11.2 Preventive/Predictive Maintenance & Decommissioning

Modern industrial maintenance integrates proactive condition-monitoring technologies, structured reliability frameworks, and systematic commissioning and mothballing protocols to maximize equipment uptime, ensure worker safety, and protect capital assets.

Quick Answer: Maintenance strategies evolve from Run-to-Failure to Preventive (time-based), Predictive (condition-based), and Reliability Centered Maintenance (RCM). Oil analysis tracks asset health using viscosity, ICAP wear metals, Karl Fischer water PPM, and ISO 4406 cleanliness codes (e.g. 18/16/13). Mothballing procedures require VCIs, protective coatings, and periodic 1.25 turn (450°) shaft rotation to prevent shaft sag and false brinelling.

Industrial Maintenance Strategies & RCM Framework

Plant maintenance strategies balance operational risk, repair costs, and asset criticality.

+---------------------------------------------------------------------------------------------------+
|                                INDUSTRIAL MAINTENANCE STRATEGIES                                  |
+-----------------------+-----------------------+-----------------------+---------------------------+
| Maintenance Strategy  | Trigger Mechanism     | Primary Advantages    | Disadvantages & Risks     |
+-----------------------+-----------------------+-----------------------+---------------------------+
| Run-to-Failure        | Functional breakdown  | Zero routine PM labor | Unplanned downtime, high  |
| (Reactive)            | of equipment          | or monitoring expense | repair cost, safety hazards|
+-----------------------+-----------------------+-----------------------+---------------------------+
| Preventive (PM)       | Time interval or      | Reduces catastrophic  | Replaces healthy parts;   |
| (Time / Usage Based)  | operating hours       | unexpected failures   | infant mortality risks    |
+-----------------------+-----------------------+-----------------------+---------------------------+
| Predictive (PdM)      | Measured parameter    | Maintenance performed | Requires capital sensors, |
| (Condition Based)     | breaches threshold    | only when required    | specialized training      |
+-----------------------+-----------------------+-----------------------+---------------------------+
| Reliability Centered  | Risk-based FMEA       | Optimizes total plant | Requires extensive initial|
| Maintenance (RCM)     | decision matrix       | asset life cycle cost | failure mode analysis     |
+-----------------------+-----------------------+-----------------------+---------------------------+

Reliability Centered Maintenance (RCM) Principles

RCM systematically analyzes machine failure modes using Failure Mode and Effects Analysis (FMEA) to establish the optimal maintenance task for each asset:

1. System Functions & Performance Standards: Define target operating capabilities.
2. Functional Failures: Identify states where performance falls below required standards.
3. Failure Modes: List specific mechanical, electrical, or structural causes of failure.
4. Failure Effects & Criticality: Evaluate safety hazards, environmental impact, and production downtime costs.
5. Task Assignment: Assign PdM condition monitoring to critical failure modes, PM servicing to age-dependent wear modes, and Run-to-Failure strictly to non-critical redundant assets.

Used Oil Analysis & Fluid Tribology

Used oil analysis acts as an internal medical checkup for machinery, revealing lubricant degradation, chemical contamination, and internal component wear.

