining common failure modes allows making a real impact on equipment reliability in a short time.
Operation and maintenance procedures also can contribute to the failure modes, and, therefore, also can reduce the normal working life of a component. Correct operating procedures (within equipment design parameters) provide equipment stability, and good maintenance practice extends equipment life.
Four methods, or approaches, to maintenance that reflect the type of actions carried out on equipment are proactive, preventative, reactive and predictive.
Proactive maintenance focuses on the root cause of a problem and tries to eliminate the need for maintenance by designing out the failure mode. This method cannot always be used due to financial constraints.
Preventive maintenance is time based. Equipment is overhauled after a specific time period, before the expected equipment life ends. This requires historical data, and often leads to replacement of equipment that is functioning normally.
Reactive maintenance is failure based; that is, equipment is run to failure. This method is acceptable depending on cost, production loss and, more importantly, whether there are any safety, health and environment (SHE) implications.
Predictive maintenance is condition based. Equipment is monitored to assess the operating condition. Maintenance can be undertaken when the performance parameters dictate. This often is the best option after proactive maintenance.
The financial cost of proactive maintenance often means that only limited resources are available to address reliability issues. The cost of replacing or altering the design of a machine, component or item of equipment can be substantial. One of the most economical means of efficient maintenance lies with condition-based, or predictive, maintenance.
Predictive maintenance offers the ability to assess the condition of equipment using various monitoring techniques, and is known as condition monitoring-defined as the continuous or periodic measurement and interpretation of data to indicate the condition of an item to determine the need for maintenance.
Today, this type of monitoring is applied mainly to mechanical and electrical equipment using techniques like vibration monitoring, acoustic emission, ultrasound and oil sampling together with traditional "look, listen and feel" activities. As the reliability of the monitored equipment improved, the focus changed toward the process side of the operation.
One of the benefits of thermography is its versatility, having the capability to assess the condition of a variety of applications, including process equipment and sometimes even the process itself. Thermography has a strong foothold in many industries, and the technology has advanced over the past ten years. For example, thermographic cameras have improved performance, enhanced portability, are lighter weight and cost less. Many companies that looked at the technology in the past and passed it over for a variety of reasons now are seriously considering using it. Also, many any companies already have invested in infrared programs, deriving significant benefits due to the versatility of the cameras and correct operation in the field by trained thermographers.
The most common use of thermography-apart from military applications-is within the electrical field. It is a well documented fact that infrared surveys can be used as one of the most effective condition monitoring tools to survey electrical equipment, ranging from high-voltage electrical generator components to the low-voltage uninterrupted power supply (UPS) battery systems, which most facilities use as a back-up system in case of power failure.
The payback time for the camera generally is within 3 to 6 months if a company has not used thermal imaging in the past. Once electrical systems are fully documented into a regular route, the component data can effectively be used to evaluate the condition of all electrical equipment and systems. The results, often analyzed using information from other predictive technologies, provides further insight that can be used to make a decision on the type of action required on items that display unusual characteristics or anomalies. It is not unusual for maintenance costs to rise when the initial thermographic survey takes place, but the idea of the survey is to identify, and when necessary, correct potential problems prior to catastrophic failure. The repair bill to rectify anomalies can prevent unexpected costly failures, which may occur at inconvenient times. After the early anomalies have been addressed, regular surveying of the equipment should improve the efficiency of plant electrical systems, and improve reliability.
Industries already reaping the benefits of thermography also are using the technology to monitor the operating condition of critical mechanical components, including motors, pumps, fans, gearboxes, compressors, etc. Because thermography normally is used as a noncontact, nondestructive form of monitoring, it has the advantage of assessing equipment operating under normal loads and environmental conditions. Mechanical equipment naturally produces friction when running, and the machine emits a thermal signature as mechanical energy is converted to thermal energy. Monitoring changes in the signature readings can point toward machine deterioration, which often can be detected at an early stage. The information can be very useful when planning structured downtime to carry out planned maintenance.
Another aspect to a successful condition-monitoring program is the evaluation of process applications. The operation of an infrared radiometric camera without interference of the target object or the environmental conditions can record the natural signature reading of an object. The camera displays a thermogram, or density picture, which allows the operator to see the thermal information specific to the object being viewed. This makes it possible to build up a reference report of critical process equipment operating under normal conditions. This procedure relies on the fact that the target object will emit thermal energy above or below the levels of the surrounding equipment and the environment.
Today, trained thermographers understand the operation and limitations of thermography equipment and the factors that can affect the information on the viewed image, and they can record accurate data that has a repeatability aspect to it. Good technique and attention to detail pave the way to establishing an effective infrared program to analyze critical process equipment such as that shown in Table 1.
To maximize the effectiveness of any process survey, the operator must collate every available detail regarding the equipment to be surveyed, such as materials of construction, historical data, process operation and process loads, pressures and temperatures. The process control and/or maintenance teams usually have access to operational and historical data, which can be useful during analysis.
While documenting and surveying numerous plant items is time consuming, and initially may have limited payback, just one application that identifies a production problem could save many thousands of dollars. Other potential benefits of documenting equipment include:
- Safety: Preventing hazardous situations exposing the workforce and the public to unwanted risk created by unexpected equipment failures
- Environmental: Preventing loss of containment due to leaks or overflow from vessels
- Energy efficiency: Minimizing inefficient systems and machines including steam, heating and cooling systems and electrical motors