Application Study of Vanconol® IR-902 Corrosion Inhibitor for Carbon Steel Acid Pickling

Abstract

This application report systematically compares the corrosion inhibition performance of Vanconol®IR-902 and a competitive product on different grades of carbon steel substrates in various acid baths, aiming to provide data support for engineering selection.

1 Introduction

In industrial cleaning, acid pickling is a core process that uses acidic solutions to remove oxide layers, rust, and dirt from metal surfaces. It is widely applied in metalworking, equipment maintenance, and other metal surface pretreatment fields. However, while dissolving scale, the acid can also cause corrosion damage to the base metal, leading to significant economic losses from equipment repair, production downtime, and product scrap. Therefore, selecting an appropriate acid pickling corrosion inhibitor becomes a key approach to balancing pickling efficiency with metal substrate safety.

Common pickling systems include: inorganic acid solutions such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and hydrofluoric acid; organic acid solutions include sulfamic acid, citric acid, tartaric acid, glycolic acid, oxalic acid, and chelating agent-type organic acids. Various acids have different corrosion (dissolution) capabilities on metals, and their adaptability to metal substrates during cleaning also differs. The adaptability of common pickling solutions to metal substrates is shown in Appendix 1.

Carbon steel is a major class of metal material in industrial cleaning. The development of efficient corrosion inhibitor products is crucial for protecting these substrates. This application report systematically compares the corrosion inhibitor product Vanconol®IR-9022 with a competitive product for their corrosion inhibition performance on different grades of carbon steel substrates in various acid baths, aiming to provide data support for engineering selection.

Experimental Section

Experimental Materials

Metal substrates: No. 20 carbon steel, No. 45 steel;

Corrosion inhibitors: Vanconol®IR-902 and a competitive product (typical parameters of each product are listed in Table 2);

Table 2 Parameters of Corrosion Inhibitors Used in Tests

Parameter	Vanconol®IR-902	Competitive Product
Appearance	Reddish brown uniform transparent liquid	Brownish yellow transparent liquid
Density (20°C)	0.95~1.05 g/cm³	1.06~1.08 g/cm³
Solid Content	32%~36%
pH Value	3.0-4.0	≥7
Solubility	Easily soluble in water/alcohol, miscible with acid solutions	Easily soluble in acid solutions
Temperature Resistance	≤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 pickling systems: 10% HCl solution, 10% H₂SO₄ solution, 10% H₃PO₄ solution, 10% sulfamic acid solution;

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

Evaluation Method

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

Prepare test coupons and treat them according to HG/T3523. The coupon grades are No. 20 carbon steel, N80 steel coupons, and XT45 steel coupons.

Perform static coupon immersion testing to measure corrosion.

Evaluation Criteria

Corrosion Rate

Where:

V —— corrosion rate, unit mm/a;

m₀ —— coupon mass before test, unit g;

m₁ —— coupon mass after corrosion test, unit g;

87600 —— calculation constant;

S —— coupon surface area, unit cm²;

ρ —— coupon material density, unit g/cm³;

t —— test duration, unit h;

Calculation of Inhibition Efficiency

Where:

V₀ —— corrosion rate without inhibitor, unit mm/a;

V₁ —— corrosion rate with inhibitor, unit mm/a;

Evaluation Criteria

The rating criteria for substrate corrosion tests are shown in Table 2.

Table 2 Rating Criteria for Metal Corrosion Tests

Metal Substrate	Grade	Coupon Condition
		Appearance	Mass Change (unit: mg)
Steel and Cast Iron	Grade 0	No corrosion pits on surface, no obvious discoloration	＜2
	Grade 1	No corrosion pits, slight discoloration or loss of luster	＜2
	Grade 2	Obvious discoloration and loss of luster on surface	≥2
	Grade 3	Visible corrosion pits on surface	≥2

Note: Extracted from JB/T4323-2019 standard “Water-based Metal Cleaners”.

Results and Analysis

Corrosion Results Analysis for No. 20 Carbon Steel

Figure 1 Comparison of corrosion rates of No. 20 carbon steel in different acid solutions

Figure 2 Comparison of inhibition efficiency of corrosion inhibitors on No. 20 carbon steel in different acid solutions

No. 20 carbon steel is a low-carbon steel with good toughness, plasticity, and weldability. It can be used for welded structures, pipe fittings, flanges, light-duty gears/sprockets, bolts, low-load shafts, etc. From the data in Figures 1 and 2, Vanconol®IR-902 corrosion inhibitor<span style="font-size:0