Key Laboratory Oil Analysis Tests

1. Kinematic Viscosity (ASTM D445): Measured in centistokes (ext{cSt} or ext{mm}²/ ext{s}) at 40°C and 100°C. Viscosity increases due to oil oxidation, thermal nitration, or soot accumulation; viscosity decreases due to fuel dilution or mechanical shear of Viscosity Index (VI) improvers. Industrial lubricants follow ISO Viscosity Grades (e.g., ISO VG 220 has a nominal viscosity of 220 cSt ± 10% at 40°C).
2. Inductively Coupled Plasma (ICAP) Spectroscopy: Measures dissolved wear metals and additive concentrations in parts per million (PPM):
   • Iron (Fe): Gear teeth, bearing raceways, cylinder liners.
   • Copper (Cu): Bronze bushings, brass cages, oil cooler tubes.
   • Lead (Pb) & Tin (Sn): Babbitt journal bearing overlays.
   • Aluminum (Al): Pistons, blower housings, thrust washers.
   • Silicon (Si): Environmental dirt and sand contamination (dirt ingress).
3. Karl Fischer Water Titration (ASTM D6304): Quantifies total dissolved, emulsified, and free water in PPM. Water content exceeding 200 PPM in turbine oils or 500 PPM in gearboxes causes rapid additive depletion, oil emulsion, hydrogen embrittlement, and accelerated bearing fatigue spalling.
4. Chemical Degradation (TAN & TBN):
   • Total Acid Number (TAN): Measures accumulated acidic oxidation byproducts in industrial gear and turbine oils.
   • Total Base Number (TBN): Measures remaining alkaline reserve in engine oils available to neutralize combustion acids.
5. ISO 4406 Particle Cleanliness Code: Classifies solid particle contamination based on three scale numbers corresponding to particle counts per milliliter at >4 µm, >6 µm, and >14 µm.

                  ISO 4406 CLEANLINESS CODE EXAMPLE: 18 / 16 / 13

      +-----------------------+-----------------------+-----------------------+
      |     > 4 Micron        |     > 6 Micron        |     > 14 Micron       |
      |  Scale Code: 18       |  Scale Code: 16       |  Scale Code: 13       |
      | (1,300 - 2,500 / mL)  |   (320 - 640 / mL)    |    (40 - 80 / mL)     |
      +-----------------------+-----------------------+-----------------------+

Each increase of 1 in the ISO scale number represents a doubling of the upper particle concentration limit per milliliter.

Non-Destructive Testing (NDT) Methods

NDT techniques evaluate component structural integrity without compromising future serviceability.

+---------------------------------------------------------------------------------------------------+
|                                 NON-DESTRUCTIVE TESTING COMPARISON                                |
+-----------------------+-----------------------+-----------------------+---------------------------+
| NDT Method            | Target Flaw Location  | Material Compatibility| Key Operating Principle   |
+-----------------------+-----------------------+-----------------------+---------------------------+
| Dye Penetrant (PT)    | Surface-breaking      | Non-porous materials  | Liquid penetrant enters   |
|                       | cracks and pores      | (Metals, plastics)    | flaw via capillary action;|
|                       |                       |                       | developer draws out dye   |
+-----------------------+-----------------------+-----------------------+---------------------------+
| Magnetic Particle (MT)| Surface and shallow   | Ferromagnetic metals  | Magnetic flux leakage     |
|                       | sub-surface (<3 mm)   | only (Iron, steel)    | attracts iron particles   |
+-----------------------+-----------------------+-----------------------+---------------------------+
| Ultrasonic (UT)       | Internal volumetric   | Metals, composites,   | High-frequency sound pulse|
|                       | flaws & thickness     | ceramics              | reflects off internal     |
|                       |                       |                       | density discontinuities   |
+-----------------------+-----------------------+-----------------------+---------------------------+
| Radiography (RT)      | Internal volumetric   | All metals and        | X-ray / Gamma-ray radiation|
|                       | voids & weld flaws    | dense materials       | differential attenuation  |
|                       |                       |                       | captured on film/detector |
+-----------------------+-----------------------+-----------------------+---------------------------+

Detailed Inspection Procedures

• Dye Penetrant Testing (PT): Surface must be cleaned and degreased. Liquid dye penetrant is applied and allowed to dwell for 10–30 minutes. Excess surface penetrant is wiped away, and a chalky white developer is applied. Capillary action draws trapped penetrant back out of surface cracks, creating vivid red or fluorescent indications.
• Magnetic Particle Testing (MT): An electromagnetic yoke establishes magnetic flux lines through a ferromagnetic part. Surface or sub-surface cracks disrupt magnetic lines of force, creating localized magnetic flux leakage fields that attract dry iron powder or wet fluorescent particles.
• Ultrasonic Testing (UT): Piezoelectric transducers inject high-frequency acoustic waves (0.5 to 15 MHz) into the material. Internal cracks, inclusions, or back-wall boundaries reflect sound energy back to the receiver, displaying echo amplitude versus travel time (depth) on an A-scan, B-scan (cross-section), or C-scan (plan view) display.

