How to Control the Use of Inhibitors in the Iron-Steel Pickling Line?

What Does the Pickling Inhibitor Try to Protect?

Hydrochloric acid (HCl) is used in the pickling lines of iron-steel sheet, pipe, profile and hot-dip galvanizing facilities to dissolve the scale (iron oxide) layer on the steel surface. However, after the scale is cleaned, the acid reacts with the underlying solid base metal (Fe), causing both metal loss, waste of fresh acid and the release of hydrogen gas. The purpose of the pickling inhibitor is to limit over-pickling, surface darkening and the risk of hydrogen embrittlement by creating a protective adsorption film on the bare metal surface without hindering the rate of oxide descaling. On Elif Çevre Kimya's iron and steel sector page, HCl pickling inhibitors are among the basic process product groups.

Surface Quality, Temperature and Iron Accumulation are Monitored Together

Just because the steel coming out of the bath looks shiny does not mean that the process is under full control. Bath temperature, free HCl concentration, dissolved iron (Fe²⁺ / Fe³⁺) concentration accumulated in the bath, immersion or line transit time and steel quality should be evaluated together. In addition, it is important that the steel will enter the cold rolling, galvanizing or painting step after pickling in order to avoid any unwanted inhibitor residue or stains on the surface. Product suitability must be verified at the quotation and laboratory stages.

Bathroom Analysis and Controlled Site Plan

The operating team should record bath acidity (% HCl), iron concentration (g/L Fe), temperature and fresh acid additions during each shift. Inhibitor dosage should be proportional and controlled with fresh acid feeding; Fixed dosage or performance guarantees should not be made without site bath data and coupon weight loss testing.

Field Control and Monitoring List

Chemical dosage and system capacity decisions should be determined by analysis and facility conditions; There is no guarantee of fixed dosage or performance.

• Shift monitoring of free HCl (%), dissolved iron (g/L Fe) and bath temperature (°C) in pickling baths
• Comparison of inhibition efficiency and scale dissolution time in laboratory with steel coupons
• Proportional matching of inhibitor feed with fresh HCl acid addition
• pH, chloride transport and surface stain/residue control in rinsing baths
• Confirmation of compatibility of the inhibitor with the regeneration process if an acid regeneration (ARP) unit is present