Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1449093
34 | January - February 2022 | www . machinerylubrication.com corrosion, erosion corrosion and galvanic corrosion mechanisms advance general corrosion rates by orders of magnitude. Elec- tric discharge erosion reduces the capacity for surface metals to resist pitting from rolling fatigue. Condition Monitoring Table 2 updates the table from the March 2003 Machinery Lubrication article, "How Machinery Wear Rates Impact Maintenance Priorities." is revised table demonstrates how vibration analysis, oil analysis, thermog- raphy, motion amplification, spark detection and visual inspection are complementary tech- niques to proactively evaluate root cause issues and predictively quantify failure mechanisms in progress. Vibration monitoring and analysis employ a measurement configuration (maximum frequency of interest, sonic and ultrasonic frequency stress wave and heterodyne ultra- sonic) appropriate for detecting and trending desired measurement information. Machine vibration monitoring is often the core condition-based monitoring methodology for drives and driven rotating machinery. Proactive measurement of sinusoidal mechan- ical vibrations quantifies troublesome root cause issues such as misalignment, imbalance, looseness, and resonance and facilitates early detection and correction. Sonic and ultrasonic frequency range impact monitoring measures the progression of roller and gear defects. is predictive information is helpful to identify failing components, evaluate severity and schedule planned maintenance. Oil analysis includes sampling in-ser- vice lubricants and testing those samples to evaluate f luid chemistry, system contam- ination and machinery wear. Proactive monitoring for fluid condition and system contamination supports precision lubrication practices. Predictive monitoring for ferrous and nonferrous wear debris, together with particle shape classification, is helpful to identify failure mechanisms, evaluate severity and schedule planned maintenance. Oil and vibration analysis together are complementary, not redundant. ermal monitoring and analysis include single point, line-scanning and thermal imaging measurements. Proactive temperature Contributing factors include sharp fillet radius, corrosive substance and stress concen- tration. Mitigating factors include pre-stressed compression, surface sealing and material frac- ture toughness. Galvanic corrosion affects structures, fasteners, electrical and mechanical compo- nents. is occurs when an electrochemical corrosion corrosive substance couples a noble cathode, such as stainless steel, with a less noble anode, such as carbon steel. Contributing factors include the presence of corrosive substances together with the electrical connection of more noble with less noble metals. Mitigating factors include insu- lating interfaces between dissimilar metals, protecting/coating/sealing surfaces, contami- nation control and visual inspection. Erosion corrosion is an erosion process accompanied by a corrosive substance. Erosion removes oxidized surface material, exposing underlying metal for r a pid a nd sustained oxidation. It affects impellers, pumps, valves and piping. Contributing factors include corrosive fluid with eroding flow. Mitigating factors include providing surface protection or sealing. Deposition results from a dysfunctional and progressive accumulation of foreign material on a critical electrical or mechanical component. Examples include precipitated varnish formation and accumulation on a control valve, fibrous material accumulation on a fan and polar substance accumulation on an electrical circuit. Varnish accumulation on a control valve may lead to plugging and sticking, while fibrous mate- rial accumulations on a fan may cause imbalance and a potential fire risk. is failure mechanism can be prevented by detecting, interpreting and addressing the specific accumulation process. e corrective action plan should be specific to its characteristic process. Interaction of corrosion and/or electric discharge mechanisms with the other failure mechanisms described above is synergistic, as portrayed in the Venn diagram in Figure 1. Time-to-fail accelerates with interacting factors. Remaining useful life, e.g., incipient to catastrophic failure, shortens from decades to years, and even to months under these combined effects. Corrosion and electric discharge dete- riorate surface morpholog y and destroy remaining useful life. Corrosion contributes to mechanisms of electric circuit discharge, deposition, abrasion, adhesion, rolling fatigue, bending fatigue and cavitation fatigue. Stress Measurrement Method Proactive Detect Root Cause Predictive Quantify Failure in Progress Vibration Balancing Alignment Roller/gear defects Failure progres- sion Oil Contamination control Adequate lubrication Ferrous debris Particle shape classification Thermal Normal lines Normal connects Electrical faults Mechanical adhesion Motion Acceptable resonance Acceptable timing Synchronous resonance Timing faults Spark Survey motor shaft brushes Survey before entry Low voltage spark events High voltage are events Inspect Preventive maintenance Quality control Substance deposition Procedure misapplication No Root Cause = No Damage = Very Long Life Failure Table 2: Condition monitoring techniques to monitor failure mechanisms and root causes. MECHANICAL FAILURE