FRP vs steel life-cycle cost calculator

Each cost is brought back to today with a real discount rate: a cost C in year t counts as C / (1 + r)^t. The total adds the installed cost, maintenance events, yearly inspection, replacements and the shutdown or access cost of each event, and takes off the unused life left at the end of the study, straight line. This is the present-value method of ISO 15686-5; ASTM E917 and AS/NZS 4536 do the same arithmetic.

Roughly the coating thickness divided by the zinc corrosion rate. ISO 9223 gives a first-year rate for each atmospheric corrosivity category, for example 0.7 to 2.1 µm a year in C3 and 4.2 to 8.4 µm in C5, and ISO 1461 requires at least 85 µm on steel over 6 mm thick. That is 10 to 20 years in C5 and 40 years or more in C3. Zinc usually corrodes more slowly after the first year (ISO 9224), and splash zones, immersion and chemical fumes are outside these categories, so use site experience where you have it.

The real rate your organization uses to appraise investments, which excludes inflation. Public-sector guidance sets real rates of a few per cent, such as 3.5% in the UK Green Book. A higher rate makes later maintenance count for less and favors the option that is cheaper to install; try two or three rates to see whether the answer changes.

It needs no corrosion protection, which is where the saving comes from in corrosive sites. Faces exposed to strong sunlight can weather and may need a UV-resistant coat after years of exposure, and every structure needs inspection. The example books one coat at 25 years; enter the interval and cost the supplier recommends for the resin and surface offered.

In mild, dry environments such as C2 and C3, where galvanizing outlasts the study period and nothing is spent after installation, galvanized steel usually costs less over its life as well as on day one. The case for FRP grows with the corrosivity of the site, the cost of access and shutdowns, and where weight or electrical insulation matters.