Data Collection Necessary for Effective Failure Analysis
Equipment reliability is the ability of a component or system within the machine or the machine itself to perform its function under a specific set of conditions for a specific period of time. It is usually expressed as the mean time between failures during a machine’s lifecycle.
Reliability ends (or is reduced) when a failure occurs. A failure is any incident or condition that causes a machine to become unable to perform its intended function or purpose safely, reliably, and cost-effectively. In order to eliminate failures that reduce reliability, it is essential to thoroughly understand how and why failures occur, so that reoccurrence can be avoided.
The first step necessary is a complete review of any recent change(s) to the machine’s operational and maintenance history.
1. In your plant, do you believe that failure is related to the age of the machine?
Logic: This is a mistaken assumption. Research related to the relationship between equipment failure and age has shown some surprising results, including the following:
a)Failure isn’t related directly to age, but to the operating conditions to which the equipment is subjected. Failures resulting from age might only be attributed to the fatigue life of the machine or any of its components.
b) Failure cannot be predicted unless effective condition monitoring is regularly scheduled and consistently applied, so restorative maintenance or replacement, based on time or the manufacturer’s recommendations, won’t reduce the failure odds.
c) Major overhauls or component replacements based on age can be ineffective because the result may be a higher lifecycle cost that many people erroneously begin to believe is “normal.”
d) Major repairs or component replacements can actually cause an increase in premature equipment failure due to careless workmanship; rushing because of time constraints; or the use of improper methods, assembly procedures, or incorrect specifications.
2. Are your plant’s machine reliability problems (and premature failures) associated with any of these conditions?
Logic: All these potential causes with examples should raise questions during the investigation of every failure.
a) Design considerations: operators complain that hydraulic systems operate at higher-than-normal temperatures often caused by hydraulic reservoirs of inadequate capacity to dissipate heat.
b) @Installation and commissioning considerations: machine installations and their commissioning are often done carelessly. No amount of maintenance can correct poor machine design or improperly commissioned installations.
c) Poorly engineered modifications: increased production demands can cause excessive loads or speeds on machine components. For example, if a bearing load is doubled, the bearing life may be reduced by as much as 90 per cent. If the speed on a rolling element bearing is doubled, the bearing life may be reduced by as much as 50 per cent.
d) Machine vibrations: 70 per cent of vibrations are caused by conditions such as mechanical looseness, misalignment, or unbalanced conditions.
e) Overheating components or systems: extreme or erratic operating temperatures may cause premature component failures. For example, a rolling element bearing lubricated by standard mineral oil operating at temperatures that exceed 70 C (160 F) can fail prematurely due to oil oxidation.
f) Excessive contamination conditions: inadequate filter quality, or careless or infrequent application of oil analysis programs can result in premature failures in lubrication systems. For example, 70 to 80 per cent of hydraulic system failures can be attributed to contaminated oil.
g) Poor operating practices and poorly designed or inadequately applied maintenance programs: can cause potential and unexpected component or machine failures.
h) Incompatible component selection: leaking seals at gear reducers and weeping hoses in hydraulics are often the result of seal or hose selection that may be incompatible with the lubricant used. For example, nitrile seals have poor compatibility with some EP additives used in gear oils and phosphate ester fluids used in hydraulic systems.
Developing Failure Codes for Root Cause Analysis
When designing work orders or other documents that are intended to gather information about failures or failure causes, it is highly recommended that a section of the work order be devoted to the collection of failure information. This can be as simple as providing a checklist of potential reasons for failure. These failure codes include, but are not limited to, the following list, with a corresponding reporting format that can be designed in any form and included on the work order as part of the tradesperson’s report.
When investigating failures design a potential cause(s) report similar to the example is below. MRO