I. Introduction
During long-term operation of industrial equipment, various types of fouling inevitably accumulate on heat transfer surfaces, pipe inner walls, and vessel interiors. From water scale in heat exchangers to polymer coking in reactors, from silicate hard scale in boilers to biofilm in cooling towers — fouling comes in many forms, but its damage converges on the same result: equipment performance degradation, rising operating costs, and increased safety risks. According to statistics from the China Industrial Cleaning Association, energy waste caused by equipment scaling in industrial sectors nationwide amounts to hundreds of billions of yuan annually, and corrosion-induced equipment incidents account for over 15% of all industrial accidents. Regular, scientific equipment cleaning is not optional — it is fundamental work to ensure safe production and control operating costs. This article systematically elaborates on the necessity of industrial equipment cleaning from four dimensions: scaling mechanisms, hazard analysis, economic value, and cleaning timing.
II. Types and Sources of Fouling
2.1 Water Scale
Water scale is the most common type of scale layer in industrial equipment, primarily composed of CaCO₃, Mg(OH)₂, CaSO₄, and silicates. When Ca²⁺ and Mg²⁺ concentrations in circulating cooling water are high, carbonates and sulfates crystallize and precipitate on heat exchange surfaces as water temperature rises and water evaporates, causing solubility decrease. The higher the water hardness, the faster the scaling rate. Taking circulating water with total hardness of 300 mg/L (as CaCO₃) as an example, for a shell and tube heat exchanger with 100 m² heat exchange area, water scale thickness on tube walls can reach 1.5–2.5 mm after 6 months of continuous operation. Silicate scale (SiO₂-dominated) is even more troublesome — hard and dense in texture, conventional acid cleaning has limited dissolution capability, requiring specialized NH₄HF₂-containing formulations or combined processes of alkaline boil conversion followed by acid cleaning.
2.2 Process Media Scaling
Process media contacted by equipment in chemical, petrochemical, pharmaceutical and other industries inherently contain substantial amounts of depositable substances. Unreacted monomers or oligomers in polymerization reactions cross-link at high temperatures to form dense organic scale, commonly seen on the walls of resin reactor vessels at a certain chemical group company; vacuum residue in refinery heat exchangers precipitates asphaltenes and coke precursors due to temperature gradients; proteins and starches in food processing form biofilm on plate heat exchanger surfaces. These organic scales are characterized by strong adhesion and high thermal stability, making conventional acid cleaning ineffective. Alkaline boiling or organic solvent pre-treatment followed by chemical cleaning is typically required.
2.3 Corrosion Products
Carbon steel equipment continuously undergoes electrochemical corrosion in oxygenated water environments, generating Fe₂O₃, Fe₃O₄ and other corrosion products. These rust scales not only occupy effective volume and reduce heat transfer themselves, but also form occluded cells beneath the scale layer, accelerating localized corrosion (under-deposit corrosion). Stainless steel equipment in Cl⁻-containing environments may experience pitting and stress corrosion cracking, with corrosion products further exacerbating scale accumulation. Corrosion and scaling often form a vicious cycle — the scale layer promotes corrosion, and corrosion products thicken the scale layer.
2.4 Biofilm/Slime
Circulating cooling water systems and central air conditioning cooling towers are breeding grounds for microorganisms. Bacteria, algae, and fungi multiply rapidly under suitable temperature (25–40°C) and nutrient conditions. Their metabolic products and bacterial cells form slime that adheres to tube walls and packing surfaces. Biofilm not only reduces heat exchange efficiency but also produces corrosive metabolites such as H₂S, triggering microbiologically influenced corrosion (MIC). Pathogenic bacteria such as Legionella multiplying in cooling towers that are not regularly cleaned and disinfected may also pose public health risks.
III. Severe Consequences of Not Cleaning
3.1 Drastic Decline in Heat Transfer Efficiency
The thermal conductivity of fouling is far lower than that of metal materials. Thermal conductivity data for common scale layers: CaCO₃ water scale approximately 0.5–2.0 W/(m·K), while carbon steel is approximately 45 W/(m·K) and stainless steel approximately 16 W/(m·K). Just 1 mm of water scale can reduce the overall heat transfer coefficient of a heat exchanger by 10%–20%, and 2 mm of scale can cause efficiency losses of 30%–40%. For large chemical plants, every 10% decline in heat exchange efficiency can increase annual steam consumption by over a thousand tons.
