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Practical Condition Monitoring for Preventive Maintenance
Practical Condition Monitoring for Preventive Maintenance
Torbjörn Idhammar, IDCON INC
This article will touch on elements of practical condition monitoring
Condition monitoring (CM) is not a life-extending activity. Life-extending activities are things such as lubrication, alignment, balancing and operating procedures.
It’s very important to keep this very basic fact clear in all communications within your plant; otherwise, too little importance may be placed on the planning and scheduling of corrective work orders originated in condition monitoring.
Condition monitoring only provides information on failures before there is a breakdown. You can do it with inspection tools – vibration monitors, infrared temperature guns, pressure gauges, volt meters and others. You can also execute practical condition monitoring subjectively by looking, listening, feeling and smelling (let’s avoid tasting, shall we?).
This article is dedicated to the somewhat lost skill of subjective (look, listen, feel, smell) inspections.
These days, we tend to rely more and more on technology. Computers are great, but they can be awfully bad at interpreting machine condition.
For example, how do we get a computer to:
find a loose bolt for a reasonable cost before there is mechanical looseness?
see dirt buildup on an electrical motor before heat increases?
find a recently plugged breather on a gearbox?
find the location of a leak in a pneumatic system?
pinpoint a problem with a photocell that is knocked out of alignment?
These problems could somehow be found accurately with a computer, but a properly trained person would only need about 10 seconds to see the problems.
How well is your plant doing with mechanical, instrumentation and electrical inspections? While articles often talk about the management systems needed, I’d like to list some basic examples in order to rediscover the subjective inspection methods.
Regardless of whether you’re doing inspections with handheld computers or a paper system, can trend data or not, or have key performance indicators or not, you won’t be successful unless your people can do quality inspections on equipment. Here are the examples:
Example 1: AC motor temperature
If your inspectors look at motor temperature, do they take the time to think about the significance of a hot temperature on the coupling side of the motor vs. a hot temperature at the center of the motor? A hot temperature in the center often means a damaged winding or an overload situation, while a hot temperature at the coupling side of the motor means a bearing problem of some kind.
Example 2: Couplings
Are couplings and the equipment attached to the coupling operated to breakdown mode, or are problems found before a breakdown occurs? All couplings that can cause a breakdown costing more than a few hundred dollars should have an inspection lid so the coupling element, bolts and keyways can be checked easily. (The cost of inspection would be, at maximum, $100 per year.) Preferably, the inspection should be done with a stroboscope while the equipment is running (see Figure 1).
Figure 1. A coupling can be inspected on-the-run with a stroboscope. Note that this plant has followed OSHA 1942 regulations for guard safety.
Example 3: Heat exchanger sacrificial anode
The basic function of a sacrificial anode is to protect surrounding material. A common use is to place a plug in a heat exchanger’s cast iron shell (Figure 3). The anode is usually made of zinc and will slowly corrode instead of the iron shell.
The phenomenon is called galvanic corrosion. How would you inspect the zinc plug before it starts to leak in a critical application? Drill a small hole to a shallow depth in the center of the zinc plug. A small leak will be visible in the center of the plug well before it is time to change it.
Figure 2. Inspections of zinc anodes in a heat exchanger are simplified by drilling a small hole. When the anode wears away, a small leak will develop so that the need for replacement can be detected earlier.
Example 4: Pump packing
Pump packing replacements turn into emergencies in some plants because the wrong mind-set is in play. If it doesn’t leak more than the recommended one to two drops per second, it’s usually not examined. Why not change the mind-set? Make sure packing is changed when there is only one-eighth of an inch of takeup left in the packing (Figure 2)?
Figure 3. Change the pump packing when there is one-eighth of an inch of takeup left in the packing.
The Numbers
IDCON recently collected information on how work requests were initiated in a large process plant. We collected all work requests over seven months and analyzed how the work was found.
The data showed that close to 70 percent of all problems found from condition monitoring were picked up subjectively by operators and mechanics through detailed look, listen, feel and smell inspections.
Many problems wouldn’t have been found if it wasn’t for vibration analysis, infrared technology and oil analysis.
But the data makes you wonder if we don’t underutilize subjective inspections. They are a very powerful and cost-effective maintenance tool.
Torbjörn Idhammar
Torbjörn Idhammar was the president and CEO of IDCON INC., a Reliability and Maintenance Management Consulting Firm. Before his retirement from the company, Tor’s responsibilities included training IDCON consultants, product development, sales, and marketing. He provided advice to IDCON’s multi-site and international clients to ensure outcomes and deliverables were met.
