Is My Machine OK?. Robert Perez X.
may be justified if a more detailed risk assessment is performed.
Once the maximum amount of condition monitoring equipment justified is determined, work with the condition monitoring hardware provider to determine how to best spend this money. The types of condition monitoring hardware will depend on the answers to the following questions:
1.What types of machines are going to be monitored? Compressors, pumps, gearbox, etc.?
2.What are most predominant machine failure modes? Bearings, seals, etc.?
3.What bearing types do you have? Rolling element bearings (REB) or hydrodynamic?
4.What is the transmissibility ratio at the bearings, i.e., the ratio of casing vibration to shaft vibration?
5.What are the machine/shaft operating speeds?
6.How will the failure of the critical components manifest themselves? Vibration, temperature, acoustic energy?
7.How do these components usually fail? Gradually or suddenly?
Finally, determine if the proposed condition monitoring installation will actually yield the reduction in annualized risk assumed in the original analysis. If not, the user must either consider other design options or rerun the analysis considering the new assumptions.
To begin a comprehensive machinery assessment, you need to know everything you can about the machine in question: details of its construction, its history, how it’s being operated, etc. Then, you need to collect some field data and analyze it. Finally, you have to make a decision considering all the field analysis results and pertinent factors. This sounds easy, but in practice machinery assessments are challenging and sometimes frustrating. To simplify the process, we will break the steps down in to manageable steps.
In a nutshell, here are the basic recommended steps that will help you in your quest:
Step #1. Ask a lot of questions.
Step #2. Collect equipment information.
Step #3. Collect machine field data.
Step #4. Make a decision.
Remember to ask questions if you have any doubts. Operators, co-workers, and supervisors may have some additional knowledge or insights into the problem at hand. The help of the original equipment manufacturers (OEMs), co-workers, consultants, etc. should all be enlisted if you are unsure of how to proceed or if you need additional machine information.
Remember:
The information in this reference guide should be considered as only one facet of a comprehensive assessment methodology—not the final word. The guidelines contained in the following pages must be used judiciously, ensuring that all the collected data is accurate and trustworthy and that ample machinery information is at hand.
Here’s a basic outline to help you navigate through the machinery assessment maze:
What questions should I ask operating personnel?
1.Which machine element is acting up?
a.Driver
b.Driven
c.Piping/attachments
d.Auxiliary equipment
2.What’s the problem?
a.Vibration
b.Temperature
c.Erratic flows or pressures
d.Pulsations
e.Loss of flow or pressure
f.Frequent machine trips
3.Did the problem develop suddenly or gradually?
4.Is the problem intermittent?
a.Does the problem come and go with flow changes?
b.Does the problem come and go with pressure changes?
c.Does the problem come and go with suction level changes?
d.Does the problem come and go with speed changes?
e.Does the problem come and go with fluid property changes?
5.What is the machine’s status?
a.New installation
b.Recent modifications
c.Recent repair
d.Recent preventative maintenance activity
e.Has it been running OK for over 90 days, but has recently started acting up
f.Has it been recently idled
g.Are you operating at off-design conditions?
i.High or low flows
ii.High or low pressures
iii.High or low speeds
6.What is the machine’s history?
a.What’s the historical mean time between repairs (MTBR)?
b.What are the common failure modes?
c.Are there any known design problems?
d.Are there any known operational issues?
What machine information do I need before getting started?
1.Machine spec-sheets
2.Machine drawings
3.Machine trend data
4.Machine test stand data, if available
5.Machine’s maintenance history
What analysis equipment do I need?
1.Vibration sensors and analyzers
2.Temperature gun
3.Pressure gauges
4.Dynamic pressure transducer and analyzers
5.Tachometer or strobe light
6.Strain gauges for piping studies
7.Sample bottles for oil analyses
8.Camera if permitted
Making a decision:
Once you have collected some field data, you will need to make a decision. Your choices are:
•Do nothing.
•Monitor: Continue monitoring as scheduled, or increase monitoring intervals and/or points.
•Test and assess: Vary operating conditions and observe how equipment responds.
•Switch to spare, if available.
•Plan a shutdown for balancing, alignment, oil change out, piping modification, etc.
•Plan a shutdown for repair (e.g., full machine overhaul if needed).
•Shut down immediately for balancing, alignment, oil change out, piping modification, etc.
•Shut down immediately for repair.
The Potential to Failure Time Interval
For most classes