Application Study of Carbon Steel Pickling Corrosion Inhibitor

Abstract

This application report systematically compares the corrosion inhibition performance of Vanconol® IR-90 and a competitor on various carbon steel substrates in different acid solutions, with the aim of providing data to support engineering selection.

1 Introduction

In industrial cleaning, pickling is a core process that uses acidic solutions to remove oxide layers, rust, and dirt from metal surfaces. It is widely used in metal processing, equipment maintenance, and other metal surface pretreatment applications. However, while the acid dissolves the scale, it can also cause corrosion damage to the base metal, leading to high economic losses from equipment repair, downtime, and product rejection. Therefore, selecting an appropriate pickling corrosion inhibitor has become key to balancing pickling efficiency and metal substrate protection.

Common pickling systems include: inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, hydrofluoric acid; and organic acids such as sulfamic acid, citric acid, tartaric acid, glycolic acid, oxalic acid, and chelating agents. Different acids have varying corrosion (dissolution) capabilities toward metals, and their suitability for cleaning specific metal substrates also differs. The compatibility of common pickling solutions with metal substrates is shown in attached Table1.

Carbon steel is a major metal material in industrial cleaning, and the development of effective corrosion inhibitors is critical for protecting the substrate. This application report systematically compares the corrosion inhibition performance of Vanconol® IR-9022 and a competitor on various carbon steel substrates in different acid solutions, to provide data support for engineering selection.

Experimental Section

Materials

Metal substrates: 20# carbon steel,45# steel;

Corrosion inhibitors: Vanconol® IR-902, Competitor (typical parameters of each product are shown in Table2);

Table2 Corrosion inhibitor parameters for testing

Parameter	Vanconol® IR-902	Competitor
Appearance	Red-brown homogeneous transparent liquid	Brown-yellow transparent liquid
Density (20°C)	0.95–1.05 g/cm³	1.06–1.08 g/cm³
Solids content	32%–36%
pH	3.0–4.0	≥7
Solubility	Readily soluble in water/alcohol, miscible with acid solutions	Readily soluble in acid solutions
Temperature tolerance	≤90°C	≤90°C
Compatible acid media	Suitable for various inorganic acids, organic acids, and mixed acid pickling	Suitable for various inorganic acids, organic acids, and mixed acid pickling

Inorganic acid systems: 10% HCl solution, 10% H₂SO₄ solution, 10% H₃PO₄ solution, 10% sulfamic acid solution;

Organic acid systems: 3% citric acid solution, 3% ammonium citrate solution (pH=3–4), 10% EDTA solution.

Evaluation Method

Solution preparation: Add the weighed corrosion inhibitor to the weighed water, stir evenly to form a 0.3% aqueous solution. Then slowly add the weighed acid solution to the above inhibitor solution and stir evenly.

Prepare test coupons according to HG/T3523. Coupon grades: 20# carbon steel, N80 steel, XT45 steel.

Carry out static coupon immersion tests to assess corrosion.

Evaluation Criteria

Corrosion rate

Where:

V——Corrosion rate, in mm/a;

m₀——Mass of coupon before test, in g;

m₁——Mass of coupon after corrosion test, in g;

87600——Calculation constant;

S——Surface area of coupon, in cm²;

ρ——Density of coupon material, in g/cm³;

t——Test time, in h;

Calculation of inhibition efficiency

Where:

V0——Corrosion rate without inhibitor, in mm/a;

V₁——Corrosion rate with inhibitor, in mm/a;

V₀——Corrosion rate without inhibitor, in mm/a;

Evaluation criteria

The rating criteria for substrate corrosion testing are shown in Table2.

Table2 Rating criteria for metal corrosion testing

Metal substrate	Grade	Coupon condition
		Appearance	Mass change (mg)
Steel and cast iron	Grade 0	No corrosion pits, no obvious discoloration	< 2
	Grade 1	No corrosion pits, slight discoloration or loss of luster	< 2
	Grade 2	Obvious discoloration and loss of luster	≥ 2
	Grade 3	Visible corrosion pits on surface	≥ 2

Note: Extracted from JB/T4323-2019 standard “Water-based metal cleaners”.

Results and Discussion

Corrosion results for 20# carbon steel

Figure1 Comparison of corrosion rates of 20# carbon steel in different acid solutions

Figure2 Comparison of inhibition efficiency of corrosion inhibitors on 20# carbon steel in different acid solutions

20# carbon steel is a low-carbon steel with good toughness, plasticity and weldability, used for welding structures, pipe fittings, flanges, light-duty gears/sprockets, bolts, low-load shafts, etc. Data in Figures1 and2 show thatVanconol® IR-902 corrosion inhibitor provides better corrosion control than the competitor in all tested acid solutions. Corrosion rates in all pickling solutions are below1 g/(m²·h), and inhibition efficiencies are all >99%. The substrate surface rating is Grade 0. This indicates that the inhibitor has broad-spectrum applicability for controlling uniform corrosion of such carbon steels and improving cleaning efficiency.

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