Many power generation steam turbine generators today are required in service well beyond their intended lifetimes. Dismantling for inspection is expensive, and owners need to consider all relevant information in making the decision. Application of condition monitoring in all the applicable methods is justified, with each showing different degradation modes. Performance analysis is less well publicised, yet unlike vibration analysis and oil debris analysis, it will show conditions which reduce machine efficiency and output, such as deposits on blades and erosion of internal clearances. The paper outlines, with examples, some condition monitoring techniques that have contributed to retaining some large fossil machines in service for up to 17 years without opening high-pressure sections.
Many power generation steam turbine generators today are required in service well beyond their intended lifetimes. Dismantling for inspection is expensive, and owners need to consider all relevant information in making the decision. Application of condition monitoring in all the applicable methods is justified, with each showing different degradation modes. Performance analysis is less well publicised, yet unlike vibration analysis and oil debris analysis, it will show conditions which reduce machine efficiency and output, such as deposits on blades and erosion of internal clearances. The paper outlines, with examples, some condition monitoring techniques that have contributed to retaining some large fossil machines in service for up to 17 years without opening high-pressure sections.
It may seem that visual inspection goes beyond what thermographers are hired to do, but conscientious thermographers include notes and even images in their reports when they see code violations, broken equipment, incorrectly sized fuses, bad wiring, etc. A good thermographer will not ignore copper tubing used as a fuse, even if it looks fine in the infrared. Whether the inspection is insurance driven or a proactive stance, an infrared inspection and a visual inspection complement each other.
It may seem that visual inspection goes beyond what thermographers are hired to do, but conscientious thermographers include notes and even images in their reports when they see code violations, broken equipment, incorrectly sized fuses, bad wiring, etc. A good thermographer will not ignore copper tubing used as a fuse, even if it looks fine in the infrared. Whether the inspection is insurance driven or a proactive stance, an infrared inspection and a visual inspection complement each other.
Why do components fail? – This article explains common failure mechanisms, component types to which each applies, and suggests non-intrusive monitoring techniques to discover components in various stages of progressive failure.
Why do components fail? – This article explains common failure mechanisms, component types to which each applies, and suggests non-intrusive monitoring techniques to discover components in various stages of progressive failure.
When performing condition monitoring tasks, don’t just rely on expensive condition monitoring tools. You would be surprised at the unusual and simple tools that can be used.
When performing condition monitoring tasks, don’t just rely on expensive condition monitoring tools. You would be surprised at the unusual and simple tools that can be used.
Ultrasonic leak detection has been used for a variety of applications ranging from energy reduction by locating compressed air leaks to quality assurance inspections such as locating wind noise and water leaks in automobiles. The secret to success is to understand the nature of what type of leak produces a detectible ultrasound and what does not, along with the techniques that can be used for effective leak identification.
Ultrasonic leak detection has been used for a variety of applications ranging from energy reduction by locating compressed air leaks to quality assurance inspections such as locating wind noise and water leaks in automobiles. The secret to success is to understand the nature of what type of leak produces a detectible ultrasound and what does not, along with the techniques that can be used for effective leak identification.
A shaft centerline diagram is a plot used in the vibration analysis of journal bearings. It is also called a shaft average centerline diagram. The purpose of this graph is to display the average position of the rotor in the bearing. In short, for different bearing types, there is an expected or “normal” position of the shaft in the bearing. If this position changes, it can indicate a problem.
A shaft centerline diagram is a plot used in the vibration analysis of journal bearings. It is also called a shaft average centerline diagram. The purpose of this graph is to display the average position of the rotor in the bearing. In short, for different bearing types, there is an expected or “normal” position of the shaft in the bearing. If this position changes, it can indicate a problem.
The maritime industry is in many aspects using maintenance strategies from the past. Land based industry used to take influence from shipping to organise the maintenance in the 70:ties. Now industry is perusing new strategies that give better reliability and are more profitable. By focusing on reliability the indirect effects from doing the wrong maintenance can be reduced considerably. Shipping industry has from a maintenance aspect been doing the wrong things correct for many years. The opportunity is now to do the right thing correct instead.
The maritime industry is in many aspects using maintenance strategies from the past. Land based industry used to take influence from shipping to organise the maintenance in the 70:ties. Now industry is perusing new strategies that give better reliability and are more profitable. By focusing on reliability the indirect effects from doing the wrong maintenance can be reduced considerably. Shipping industry has from a maintenance aspect been doing the wrong things correct for many years. The opportunity is now to do the right thing correct instead.