Commissioning Checklists & Hot Run-In Monitoring

Commissioning ensures newly installed or overhauled equipment transitions safely into production.

1. Cold Pre-Commissioning Checklist

• Foundation & Grouting: Verify grout cure strength and hold-down bolt torque specifications.
• Soft Foot Verification: Measure housing foot deflection using dial indicators or laser alignment sensors; maximum allowable soft foot tolerance is 0.002 inches (0.05 mm).
• Precision Shaft Alignment: Perform final laser alignment under ambient conditions, compensating for thermal growth offsets.
• Lubrication System: Flush bearing housings and gearboxes; fill with clean, specified lubricant to the exact sight glass centerline.
• Bump Test: Briefly energize the electric motor uncoupled to verify correct rotational direction.
• Safety Guarding & Piping Strain: Confirm coupling guards are secured and piping connections exert zero external mechanical strain on pump or compressor casings.

2. Hot Run-In Monitoring Sequence

• No-Load / Light-Load Start: Run equipment uncoupled or under minimum load while monitoring oil pressure, flow sight glasses, and electrical current draw.
• Thermal Stabilization Tracking: Record bearing housing temperatures at 15-minute intervals. Temperatures should stabilize below 80°C (175°F) with a maximum rate of rise under 1°C per minute.
• Baseline FFT Vibration Spectrum: Capture baseline overall vibration and FFT spectra on all bearing points to serve as reference benchmarks for future predictive maintenance.
• Mechanical Seals & Packing: Verify mechanical seal flush flow and adjust gland packing drip rates to 40–60 drops per minute for cooling and lubrication.

Decommissioning, Isolation & Long-Term Preservation (Mothballing)

Decommissioning safely takes machinery out of service, while mothballing protects idle equipment from environmental degradation during long-term storage.

Safe Isolation Procedures

1. Energy Isolation (LOTO): Execute Lockout/Tagout on electrical breakers, hydraulic supply lines, pneumatic controls, and chemical piping.
2. Zero Energy Verification: Test system pressure gauges, bleed off stored hydraulic/pneumatic energy, and verify zero electrical voltage.
3. Fluid Draining & Purging: Drain oils, coolants, and process chemicals per environmental regulations; flush sumps with light rust-inhibited flushing oil.

Long-Term Storage & Preservation (Mothballing) Protocols

• Vapor Phase Corrosion Inhibitors (VCI): Add VCI fogging oil or solid VCI packets into sealed gearboxes, bearing sumps, and piping cavities. VCI molecules evaporate and passivate internal un-lubricated metallic surfaces.
• Desiccant & Sealed Enclosures: Place silica gel desiccant bags inside electrical cabinets and junction boxes; seal all pipe flanges and housing breathers with vapor-barrier tape.
• Shaft Rotation Protocol: Shafts of mothballed rotating equipment must be manually rotated 1.25 turns (450°) on a scheduled monthly interval.
  • Reason 1: Moving the shaft by 1.25 turns (rather than full 360° turns) changes the contact point of rolling elements on raceways, preventing false brinelling (vibration-induced fret indentations).
  • Reason 2: Redistributes protective grease or oil film over bearing surfaces and shaft journal sectors.
  • Reason 3: Prevents permanent gravity-induced shaft bending (sag).
• External Surface Protection: Coat unpainted machined surfaces, shaft extensions, and coupling hubs with heavy petroleum-wax rust preventatives (e.g., Cosmoline or TECTYL).