In previous Engineering Case History columns, I have discussed checklists and their value in avoiding errors during startups. While the rules cannot replace common sense or a logical and methodical approach, they can help avoid embarrassing situations. Here are 20 rules that are most helpful in troubleshooting:
Never assume anything. The new bearings are in stores, and they will be there if there is a failure is an assumption. The bearings may not be in inventory; likewise, they can be corroded, damaged or, worse, the wrong size.
Follow the data. The shaft failed due to a bending failure, because the bearing failed, because the oil system failed, because the maintenance schedule was extended. This is following the data.
Dont jump to a cause. Most of us want to come up with the most likely cause for a failure or other situation immediately. Such causes are usually based on our past experience, which may not be valid for this particular failure.
Calculation is better than speculation. A simple analysis is worth more than someone who tries to base the cause on past experiences.
Get input from others but realize they could be wrong. Most individuals want to be helpful and provide input as to the cause. However, such input may not be credible.
When you have conclusive data adhere to your principles. Safety issues are a good example. Your position may not be readily accepted by others because of budget, contract or time constraints. Before taking a stand, have other senior technical people agree with you because it could affect your career.
Management doesnt want to hear bad news. Do not just discuss the failure and the problems it can cause to management. Present good options that can also be used at other plant locations to avoid similar failures.
Management doesnt like wish lists. Only present what is needed, not what you would like to have. Adhering to company standards or national codes is usually a good approach.
Management doesnt like confusing data. Keep technical jargon to a minimum and present the information as clear as possible with illustrations, photos, models and examples.
Management doesnt like expensive solutions. Only present one or two cost-effective solutions with options, costs and timing.
Admit when you are wrong and obtain additional data. Admitting to being wrong is one of the most difficult acts. When other data contradicts yours, accepting the truth must be done; otherwise, you will look foolish.
Understand what results you are seeking. The analysis should be done to determine why the rotor crackednot to redesign the machine. Too often, we get so involved in the analysis that we forget to just solve the problem.
Look for the simplest explanation first. For example, a new drive belt was installed too tight and then broke the shaft.
Look for the least cost and easiest solution. You need to understand what caused the failure first. For example, if a drive belt was too tight, then train the machinists on the correct tightening procedure. Put a placard on the equipment explaining the procedure clearly and include caution areas.
Analytical results, tests or metallurgical results should agree. When the metallurgical analysis says it was a fatigue failure and your analysis says it was a sudden impact, someone is in error. They should both indicate the same failure mode.
Trust your intuition. When you feel something is wrong but cant prove it, its time to do an analysis and get additional data.
Utilize your trusted colleagues to confirm your approach. Talking with my engineering and field colleagues has been the most useful method in finding the true cause of a problem.
Similar failures usually have happened before. It is your job, as the reliability or maintenance engineer to survey your company and the literature for the cause of similar failures and to determine if it is useful data for troubleshooting this failure.
Always have others involved when analyzing high-profile failures. When safety, legal or major production issues are involved, it is unwise to make critical decisions on your own. This is the time for a team approach so that nothing is missed. Also involve others to develop and implement the final solution.
Someone usually knows the failure cause. It has been my experience from interviewing engineers, operators, machinists and technicians that some of the plant staff usually knew the true cause of a failure. A good interviewing procedure is an important part of the troubleshooting process. HP
|The author |
Dr. Tony Sofronas, P.E., was worldwide lead mechanical engineer for ExxonMobil Chemicals before retiring. He now owns Engineered Products, which provides consulting and engineering seminars on machinery and pressure vessels. Dr. Sofronas has authored two engineering books and numerous technical articles on analytical methods. Early in his career, he worked for General Electric and Bendix, and has extensive knowledge of design and failure analysis for various types of equipment.