Asset Intervention Trade-offs

Compare renewal costs and service loss, then test whether different assumptions about retained equipment would change the choice.

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A lower-cost renewal can depend on a fragile assumption

Renewing one part of an asset can leave a fault source in the equipment you retain. Comparing purchase prices alone misses planned outages, future upkeep and the service consequences of that retained condition.

Keep cost, service loss and requirements separate

Compare complete options over the same operating period. Put costs on a common discounted basis and count service-loss hours without discounting them. Check mandatory requirements separately. Then find how many hours a year could be lost to faults in retained equipment before the option exceeds the service limit.

Power-only renewal reaches the 60-hour service-loss limit at 6.67 retained-controller fault hours per year. Twelve hours per year raises service loss to 92 hours.

Illustrative example.

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The power-only option depends on the retained controller

The illustrative control system is required for six more years. Power faults cause 18 service-loss hours a year and controller faults six. Renewing the power supply or renewing both can meet the 60-hour limit.

If the retained-controller forecast increases to 12 fault hours a year, power-only renewal produces 92 service-loss hours and exceeds the limit. Its maintenance cost also needs reassessment. The table compares the four original options, before that change in the forecast.

Illustrative six-year comparison at a 5% real discount rate, including planned outages. Power-only renewal permits at most 6.67 retained-controller fault hours a year; the original six-hour forecast has 0.67 hours/year of headroom.

Original option
Six-year present cost
Six-year service loss
Keep both
Six-year present costAbout AUD 0.811m
Six-year service loss146 hours
Renew controller
Six-year present costAbout AUD 1.506m
Six-year service loss126 hours
Renew power
Six-year present costAbout AUD 1.007m
Six-year service loss56 hours
Renew both
Six-year present costAbout AUD 1.804m
Six-year service loss26 hours

Illustrative six-year comparison at a 5% real discount rate, including planned outages. Power-only renewal permits at most 6.67 retained-controller fault hours a year; the original six-hour forecast has 0.67 hours/year of headroom.
Original option	Six-year present cost	Six-year service loss
Keep both	About AUD 0.811m	146 hours
Renew controller	About AUD 1.506m	126 hours
Renew power	About AUD 1.007m	56 hours
Renew both	About AUD 1.804m	26 hours

Build the options around the cause of service loss

Use the comparison for asset improvement and renewal choices where service consequences are sufficiently comparable. Include the work sequence and planned outages. Test credible changes in the condition of equipment you retain, without assigning invented probabilities.

What you bring

Required function, horizon and interruption limits; fault causes and retained-condition evidence; complete intervention scopes and outages; initial, future and residual-value costs; capital, access and mandatory requirements.

What the comparison provides

Present cost, service-loss hours, separate feasibility conditions and the retained-condition threshold that could change the decision.

Service hours do not describe every consequence

An hour at a critical operating time may differ from an hour elsewhere. Keep affected functions, degraded operation, safety and mandatory requirements visible separately. Include later obligations and residual value over the common horizon. Meeting a numerical limit does not establish technical or operating acceptance.