3.2 Significant Increase in Energy Consumption
To compensate for declining heat exchange efficiency, systems require higher steam pressure, greater cooling water flow, or longer heating times. At a certain power plant, after the condenser scaled by 0.5 mm, the turbine back pressure increased, causing coal consumption for power generation to rise by 3–5 g/kWh. Based on annual power generation of 2 billion kWh, this means an additional 6,000–10,000 tons of standard coal consumption per year. At a certain chemical plant, a shell and tube heat exchanger that had not been cleaned for a long time saw its heat exchange temperature difference deteriorate from the design value of 12°C to 28°C, increasing annual steam costs by approximately ¥800,000.
3.3 Shortened Equipment Life
Under-deposit corrosion is one of the primary causes of premature industrial equipment retirement. The scale layer prevents corrosion inhibitors from contacting the metal surface, while simultaneously forming oxygen concentration cells at the scale-metal interface, accelerating localized corrosion rates. Statistics show that regular cleaning can extend heat exchanger service life by 50%–100%. At a certain steel enterprise, a waste heat boiler that was not regularly cleaned experienced severe under-deposit corrosion perforation of its tube bundle and was scrapped after only 5 years of operation, while equipment of the same model under standardized cleaning and maintenance has operated for over 12 years and remains in good condition.
3.4 Safety Hazards
Pipeline scaling reduces flow cross-sectional area, increases system resistance, and in severe cases leads to tube rupture incidents. Boiler water scale exceeding 3 mm thickness may cause localized overheating of furnace tubes and reduced metal strength, and in extreme cases may trigger tube rupture or even boiler explosion. Shell-side scaling of heat exchangers impedes media flow, and localized high temperatures may cause decomposition or polymerization of flammable media, resulting in process safety incidents.
IV. Economic Value of Cleaning
The return on investment for industrial equipment cleaning is very substantial. Taking a shell and tube heat exchanger with 200 m² heat exchange area as an example: Chemical cleaning cost is approximately ¥15,000–20,000; after cleaning, heat transfer efficiency recovers to over 95% of new equipment, saving approximately 200–300 tons of steam annually (at ¥200/ton, annual savings of ¥40,000–60,000); equipment operating life is extended by 3–5 years, reducing annual depreciation allocation by approximately ¥10,000. Comprehensive calculation shows the cleaning investment payback period is approximately 3–6 months, with cumulative net benefits exceeding ¥100,000 over 3 years. For key heat exchanger groups (10+ units) in large chemical plants, annual comprehensive energy savings from regular cleaning can reach million-yuan levels.
| Equipment Type | Consequences of Not Cleaning | Recovery After Cleaning |
|---|---|---|
| Shell & Tube Heat Exchanger | Temperature difference deterioration >15°C, energy consumption increase 20%–35% | Heat transfer efficiency recovers to >95% |
| Industrial Boiler | Fuel consumption increase 5%–10%, tube wall overheating risk | Unit fuel consumption recovers to design level |
| Reactor Jacket | Heating/cooling time extended 30%–50%, production capacity decline | Production cycle returns to normal |
| Condenser | Vacuum degree decline, coal consumption increase 3–8 g/kWh | Vacuum degree recovers, coal consumption normalizes |
| Cooling Tower | Cooling capacity decline, chiller efficiency reduction | Cooling temperature difference recovers to 5–7°C |
V. How to Determine if Equipment Needs Cleaning
Equipment cleaning should not wait until performance has severely deteriorated — a preventive cleaning mechanism should be established. The following are common cleaning judgment indicators: Heat exchanger outlet media temperature deviation from design value exceeds 5°C and continues to rise, or the heat exchange terminal temperature difference (log mean temperature difference) increases by over 50% compared to design value; boiler exhaust gas temperature rises 15–20°C above normal, or fuel consumption increases by more than 5% compared to the same operating conditions; heat exchanger tube-side differential pressure increases by more than 30% compared to initial value; when opening manholes or handholes for inspection, scale thickness exceeds 0.5 mm, cleaning is recommended; cooling tower packing shows visible slime or algae attachment, and circulating water turbidity remains persistently high. It is recommended that continuous production industries such as chemical and power sectors arrange at least one full-system shutdown cleaning annually, combined with quarterly online maintenance cleaning, to form a complete equipment cleanliness assurance system.
VI. Summary
Industrial equipment cleaning is not an optional auxiliary task — it is a core maintenance activity directly affecting production safety, energy consumption, and equipment life. From water scale to polymer coking, from corrosion products to biofilm — different types of fouling require targeted cleaning solutions. Enterprises should establish equipment cleaning records, documenting scaling rates, cleaning intervals, and effectiveness data, gradually optimizing cleaning strategies. Scientific cleaning maintenance not only restores equipment performance but also reduces operational risks at the source and extends asset life, achieving dual assurance of economic benefits and safe production. For professional industrial equipment cleaning services, please contact us for customized solutions.
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