Deadly Combination of Wet Environment: Analysis and Response to the Interactive Acceleration Effect of Corrosion and Wear

In industrial fields such as mining, mineral processing, coal washing, and wet metallurgy, key equipment components such as conveying pipelines, pump valves, mixers, and mill liners are exposed to slurry environments containing water and chemical media for a long time. In such wet environments, the failure of components is not simply a simple combination of mechanical wear or chemical corrosion, but a complex process of mutual promotion and synergistic acceleration between the two. The speed of damage far exceeds the sum of the effects of a single mechanism, often leading to premature equipment failure, increased maintenance costs, and production interruptions. This article aims to professionally analyze the mechanism of this interaction and propose a systematic management approach.

1、 Failure mechanism: Collaborative failure cycle of "1+1>2"

The interaction between corrosion and wear (Corrosion Wear Synergy) constitutes a self accelerating failure cycle, and its total material loss rate (T) can be decomposed into:

T = W + C + S

among which

W is the pure mechanical wear component (occurring in an inert environment).

C is the pure corrosion component (material loss without mechanical wear).

S is the synergy component, which is the core of the interaction, and its value is often significant, even accounting for more than 50% of the total loss under certain operating conditions. It includes two aspects:

Corrosion accelerates wear: The corrosion process (such as uniform corrosion, pitting corrosion, intergranular corrosion) can damage the integrity of the metal surface, causing it to soften or produce corrosion products and pits. The mechanical strength of these corroded areas decreases, making them more susceptible to cutting or peeling under subsequent abrasive erosion or particle impact.

Accelerated corrosion caused by wear: Mechanical wear (including abrasive wear, erosion wear, and cavitation) continuously removes the passivation film or corrosion product layer on the metal surface, exposing fresh and highly active metal substrates directly and rapidly to corrosive media, resulting in a sharp increase in corrosion rate. Meanwhile, the plastic deformation caused by wear distorts the surface metal lattice, increases internal energy, further enhances its electrochemical activity, and exacerbates corrosion.

This vicious cycle of "corrosion → material weakening → increased wear → exposure of newly formed surfaces → further increase of corrosion" leads to rapid thinning of component wall thickness or the formation of severe local corrosion pits and grooves.

2、 Typical failure scenarios and manifestations

1. Wet grinding system (ball mill/semi autogenous mill liner and grinding ball)

In alkaline or acidic slurries, the grinding medium and lining plate not only bear the high stress crushing and impact of grinding ore, but also soak in a chemical medium with conductivity. Corrosion will preferentially occur at microcracks or phase boundaries caused by high stress. The failure manifests as:

The weight loss rate of materials is much higher than that of dry process conditions, and the service life can be shortened by 30% -70%.

The appearance of pits and furrows interwoven on the surface may cause the grinding ball to lose its roundness.

Corrosion products contaminate materials and may affect subsequent beneficiation processes.

2. Slurry conveying pipelines and pump flow components

The high-speed flow of solid particle slurry causes erosion and wear on elbows, impellers, and protective plates. Meanwhile, water, dissolved oxygen, acid-base ions, or chemicals in the medium can cause corrosion.

The failure manifests as groove like or honeycomb like damage along the flow direction, particularly severe in local vortex zones.

The bottom of pitting pits often becomes the starting point of erosion and wear, accelerating perforation.

The failure mode shifts from simple wall thickness reduction to localized sharp perforation or rupture, with higher risk.

3. Wet flue gas desulfurization (WFGD) system agitator and spray pipe

The medium is a slurry containing acidic ions such as Cl ⁻, SO ₄² ⁻, F ⁻, etc., which has both strong corrosiveness and abrasiveness.

The failure manifests as a composite form of severe pitting corrosion, crevice corrosion, and erosion wear.

Austenitic stainless steel may undergo stress corrosion cracking in this environment, and crack propagation is rapid under the combined promotion of wear and corrosion.

3、 Key influencing factors

The chemical properties of the medium, including pH value, dissolved oxygen concentration, concentration of corrosive ions such as chloride ions, temperature, and conductivity, directly determine the type and rate of corrosion.

Abrasive properties: The hardness, particle size, shape (sharpness), and concentration of solid particles determine the strength of mechanical wear.

Fluid dynamics parameters: flow velocity, flow state (laminar or turbulent), impact angle. High flow velocity increases erosion kinetic energy and accelerates the transport of corrosive substances.

Material factors: The matching of corrosion resistance (dependent on its passivation ability and alloy composition) and wear resistance (hardness, toughness, microstructure) of metal materials is crucial. In wet environments, a single wear-resistant material (such as some high chromium cast iron) may fail due to insufficient corrosion resistance.

4、 Systematic response strategy

To address the synergistic effect of corrosion and wear, a comprehensive strategy is needed, and a single measure often has limited effectiveness.

1. Material selection: Balance between corrosion resistance and wear resistance

In environments dominated by corrosion (such as acidic slurries), sufficient corrosion resistance of materials should be prioritized. Austenitic stainless steel, duplex stainless steel, nickel based alloys, or surface treatment can be considered to enhance corrosion resistance.

In environments where wear is dominant but corrosion cannot be ignored, high chromium cast iron (Cr>20%) materials can be selected. The high chromium matrix in its structure can provide certain corrosion resistance, while the high hardness carbides resist wear. Polymer wear-resistant materials, such as ultra-high molecular weight polyethylene and rubber lining, are also a suitable choice in specific scenarios due to their excellent corrosion resistance and resistance to adhesive wear.

Surface engineering: Using processes such as surfacing wear-resistant and corrosion-resistant alloy layers, thermal spraying (such as supersonic flame spraying tungsten carbide metal ceramic coatings), and laser cladding on tough substrate materials to prepare surface functional layers with both corrosion resistance and wear resistance characteristics is an economically effective solution.

2. Environmental and working condition control

Chemical corrosion inhibition: Under permissible process conditions, corrosion inhibitors are added to the medium to form a protective film on the metal surface, blocking the corrosion process.

PH adjustment: Control the pH value of the medium within the range of stable passivation of the target material.

Reduce flow velocity and turbulence: Optimize pipeline and equipment design to avoid sharp bends and sudden cross-sectional changes, and reduce local erosion.

Deoxygenation and filtration: Reduce dissolved oxygen and excessive, hard abrasive particles in the medium.

3. Design and maintenance optimization

Anti corrosion design: Avoid gaps and stagnant areas to ensure good drainage.

Cathodic protection: For large, fixed tanks or pipelines, sacrificial anodes or externally applied current cathodic protection can be used in combination to suppress electrochemical corrosion.

Regular monitoring and predictive replacement: Establish a regular thickness measurement system for key components (such as ultrasonic thickness measurement) to monitor corrosion wear rates. Establish a life prediction model for vulnerable parts and implement planned replacement.