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Qwestrum Engineering360 · Industrial & Production · Maintenance Management

Maintenance Strategies

Maintenance strategy selects when and how to intervene to minimize total failure and downtime cost.
Exam tip: keep SI units consistent end-to-end, write the governing relation symbolically before substituting, and sanity-check magnitude and sign.

Key formulas & points

Skim these first — then read the full notes below.

  • Corrective, preventive, predictive, proactive
  • Run-to-failure for non-critical redundant items
  • Condition-based maintenance uses sensor trends

Topic details

Introduction

Industrial maintenance has evolved from reactive repairs to reliability-driven planning. Groover and Buffa both relate maintenance policy directly to capacity and profitability.

Key relations & formulas

Formulas (Indian textbook notation)

  • breakdowncost=repair+downtime×productionlossbreakdown cost = repair + downtime \times production loss

Formulas (Indian textbook notation)

  • preventiveintervalfromWeibullfailureratepreventive interval from Weibull failure rate

Formulas (Indian textbook notation)

  • availabilityA=MTBF(MTBF+MTTR)availability A = \frac{MTBF}{(MTBF+MTTR)}

Notation and sign conventions

Relation 1 —
breakdowncost=repair+downtime×productionlossbreakdown cost = repair + downtime \times production loss

Formulas (Indian textbook notation)

  • breakdowncost=repair+downtime×productionlossbreakdown cost = repair + downtime \times production loss
Write this relation with symbols exactly as in Maintenance Engineering — SRK Rao before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.
Relation 2 —
preventiveintervalfromWeibullfailureratepreventive interval from Weibull failure rate

Formulas (Indian textbook notation)

  • preventiveintervalfromWeibullfailureratepreventive interval from Weibull failure rate
Write this relation with symbols exactly as in Maintenance Engineering — SRK Rao before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.
Relation 3 —
availabilityA=MTBF/availability A = MTBF/

Formulas (Indian textbook notation)

  • availabilityA=MTBF(MTBF+MTTR)availability A = \frac{MTBF}{(MTBF+MTTR)}
Write this relation with symbols exactly as in Maintenance Engineering — SRK Rao before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

Concept in depth

Corrective maintenance is event-driven, preventive is time/usage based, predictive uses condition indicators, and proactive targets root failure mechanisms. Decision choice depends on criticality, failure consequences, and economics. Chase-style operations strategy ties maintenance policy to service level commitments.

Assumptions and validity limits

State assumptions explicitly before using any relation for maintenance strategies — steady state, uniform properties, linear elastic material, ideal gas, incompressible flow, etc., as applicable.
Wrong assumptions invalidate the entire solution even when the formula is correct. In Maintenance Management viva and GATE descriptive questions, listing valid assumptions often earns separate marks.

Step-by-step problem approach

1. Read the question and list given data with SI units (common in Maintenance Management papers).
2. Draw a neat labelled diagram where applicable — examiners in Indian universities award diagram marks even when arithmetic slips.
3. Identify which relation from this topic applies to maintenance strategies.
4. Use equation 1:
breakdowncost=repair+downtime×productionlossbreakdown cost = repair + downtime \times production loss
.
5. Use equation 2:
preventiveintervalfromWeibullfailureratepreventive interval from Weibull failure rate
.
6. Substitute values, compute, and verify units and sign (direction).
7. State conclusion in one line — e.g. safe/unsafe, stable/unstable, feasible/infeasible.

Applications & exam relevance

Maintenance Strategies appears in plant reliability teams. In Indian industrial curricula this topic is tested because it connects theory to RCM and spare parts strategy.
GATE and semester exams often combine maintenance strategies with earlier units — revise prerequisites before attempting mixed problems.
Industry interview panels sometimes ask: "Where did you use maintenance strategies?" — answer with a lab, mini-project, or plant visit example if possible.

Common mistakes in exams

A common exam mistake is assuming preventive is always best. Students often ignore downtime opportunity cost in breakdown-vs-preventive comparisons.

Quick revision checklist

Before attempting maintenance strategies problems, confirm you can:
1. Corrective, preventive, predictive, proactive
2. Run-to-failure for non-critical redundant items
3. Condition-based maintenance uses sensor trends
Revise the solved examples in Maintenance Engineering — SRK Rao and one previous-year GATE or university paper for this unit.

Worked examples

Try the problem first — open the solution when you are ready to check.

Availability from MTBF and MTTR

Problem

For a machine, MTBF = 200 hours and MTTR = 20 hours. Find availability.

Solution

A = MTBF/(MTBF+MTTR) = 200/(200+20) = 200/220 = 0.9091, i.e., 90.91%.

Conceptual check — Maintenance Strategies

Problem

In a Maintenance Management semester or GATE paper you are asked: "State the main assumption, the governing relation, and one practical consequence of maintenance strategies." What should a complete answer include?

📖 Standard books (India)

  • Maintenance Engineering — SRK Rao

    Read: Syllabus unit

    Reliability, RCM, and maintenance planning

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