A corrosion inhibitor is proven by one thing: a measured drop in the corrosion rate of the steel, under conditions like the line it will protect. A datasheet does not prove it; a falling corrosion rate on a probe or a coupon does. This page explains how that is measured — in the lab to pick a product and a dose, and in the field to confirm it keeps working.
You measure the corrosion rate of the steel with the inhibitor and without it, and compare. Corrosion rate is a penetration rate — millimetres per year (mm/yr) or mils per year (mpy), where 1 mm/yr is about 39.4 mpy. The headline number is inhibitor efficiency:
Expressed as a percentage. If the steel corrodes at 2.0 mm/yr untreated and 0.1 mm/yr with the inhibitor, efficiency is (2.0 − 0.1) ÷ 2.0 = 95%.
An inhibitor is not proven by a datasheet; it is proven by a measured drop in corrosion rate under conditions like the line it will protect — the right service (sweet or sour), the right temperature, and the right flow.
Three are standard, and they answer different questions:
| Method | What it measures | Lab or field |
|---|---|---|
| Linear polarization resistance (LPR), bubble cell | Instantaneous corrosion rate; ranks products and doses in hours; cell sparged with CO2 / H2S to match service | Lab (and field probes) |
| Weight-loss coupon | Average corrosion rate over an exposure period, from mass lost by a weighed metal coupon | Lab and field |
| Rotating cylinder / rotating cage | Film performance under controlled flow and shear, not still liquid | Lab |
| Autoclave | Behaviour at high-temperature, high-pressure downhole conditions | Lab |
| ER (electrical-resistance) probe | Metal loss over time, from the rising resistance of a thinning element | Field |
| Iron / manganese counts | Dissolved metal in the produced fluid as a proxy for steel going into solution | Field |
LPR is fast and good for ranking; the weighed coupon is slower but is the direct measure of metal actually lost. Serious qualification uses both, and adds flow with a rotating test so the film is judged under shear rather than in still liquid.
The lab picks the candidate; the field confirms it. LPR and electrical-resistance (ER) probes inserted into the line give a corrosion-rate reading over time; weight-loss coupons are installed and pulled on a schedule as the direct check; iron counts track dissolved metal in the produced fluid; and an inhibitor-residual measurement checks that the inhibitor is actually reaching the monitoring point at the intended concentration. Together they show whether the corrosion rate is being held at target — which is the real proof, not the label.
Two things, together. A general corrosion rate held to an acceptable target — many operators set that for carbon steel on the order of 0.1 mm/yr, though the number is set per line by its metallurgy and remaining-life needs. And a high inhibitor efficiency, commonly a target of 90–95% or better. But the average rate is not the whole story: localized attack — pitting — can perforate a line while the average rate still looks acceptable, so a good monitoring programme watches for pitting as well as the general rate.
Ironstone is building a production-chemicals line for this market, partner-led — China-direct material supply, formulation support, and testing discipline behind a Nigerian company’s registrations and field relationships. The point of this page is the point of the business: a corrosion inhibitor is worth what the monitored corrosion rate says it is. Message the technical desk to talk through qualifying one for your service.