HCl Converter

Aqueous HCl Solution Properties & Interpolator

Enter any single known property below — every other property is interpolated from the reference table.

Iron-free acid only — free acid in a working pickle must be titrated, not read from density. This table is headed “aqueous hydrochloric acid solutions” and contains no iron. Dissolved iron chloride raises the density of a working bath independently of the acid, so a hydrometer reading interpreted through this chart will overstate the free HCl actually present — severalfold in a heavily loaded pickle. Use it for fresh acid and make-up; for a used bath use the HCl Titration tab with a measured sample density.

Reference Table

Iron in the Pickle Bath

Steel dissolving in the acid leaves iron behind as ferrous chloride. Galvanizers quote that loading either as Fe²⁺ or as FeCl₂, so this converts between them and shows how much HCl the iron has already consumed.

Computed from molar masses, not from the source workbook. The workbook's iron sheets were checked and not reproduced: their iron scale disagrees with Fe + 2 HCl → FeCl₂ + H₂ by a factor of about 4.9, one column labelled “FeCl₃” implies a formula mass matching no iron species, and the two sheets that both name an “optimum FeCl₂” curve contradict each other. The figures below come from the reaction stoichiometry alone. No Kleingarn optimum or saturation curve is offered here — the workbook contains no source data for one, only hand-drawn lines on a chart.

Kleingarn Diagram — Where Your Bath Sits

Pickling speed depends on free acid and dissolved iron together, not on acid alone. Enter both and this shows whether the bath is in the efficient zone, and what to do if it is not.

Read this as zones, not numbers. Curve values are taken from the American Galvanizers Association Pickle Bath Maintenance Calculator (Kleingarn Curve Calculator), and are the same set the HDG Pickling Optimizer uses, so the two tools agree. They match an independent reading of Kleingarn’s printed 1988 figure to within about 6 g/L Fe. Kleingarn gives the basis as 20 °C (the AGA workbook states no temperature); at higher temperature the penalty for missing the optimum is smaller. Covers 10–180 g/L HCl, where the AGA data ends. No pickling time in minutes is offered, because neither source contains one.

Efficient pickling area (shaded in the original) Saturation line — pickling impossible above Optimum pickling time 50 % longer than the optimum Bath ageing from a zero-iron start

Neither source defines an upper +50 % curve, so the efficient area runs from the 50 % line up to saturation, and high iron is judged by approach to saturation rather than by an invented boundary. The ageing path is not tabulated at all: it is Fe = (C₀ − HCl) ÷ 1.3058, exact from Fe + 2 HCl → FeCl₂ + H₂ — Kleingarn’s own dash-dot line reads −0.776 against that −0.7658, agreeing to 1.3 %.

How Pickling Time Scales With Acid Strength

As the bath weakens the same work takes longer. Enter the strength you normally run and the strength the bath is at now, to see the ratio between them.

There is no standard pickling time — it is an average, or set by experience. It depends mainly on three things: the acid concentration; the condition of the steel surface, since newly fabricated material with light rust and heavily rusted material are not the same job; and the iron content of the bath. This tab covers the first two and still reports a ratio, never a duration in minutes. For the iron side use the Kleingarn Diagram tab — at ~100 g/L HCl iron alone swings the time by half again.

The acid-strength curve is a constructed one from the source workbook, not plant measurements — exactly 0.5c² − 17.5c + 170 on every row — and the sheet states no temperature, steel grade, inhibitor or agitation basis. Valid only for 2–15 % HCl.

Your surface factors

No published source quantifies these and they differ from plant to plant. The tool starts from 1.00 for new fabrication and 1.50 for rusted — one plant's experience, offered as a starting point, not a measurement for your line. Change them to match what you actually see: New fabrication stays at 1.00 and Rusted is relative to it, so 1.50 means rusted work takes half again as long. Anything you enter is stored in this browser only and is never sent anywhere.

Reference Table