Bharat Asarpota elaborates on the pain associated with the failure of a compressor in daily operations of a large, multi-chain facility dealing in food and beverages.
The use of refrigeration systems is almost indispensable when it comes to several activities in modern society. Such systems are responsible for everything from providing thermal comfort in office buildings to maintaining low temperatures (-25ºC to 0ºC) in refrigerated chambers, so that food products are preserved. For such systems, one of the main components is the compressor.
The main function of the compressor is to aspirate a certain amount of refrigerant vapour produced by the evaporator and increase its pressure and, consequently, its temperature.
The lifecycle of a compressor can be divided into four phases: definition and conceptual design, detailed design and development, manufacture and operation. At the onset, considering that compressors have a high rate of failure, I would like to say that efforts to improve reliability must be undertaken during the detailed design and operation phases.
In certain installations in the UAE, it has clearly emerged that failures associated with compressors represent 10% of the total failure of the equipment but nearly 45% of the total cost of maintenance, which reinforces the importance of further studies to minimise the failure of compressors.
A growing concern to those using the compressor is the efficiency of the refrigeration system, which can be achieved through proper maintenance. Indeed, faulty operation and failure of the components causes a high loss of energy. In that context, answering the following questions related to the system or equipment is necessary:
- How can each component of the system fail, or what are their failure modes? (By answering this question, a failure mode can be understood as a set of factors and demands imposed on a certain piece of equipment during its operation. Those factors and demands will promote the end of the piece of equipment’s life cycle, or they can be the mechanism that provokes that piece of equipment to fail.)
- What are the effects of such failure on the system?
- What is the evidence that failure has occurred (or, is there any)?
- In what way is the failure a threat (if there is any) to safety or to the environment?
- How does the failure affect the production or the operation of the equipment (if at all)?
- What is the physical damage caused by the failure (if there is any)?
- How critical are those effects?
- How can one detect the failure?
- What are the actions that should be implemented to avoid, prevent, or minimise the effects of that failure?
At this juncture, it is important to understand the failures, which can be classified into three types:
Early failures: There is a high occurrence of the component failing due to poor application and/or installation errors. The failure rate decreases as time passes.
Random failures: This is characterised by a very low and constant failure rate. Failure is caused by less controllable factors, such as power surges, mechanical impact and vibration. Therefore, the prediction/prevention of such failures is more difficult.
Ageing or wear out: There is an increase in the failure rate at this point due to the natural wearing away (friction and corrosion) that increases as time passes. These failures tend to be dominated by cumulative effects, such as corrosion, fatigue cracking and embrittlement.
Based on the analysis of reports and literature, compressors could produce several modes of failures. This can be inferred, because the equipment is composed of electrical and mechanical components that can fail independently and affect performance. Reliability is determined by analysing, for a predefined period, the amount and type of failures that occur and determining the warranty period for that equipment.
Based on reports analysed, typically the following failures are detected:
- Liquid refrigerant flood back (includes flooded start)
- Lubrication problems
- High superheating
- Contamination (includes humidity, air impurities, oxide contamination and copper plating)
- Electrical problems (includes electrical motor overload and breakup of the coiling of the electrical motor)
- Fabrication defects
- Other failures (This classification takes electrical failures, mechanical overloads, fatigue and high- and low-aggressive wear into consideration.)
It should be pointed out that most of the compressor failure modes have their origins in problems related to the project and/or the installation of the refrigeration system. Even though these problems are related to the system, their effects directly influence the compressor.
My personal experience has shown that in most cases, designers do no revisit their design to verify whether the design works, as planned. Facilities Management personnel have a big role to play in maintaining the capital investment made. If the design itself is at fault, the FM personnel can do little but wait and watch for the inevitable to happen, which is a premature failure of equipment.
Often, service contracts are given to the lowest bidder, all other things being equal. This may not work with the best results, in most cases. Maintenance providers should have the requisite trained personnel to carry out their tasks. With newer technology being incorporated into equipment, I find that service providers do not invest sufficiently in their personnel to engage new technology.
My specific experience is in multiple locations spread over a wide geographical area, wherein it is logistically and economically implausible to have in-house staff to maintain and service the equipment.
With the state of manpower movement in the Middle East, trained manpower tends to move to better-paying jobs. If service providers depend on certain key personnel for providing reliable service, absence of these personnel causes a huge impact on the end-user’s equipment
To increase the reliability of compressors in the operation phase, it is recommended that the refrigeration system installation be carefully designed, installed and maintained, because a fault in installation can induce failure modes in a compressor.
A detailed study of failures will help to improve the performance of refrigeration compressors, as such studies share information that will help others better understand the failures and provide more qualified information for the maintenance staff.
The writer is Building Maintenance Manager with Emarat (Emirates General Petroleum Corporation). He can be contacted at email@example.com